Separations doi: 10.3390/separations13070202

Authors: Yikai Chen Zhiying Pan Hongcheng Li Shichao Du Yan Wang Fumin Xue

This study develops a spherical crystallization approach using a small amount of water, which avoids adding extra bridging agents. Notably, a new ternary solvate of pantoprazole sodium (PS–BuOH–H2O) was obtained, and its crystal structure was determined by single–crystal X-ray diffraction. The crystal packing and Hirshfeld surface analyses were performed to identify intermolecular interactions within the crystal. In the crystal lattice, water molecules not only coordinate to the sodium ion of pantoprazole sodium but also form a hydrogen bond with n-butanol via O6–H6A···O5. In order to regulate the particle morphology, the effects of crystallization conditions were investigated, including water content, feeding rate of water, solute concentration, temperature, cooling rate, and stirring rate. It was discovered that water plays a key role in promoting the spherical crystallization of PS–BuOH–H2O. In addition, the morphology of the solvate was closely related to the competition process of crystal agglomeration and spherulitic growth. By optimizing the process parameters, well–developed spherical particles could be prepared and stepwise evolution of spherulites via noncrystallographic branching was observed. This study established a water–induced spherical crystallization technique, offering a promising strategy for preparing new crystal forms and improved particle morphology.

Separations doi: 10.3390/separations13070201

Authors: Hayley Corbett Brian Solan Svetlana Tretsiakova-McNally Pilar Fernandez-Ibañez Bárbara Luíza Souza Freitas Rodney McDermott

The intensifying rate of global water stress is motivating the exploration of alternative water sources. This research aims to unlock conventionally unusable wastewater effluent for reuse with the aid of slow sand filtration (SSF). In this study, a traditional SSF reactor was constructed and later modified by replacing a section with sawdust, a sustainable material. The two filter configurations were asynchronously investigated to evaluate their potential capacity for the removal of antibiotics and common surface-water nutrients, i.e., nitrates and phosphates. Each filtration system was operated in a recirculating mode over four weeks to develop the biological component referred to as the “schmutzdecke”. Standard water-quality testing indicated that the SSF with an incorporated sawdust layer buffered shock events (e.g., turbidity spikes) while still cultivating a healthy schmutzdecke. Furthermore, the sawdust facilitated greater microbial activity, which is associated with the biodegradation of various contaminants and pathogens. Following filtration of a simulated wastewater effluent containing sulfamethoxazole (SMX) and trimethoprim (TMP) antibiotics (ca. 1 mg∙L−1), it was found that the TMP removal exceeded 93% in both configurations. The SMX removal rate was much lower and varied significantly, ranging from 1.2 to 38.6% and from 1.4 to 3.4% for the traditional and modified filters, respectively. These findings suggest that the proposed configuration has the potential to address some emerging contaminants but that refinements are needed to address other contaminants such as SMX.

Separations doi: 10.3390/separations13070200

Authors: Ying Yang Xiaofei Xie Jingchang Zhang Jirui Sui Chuancheng Lin Mingxing Li Weixue Liu Chunying Li Chunjian Zhao

Chlorogenic acid (CA) is an important natural antioxidant component and holds strong potential for health food and cosmetic applications. In this study, a silica-based photo-responsive molecular imprinting material (PMI-PDA@NH2-SiO2) was designed as a solid-phase extraction (SPE) adsorption filler and applied for the efficient separation of CA in Ficus carica L. Using polydopamine-modified NH2-SiO2 silica as the base, combined with the photo-responsive monomer 4-methacryloyloxyazobenzene (AZO-MAA), a molecular imprinting layer with photo-responsive regulation function was constructed. Under 365 nm ultraviolet light irradiation, the azobenzene group was isomerized to the cis structure, causing the imprint cavity to shrink, thereby enabling controlled release of CA, with complete desorption within 40 min, and a desorption rate of 94.33%. Importantly, the material retained 85.56% of its initial adsorption capacity and 91.38% of its original desorption efficiency after 6 consecutive adsorption/desorption cycles, confirming robust operational stability and reproducibility. PMI-PDA@NH2-SiO2 was applied to the extract of Ficus carica L., achieving an adsorption rate of 92.3% for CA and a desorption rate of 87.27%. Density functional theory (DFT) calculations and NOESY spectroscopic analyses revealed that CA interacted with functional monomers via hydrogen bonding and van der Waals forces. This study advances a green separation strategy for bioactive phytochemicals in complex natural matrices.

Separations doi: 10.3390/separations13070199

Authors: Zilong Liu Jiawei Wang Shuyuan Zhu Shangyi Li

With the widespread application of new chemicals, the concentration of emerging contaminants (ECs), such as antibiotics, per- and polyfluoroalkyl substances (PFAS), microplastics, and new pesticides, in aquatic environments is on the rise. ECs such as those examined in the studies exhibit high toxicity, persistence, and a propensity for bioaccumulation, which can lead to significant risks for ecosystems and human health. Traditional water treatment technologies exhibit limited removal capabilities for ECs, whereas micro-nano bubbles (MNBs) exhibit great potential in the field of ECs treatment, due to their unique physicochemical properties. This article systematically reviews the research progress on the treatment of ECs using MNBs combined with other technologies, including physical methods (adsorption enhancement), chemical methods (ozonation, persulfate oxidation, photocatalysis, and material catalysis) and biological methods (microbial synergy). This review summarizes the research progress and mechanisms of MNBs combination technologies, outlining the critical knowledge gaps and future research perspectives to advance the rational design and engineering application of MNBs for ECs’ elimination in water treatment.

Separations doi: 10.3390/separations13070198

Authors: Haicheng Zhao Lihui Gao Xinmeng Jiang Yijing Zhang

Coal gasification slag (CGS), a massive industrial solid waste, possesses inherent adsorptive potential that remains underutilized due to pore blockage by amorphous siliceous phases. Conventional modification strategies typically rely on energy-intensive high-temperature processes. Herein, we report a facile, low-temperature alkaline activation approach to transform CGS into a high-efficiency adsorbent (denoted NCGS) for Cd2+ removal. Sodium hydroxide (NaOH) solution was employed under mild conditions (90 °C) to selectively etch siliceous species, thereby generating a porous architecture and enriching surface oxygen-containing functionalities. Orthogonal experimental design identified optimal synthesis parameters (1 mol/L NaOH, solid–liquid ratio of 1:30 g/mL, 12 h), yielding NCGS with significantly enhanced textural properties. The adsorption isotherm was well described by the Langmuir model, with a maximum capacity of 87.06 mg/g at pH 6.0, while kinetic studies indicated the adsorption process could be described by pseudo-second-order kinetic model. Comprehensive characterization via SEM-EDS, FTIR, and XPS elucidated a multi-mechanistic adsorption pathway mainly involving ion exchange (Na+/Cd2+) and coordination complexation. Life cycle assessment analysis revealed that NCGS production generates 11.23 kg CO2 eq emissions, with transportation accounting for 88%. This study presents an energy-saving and environmentally friendly strategy to unlock the adsorptive potential of CGS, providing a highly promising waste-based adsorption material for the remediation of Cd2+-contaminated water.

Separations doi: 10.3390/separations13070197

Authors: Zhuowen Feng Jieshan Wu Tingwei Huang Liang Pan Yue Zhao Yun Cui Shiwei Ren Abderrahim Yassar

An analytical method was established for the rapid determination of 45 pigments and preservatives in edible ink by ultra-high performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry (UHPLC-MS/MS), which provides technical support for the composition analysis and industrial development of edible ink. The samples were easily extracted with 75% aqueous methanol solution and purified with a Captiva EMR-Lipid HF solid-phase extraction cartridge. After filtration through a polytetrafluoroethylene (PTFE) membrane, the analytes were determined by UHPLC-MS/MS under multiple reaction monitoring (MRM) mode in both positive and negative ion modes. Poroshell 120 AQ-C18 was selected as the analytical column, and valve switching timing control was adopted during the gradient elution process. The external standard method was used for quantitative analysis. In the established method, the 45 pigments and preservatives exhibited good linear relationships within the mass concentration range of 0.0002–200.0 μg/mL. The limits of detection (LOD) and limits of quantification (LOQ) were 0.0004–8.00 mg/kg and 0.001–20.00 mg/kg, respectively. Using 25% aqueous glycerol solution as the blank matrix, the recoveries of analytes at different spiked levels met the detection requirements. The established method is simple and rapid, and can be applied to the qualitative and quantitative detection of typical pigments and preservatives in edible ink.

Separations doi: 10.3390/separations13070196

Authors: Guoqiang Liang Chenpeng Wang Qianwei Ji Xusheng Zhang Liang Zhao Xinchun Liu Zhisheng Yu Hongxun Zhang Guoqiang Zhuang Jianzhong Zheng Ruyin Liu

Facing the severe environmental challenge of massive red mud (RM) stockpiles, iron extraction research is accelerating from traditional pyrometallurgy and other conventional processes toward green low-carbon, multi-source synergistic, and total-component high-value utilization approaches—a transition that continues to evolve. This review systematically examines three frontiers: green reduction technologies, synergistic valorization via waste-treating-waste, and integrated cascading strategies for total-component high-value utilization. Evaluation focuses on the principles, advantages, and challenges of biomass reduction, hydrogen metallurgy, selective flocculation, advanced heating techniques, co-processing with other solid wastes, and multi-metal cascading extraction. Evidence suggests that future RM iron extraction technology lies in establishing cross-industry circular economy networks, transforming RM from a singular waste into a resource hub linking aluminum, steel, and construction industries to maximize environmental and economic benefits.

Separations doi: 10.3390/separations13070195

Authors: Rosella Prestia Damian Hauri Mattia Sponchioni Sebastian Vogg Thomas Müller-Späth

Peptide purification by preparative reversed-phase liquid chromatography remains one of the most resource-intensive stages in synthetic peptide manufacturing. Production processes commonly rely on acetonitrile/trifluoroacetic acid (ACN/TFA) mobile phases mainly because of their high chromatographic resolution. However, both components raise significant environmental and safety concerns related to toxicity, flammability, waste generation, and, in the case of TFA, environmental persistence as a per- and polyfluoroalkyl substance (PFAS, known as a “forever chemical”). Green alternatives based on ethanol, dimethyl carbonate, and sustainable acidic additives such as acetic acid have been proposed, but their industrial adoption remains limited due to reduced chromatographic performance, often resulting in lower yield and productivity under conventional batch operation. In this work, multi-column counter-current solvent gradient purification (MCSGP) was investigated as a strategy to integrate the use of green eluent systems without compromising process performance. Two therapeutic peptides, Tirzepatide and Tetracosactide, were selected as representative case studies with different structural complexity. Using ethanol/acetic acid for Tirzepatide and dimethyl carbonate/acetic acid for Tetracosactide, the MCSGP process achieved purity levels equivalent to those obtained with conventional ACN/TFA batch chromatography, with 88.1% yield at 89.0% purity for Tirzepatide and 93.8% yield at 94.0% purity for Tetracosactide. Productivity for Tirzepatide was improved, reaching 6.3 g/Lresin/h. These results demonstrate that MCSGP can compensate for the reduced separation efficiency typically associated with green eluent systems, enabling sustainable peptide purification without compromising process performance. By combining green solvents with the MCSGP process, this work paves the way for more sustainable peptide purification processes while maintaining high yield and productivity.

Separations doi: 10.3390/separations13070194

Authors: Xin-Wen Huang Xiang Li Yi-Jing Lang Ran-Xu Song Jing-Jing Ren Yan-Hua Xie Hui-Min Xiao Si-Wang Wang

To establish a comprehensive quality control method for Qili Qiangxin Capsules, an HPLC-DAD-ESI-MS/MS approach was developed for characteristic chromatogram analysis, marker compound identification, and multi-compound quantification. Similarity analysis of the characteristic chromatogram was conducted, and 25 characteristic peaks were identified using MS/MS fragment information. Methodological validation (specificity, linearity, precision, stability, repeatability, spiked recovery) was performed, followed by content determination of the 25 marker compounds. Results showed that the similarity of 10 batches of samples was >0.9 (Peak 6 as reference peak). The methodological validation for the quantitative analysis of 25 compounds met the requirements. All 25 compounds exhibited good linearity (R2 > 0.999), with spiked recoveries of 98–103% (RSD < 2.0%). All validation indicators met Chinese Pharmacopoeia requirements. The established method is specific, precise, and stable, enabling simultaneous characteristic chromatogram identification and multi-compound quantification of Qili Qiangxin Capsules. It provides technical support for production quality supervision and clinical medication safety, and offers a reference for quality control of similar traditional Chinese medicine preparations.

Separations doi: 10.3390/separations13070193

Authors: Zi-Ying Zeng Cheng-Xiang He Qin Tian Jun Long Bing-Yan Du Er-Cheng Zhao Zhong-Hua Yang

The increasing prevalence of multiclass pesticide residues in aquatic environments poses a significant threat to ecosystems and human health. To address this challenge, magnetic Fe3O4@Co5Al-LDH nanoparticles were synthesized as high-performance, easily recoverable catalysts for the peroxymonosulfate (PMS)-mediated degradation of epoxiconazole, atrazine, and metalaxyl. Under optimized conditions (pH 7.0, 35 mg catalyst, and 4.0 mM PMS), the system achieved 100% degradation of the three coexisting pesticides within 15 min. Quenching experiments and electron paramagnetic resonance (EPR) spectroscopy confirmed that SO4− and •OH radicals were the primary reactive species driving the process. Liquid chromatography–mass spectrometry (LC-MS) analysis identified four intermediates for epoxiconazole, three for atrazine, and four for metalaxyl, facilitating the proposal of distinct degradation pathways. The degradation mechanism revealed that electron transfer between Fe/Co and PMS promoted the generation of reactive oxygen species, leading to dechlorination, hydroxylation, and dealkylation of the pesticides transiently adsorbed on the surface of Fe3O4@Co5Al-LDH. In summary, this study demonstrates that Fe3O4@Co5Al-LDH is an easily recoverable, reusable, and cost-effective catalyst for the simultaneous remediation of complex pesticide mixtures in water.

Separations doi: 10.3390/separations13070192

Authors: Yao Zhang Yong Yu Zhi-Bin Zhou Zheng-Hao Yang Yu-Long Chang Li-Wang Wang Ben-Shuai Guo

The complex behavior of multi-scale droplets in Hydro-jet Cyclone (HJC) systems constrains the parametric study of gas–liquid separation and interfacial transfer. To investigate droplet dynamics at a specific scale in swirling flows, this study employed 500-μm simulated droplet particles (SDPs) and examined the effects of inlet gas rate, column height, and cone angle on trajectories, revolution speed, and self-rotation speed using the Computational Fluid Dynamics-Discrete Phase Model (CFD-DPM). The results demonstrate that SDPs exhibit suspended circulation within the cyclone. The suspension zone expands toward the overflow pipe with increasing gas rate and cone angle, but migrates downward with increasing column height. The revolution speed increases from about 50 rad/s to 80 rad/s as inlet gas rate rises, but decays with increasing column height, while cone angle has little influence. The self-rotation speed is driven by near-wall shear, reaching an instantaneous peak of 4500 rad/s at the inlet; after stable suspension, it increases markedly with gas rate, from <3500 rad/s at 12 m/s to 12,000 rad/s at 22 m/s. Inlet gas rate is the dominant factor governing self-rotation, followed by cone angle, whereas column height mainly affects suspension position. This study provides a numerical reference for droplet dynamics in HJC gas–liquid systems.

Separations doi: 10.3390/separations13070191

Authors: Qiyuan Wei Yanru Cui Hongqiong Zhang Jianbo Li

Coal plays a vital role in energy production, but its combustion releases SO2, causing serious environmental problems. In this study, indigenous microorganisms with sulfur-metabolism potential were isolated from raw coal and evaluated for coal biodesulfurization. The isolated strain, Arthrobacter sp. DBW, degraded 50% of DBT within 100 h and reduced the total sulfur content of coal by 42%. Since pyrite remained after treatment, the sulfur removal was mainly attributed to organic sulfur removal. Mechanistic analysis indicated that Arthrobacter sp. DBW may remove organic sulfur through enzyme binding to DBT and subsequent C-S bond cleavage via the 4S pathway. In addition, partial kaolinite dissolution occurred during biodesulfurization, reducing the ash content by 1.06%. These results suggest that Arthrobacter sp. DBW has potential for organic sulfur removal from coal and may help reduce SO2 emissions during subsequent combustion.

Separations doi: 10.3390/separations13070190

Authors: Nianzi Liu Yilin Wang Qing Long Anyan Long Guihua Liu Tiangui Qi Qiusheng Zhou Leiting Shen Jian Guo

Secondary aluminum dross (SAD) from the aluminum industry is a hazardous residue that restricts sustainable aluminum production. Residual aluminum nitride (AlN) and insoluble fluorides after conventional pretreatment are major barriers to the safe utilization of SAD. In this study, a low-temperature intensified roasting–alkaline leaching process was developed to remove harmful elements by using reaction heat and waste heat to expose enveloped AlN and fluoride phases, form soluble sodium-bearing compounds, and intensify AlN oxidation. Without additives, roasting at 750 °C for 3 h converted 91.65% of AlN, leaving 1.37% AlN in the roasted SAD. With Na2O2 as an oxygen donor in situ, NaF as a mineralizer to reduce roasting temperature, and sodium-bearing species as reactants for soluble NaAlO2/Na2SiO3 formation, the AlN conversion increased up to 97.01% under 5% NaF and 2.5% Na2O2 at 750 °C for 3 h. Afterwards, higher temperature, longer duration, lower roasted SAD dosage, and higher caustic soda concentration all improved fluorine removal in the subsequent alkaline leaching. Under 100 g/L Na2O, 20 g/L roasted SAD, and 100 °C, fluorine and chlorine removal efficiencies reached 92.52% and 99.47%, respectively. The final high-alumina residue contained 74% Al2O3, mainly in the forms of α-Al2O3, NaAl11O17, and MgAl2O4, with only 0.19% F and 0.03% Cl, making it suitable for the preparation of various alumina-bearing materials and alumina production.

Separations doi: 10.3390/separations13070189

Authors: Jieru Zhang Ying Yang Xiaoming Peng

Ionic liquid-assisted extraction can improve the recovery of monoterpene glycosides from Radix Paeoniae Alba, whereas post-extraction purification and ionic-liquid-associated marker-level quality control remain necessary before further bioactivity evaluation. In this study, a macroporous resin-based purification process was developed for monoterpene glycoside-enriched extracts obtained by conventional reflux extraction and ionic liquid-assisted microwave–ultrasound extraction. Among the five tested resins, AB-8 resin showed the best adsorption performance and was selected for further process optimization. The optimized purification conditions were a loading concentration of 13 mg/mL, loading pH of 7, elution with 70% ethanol, loading volume of 6 BV and elution volume of 9 BV. After purification, the total quantified monoterpene glycoside content increased from 6.59% to 51.68% in the conventional extract and from 15.30% to 75.30% in the ionic liquid-assisted extract. The ionic-liquid-associated elemental marker content in the ionic liquid-assisted extract decreased from 5.593% to 0.072% after purification, corresponding to an approximately 98.7% reduction at the elemental-marker level. Stability evaluation indicated that Na2SO3, Fe3+, ascorbic acid, sucrose and light exposure affected the detected monoterpene glycoside content to different extents, whereas short-term heating within 20–80 °C caused only slight fluctuations. The purified extracts showed stronger DPPH and ABTS radical scavenging activities and reducing power than the crude extracts. In LPS-stimulated RAW264.7 cells, the purified extracts reduced NO production and downregulated the mRNA expression of IL-6, IL-1β, TNF-α, iNOS and COX-2, suggesting anti-inflammatory potential at the NO and gene-expression levels. AB-8 resin purification enriched the monitored monoterpene glycosides, reduced the selected ionic-liquid-associated elemental marker, and generated purified fractions suitable for subsequent stability and bioactivity evaluation.

Separations doi: 10.3390/separations13070188

Authors: Petr Česla Václav Kašička

Research in the analytical and preparative fields of separation science has a long-standing tradition in the Czech Republic and former Czechoslovakia. Czech and Slovak scientists recognized the advantages of the two most widely used separation techniques, i.e., chromatography and electrophoresis, soon after their discovery and broader adoption. Their contributions to the development of the fundamentals and applications of chromatography and electrophoresis are demonstrated not only by numerous publications in renowned scientific journals and books, but also by several breakthrough innovations that led to patents and sometimes also to successful commercialization. The contributions of the earlier most prominent Czech scientists to the development of separation sciences have already been summarized in the literature. In the following lines, we instead aim to highlight less well-known, yet important, contributions within the Czech chromatographic and electrophoretic community. Moreover, recent developments since the last comprehensive reviews are covered in greater depth.

Separations doi: 10.3390/separations13070187

Authors: A K M Ahsan Ahmed Douglas E. Raynie

This study investigated the effect of ethanol on the relative headspace percent composition of evaporative emissions from gasoline at different temperatures using HS-SPME-GC-MS. The results showed that the relative abundance of monoaromatics in the headspace decreased with increasing ethanol content in all tested fuels at all temperatures examined. The paraffins and i-paraffins exhibited a similar decreasing trend in most samples, with reductions more pronounced in E20 (20% ethanol content) than in E10 (10% ethanol content) fuels. The experimental results for the temperature effect on headspace composition were variable: monoaromatics showed slight increases at higher temperatures, whereas paraffins, iso-paraffins, and mononaphthenes generally decreased. However, ethanol addition did not significantly alter these temperature-dependent trends, as similar patterns were observed in both ethanol-blended and ethanol-free fuels. The magnitude of the ethanol effect depended on fuel composition, with the largest reductions in monoaromatic hydrocarbons observed for the high-density gasoline samples. These findings demonstrate that ethanol modifies the relative distribution of hydrocarbon classes in gasoline headspace, with the most pronounced effect being a reduction in monoaromatic hydrocarbons, and highlight the value of class-resolved analysis for understanding fuel evaporation behavior.

Separations doi: 10.3390/separations13070186

Authors: Zhe Wang Hongquan Jing Bingbing Liu Yixuan Zhang Jiangli Li Cuihong Hou

Phosphate tailings (PTs), a solid waste generated from phosphate flotation, are a low-grade phosphate resource rich in quartz and dolomite. Their long-term accumulation leads to both resource loss and environmental risks, making valorization increasingly important for the sustainable development of the phosphorus chemical industry. In this study, calcareous–magnesian PTs were used as raw materials, and selective hydrothermal leaching with weakly acidic AlCl3 solution was employed to separate the dolomite phase and directly construct a Ca-Mg-Al precursor solution for layered double hydroxides (LDHs). The LDHs were subsequently synthesized by co-precipitation and evaluated for phosphate removal from wastewater. The results showed that the precipitation pH markedly affected the phase composition and platelet morphology of the LDHs, while appropriate aging conditions further improved their adsorption performance. Under the optimal conditions of pH 12, aging at 40 °C for 2 h, the obtained LDHs exhibited the best phosphate uptake. Adsorption kinetics followed the pseudo-second-order model, and the maximum adsorption capacity calculated from the Langmuir model reached 38.61 mg-P/g. Characterization by XRD, FTIR, TG-DTA, point of zero charge, and XPS indicated that phosphate removal was dominated by surface complexation, accompanied by anion exchange, ionic precipitation, and electrostatic attraction.

Separations doi: 10.3390/separations13070185

Authors: Sheng Li Yaying Wang Lidan Lv Lingyuan Liao

212Pb is an important medical radionuclide for targeted alpha therapy, and its reliable supply depends on the efficient production of parent nuclides such as 228Ra, 228Th, and 224Ra. Natural thorium resources are abundant and represent a potential source of these radionuclides. However, the separation and enrichment of trace radium from thorium-rich high-salinity systems remain challenging due to extremely low radium concentrations and Th/Ra mass ratios on the order of 109. In this work, a radium separation strategy based on BaSO4 co-precipitation was developed. The precipitation behavior of BaSO4, precipitation kinetics, radium co-precipitation efficiency, and thorium recovery in concentrated thorium nitrate solutions were systematically investigated. The results show that elevated ionic strength and competitive interactions between Th4+ and SO42− reduce the effective sulfate activity under high-thorium conditions, making excess sulfate necessary to achieve efficient BaSO4 precipitation. Under optimized conditions, the radium co-precipitation recovery exceeded 80% at a Ba2+ concentration of 3 mM. Meanwhile, thorium exhibited negligible incorporation into the BaSO4 phase and could be almost completely recovered via subsequent hydroxide precipitation. The proposed method features operational simplicity, use of common reagents, low cost, and compatibility with high-salinity matrices. It provides a feasible technical pathway for the subsequent production of high-purity 228Th or 224Ra and the preparation of 228Th/212Pb or 224Ra/212Pb generator systems.

Separations doi: 10.3390/separations13060184

Authors: Ioannis P. Gerothanassis

Qualitative and quantitative analysis of complex mixtures and structure elucidation is generally impeded by the intrinsic complexity of the NMR spectra and the extensive signal overlap. The conventional approach to characterizing individual metabolites from complex crude extracts of natural products relies on multistep separation workflows employing diverse liquid chromatographic approaches and/or hyphenated techniques, which combine online integration of NMR with separation methods and other forms of spectroscopy. In recent decades, considerable efforts have been devoted to NMR applications in crude extracts without previous separation and isolation of the individual analytes. We present herein a critical overview of several NMR applications using chemical shift ranges of common organic functional groups, which can provide significant resolution advantages under specific experimental conditions. Particular emphasis is placed on: (i) characteristic chemical shift regions of strongly deshielded phenol OH groups, aldehyde CHO groups, hydroperoxide C-O-O-H groups and olefinic protons in conjugated double bonds; (ii) the advantages of using 13C chemical shift ranges through 2D 1H-13C HSQC and HMBC experiments of strongly deshielded phenol OH groups, aldehyde CHO groups, hydroperoxide groups, conjugated double bonds, and deshielded aliphatic CH groups; (iii) selective 1D NMR-spin chromatography techniques (1D TOCSY, 1D NOE); (iv) multiple suppression of strong resonances for minor analyte identification and (v) band-selective excitation techniques for minor analyte identification and quantification. The complementary contributions of statistical heterospectroscopy and computational chemical shift prediction are also considered, together with a brief assessment of the NMR experimental parameters and performance characteristics.

Separations doi: 10.3390/separations13060183

Authors: Yan Zheng Yan Li Dongbo Li Lujun Wang

A novel wide-neck classifier (WNC) was designed to address the problem that thickeners cannot achieve classification prior to flocculation in a single unit. Using the computational fluid dynamics-discrete phase method and PIV experimental method, the reliability of the model was validated. We studied the motion characteristics of different particles within the novelty-designed WNC. The primary forces acting on coal slime particles in the composite force field were gravity, drag force, pressure gradient force, and virtual mass force. Drag force dominated the classification and sedimentation processes. In contrast, gravity, pressure gradient, and virtual mass forces promoted downward sedimentation but hindered upward overflow. The classification of slime particles in WNC was divided into initial classification after tangential feeding and centrifugal classification in a cone. Both simulation and experimental results demonstrate that, under consistent feed conditions, mineral density significantly affected the distribution of particles at the classification underflow and classification overflow. Among the three minerals, kaolinite has the highest classification effect, followed by quartz, while coal has the lowest classification effect.

Separations doi: 10.3390/separations13060182

Authors: Antons Podjava Artūrs Šilaks

Metanephrine (MN) and normetanephrine (NMN) are critical biomarkers for neuroendocrine tumors (pheochromocytoma and paraganglioma). Following our previous development of a molecularly imprinted solid-phase extraction (MISPE) sorbent for urine analysis, this study evaluated MISPE coupled with HILIC-MS/MS for determining metanephrines in human plasma. Unlike conventional phases, the novel polymer selectively binds analytes as in situ-generated anions via quaternary alkylammonium groups in hydroxide form, ensuring accurate extraction from just 25 µL of plasma. Validated per U.S. FDA guidelines, the assay showed good intra- and interday precision (CV < 10.8%), accuracy (bias < −10.6%) and excellent linearity (R2 > 0.99) across pathological ranges (184.3–877.8 ng/L for MN; 174.8–923.0 ng/L for NMN), with low relative standard errors (<6.9%). Excellent selectivity was demonstrated in the presence of structurally close analogs (catecholamines, DOPA and its derivatives). Compared with commercial WCX, the sorbent yielded cleaner extracts, significantly reducing the phospholipid interference. Although lower limits of quantification (92.2 ng/L MN; 87.4 ng/L NMN) slightly exceeded healthy upper thresholds, the method has potential for use in specific clinical scenarios with pronounced biomarker elevations: diagnosis of pheochromocytoma/paraganglioma, monitoring post-treatment metanephrine decline, and tracking tumor-induced hypertensive crises in emergencies. This accessible protocol forms a solid foundation for advanced diagnostics.

Separations doi: 10.3390/separations13060181

Authors: Rui Mei Qinghan Wang Kangyixin Sun You Hu Fuqiang Xu Fan Jia

Background: Viral vectors are indispensable tools in gene therapy and neural circuit mapping, offering promising therapeutic strategies for diverse genetic diseases and advancing neuroscience research. To achieve high transduction efficiency while mitigating impurity-induced immunogenicity, the development of viral vectors with improved purity and quality is essential. However, this critical requirement is often unmet by conventional purification methods such as ultracentrifugation, which are time-consuming and frequently result in limited product purity. The pseudorabies virus (PRV) is extensively employed as a viral tool for mapping neural circuits, where improved purity contributes to enhanced accuracy of neural tracing. PRV531 is a retrograde trans-synaptic tracer modified from the PRV Bartha strain, specifically designed to facilitate the precise visualization of hierarchical neural networks. Methods: In this study, we developed a method for the concentration and purification of PRV531 by integrating hollow fiber ultrafiltration (HF) with CaptoTM Core 700 (CC700) chromatography. Initially, to concentrate the viral supernatant, a 500 kDa HF membrane was employed, maintaining a feed flow rate of 80 mL/min, a shear rate ranging from 2000 to 6000 s−1, and a transmembrane pressure (TMP) between 0.5 and 1 bar. Following concentration, the virus underwent purification through CC700 chromatography, operating at linear flow rates ranging from 100 to 300 cm/h. Results: Sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) revealed distinct bands consistent with the expected sizes of major PRV structural proteins, each with molecular weights ranging from 25 kDa to 150 kDa, concurrently demonstrating a substantial reduction in host cell proteins (HCPs) contamination. The purified PRV531 achieved a high final infectious titer of 3.55 × 109 PFU/mL, with an overall functional virus recovery of 8.88% from the crude supernatant to the final product. Conclusion: These data demonstrate that TFF combined with CC700 resin can efficiently purify retrograde trans-synaptic PRV tracer. Furthermore, this approach provides a promising strategy for purifying other viral-based tracers that traditionally rely on conventional centrifugation methods.

Separations doi: 10.3390/separations13060180

Authors: Kaikai Zhang Wen Ye Shunquan Shi Jiale Yang Yuyu Zhang Ping Hou Feng Xie Yujie He Jinze Zhao Shaogang Hu

Mercury (Hg) is a global pollutant that poses a serious threat to ecosystems and human health. Biochar has shown great potential for mercury removal due to its porous structure and abundant surface functional groups. However, redox-active moieties on biochar can reduce adsorbed Hg2+ to volatile Hg0, leading to secondary mercury dispersion. To suppress this reduction, this study proposes a strategy of co-pyrolyzing coal gangue with rice husk to prepare composite biochars (RHB/CG), leveraging the abundant metal oxides in coal gangue to tailor the surface chemistry of biochar. The materials were characterized by FTIR, Raman, and XRD; static adsorption, mercury speciation analysis, and kinetic experiments were conducted. The results show that coal gangue incorporation significantly enhances the Hg2+ adsorption capacity of biochar, with the equilibrium adsorption capacity calculated by the pseudo-second-order kinetic model, increasing from 20.6 mg/g for pristine RHB to 38.7 mg/g for RHB/CG-1:1. More importantly, RHB/CG composites effectively suppress the reduction of Hg2+ to Hg0, and the amount of Hg0 accumulated in the system is 57.1% lower than that of pristine RHB. Mechanistic studies reveal that coal-gangue-derived basic functional groups (e.g., C–O–C, Si–O–M) inhibit reduction via sequestering Hg2+ through coordination and disruption of electron transfer pathways. PHREEQC simulations (pe = 6.0) confirm the decreased tendency of Hg2+ reduction to Hg0 with increasing pH, in good agreement with the experimental results showing reduced Hg2+ reduction. The corresponding results provide a green and sustainable solution for mercury-contaminated water and soil remediation.

Separations doi: 10.3390/separations13060179

Authors: Peng Bian Qinchen Meng Xianyin Yu Jinou Han Zhichen Zeng Xudong Wang

Amid growing pressure to reduce carbon emissions, carbon capture, utilization, and storage (CCUS) has become an important pathway toward deep decarbonization. However, the conventional separated “capture–release–conversion” process suffers from high energy consumption and system complexity, which severely limits its large-scale application. Integrated CO2 Capture and Utilization (ICCU), which enables the capture, activation, and conversion of CO2 within a single system, has attracted widespread attention because it can effectively reduce intermediate energy-intensive steps and improve carbon utilization efficiency. This review systematically summarizes recent progress in ICCU technology, with particular emphasis on reaction mechanisms and interfacial coupling characteristics. The performance features of solvent-based chemical absorption and solid-sorbent adsorption, two widely studied capture routes, are summarized, and typical integrated conversion pathways, including reverse water–gas shift, methanation, and dry reforming of methane, are discussed. On this basis, the roles of non-conventional energy-assisted strategies, such as photocatalysis, electrocatalysis, non-thermal plasma, and microwave irradiation, in expanding ICCU systems are further examined, together with their system-level coupling potential in carbon-intensive industries such as steel, cement, and power generation. Finally, the key scientific issues and engineering challenges currently facing ICCU are analyzed from the perspectives of fundamental mechanisms, material design, and system engineering, and future development directions are proposed. This review highlights that elucidating multiscale synergistic mechanisms, developing high-performance dual-function materials, and optimizing system integration are crucial to promoting the industrial application of ICCU technology.

Separations doi: 10.3390/separations13060178

Authors: Tianyi Chen Xudong Liu Yaobin Lai Jiayi Zan Xuxia Zhang

The thiourea grafting method can effectively improve the ability of activated carbon to recover chloroauric acid (AuCl4−). Conventional grafting strategies rely on acyl halide reactions using reagents such as SOCl2 and CH2Cl2, which suffer from instability and high toxicity. Herein, we propose a green grafting strategy for thiourea by activating carboxyl groups with EDC-HCl/NHS in acetonitrile, followed by the amidation reaction to obtain thiourea-modified carbon (AC-NCS). FT-IR and XPS analyses confirm the successful grafting of thiourea onto the activated carbon surface. Compared with pristine activated carbon, the adsorption capacity of AC-NCS is 104.8 mg/g, increased by 5.76 times. Furthermore, it maintains a recovery rate of 84.2% after three cycles. XPS and FT-IR further reveal that adsorption occurs on the thiourea sulfur atoms (C=S) and protonated primary amines(-NH3+), and the recovery of chloroauric acid is achieved through a synergistic “reduction–electrostatic attraction” mechanism. This method reduces the dependence on highly toxic reagents and provides a promising approach for the efficient and green recovery of gold from secondary resources.

Separations doi: 10.3390/separations13060177

Authors: Ruiyang Chen Qinghui Jia Anzhen Fu Fan Yang Yixin Dai Jingzhe Sun Liya Liu Ye Liu Shuang Bi

Fruity natural flavors are widely used in food, cosmetics, and tobacco products, and their flavor profiles directly affect the sensory quality of the final products. However, the volatile organic compound systems in these flavors are highly complex, and severe co-elution among volatile components makes effective component resolution a persistent analytical challenge. In this study, comprehensive two-dimensional gas chromatography–olfactometry–time-of-flight mass spectrometry (GC×GC-O-TOF-MS) was employed to separate and identify volatile odor compounds in three natural fruit flavor extracts: plum, jujube, and grape. A total of 113, 103, and 85 volatile odor compounds were identified from the plum, jujube, and grape extracts, respectively. By progressively adjusting the split ratio, aroma extract dilution analysis was performed, leading to the screening of 14, 11, and 32 aroma-active compounds from the three extracts, respectively. Compounds with high flavor dilution factors were subjected to quantitative analysis, and their odor activity values were calculated. Subsequently, omission and recombination experiments were conducted to confirm the key aroma-active compounds in each extract. The results showed that octanal was a key aroma compound shared by the plum and jujube extracts, while ethyl cinnamate was common to both the plum and grape extracts. Through a molecular sensory science approach and utilizing GC×GC-O-TOF-MS chromatographic separation technology, this study provides a reliable analytical platform for aroma characterization in complex samples. It also establishes a critical theoretical and data foundation for precisely identifying key aroma-active components and implementing targeted aroma modulation to enhance the natural flavor quality of fruits.

Separations doi: 10.3390/separations13060176

Authors: Priyanka Mondal Iris Cornet Inge Noëlle Adrienne Van Bogaert Anita Buekenhoudt Kristien De Sitter

Efficient recovery of long-chain dicarboxylic acids (LCDAs) from aqueous fermentation broths is a key challenge for the industrial development of bio-based LCDA production. This study evaluates liquid–liquid extraction (LLE) as a downstream recovery strategy, comparing physical extraction (PE) and reactive extraction (RE) for DCA 12, DCA 16, and DCA 18. The novelty of this work lies in demonstrating that LCDA extraction is governed by mechanisms fundamentally different from those of short- and medium-chain dicarboxylic acids. Whereas shorter chain dicarboxylic acids are mainly controlled by dissociation degree, LCDA recovery is strongly influenced by carbon-chain apolarity, low aqueous solubility, and compound losses through agglomeration, precipitation, and/or micellization. PEs enabled the selective recovery of the more hydrophobic DCA 16 and DCA 18 over DCA 12, confirming the dominant role of chain length in LCDA separation. In contrast, RE with Aliquat®336 maximized total LCDA recovery, achieving extraction efficiencies above 85%, but with reduced selectivity. Validation in autoclaved fermentation broth from UCO feedstock confirmed the potential of Aliquat®336 in octanol for high LCDA recovery, while revealing lower extraction efficiencies than in model mixtures due to broth matrix complexity. Overall, this study establishes LLE as a promising platform for LCDA recovery and highlights that future downstream process design must balance total recovery, chain-length selectivity, and broth-specific matrix effects.

Separations doi: 10.3390/separations13060175

Authors: Miljana G. Stojanović Ivan M. Savić Jovana Vunduk Ivana M. Savić Gajić

In contemporary research on natural bioactive compounds, increasing emphasis is placed on the development of efficient and sustainable extraction technologies. This study aimed to develop and optimize an innovative extraction process for wild cyclamen (Cyclamen purpurascens Mill.) tubers to maximize the yield of total extractives using a Box–Behnken design. The effects of four extraction parameters were evaluated on the system response. A second-order polynomial model accurately described the extraction process, yielding a coefficient of determination of 0.919. The liquid-to-solid ratio was identified as the dominant factor affecting the extraction efficiency compared to the other factors investigated. The optimal extraction conditions were as follows: extraction time of 15.5 min, 13% (v/v) ethanol, liquid-to-solid ratio of 13.5 mL/g, and extraction temperature of 34 °C, resulting in a yield of 53.44%. The optimized process yielded a significant saponin content of 16.19 g/100 g, while the levels of phenolic compounds (132.52 mg GAE/100 g) and flavonoids (12.04 mg QE/100 g) were also quantified. UHPLC–ESI–MS/MS analysis confirmed the presence of triterpene saponins, flavonoids, and terpenoids. DPPH, ABTS+, and CUPRAC assays indicated the antioxidant potential of the extract, while the minimum inhibitory concentration assay showed antibacterial activity against Staphylococcus aureus and Escherichia coli. The established chemical profile and observed biological activities provide the basis for further evaluation of wild cyclamen tubers as a source of bioactive secondary metabolites.

Separations doi: 10.3390/separations13060174

Authors: Qiming Zhuo Rong Zou Xuan Du Leilei Gao Hongxiang Xu Jiushuai Deng Wenli Liu He Zhang Kejia Ning

Low-rank ultrafine flotation clean coal typically yields filter cake moisture above 20% due to abundant oxygen-containing functional groups and strong surface hydrophilicity. Conventional polyacrylamide (PAM) flocculants are hydrophilic and improve dewatering only by altering cake porosity, not by reducing particle surface hydrophilicity, so they remove little adsorbed water. In this study, hydrophobically modified anionic polyacrylamides (HMAPAM) were synthesized by grafting lauryl acrylate onto APAM. FTIR, 1H NMR, XPS, and SEM confirmed the grafting and progressive enrichment of hydrophobic alkyl chains on the surface. Moderate hydrophobic modification markedly improved solid–liquid separation. HMAPAM-D (APAM/LA = 4.5:0.5) achieved a settling velocity of 0.817 cm/s at 9 mg/L, 50.2% higher than APAM, and reduced filter cake moisture to 16.64% at 1 mg/L under 0.6 MPa versus 19.39% for unmodified APAM. Excessive modification (HMAPAM-E, 4:1) promoted intramolecular self-association, producing heterogeneous flocs and higher filtration resistance that degraded dewatering efficiency. The performance gain stems from hydrophobic association combined with adsorption bridging. These results clarify how hydrophobic group content controls flocculation and dewatering, informing the design of better flocculants for this type of coal slurry.

Separations doi: 10.3390/separations13060173

Authors: Héctor Calvopiña Wilson Pavón Kevin Chacha Eduardo Bazurto Aleph Salvador Acebo Arcentales Angel Fabian Moreira Romero

This study aims to optimize the performance of cyclone separators by simultaneously maximizing separation efficiency and minimizing pressure drop through a CFD-based multi-objective optimization framework. The research objectives are explicitly focused on (i) developing accurate predictive surrogate models for cyclone behavior and (ii) identifying optimal geometric configurations that balance both performance criteria. The methodology integrates Design of Experiments (DOE), Response Surface Methodology (RSM), and the Non-dominated Sorting Genetic Algorithm II (NSGA-II), using a full factorial design of 25 simulations to construct fourth-order surrogate models. This formulation was strictly necessary to capture the severe non-linearities observed in preliminary CFD runs. These models exhibited high predictive capability, with coefficients of determination (R2) above 0.94. The NSGA-II optimization generated a Pareto-optimal front that clearly describes the trade-off between separation efficiency and pressure drop, enabling systematic decision-making. The selected optimal configuration achieved a separation efficiency of 94.5% and a pressure drop of 194.78 Pa. CFD validation confirmed the robustness of the surrogate models, with relative errors below 1% for efficiency and below 5% for pressure drop. Overall, the results demonstrate that integrating CFD, surrogate modeling, and evolutionary optimization provides a reliable and computationally efficient strategy for cyclone separator design optimization.

Separations doi: 10.3390/separations13060172

Authors: Murat Altan Uğur Şahin

Dialysis is a widely used and effective method for removing urea from protein solutions, particularly following protein denaturation or solubilization. Due to its small molecular weight (~60 Da), urea can pass through semipermeable membranes, while larger protein molecules are retained. Therefore, the performance of dialyzers in urea removal is critically important. Dialyzer performance is commonly evaluated according to the method specified in the ISO 8637-1 standard, which is based on the measurement of urea concentrations in aqueous solutions before and after dialysis. In this study, a novel diol-modified silica, typically used as a column packing material in HPLC, was synthesized and applied as a new column. Using this column, a new HPLC method combined with a refractive index detector (RID) was developed for the sensitive and accurate determination of urea in aqueous sample solutions. This study is the first to report quantitative urea analysis using a diol-modified column packing material. Method accuracy was evaluated through standard addition-recovery experiments. The method showed recovery values between 99 and 110%, a limit of detection (LOD) of 0.66 mg/L, a limit of quantification (LOQ) of 2.0 mg/L, and a relative standard deviation (RSD) of 4.4%.

Separations doi: 10.3390/separations13060171

Authors: Tao Zhang Yonghong Zhao

As eutrophication worsens, countries including China, the US, France, Sweden, and South Korea have tightened phosphorus (P) discharge limits for wastewater treatment plants (WWTPs). This paper first reviews China’s evolving P regulations, then classifies P removal technologies into physical, chemical, biological, and combined methods. Analysis of current WWTPs in China shows that biological P removal alone is insufficient, making chemical P removal (CPR) a necessary supplement or primary approach. Thus, the review focuses on CPR technologies: chemical precipitation, ion exchange, adsorption, electrocoagulation, magnetic methods, hybrid biological-chemical methods, and P recovery technologies. For each, the principles, materials, application conditions, advantages, and disadvantages are discussed. This review aims to guide the selection, application, and future research of CPR processes.

Separations doi: 10.3390/separations13060170

Authors: Runxi Gui Xiaogang Lian Maolin Li Mingdi Liu Lina Zhou Songgu Wu Qiuxiang Yin

Accurate measurement and control of impurities are critical for ensuring the quality and therapeutic performance of solid-state pharmaceutical formulations. This study introduces a rapid, minimal sample preparation analytical approach for quantifying low-level dalmelitinib impurities in dalmelitinib mesylate, employing near-infrared (NIR) spectroscopy combined with partial least squares regression (PLSR). To mimic actual manufacturing conditions, a mixture system was designed comprising dalmelitinib mesylate, dalmelitinib impurity, and formulation excipients. Various spectral preprocessing strategies were systematically evaluated, including Savitzky–Golay first derivative (SG1st), Savitzky–Golay second derivative (SG2nd), multiplicative scatter correction (MSC), standard normal variate (SNV), wavelet denoising, wavelet compression, and their combinations. The optimal model was obtained using SG1st combined with wavelet denoising. The resulting PLSR model (7 latent variables) showed good predictive performance, with an R2 of 0.99569 and an RMSECV of 0.00315. The limit of detection (LOD) and limit of quantification (LOQ) were 0.234% and 0.708%, respectively, demonstrating applicability for monitoring low-level impurities in pharmaceutical formulations. Method validation demonstrated satisfactory precision (RSD < 3%), accuracy (100.77–102.01%), and stability over 24 h (RSD ≤ 4.75%). Compared with conventional solid-state analytical techniques, the proposed NIR–PLSR framework enables rapid, non-destructive analysis with minimal sample preparation. The combination of derivative preprocessing and wavelet denoising improved extraction of impurity-related spectral information in complex pharmaceutical systems, highlighting the potential of this approach for process analytical technology (PAT) and pharmaceutical quality monitoring.

Separations doi: 10.3390/separations13060169

Authors: Huanping Zhang Huichao Lv Xue Gao Shuhong Wang Jinhong Song Yang Jiao Rongrong Cai

Subcritical water extraction (SWE) is an eco-friendly and efficient technique for isolating bioactive ingredients from natural products. To improve the extraction yield of Artemisia argyi leaf polysaccharides (AAPs), a three-stage hybrid optimization strategy combining single-factor experiments, response surface methodology (RSM), neural network (NN), and direct search algorithm (DSA) was proposed. Single-factor experiments were used to screen key parameters. A Box–Behnken design (BBD)-based RSM was applied for preliminary optimization. A {3, 5, 1} structured NN was trained using 63 datasets from RSM, and DSA was used to determine the globally optimal process parameters. The optimal conditions were obtained as follows: extraction time 17.72 min, liquid-to-solid ratio 92.83 mL/g, extraction temperature 123.35 °C, stirring speed 1800 r/min, and natural pH. Under these conditions, the experimental AAP extraction yield reached 6.99%, with a relative error of only 1.16% compared with the predicted value of 6.91%. Fourier transform infrared (FT-IR) spectroscopy confirmed that the product exhibited typical polysaccharide structural characteristics. The integrated RSM–NN–DSA framework provides a reliable and high-precision approach for optimizing SWE of plant polysaccharides, showing good potential for industrial applications.

Separations doi: 10.3390/separations13060168

Authors: Stéphanie Mireille Tsanang Atzin Moran Mendoza Ali Zgheib Maximilian Hans Fischer Annett Wollmann Ursula E. A. Fittschen Thomas Schirmer Andreas Schmidt

Five pH- and light-switchable punicine derivatives were investigated as collectors in the flotation of spodumene and quartz. At the natural pH of the minerals, the punicine substituted with a C17 alkyl residue showed the best recovery under daylight (>5000 lux), with values up to 65.0% and 97.8%, and also the highest absolute recovery difference between the two minerals. For pH values of 2 and 12, the punicine collector with a viologen moiety and a C9 alkyl residue shows the best absolute recovery difference, with values of 32.45% and 32.88%, respectively. Studies on the influence of pH, particle size distribution, UV light and darkness, ζ-potential measurements, and IR spectroscopic measurements were carried out to gain insight into the mechanisms.

Separations doi: 10.3390/separations13060167

Authors: Yibo Bai Rui Li Liman Zheng Yu Zhang Huanlu Song Jing Liu Weining Huo Wen Nie Suyan Wan

The flavor profile of Longmen rice vinegar directly influences consumer purchase intention, and understanding its variation during fermentation is crucial for final product quality control. In this study, the flavor dynamics during the fermentation of Longmen rice vinegar were systematically investigated. Sensory evaluation indicated that acidity increased significantly during the acetic acid fermentation stage, while alcoholic and fermented odors decreased continuously. Instrumental analysis identified 129 volatile compounds, predominantly esters, alcohols, and acids. Based on relative odor activity value (r-OAV) analysis, acetic acid, 3-methylbutyl acetate, 2,3-butanedione, benzeneacetaldehyde, phenethyl alcohol, ethyl acetate, 2-phenylethyl acetate, ethyl 4-methyl-pentanoate, 3-methyl-1-butanol, and 3-methylbutanal were determined to be the major contributors to the overall aroma. Orthogonal partial least-squares discriminant analysis (OPLS-DA) further screened 21 key differential compounds. Significant variations in organic acid and amino acid contents during fermentation were also observed. Correlation analysis revealed relationships between key aroma compounds and organic, as well as amino, acids. These findings establish a foundation for monitoring flavor dynamics during the fermentation of Longmen rice vinegar.

Separations doi: 10.3390/separations13060166

Authors: Giovanna Lo Vecchio Rosaria Costa Rossella Vadalà Laura De Maria Rita De Pasquale Giuseppe Tardiolo Nicola Cicero

The chemical composition and sensory profile of coffee are influenced by brewing method, namely extraction pressure, temperature, contact time, and equipment. This study compared coffee prepared with a traditional moka pot, a conventional espresso machine, and a novel Italian device (Kamira). Volatile compounds were analyzed by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography–mass spectrometry (GC–MS), leading to the determination of furan (34–42%), pyrrole (4–10%), and pyrazine (13–14%) derivatives. The most abundant fatty acids were palmitic (36–37%), linoleic (40%), and oleic (11%) acids. Physicochemical parameters (total solids, pH, and refractive index) were also measured. Caffeine and chlorogenic acids were quantified by liquid chromatography (HPLC). Differences in chlorogenic acids and volatile compounds were associated with variations in bitterness, acidity, astringency, and aroma intensity. Finally, a trained panel performed sensory evaluation to evaluate the olfactory and flavor attributes of the three types of coffee brews. Significant differences emerged among brewing systems. Espresso showed the highest caffeine content (55.3 ± 4.1 mg/100 g) and total solids (2.61 ± 0.11 g/100 g), together with a stable crema and intense sensory attributes. Moka coffee exhibited a rich aromatic profile but limited crema. The Kamira device produced an abundant crema and a chemical profile partially comparable to espresso. These findings confirm that brewing technology markedly affects coffee composition and sensory perception.

Separations doi: 10.3390/separations13060165

Authors: Metodi Mladenov Ina Yotkovska Milena Nedkova-Shtipska Irina Karadjova Galia Gentscheva

The present work investigates the chemical composition of black cumin (Nigella sativa L.) cake obtained as a by-product of cold-pressed oil extraction. The aim of the study is to assess its potential for further utilization and secondary applications. By applying a combination of analytical techniques, including chemical analysis, Soxhlet extraction, ICP-OES, ICP-MS, FTIR, and SEM-EDS, the material was characterized as a rich organic matrix with a significant residual fat content (approximately 20%), proteins, and essential mineral elements such as K, Ca, Fe, Cu, Zn, and P, while containing low levels of toxic elements. Since cold pressing preserves residual bioactive compounds, and considering the high content of essential elements, black cumin cake represents a promising ingredient for food supplements. In addition, its porous surface structure observed by SEM-EDS, together with the functional groups identified by FTIR analysis, suggests potential sorption properties. These findings position black cumin cake as a promising resource within the framework of sustainable agro-industrial waste valorization strategies.

Separations doi: 10.3390/separations13060164

Authors: Haibo Wang Duo Chen Linglang Meng Haobin Li Yanbing Lin Aowei Liu Xia Huang Juan Li

Atractylodis lancea (Cangzhu) and Atractylodes macrocephala (Baizhu) are two traditional Chinese medicines with complex chemical compositions. However, a comprehensive comparative analysis of their constituents remains lacking. In this work, an ultra-high-performance liquid chromatography coupled with quadrupole-Orbitrap tandem mass spectrometry (UPLC-Q-Orbitrap-MS/MS) method was developed for the rapid characterization and differentiation of chemical components in Cangzhu and Baizhu. Chromatographic separation was achieved on a C18 column with gradient elution, and compounds were detected using electrospray ionization in both positive and negative modes. By analyzing characteristic fragmentation patterns and neutral losses, a total of 111 compounds were tentatively identified, including 14 common components (present in both species) and 97 differential components (unique to one species). This study presents the first comprehensive comparative chemical profiling of the two Atractylodes species, offering valuable references for pharmacodynamic material basis studies and quality control.

Separations doi: 10.3390/separations13060163

Authors: Jingyi Wang Yu Zhang Lingen Zhang

Spent lithium-ion battery electrolytes contain fluorine-, sulfur-, and phosphorus-bearing toxins, necessitating deep detoxification and directional conversion into C1–C6 light hydrocarbons. To elucidate the specific catalytic roles and sequential activation of cathode metals (Li, Ni, Co, Mn), this work systematically deconvolutes their mono- and multi-metallic migration mechanisms over a CaO-ZSM-5* catalyst during vacuum catalytic pyrolysis (530 °C, 100 Pa). Results reveal that Li+ and Ni2+ dominate C–O bond cleavage in carbonates and CaO-ZSM-5*-assisted decarboxylation and oxygen fixation, significantly increasing the relative hydrocarbon content. Conversely, Co2/3+ and Mn4+ release reactive oxygen species, causing deep oxidation of hydrocarbons into CO2 and antagonizing the targeted conversion. In multi-metallic systems, forming composite metal oxides (MxNyOz) increases the energy barrier for releasing active catalytic ions, hindering carbonate cleavage and leaving unreacted carbonate feedstocks. For detoxification, F and P are effectively immobilized as CaF2 and Ca2P2O7. The relative content of detected gas-phase nitriles is minimized to <2% due to the strong antagonistic effect of Ni2+ on Li+-promoted hexanedinitrile cleavage, while sulfur species derived from 1,3-propane sultone are converted to SO2 and ultimately mineralized as calcium and metal-sulfur salts. Mechanistically, product distributions and crystallographic properties suggest a hypothesized sequential activation model—Li+ → Ni2+ → Mn4+—governing reactivity, whereas Co2/3+ does not participate in the synergistic detoxification and selective upgrading process. This migration–reaction coupling framework provides critical insights for cathode-assisted in situ catalytic pyrolysis and closed-loop electrolyte recycling.

Separations doi: 10.3390/separations13060162

Authors: Jasmina Petreska Stanoeva Marina Stefova

Chromatography represents a cornerstone of modern analytical chemistry, enabling the separation, identification, and quantification of constituents of complex chemical systems. Its development in the Republic of North Macedonia is closely linked to the evolution of national academic institutions and industrial analytical capacity. This study provides a combined historical overview and Scopus-based scientometric analysis of chromatography research in North Macedonia, focusing on institutional development, research groups, methodological evolution, and industrial contribution. Data were obtained from Scopus-indexed publications, institutional records, and key publications. Ss. Cyril and Methodius University in Skopje (UKIM) emerges as the dominant research hub, particularly through the Institute of Chemistry, Faculty of Natural Sciences and Mathematics, and the Faculty of Pharmacy, Faculty of Agriculture, supported by the Macedonian Academy of Sciences and Arts (MANU), Goce Delčev University in Štip, and several specialized applied research institutions. The pharmaceutical industry, particularly Alkaloid AD Skopje and Replek Farm, plays a significant role in chromatographic method application and validation. High-performance liquid chromatography (HPLC), gas chromatography (GC), and liquid chromatography–mass spectrometry (LC–MS) dominate research applications, primarily in phytochemistry, pharmaceutical analysis, food chemistry, and environmental science, while MALDI-TOF mass spectrometry has been integrated into the proteomics activity at MANU. The results demonstrate a highly centralized but scientifically productive research system with increasing methodological sophistication and international cooperation.

Separations doi: 10.3390/separations13060161

Authors: Suzan Makawi

This study provides a comprehensive phytochemical and biological evaluation of Acacia nilotica and Acacia seyal samples collected from Khartoum State, Sudan. Methanolic extracts of A. nilotica leaves (SN), A. seyal leaves (TL), and A. nilotica seeds (S) were evaluated for total phenolic content (TPC), total flavonoid content (TFC), antioxidant activity (DPPH radical scavenging and reducing power), and antimicrobial activity against selected pathogenic microorganisms. High-performance liquid chromatography coupled with diode array detection (HPLC-DAD) was used to identify and quantify individual phenolic compounds. The SN sample exhibited the highest TPC (287.527 mg GAE/g), DPPH scavenging activity (96.815%), and reducing power (2.356), whereas TL showed the highest flavonoid content (155.296 mg QE/g). All samples demonstrated considerable antifungal activity against Candida albicans, while antibacterial activity varied according to species and extract type. HPLC-DAD analysis revealed the presence of major phenolic compounds, including naringenin, gallic acid, catechin, and methyl gallate, with notable variations among the investigated samples. In addition, several unidentified peaks were observed in the chromatographic profiles, suggesting the presence of additional phytochemical constituents under the applied analytical conditions. A strong positive correlation was observed between total phenolic content and antioxidant activity (R2 > 0.97), indicating the possible contribution of phenolic compounds to the observed bioactivity. Overall, this study provides further insight into the relationship between phenolic composition and biological activity in Acacia species and highlights their potential as natural sources of bioactive compounds for pharmaceutical and food applications.

Separations doi: 10.3390/separations13060160

Authors: Guang Shi Liu Yang Ling Wu Zheng Ma Bowen Tan Ji Li

Carbon dioxide emissions are a major concern for coal-fired power plants. A capture and utilization method is highly demanded. The wastewater generated by a power plant contains a high concentration of Na+. Using wastewater salts to absorb carbon dioxide for sodium carbonate production is a promising strategy, as it can achieve carbon capture and utilization and wastewater resource utilization. However, the salt concentration in raw wastewater from coal-fired power plants is generally insufficient to achieve sustainable carbon capture; thus, concentrating the Na+ in the wastewater is key. In this study, desulfurization wastewater was investigated as a source of salts. The reverse osmosis (RO) process was selected for salt concentration. As wastewater is significantly complex and unsuitable for direct RO treatment, pre-treatment was conducted. For chemical oxygen demand (COD) removal, Fenton oxidation (49.7%) and electrochemical oxidation (49.3%) achieved better results than microelectrolysis (25.3%). Precipitation showed a strong ability to remove hardness. The removal efficiencies for Mg2+ and Ca2+ were 99.9% and 99.8%, respectively. It gave 8.6% COD removal as well. Additionally, 89.8% of ammonia was removed by stripping. To further decrease the pollutant concentrations, activated carbon was used for adsorption. RO then concentrated the pre-treated wastewater after nanofiltration. The final level of NaCl was 40.4 g/L after concentration. This was lower than that required to concentrate the water, which contained only NaCl. This is due to the presence of impurities left in the wastewater after pre-treatment. The study reveals that pre-treatment is essential to achieve the desired NaCl concentration in RO with the ultimate goal of CO2 capture.

Separations doi: 10.3390/separations13060159

Authors: Xin Chen Yifan Li Qian Wu Ting Wang Na Wang Lina Zhou Hongxun Hao Jingkang Wang

Guanidinoacetic acid (GAA), an important feed additive, shows poor powder properties due to its morphological characteristics. In this study, GAA was employed as a model compound to investigate the regulatory effects of polymeric additives (hydroxypropyl methyl cellulose, hydroxypropyl cellulose, and polyacrylamide) on its crystal growth and powder properties through integrated experimental and molecular simulation approaches. In situ single-crystal growth experiments reveal that hydroxypropyl methyl cellulose (HPMC) and hydroxypropyl cellulose (HPC) can selectively suppress the growth of the (11–1) crystal face while slightly promoting the growth of the (011) crystal face, thereby altering the relative growth rates and modifying the final crystal morphology. However, polyacrylamide (PAM) inhibits the growth of both the (11–1) and (011) crystal faces, resulting in negligible alteration of GAA crystal morphology. Growth kinetic analysis indicates that crystal growth is governed by a surface integration-controlled mechanism. Molecular dynamics simulations further demonstrate that the additive preferentially adsorbs onto specific crystal faces, reducing interfacial solute accumulation and inhibiting molecular diffusion. Collectively, these findings demonstrate that additives exert synergistic control over crystal morphology and particle size distribution through selective adsorption and modulation of interfacial mass transfer. This research provides mechanistic insights and theoretical guidance for the regulation of crystallization processes via additive intervention.

Separations doi: 10.3390/separations13060158

Authors: Aleksandras Chlebnikovas

Contaminated gas flows are encountered in most industrial processes and require efficient removal of fine dispersed particles of various types and characteristics. Conventional cyclones are widely used under harsh operating conditions; however, their separation efficiency for fine particulate fractions remains relatively low. In this study, next-generation cyclones with a multichannel design featuring cylindrical and spiral casings are investigated, enabling particle collection efficiencies of approximately 90% for particles with a diameter of 2 µm. Under harsh microclimatic conditions—particularly at high humidity levels of 70% or higher and elevated temperatures of 50 to 200 °C—such technology is prone to clogging, necessitating complex regeneration procedures. Recent research has focused on improved channel geometries incorporating secondary peripheral flows, adapted for gas cleaning in harsh environments. Experimental results demonstrate effective removal of fine-dispersed glass and clay particles up to 20 µm in size at initial concentrations of 0.5–15 g/m3. The theoretical assessment of the influence of harsh gas flow conditions includes analyses of critical flow characteristics and the mechanical forces acting on fine particles under varying temperature and humidity conditions. The results indicate a maximum purification efficiency of up to 87.3% with an aerodynamic pressure drop of 440 Pa. The impact of harsh microclimatic conditions is most pronounced in the magnitudes of the centrifugal and drag forces: with an increase in the gas flow temperature by every 50 °C within the range from 0 to 200 °C, these forces increase by factors of 7.3–32.7 and 4–6.3, respectively.

Separations doi: 10.3390/separations13060157

Authors: Qinchuan Xu Haiyang Wen Mengna Xu Chuanlei Liu Hui Sun Chao Zhu Feifei Long Jingwen Luo

The antifoaming performance of natural gas desulfurization solvents is critical for maintaining product gas quality and ensuring the safe operation of processing units. Hydrocarbon impurities can enter amine solutions through feed-gas entrainment, wellhead flowback carryover, and leakage of equipment lubricants. These contaminants may gradually accumulate in the solvent system and become a significant contributor to foaming. To address the industrial demand for rapid quantitative determination of hydrocarbon contaminants in desulfurization solvents, this study investigates in-service UDS-series solvents and representative samples collected from a natural gas purification plant in western Sichuan. NMR spectroscopy and GC-MS analyses reveal that the impurities are predominantly n-alkanes in the C13-C18 range, based on which a corresponding reference standard oil was prepared. COSMO-RS calculations combined with molecular interaction analysis identify n-hexane as the optimal extraction solvent. The ultraviolet spectrophotometric method commonly used to determine hydrocarbons in environmental water samples shows limited sensitivity to long-chain n-alkanes and requires strong acid pretreatment that disrupts the amine solvent matrix, rendering it unsuitable for UDS solvents. In contrast, the n-hexane extraction-GC-FID method showed good linearity, precision, and accuracy, meeting engineering analytical requirements for monitoring hydrocarbon contamination in MDEA-based UDS desulfurization solvents.

Separations doi: 10.3390/separations13060156

Authors: Shuxun Li Yuqiong Li Haibin Li Wenjie Zhang Ci Qu Meiguang Jiang Xi Yang

During flotation, the hydration behavior of collector head groups plays an important role in determining collector hydrophilicity and interfacial adsorption behavior. However, although computation-assisted flotation studies have extensively investigated collector–mineral interactions, systematic comparisons of the intrinsic hydration characteristics of different collector head groups under unified computational conditions remain limited. In this work, density functional theory (DFT) calculations using the B3LYP functional with Grimme dispersion correction were conducted to investigate the hydration interactions between water molecules and representative head groups of five sulfide mineral collectors, including xanthate (X), dithiocarbamate (DTC), dithiophosphate (DTP), dithiophosphinate (3418A), and thiocarbamate (Z-200), and five oxide mineral collectors, including oleate (OA), oxidized paraffin soap (OPS–C12), dodecyl sulfonate (DS), styrene phosphonic acid (SPA), and salicylhydroxamic acid (BHA). The results show that oxide mineral collectors exhibit significantly stronger hydration interactions than sulfide mineral collectors. Sulfide collectors mainly form weak S···H–O hydrogen bonds with relatively long H-bond distances (2.27–2.61 Å), whereas oxide collectors predominantly form stronger O···H–O hydrogen bonds with shorter distances (1.66–2.24 Å). The total hydration binding energies of sulfide collectors range from −150 to −290 kJ/mol, while those of oxide collectors range from −244 to −491 kJ/mol. Among the studied collectors, SPA exhibits the strongest hydration tendency due to its highly charged phosphonate group, whereas Z-200 shows the weakest hydration interaction. The results indicate that hydration behavior is strongly influenced by head group type, charge state, and hydrogen-bond characteristics.

Separations doi: 10.3390/separations13050155

Authors: Duanxu Hou Haihao Wang Daqing Hou Hongying Zhu Hongrun Song Jingyan Zhang Qingguo Shao

The cylindrical hydrocyclone can be regarded as a special-shaped hydrocyclone comprising entirely cylindrical sections without conical sections, featuring a unique flat-bottom design combined with central discharge, which promotes substantial particle circulation flow in the separation chamber, directly affecting separation performance. A validated TFM model is employed to investigate the flow field and particle motion behavior in the cylindrical hydrocyclone. The results indicate that the distributions of tangential velocity, radial velocity, pressure, and pressure gradient in the cylindrical hydrocyclone are consistent with patterns observed in the conventional hydrocyclone. The flat-bottom design combined with the central discharge configuration of the cylindrical hydrocyclone results in two distinct axial velocity transitions in the bottom region, forming downward axial velocity flow around the air core. Accordingly, particles moving toward the spigot must pass through the internal swirling flow region, facilitating the fine particles entrained by the coarse particles to enter the internal swirling flow, reducing the misplacement of fine particles in the underflow. Simultaneously, coarse particles entrained by the internal swirling flow return to the external swirling flow region under centrifugal force, forming a substantial coarse particle circulation flow. As a result, a mass of coarse particles accumulates in the separation chamber, hindering the centrifugal settling of medium particles and resulting in an enlarged cut size and severe coarse particle misplacement.

Separations doi: 10.3390/separations13050154

Authors: Qiaorui Sui Xuan Hao Jiale Li Jin Zhou Suliang Yang

This work reports a novel dithiophosphinic acid extractant, bis(isobutylphenyl)dithiophosphinic acid (HL), for the mutual separation of Am(III) and Cm(III) and for the separation of trivalent actinides (An(III)) from lanthanides (Ln(III)). The compound was successfully synthesized and structurally confirmed by 1H and 31P NMR spectroscopy. Focusing specifically on Am(III) and Cm(III), the extraction behavior was systematically investigated as a function of pH, ligand concentration, nitrate concentration, and temperature. Compared with the conventional extractant, bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HL301), HL exhibits stronger extraction efficiency (pH1/2 = 3.39 for Am(III) and 3.64 for Cm(III)) and a notably improved separation factor for Am(III) over Cm(III) (SFAm(III)/Cm(III) = 4.8), while retaining excellent separation ability for An(III) from Ln(III). The extraction proceeds via a cation-exchange mechanism, yielding a 1:3 metal-extractant complex with the release of three protons. Increasing nitrate concentration suppresses extraction due to the competition for metal ion between NO3− in the aqueous phase and the extractant. The extraction reaction is endothermic with negative entropy changes, exhibiting ΔH° values of 24.06 kJ·mol−1 for Am(III) and 27.12 kJ·mol−1 for Cm(III) at 298.15 K, along with ΔS° values of −90.63 J·mol−1·K−1 and −89.11 J·mol−1·K−1, respectively. This work offers a promising extractant for the separation of Am(III) from Cm(III) and An(III) from Ln(III), and mechanistic insights into coordination–selectivity relationships involving soft sulfur donors.

Separations doi: 10.3390/separations13050153

Authors: Shaomeng Huang Junhan Huyan Xinyuan Li Haiting Zhang

Poorly soluble hydrophobic organic pollutants, such as indole and diethyl phthalate (DEP), are difficult to remove efficiently from complex industrial wastewater due to low solubility and competitive adsorption. In this study, low-rank coal-based activated cokes derived from Wanli long-flame coal and Zhaotong lignite were modified through a combined process of acid-washing pretreatment and trimethylchlorosilane (TMCS) grafting. The acid-washing step effectively removed ash and unblocked pores, increasing the specific surface area and pore volume of the optimized Zhaotong lignite-based sample by 43.7% and 53.3%, respectively. Subsequent TMCS grafting successfully introduced hydrophobic methyl groups onto the surface, significantly enhancing hydrophobicity. The water contact angles of the composite materials (acid-washed plus TMCS-grafted) increased to 127.3° and 139.7°, compared to 117.8° and 112.6° for the original samples. The modified adsorbent derived from Zhaotong lignite exhibited high adsorption capacities, reaching 139.47 mg·g−1 for indole and 120.19 mg·g−1 for DEP in single-component systems, representing an increase of 20.1% for indole and 28.7% for DEP compared to the unmodified adsorbent. More importantly, in a competitive system containing phenol at PH = 10, the materials demonstrated superior selectivity towards the target hydrophobic pollutants. The phenol removal rate was 65.97%, and the removal rates for indole and DEP increased sharply to 98.17% and 92.17%, respectively. This work provides a feasible strategy for the advanced treatment of complex organic wastewater using coal-based adsorbents, achieving a dual enhancement in both adsorption capacity and selectivity.

Separations doi: 10.3390/separations13050152

Authors: Chunli Li Tianzhu Ma Yuze Sun Kaile Shi Wen Liu Rui Wang Jiapeng Liu

Fatty alcohols and aliphatic hydrocarbons occur abundantly in nature and serve as critical feedstocks for the surfactant and fuel industries, respectively. However, their industrial-scale separation and purification are significantly hampered by high boiling points and the formation of complex azeotropes. To address these challenges, this study explores a five-column high-vacuum pressure-swing distillation (HVPSD-5C) strategy. Vapor–liquid equilibrium (VLE) analysis of the key components (n-hexanol, n-octanol, n-dodecane, and n-tridecane) validated the thermodynamic viability of the process and established optimal operating conditions. To further enhance efficiency, a heat-pump-integrated configuration (HPI-HVPSD-5C) featuring vapor recompression and heat integration was designed, optimized, and evaluated. Comparison with the baseline HVPSD-5C process demonstrates that the HPI-HVPSD-5C configuration significantly improves sustainability and economics, reducing the total annual cost (TAC) by 17.48%, CO2 emissions by 16.09%, and energy consumption cost by 12.79%. These findings provide a robust framework for the efficient separation of fatty alcohols from aliphatic hydrocarbons, offering a valuable reference for the purification of other pressure-sensitive azeotropic mixtures.

Separations doi: 10.3390/separations13050151

Authors: Duanxu Hou Haihao Wang Daqing Hou Hongying Zhu Hongrun Song Honghe Deng Qingguo Shao

The outlet diameter of hydrocyclones is a critical structural parameter that impacts product distribution and separation performance, drawing significant attention. In this paper, the separation efficiency and particle motion behavior in the cylindrical hydrocyclone with varying spigot diameters and vortex finder diameters are systematically analyzed using a TFM model. The numerical results indicate that a larger spigot diameter and a smaller vortex finder diameter reduce the axial velocity and expand the external swirling flow region, while a smaller spigot diameter and a larger vortex finder diameter enhance the particle circulation flow ratio and the coarse particle circulation flow proportion, thereby increasing the cut size. Slightly reducing the spigot diameter and increasing the vortex finder diameter enhances the separation accuracy. Nevertheless, for Du = 0.075 D and Do ≥ 0.4 D, the recovery rate in the underflow remains below 50% for all particle sizes, exhibiting severe particle misplacement and loss of separation efficiency. For Du = 0.125 D, the reduction in coarse particle misplacement in the overflow is attributed to the abrupt changes in the coarse particle circulation flow proportion and medium particle circulation flow proportion. Generally, an appropriate coarse particle circulation flow proportion in the cylindrical hydrocyclone is beneficial for alleviating particle misplacement and improving separation accuracy.

Separations doi: 10.3390/separations13050150

Authors: Haiyang Wen Qiyue Zhao Yaolin Wang Zhenwu Jiang Yupeng Cui Mengna Xu Chuanlei Liu Hui Sun

Severe foaming and a significant decrease in desulfurization performance were noted in a novel UDS solvent applied in a natural gas field in western Sichuan, China. The effects of hydrocarbon and ionic impurities on foaming behavior and the purification performance of candidate adsorbents were investigated. An extraction-gas chromatography method was established and validated for determining total hydrocarbons in amine solutions, enabling quantitative evaluation of hydrocarbon contamination. Controlled contamination experiments revealed that hydrocarbons had the strongest effect on foaming, while sulfate and chloride strongly promoted foam formation; organic acid anions showed only minor effects. Fixed-bed screening identified A-98FM anion-exchange resin as the most effective for anionic impurity removal and AC-02 activated carbon as the best candidate for hydrocarbon purification, with a cumulative adsorption capacity q0–12 of 14.86 mg/g over 12 h. Pore-structure and thermal-release analyses suggested that conventional pore descriptors alone could not fully explain the dynamic purification performance, while hydrocarbon-related loadings in spent AC-02 occupied accessible pore space and contributed to performance decay. Treatment of a field-aged UDS lean solvent further showed that reductions in target impurities were accompanied by lower foam height and shorter defoaming time. This work provides experimental support for impurity monitoring, foaming-risk identification, and adsorptive purification of UDS desulfurization solvent under flowback-contamination conditions.

Separations doi: 10.3390/separations13050149

Authors: Ruguo Dong Yongli Liu Lixin Li

Coal mine methane (CMM) separation faces significant challenges due to high humidity and multicomponent conditions, under which the selective adsorption performance of CH4 is substantially degraded compared with idealized laboratory scenarios. This review systematically analyzes the fundamental causes of this discrepancy by integrating water vapor occupation, competitive adsorption, and structural constraints into a unified framework. Water molecules preferentially occupy high-energy adsorption sites and reconstruct the interfacial energy landscape, while strongly adsorbing components such as CO2 further suppress CH4 uptake through competitive displacement. These coupled effects lead to a pronounced deviation between theoretical adsorption capacity and actual separation performance. To address this issue, this work proposes an evaluation paradigm centered on effective working capacity, which reflects the practically recoverable CH4 under cyclic operation rather than equilibrium limits. The applicability of this framework is demonstrated through comparative analysis across different adsorbent systems, highlighting the critical roles of moisture resistance, structural stability, and competitive resilience. Finally, key material design strategies and process-level optimization approaches are discussed to enhance sustainable CH4 separation under realistic conditions. This review provides a process-oriented perspective for bridging the gap between material performance and engineering application in CMM utilization.

Separations doi: 10.3390/separations13050148

Authors: Siyu Wang Junyang Du Junsu Jin Jianguo Mi

Metal–organic frameworks (MOFs) show great potential for post-combustion carbon capture, yet their practical application is often constrained by challenges such as powder handling difficulties, limited structural stability during shaping processes, and performance degradation under high-humidity conditions. In this study, Mg-gallate was structured into millimeter-sized Mg-gallate/CA composite beads via the ionotropic gelation method, and then a hydrophobic layer of vinyltrimethoxysilane (VTMS) was constructed on the bead surface by chemical vapor deposition. The synthesized Mg-gallate/CA and V-Mg-gallate/CA are characterized by XRD, FT-IR, and other techniques, and their CO2 adsorption behavior, adsorption–desorption kinetics, breakthrough performance, and cyclic stability are systematically evaluated. At 298 K and 0.1 bar, the CO2 adsorption capacity of Mg-gallate/CA reached 94.2% of that of Mg-gallate powder. The microporous–microporous hierarchical structure constructed by the ionotropic gelation method improved the CO2 capture efficiency of the composite beads by 16.7% at 0.1 bar. V-Mg-gallate/CA maintained a high dynamic CO2 adsorption capacity of 2.87 mmol/g for a 10 vol.% CO2/90 vol.% N2 gas mixture at 298 K under 80% RH, corresponding to 2.04 times the capacity of Mg-gallate/CA, and retained 98.8% of its initial adsorption capacity at 0.1 bar after 10 cycles. Combining ionotropic gelation shaping with surface hydrophobic modification represents an effective strategy for developing MOF-based adsorbents suitable for post-combustion CO2 capture.

Separations doi: 10.3390/separations13050147

Authors: Irina Zweig Alexey Kamyshny

Elemental sulfur frequently coexists with organic polysulfides in environmental samples and laboratory sulfurization experiments, complicating the accurate analysis of sulfur speciation. Reliable methods for selective sulfur removal are therefore required to avoid analytical artifacts. In this study, we systematically evaluated commonly used chemical sulfur removal approaches, including treatment with metallic copper and silver and reaction with tetrabutylammonium sulfite, and compared them with a chromatographic separation method based on C18 reversed-phase silica gel column chromatography. Model organic polysulfides, dimethyl polysulfides, diallyl polysulfides, dibenzyl disulfide, and cyclic polysulfide lenthionine were used to assess method performance under controlled conditions. The results demonstrate that chemical treatments are non-selective and lead to substantial decomposition of organic polysulfides, particularly for longer-chain compounds. In contrast, C18 reversed-phase silica gel column chromatography enables efficient and selective removal of elemental sulfur while preserving the original composition of organic polysulfides, with recoveries in the range of ~90–107%. These findings indicate that commonly applied sulfur removal procedures may introduce significant biases in sulfur speciation analyses. The chromatographic approach presented here provides a reproducible and non-destructive alternative for sample preparation, improving the reliability of studying sulfur speciation and transformation in natural and laboratory systems.

Separations doi: 10.3390/separations13050146

Authors: Feifan Leng Jiale Wang Lizhe Hu Minmin Li Yongwei Sun Yonggang Wang Jieyin Chen Xiaofeng Dai Bin Ma Qing Lv Zhiqiang Kong

This study systematically evaluated the effects of five drying methods (sun drying, freeze drying, shade drying, and hot air drying at 40 °C and 60 °C) on the multidimensional quality of Astragalus membranaceus var. mongholicus slices using multiscale techniques and multivariate analysis. The results showed that the drying methods significantly influenced color, microstructure, volatile organic compound profiles, the content of 13 bioactive constituents, and antioxidant activity. Among all treatments, hot air drying at 40 °C achieved the highest composite score in the comprehensive evaluation. This treatment was associated with a marked increase in surface microroughness (Ra), higher levels of the pharmacopoeial markers astragaloside IV and calycosin-7-O-β-D-glucoside, and enhanced ABTS radical scavenging activity. However, other methods performed better in individual parameters: shade drying showed higher DPPH and FRAP values, while freeze drying gave the highest total phenolic content. Based on the observed strong correlations (e.g., roughness vs. astragaloside IV: r = 0.94; astragaloside IV vs. ABTS: r = 0.83), we propose a testable hypothesis that hot air drying at 40 °C may influence bioactivity partly through physical microstructural changes. The multidimensional evaluation framework established here provides a methodological reference for quality optimization of medicinal and edible herbs.

Separations doi: 10.3390/separations13050145

Authors: Qian Yu Feng Zhang Wenchao Lv Yan Wang Lei Zhong Wenting Gu Junmei Liu Xinyan Liu Donghui Xu Guangyang Liu Guoke Chen Nasi Ai

The identification of dyes in ancient textiles is crucial for provenance research and scientific conservation. However, the extremely significant value of these cultural relics necessitates the use of non-destructive analytical techniques. To establish a non-destructive, in-situ, accurate, and rapid method for identifying natural dyes in ancient silk fabric samples, we employed desorption electrospray ionization high-resolution mass-spectrometry imaging (DESI-MSI). By optimizing key instrumental parameters—including sample pretreatment method, DESI spray solvent composition, and DESI heated transfer line (HTL) temperature—we determined the optimal mass-spectrometry imaging conditions. The optimal conditions for achieving the highest mass-spectrometry ion peak signal intensity and the best imaging quality were as follows: employing sample pretreatment using double-sided adhesive tape; a spray solvent composed of methanol (100%, v/v) with 0.1% formic acid and 0.1 μg/mL of leucine enkephalin; and an HTL temperature of 400 °C. The characteristic compound in the G42 silk fabric sample was successfully separated. Based on the characteristic mass-to-charge ratio of the major component, the compound was preliminarily identified as berberine. This result was further verified by tandem mass-spectrometry imaging and tandem mass spectra and finally confirmed by comparison with the mass spectrum of a reference standard. Consequently, the source of the dye in the sample was determined to be amur cork tree. The experiments confirmed the applicability and accuracy of the DESI-MSI method for the non-destructive analysis of precious textiles. This work underscores the urgent need to use such non-destructive techniques to provide technical support for the identification of high-value, inaccessible, or fragile silk artifacts and guide the historical tracing and preservation of these cultural relics.

Separations doi: 10.3390/separations13050144

Authors: Victoria Samanidou

Chromatography started to grow in Greece in the 1980s and it has expanded from basic primary separation methods to a sophisticated, multidisciplinary scientific infrastructure operated today by various expert groups distributed in universities and research institutes located in several cities. Over time, chromatography has become a fundamental scientific field constituting a substantial portion of Greece’s scientific output. Food authentication, environmental analysis and monitoring, biomedical and pharmaceutical research, archeological science, dentistry, veterinary medicine, etc., are, to a great extent, progressing based on advances and applications of chromatographic techniques. The contribution to the scientific field is profound, well established and globally recognized. The proof of this international recognition is reflected in the fact that Greece has been recently accepted in the Central European Group of Separation Sciences after being invited by the Steering Committee of the Group, during the 29th International Symposium on Separation Sciences (ISSS 2025) that took place in Belgrade, Serbia, in September 2025. Herein, a brief historical overview is provided briefly describing the main institutional and group contributors in chromatography all over Greece.

Separations doi: 10.3390/separations13050143

Authors: Yajaira Cecilia Torruco-Ortiz Kevin Alejandro Avilés-Betanzos Manuel Octavio Ramírez-Sucre Ingrid Mayanin Rodríguez-Buenfil

Habanero pepper leaf, annually discarded as a by-product, is a source of phenolic compounds with functional activity. However, their recovery requires sustainable strategies that overcome the limitations of conventional organic solvents and low extraction yields. In this study, a sustainable and adjustable approach for phenolic compound recovery was developed using natural deep eutectic solvents (NADES) combined with ultrasound-assisted extraction and optimized by response surface methodology. Initially, different hydrogen bond donors (HBDs) like glycerol, glucose, and fructose (Fru), molar ratios (MR) of choline chloride (ChCl):HBD (1:1 mol/mol–1:2 mol/mol), and added water (Aw, 50–70%) were evaluated. The ChCl:Fru system (1:1 mol/mol, 70% Aw) was identified as the most efficient, showing the highest total polyphenol content (TPC) and antioxidant capacity (Ax). Simultaneous optimization yielded 147.30 ± 2.71 mg gallic acid equivalent/100 g dry leaf (DL) and 93.00 ± 0.14% Ax (predictive capacity, error < 5%). UPLC analysis identified protocatechuic acid (1285.98 ± 2.83 mg/100 g DL) and catechin (131.82 ± 0.99 mg/100 g DL) as the major compounds during the optimization process with Fru. These results position NADES as a sustainable tool for habanero pepper leaf valorization and targeted phenolic recovery, while designing greener extraction processes for agro-industrial residues.

Separations doi: 10.3390/separations13050142

Authors: Mixuan Huan Wenhan Sun Chunlin He Xiaohao Pu Mingzhou Li Huawu Mo Mingyue Fei

Heavy rare earth elements (HREEs) are widely used in permanent magnets, phosphors, catalysts, and advanced electronic devices because of their unique optical, electrical, and magnetic properties. However, their efficient separation remains a major challenge in hydrometallurgy because neighboring rare earths have highly similar ionic radii and chemical behavior. In this work, a silane-grafted aminophosphonate resin, D152-AMPA, was used to systematically investigate the adsorption behavior, adjacent-pair separation, impurity effects, and dynamic column performance of a mixed rare-earth system under different pH conditions. In the presence of Al, Fe, Ca, and Mg, the Er/Ho separation factor increased from 1.031 at pH 2 to 2.298 at pH 4, indicating that the partitioning advantage of Er over Ho was retained and further strengthened despite the presence of impurities. During elution, the purities of the Er-rich and Ho-rich fractions reached 92.79% and 94.34%, with cumulative recoveries of 88.32% and 83.05%, respectively. XPS and FT-IR analyses further indicated that Lu(III) adsorption mainly involved the oxygen donor sites of the aminophosphonate groups. These results demonstrate that D152-AMPA is capable of selective adsorption and dynamic fractionated separation in mixed and impurity-containing rare-earth systems, providing an experimental basis for greener separation and enrichment of complex rare-earth solutions.

Separations doi: 10.3390/separations13050141

Authors: Phillimon Tlamelo Odirile Nkgopolang Matthews Boima

Water pollution due to insufficient wastewater treatment is a global concern. In this paper, coagulation and flocculation as a tertiary polishing unit process were investigated to find a solution for a non-compliant wastewater treatment facility. The Palapye Pond Enhanced Treatment and Operation (PETRO) system has not been compliant for a long time with effluent characterised by high turbidity, Biological Oxygen Demand/Chemical Oxygen Demand (BOD/COD), Total Suspended Solids (TSS), Nitrates (NO3−), and Phosphates (PO43−) The effluent from the plant is released into the stream that drains into the nearby Lotsane dam, posing significant danger to the water quality of the dam. The main objective of the study was to investigate the effect of coagulation and flocculation processes at the tertiary stage of the wastewater treatment process. Response Surface Methodology (RSM), Central Composite Design (CCD) and Multi Response Surface (MRS) were used to optimise the coagulation process and generate regression models to predict the coagulation and flocculation. The performance was evaluated using turbidity, Colour, COD and TSS as response variables. Response surface analysis indicated that the experimental data could be adequately fitted to quadratic polynomial models. Under optimum conditions the removal efficiency for Al2(SO4)3·18H2O: 91.1% (turbidity), 88.2% (colour), 58.9% (COD), 83.0% (TSS); for FeCl3·6H2O: 93.2%, 88.7%, 63.8%, 91.3%; for Moringa: 91.8%, 85.4%, 56.6%, 83.7%. The optimal removals based on MRS for Al2(SO4)3.18H2O, FeCl3.6H2O and Moringa oleifera were 90.7%, 89.7%, 59.9% and 88.5%; 94.7%, 90.8%, 58.1% and 93.8%; 94.0%, 87.2%, 60.1% and 82.1% for turbidity, colour, COD and TSS respectively. This research has demonstrated that the coagulation/flocculation process, operating synergistically with pH-induced precipitation softening, can be incorporated as an enhancement to the secondary treatment stage of the wastewater treatment facility. At the optimal alkaline conditions (pH 12–12.6), the dominant mechanism is the precipitation of native hardness ions (Mg2+, Ca2+) as Mg(OH)2 and CaCO3, which enmesh colloidal particles, while the added coagulants play a refining role by enhancing floc structure and settling. The study introduces a comparative evaluation of three coagulants within a single RSM-CCD optimisation framework, employing desirability functions for multi-response optimisation.

Separations doi: 10.3390/separations13050140

Authors: Yanxin Xie Jiuyang Lin Yinhua Wan Chao Wang Kaibo Hu Wenjing Yuan Ning Li Xuewei Li

The treatment of high-salinity wastewater generated from the use of sodium hydroxide (NaOH) in rare-earth metallurgy poses significant environmental and resource-recovery challenges. Conventional methods are often economically unfeasible due to their high energy consumption and limited value recovery. To address these limitations, this study proposes an innovative integrated electrochemical process designed not only to desalinate the wastewater efficiently but also to valorize it through the simultaneous co-production of NaOH, chlorine (Cl2), and hydrogen (H2). Systematic optimization reveals a critical trade-off between ion transport efficiency and side reactions, with optimal performance achieved at 2 mol L−1 NaCl, 80 mA cm−2 current density, 2 mm electrode spacing, 30 mL min−1 flow rate, and 5000 mg L−1 initial NaOH concentration. The system maintains exceptional long-term stability, sustaining 97.5% Cl− removal over 4410 min of continuous operation without membrane fouling, a key advantage over conventional processes. Validation with authentic rare earth wastewater achieves 90.3% desalination within 5 h. Techno-economic analysis shows that the market value of recovered NaOH nearly offsets the energy cost, achieving near-cost-neutrality. This work establishes electrolysis–membrane coupling as a technically viable and economically attractive strategy for transforming high-salinity industrial waste streams into valuable resources.

Separations doi: 10.3390/separations13050139

Authors: Xinhan Fan Wei Wang

Elaeagnus angustifolia L., belonging to the family Elaeagnaceae and genus Elaeagnus, which is a medicinal and edible homologous material with significant economic and ecological value. Its polysaccharides are one of its key active components, exhibiting bioactivities, including antioxidant, immunomodulatory, antitumor, anti-fatigue, and hypolipidemic effects. This paper reviews the research progress on the extraction, purification, structural features, and bioactivities of E. angustifolia polysaccharides, aiming to provide a theoretical basis and reference for their high-value development and utilization.

Separations doi: 10.3390/separations13050138

Authors: Tijana Radojičić Katarina Trivunac Marina Maletić Ivona Janković-Častvan Miloš Simić Ana Kalijadis Marija Vukčević

In this study, carbonaceous and hybrid adsorbents were synthesized from waste flax fibers and fly ash, integrating two abundant waste streams into a single functional material. Materials were thermally modified and activated with NaOH at 500 °C in a nitrogen atmosphere. The prepared adsorbents exhibit high efficiency for scandium ion removal, with the hybrid systems significantly outperforming the individual components. The obtained Langmuir maximum adsorption capacities for the adsorption of scandium onto hybrid adsorbents were 18.28 and 32.32 mg/g, depending on the flax fibers/fly ash ratio. The contrasting thermodynamic behavior between hybrid adsorbents of different composition highlights the significant influence of material structure on the adsorption mechanism. The results demonstrate that the synergistic integration of waste flax fibers and fly ash in hybrid materials produces efficient and environmentally sustainable adsorbents, offering a novel approach for REE recovery from aqueous systems.

Separations doi: 10.3390/separations13050137

Authors: Jhapindra Adhikari Gehui Pang Shintaro Morisada Hidetaka Kawakita Keisuke Ohto Mikihide Demura Kazuya Urata

Four algal adsorbents were prepared from two types of green sea algae (Ulva lactuca and Ulva pertusa), either by treatment with concentrated sulfuric acid or without treatment. A comparative study of Au(III) adsorption in an HCl medium was performed. While both untreated adsorbents showed good performance at low HCl concentrations, the treated adsorbents achieved quantitative adsorption and high selectivity for Au(III) across a broad range of HCl concentrations. The adsorption of Au(III) onto the algal biomass adsorbents followed the typical Langmuir monolayer adsorption model. At an HCl concentration of 0.010 M, the maximum adsorption capacities were 1.14, 0.86, 6.57, and 6.28 mol kg−1 for DUL, DUP, TUL, and TUP, respectively. A kinetic study conducted at different temperatures was consistent with the pseudo-first-order kinetic model and enabled estimation of the activation energy of the adsorption reaction. Structural changes before and after treatment were analyzed using FT-IR spectroscopy. Confirmation of Au(III) adsorption and its subsequent reduction to the elemental state was achieved through XRD and SEM/EDX analyses as well as digital imaging of the Au-loaded adsorbents. Finally, the adsorbed and reduced Au was successfully desorbed using an acidic thiourea solution.

Separations doi: 10.3390/separations13050136

Authors: Weihui Xu Xueying Li Guangjin Zhao Weishu Wang Kun Zheng Yulu Zhang Yue Wang Yunlong Duan

The growing demand for portable power has triggered a sharp increase in end-of-life lithium–nickel–cobalt–manganese oxide (NCM) batteries. Efficient recovery of NCM cathode materials is crucial for resource security. This study investigates an ascorbic acid–tartaric acid leaching system for extracting cobalt and manganese from spent NCM batteries. Temperature influences the leaching efficiencies of cobalt and manganese. Leaching efficiencies increase from 50 to 80 °C, consistent with the Arrhenius law. However, beyond 80 °C, side reactions inhibit cobalt leaching. Leaching efficiency increases with time over the range of 40 to 120 min, and then stabilizes at equilibrium. Ascorbic acid concentration plays a critical role. Within 0–1.5 mol/L, ascorbic acid promotes dissolution through reduction and coordination. At higher concentrations, excess H+ ions hinder complex formation. Similarly, tartaric acid concentration has an optimum range of 0.2–0.5 mol/L, where both H+ and ligands are supplied effectively. Outside this range, ligand availability is reduced. The solid–liquid ratio also affects performance. The optimal range of 5–15 g/L promotes mass transfer. Outside this range, efficiency declines due to solid accumulation or reduced diffusion. The results show that under optimal conditions, leaching recovery reaches 94.8% for Co and 99.3% for Mn. The optimal leaching conditions were determined as follows: tartaric acid, 0.5 M; ascorbic acid, 1.5 M; liquid-to-solid ratio, 15 g/L; stirring speed, 300 rpm; temperature, 80 °C; and leaching time, 120 min. This system represents a promising laboratory-scale approach for recovering cobalt and manganese from spent NCM batteries, pending further validation in larger-scale studies.

Separations doi: 10.3390/separations13050135

Authors: Hong-Hu Tang Chuan-Yu Liao Xiong-Xing Zhang Li Wang Qing-Jun Guan Yang Cao Wei Sun

Stone coal is an important vanadium-bearing resource and a potential source of rare earth elements (REEs). Previous studies have mainly focused on the bulk occurrence, resource potential, and leaching behavior of V or REEs in stone coal, whereas the microscale spatial relationships between V and REEs and their evolution during leaching remain poorly constrained. In this study, three representative stone coal samples were analyzed by synchrotron radiation micro-X-ray fluorescence (μXRF) to characterize the microscale distributions of V and REEs in raw samples and corresponding leaching residues. Pearson correlation analysis was further used to quantify changes in V–REE spatial relationships during leaching. The results showed that V–REE relationships were generally weak and were modified to different extents after leaching. In the GZ sample, the V–Eu correlation coefficient decreased from 0.63 to 0.34, indicating that the migration of V and REEs was not fully synchronized. The three samples also showed different REE distribution tendencies after leaching: GZ showed partial transfer of REEs to the leachate with residual retention, PX showed mixed behavior with appreciable retention in the residue, whereas PZ retained REEs predominantly in the residue. These results suggest that the integrated utilization of V and REEs in stone coal can be better achieved through a staged recovery route, in which the REE recovery pathway is determined according to their actual distribution between the leachate and the residue after V leaching. This study provides a microscale basis for the comprehensive utilization of coal-related critical metal resources.

Separations doi: 10.3390/separations13050134

Authors: Maria Beatriz Pereira Joana M. N. Sá Gonçalo C. Justino Alexandre Quintas Nuno R. Neng

Cannabis is the most widely consumed illicit substance worldwide, and the rise of synthetic and semi-synthetic cannabinoids poses growing public health concerns due to their high potency and unpredictable effects. This study presents a new analytical methodology for the simultaneous determination of natural and semi-synthetic cannabinoids (cannabidiol (CDB), Δ8-tetrahydrocannabinol (∆8-THC), Δ9-tetrahydrocannabinol (∆9-THC), and hexahydrocannabinol (HHC)) in saliva using gas chromatography coupled with mass spectrometry (GC-MS) in combination with bar adsorptive microextraction (BAμE) as a green sample preparation. The optimized method showed satisfactory recoveries (57.3–80.6%), low detection and quantification limits (1.25 and 4.13 ng/mL, respectively), excellent linearity (r2 ≥ 0.9963), and robust precision and accuracy. Application to authentic saliva samples demonstrated cannabinoid levels consistent with literature values. Overall, the proposed methodology offers a cost-effective, miniaturized, and environmentally sustainable platform for routine oral fluid cannabinoid analysis, highlighting its potential for forensic, clinical, and toxicological applications.

Separations doi: 10.3390/separations13050133

Authors: Yong Bai Xiaoli Zhao Dengxin Li Fang Li

Solar interfacial evaporation is promising for freshwater production, yet thermodynamic energy limits and mass transfer attenuation in high-salinity environments restrict practical applications. To address these challenges, a 3D high-efficiency evaporator is developed by cross-linking a hydrophilic composite gel onto a macroporous sponge scaffold. This spatially decoupled architecture enables fundamental water-state regulation and efficient environmental heat harvesting. Specifically, hydrophilic functional groups in the gel network reduce the equivalent enthalpy of vaporization of water to 1181.8 J g−1. Simultaneously, the 3D columnar structure induces a sidewall cold sink effect to extract additional ambient thermal energy. Through this synergy, the PCPH delivers a remarkable apparent evaporation rate of 8.59 kg m−2 h−1 under one standard sun. Furthermore, interconnected macropores within the sponge establish excellent convective pathways for rapid ion diffusion. Consequently, the device operated continuously for 8 h in a 10 wt% NaCl solution without significant blockage and decreased key metal ion concentrations in 3.5 wt% simulated seawater by 4 to 5 orders of magnitude. The purified water fully satisfies World Health Organization standards. This study offers an innovative strategy to surpass conventional photothermal bottlenecks and design highly durable water treatment materials.

Separations doi: 10.3390/separations13050132

Authors: Qian Cheng Yongxiang Wang Xiangyu Liu Wenxi Zhang Panfeng Gao

Recycling spent lithium-ion batteries (LIBs) is critical for resource sustainability and carbon neutrality. This work presents a green strategy in which NaA zeolite is used to preferentially recover lithium from leachate of spent NCM111 batteries, combined with temperature-regulated stepwise separation of transition metals. Benefiting from the distinct hydrated ionic radii and charge density between Li+ and divalent metal ions, NaA zeolite selectively adsorbs Ni2+, Co2+ and Mn2+, leaving Li+ in the raffinate. Under optimized conditions, two-stage adsorption achieves 95.6%, 96.7% and 99.7% removal of Ni2+, Co2+ and Mn2+, respectively, with 11% Li+ co-adsorption. Thermodynamic analysis reveals that the adsorption process is endothermic and thermodynamically spontaneous. The interaction strength between metal ions and NaA zeolite follows the order Ni2+ > Co2+ > Mn2+, and ion exchange is identified as the dominant mechanism. It is determined that 96.8% of Mn2+ can be recovered at 0 °C, followed by the desorption of 93.5% of Co2+ at 90 °C, and the sequential separation of Mn, Co and Ni is realized. Three consecutive adsorption–desorption cycles demonstrate the acceptable reusability of the Ni-loaded NaA adsorbent. High-purity Li2CO3 (purity 96.7%, yield 93.5%), MnO2 (purity 99.3%, yield 98.4%) and Co3O4 (purity 98.8%, yield 97.6%) are obtained from the corresponding solutions. This approach provides a scalable closed-loop pathway for full-component recovery of valuable metals from spent LIBs.

Separations doi: 10.3390/separations13050131

Authors: Haolei Wu Feng Wei Huagang Ni

Crude fidaxomicin contains difficult-to-separate impurities, and conventional dual-step purification usually requires intermediate concentration and transfer, which increases process complexity and may aggravate product loss or degradation. To address this challenge, this study exploits the complementary selectivity of methanol/water (80/20, v/v) and acetonitrile/water (70/30, v/v) binary mobile phases and proposes two purification processes based on step-gradient twin-column recycling chromatography, namely spatial integration and system integration. In the spatial integration strategy, dual-stage separations that are conventionally performed in separate chromatographic systems are sequentially integrated into a single twin-column recycling system in combination with on-line heart-cutting, thereby eliminating intermediate off-line processing steps. In contrast, the system integration strategy merges the two binary mobile phases in defined proportions to construct a single ternary mobile phase composed of methanol/acetonitrile/water (37.5/37.5/25, v/v/v), enabling one-step complete separation. The results demonstrate that the spatial integration strategy, employing binary mobile-phase switching, produces fidaxomicin with a purity of 99.9%, recoveries ranging from 75.27% to 78.77%, and productivities ranging from 307.22 to 328.82 g·L−1·day−1, regardless of the switching sequence. The system integration strategy, based on one-step elution with the ternary mobile phase, achieves the same product purity of 99.9% without mobile-phase switching, with a recovery of 70.41% and a productivity of 246.33 g·L−1·day−1. These results confirm the applicability and flexibility of both integrated strategies for fidaxomicin purification, while indicating that the spatial integration strategy provides better overall preparative performance and the system integration strategy offers a simpler one-step operation.

Separations doi: 10.3390/separations13050130

Authors: Yanlin Wu Lanhua Luo Yuan Li Shanghua Shi Xiaoning Wang Wenbo Dong Gilles Mailhot

Over the past 20 years, the iron-activated persulfate systems have been widely used for removing pharmaceuticals and personal care products (PPCPs) from water. However, slow Fe(III)/Fe(II) redox cycling and precipitation of iron, unless in very acidic conditions, were the main limitations. Thus, two ligand-assisted Fe(III)/persulfate systems, Fe(III)-acetohydroxamic acid (AHA)/peroxydisulfate (PDS) and Fe(III)-nitrilotriacetic acid (NTA)/peroxymonosulfate (PMS), were comparatively investigated for the degradation of atenolol (ATL) in this study. The experimental results showed that the Fe(III)-NTA/PMS system worked much better than the AHA system. However, the cost of PMS is higher than that of PDS, which should be considered. The primary advantage of the NTA system was its ability to overcome the pH limitations. It worked well over a wide pH range (3.0–10.0), whereas the AHA system could only be used in a narrower pH window (pH 2.4 to 6.5). The investigation of radicals that contributed to ATL degradation revealed that sulfate radicals (SO4•−) were dominant in the NTA system, while hydroxyl radicals (•OH) and SO4•− were the primary and secondary radicals in the AHA system. These results provided useful insight into the comparative behavior of two ligand-assisted Fe(III)/persulfate systems for ATL degradation, with the Fe(III)-NTA/PMS system showing clear potential under neutral or near-neutral conditions, while Fe(III)-AHA/PDS may still represent a lower-cost option under acidic conditions.

Separations doi: 10.3390/separations13050129

Authors: Song Huang Yusong Zhang Bingdi Cao

Sludge electro-dewatering has emerged as a research hotspot in advanced sludge treatment due to its ability to effectively remove interstitial water that is difficult to separate by mechanical dewatering. This paper systematically reviews the fundamental principles, key influencing factors, evolution of electrode materials, and engineering applications of electro-dewatering technology. Emphasis is placed on analyzing the effects of sludge properties, electric field parameters, and electrochemical reactions on dewatering efficiency. The characteristics and applicable scenarios of three generations of electrode materials—from conventional metal electrodes and carbon-based materials to dimensionally stable anodes (DSA)—are summarized. Current challenges include insufficient electrode stability, the trade-off between energy consumption and efficiency, limited understanding of underlying micro-scale mechanisms, and difficulties in process scale-up. Future efforts should focus on the development of high-performance electrode materials, investigation of multi-field coupling enhancement mechanisms, establishment of machine learning-based intelligent control strategies, and engineering design of continuous electro-dewatering equipment to promote its large-scale application in sludge treatment and disposal.

Separations doi: 10.3390/separations13050128

Authors: Miaomiao Huang Qing Wang Shuai Wang

The separation of rare earth elements (REEs) is challenging due to their similar chemical properties. This study developed a series of novel polystyrene–ion-imprinted poly(hydroxamic acid) interpenetrating polymer networks (PS-IIPHAs) for the highly selective adsorption of La3+, Ce3+, and Y3+. The effects of the solution pH, contact time, initial concentrations, and temperature on the adsorption performance of the resins were systematically investigated. The results showed that adsorption equilibrium was reached within 4 h at a pH of 1.0, following the Langmuir isotherm, with maximum adsorption capacities of 2.425, 3.012, and 2.927 mmol/g for La3+, Ce3+, and Y3+, respectively. The resins exhibited excellent selectivity toward the template ions, with separation factors of 35.45 for Ce3+-La3+, 17.52 for Y3+-La3+, and 11.04 for Ce3+-Y3+. These results indicate PS-IIPHAs as promising adsorbents for the efficient, highly selective recovery of REEs.

Separations doi: 10.3390/separations13040127

Authors: Qiang Geng Tianshi Lan Guoqiang Huang

With the increase in the demand for electronic-grade high-purity silane in the semiconductor chip industry, it is of great significance to develop a green and economical method for silane production. Therefore, a novel energy-saving fixed-bed process was proposed innovatively. In this paper, the thermodynamics and kinetics of the trichlorosilane disproportionation system were studied, and the optimal reaction conditions for the resin catalyst were determined, which were used for the subsequent simulation. Based on the conventional DR1 + DR2 process (which includes one trichlorosilane disproportionation reactor (DR1) and one dichlorosilane disproportionation reactor (DR2)), by adding an additional disproportionation reactor to the TCS recycle loop and/or DCS recycle loop, three improved process configurations were designed, including 2DR1 + DR2, DR1 + 2DR2, and 2DR1 + 2DR2 processes. Then, combined with four-column heat integration, the HI + 2DR1 + 2DR2 process was proposed to solve the bottleneck problems of high energy consumption and large circulation flow rate. The results show that the HI + 2DR1 + 2DR2 process achieved the best energy-saving effect. The TCS recycle loop flow rate reduced by 36.87%, the DCS recycle loop flow rate reduced by 12.41%, total energy consumption decreased by 62.8%, and CO2 emissions decreased by 56.72%. The unit energy consumption is 13.8 kg steam/kg SiH4, and the silane purity is greater than 99.9999%. This design can be easily applied to the existing production process of the silane plant, achieving energy-saving and low-cost production of silane.

Separations doi: 10.3390/separations13040126

Authors: Yining Wang Yinghua Sun Wuying Li Shuqian Xia

A water acetone biphasic extraction system was developed for the separation and purification of erythromycin thiocyanate. Response surface methodology based on a Box-Behnken design was used to evaluate the effects of pH, liquid-to-solid ratio, extraction temperature, and acetone-to-water volume ratio on mass yield. All four variables influenced the extraction performance, and acetone-to-water volume ratio and liquid-to-solid ratio were the most significant factors. Under the optimized conditions of 50.5 °C, pH 9.2, a liquid-to-solid ratio of 3.0 mL/g, and an acetone-to-water volume ratio of 2.5 mL/mL, the mass yield reached 81.58 percent. The predicted and experimental values were in good agreement, confirming the adequacy of the model. The product obtained under the optimized conditions met the relevant requirements of the Chinese Pharmacopoeia. The proposed process is simple and effective, and provides a basis for the purification and scale up of erythromycin thiocyanate and related derivatives.

Separations doi: 10.3390/separations13040125

Authors: Kayla Laguana Sonia Egenberger Jack Tobin Claudia Wong Logan Lu Jack G. Webster Mingheng Li

This study investigates how sintering temperature affects phase evolution, titanium carbide (TiC) formation, and oil-repellent performance in TiO2–carbon-coated 304 stainless-steel mesh for oil–water separation applications. Coated meshes sintered at 400, 500, 600, 700, and 800 °C were evaluated using gravity-driven oil permeation tests with 5W-20 motor oil and oil contact-angle measurements, while coating morphology, composition, and phase evolution were characterized by SEM, EDS, and XRD. Sintering temperature strongly influenced coating structure and wettability. Among the tested conditions, the mesh sintered at 600 °C showed the highest oil contact angle (105°) and the highest initial oil retention efficiency (80%), indicating the most favorable balance between oleophobicity and coating stability within the tested range. XRD analysis showed that 600 °C corresponded to the onset of the anatase-to-rutile transition and the initial formation of TiC. These results suggest that intermediate sintering temperatures can provide a favorable balance between retention of beneficial anatase content and enhanced interfacial interaction within the TiO2–carbon coating. Within the tested conditions, 600 °C was the best-performing sintering condition among the temperatures examined for this coating system.

Separations doi: 10.3390/separations13040124

Authors: Chaoyong Li Hui Zhou Haisheng Li Yinghua Chen Ziyin Xu Jie Li Qiqiang Gao Qiang Zhao

As an efficient dry separation technology, electrostatic separation exhibits significant potential for application in the sorting and recovery of carbon-rich resources from coal gasification fine slag (CGFS). The small particle size and high moisture content of CGFS particles are the main factors affecting the efficiency of separation. This study proposes a method integrating particle moisture reduction and charging promotion based on molecular sieves, with the aim of investigating its feasibility in improving the electrostatic separation efficiency of CGFS particles. The results indicate that molecular sieves can effectively adsorb moisture from the ambient humid air and the surface of particles, allowing for rapid drying of wet particles. The reduction in moisture content on the particle surfaces significantly promotes their charging capability, creating favorable conditions for electrostatic separation. After molecular-sieve-assisted charging enhancement, the carbon content in the ash-enriched positive plate product decreased by 4.96%, while the carbon content in the carbon-enriched negative plate product increased by 12.15%, indicating a significant improvement in carbon–ash separation efficiency. Correspondingly, the decarbonization efficiency of the positive plate and carbon recovery efficiency of the negative plate were increased by 21.30% and 52.17%, respectively. Furthermore, when the moisture content exceeds 10%, the phenomenon of inter-particle agglomeration can adversely affect the separation of carbon and ash particles. The most suitable operating conditions are a moisture content no higher than 10%, an electric field density of 30 kV/m, a filling molecular sieve of 400 g, and a gas velocity of 12 m/s (volumetric flow rate 84.78 m3/h). In practical industrial applications, it is advisable to consider pre-treating the particles for drying or employing secondary separation to enhance sorting accuracy.

Separations doi: 10.3390/separations13040123

Authors: Tong Liu Fei Zhu Xijun Tian Zhenping Cai Kai Huang Song Chen

This study addresses the issue of insufficient product purity caused by the co-deposition of three major impurity ions—zinc, nickel, and lead—during the electrodeposition process of high-purity manganese. A targeted deep purification method for manganese sulfate electrolyte was developed using dithiocarbamate chelating agents (sodium dimethyldithiocarbamate, SDD). By optimizing key process parameters such as precipitant concentration, reaction temperature, reaction time, and solution pH, combined with density functional theory (DFT) calculations, to elucidate the selective impurity removal mechanism at the molecular level, a novel process for the efficient synergistic removal of Zn2+, Ni2+, and Pb2+ was established. The results showed that under the conditions of precipitant concentration of 1 g/L, solution pH of 6.5, reaction temperature of 55 °C, and reaction time of 2 h, the residual concentrations of Zn, Ni, and Pb in the electrolyte were all below 0.2 mg/L. DFT calculations revealed that SDD coordinates with metal ions through four sulfur atoms, and the absolute values of binding energies follow the order Ni2+ > Pb2+ > Zn2+ > Mn2+, indicating thermodynamically preferential capture of impurity ions. After purification, the manganese metal obtained by electrodeposition from the manganese sulfate solution achieved a purity exceeding 99.999%, with Zn, Ni, and Pb contents of 0.11 mg/kg, 0.038 mg/kg, and 0.05 mg/kg, respectively, meeting the raw material requirements for semiconductor-grade copper–manganese alloy targets.

Separations doi: 10.3390/separations13040122

Authors: Salim Mokraoui Lahssen El Blidi Irfan Wazeer Attiyah A. Al-Zahrani Mohamed K. Hadj-Kali

This study demonstrates the high efficiency and selectivity of p-toluenesulfonic acid-based deep eutectic solvents (DESs) for simultaneous extractive denitrogenation (EDN) and desulfurization (EDS) of model fuel. Three DESs—TBPB:PTSA, TBAB:PTSA, and ChCl:PTSA (1:1 molar ratio)—were synthesized and evaluated for their effectiveness against representative heteroaromatic pollutants: thiophene, dibenzothiophene, pyridine, and carbazole. The phosphonium-based TBPB:PTSA exhibited the highest extraction performance, achieving over 96% removal of nitrogen species and up to 85% removal of sulfur species at 40 °C. Increasing the temperature enhanced desulfurization by reducing viscosity, thereby improving mass transfer kinetics. Additionally, a 3:1 ratio of DES to fuel provided an optimal balance between solvent economy and operational efficiency. Denitrogenation was driven by strong acid–base protonation facilitated by PTSA, while desulfurization was governed by π–π and dispersion interactions, modulated by the hydrophobicity of the cations. The DES achieved nearly quantitative nitrogen removal and satisfactory sulfur extraction after three reuse cycles, while multistage operation enabled complete purification within four extraction steps. 1H NMR analysis confirmed that no DES components were found in the raffinate phase, verifying the immiscibility and stability of the solvent. These results indicate that TBPB:PTSA is a robust, regenerable, and environmentally benign solvent, effectively enabling simultaneous EDN–EDS of hydrocarbon fuels and positioning it as a promising green alternative to traditional hydrogen-based refining methods.

Separations doi: 10.3390/separations13040121

Authors: Diana Samantha Villarreal-Lucio Karla Ximena Vargas-Berrones Brenda V. Loera-García Vanessa Sarahí Galván-Romero Carolina López-Saldaña Raúl Ocampo-Pérez Héctor Hernández-Mendoza Rogelio Flores-Ramírez

This research focused on the development and characterisation of molecularly imprinted polymers (MIPs) modified with titanium dioxide (TiO2) for the adsorption and photocatalytic degradation of sodium naproxen (NPX). Different percentages of TiO2 (5% and 25%) were tested and compared to non-imprinted polymers (NIPs). FT-IR analysis confirmed the interaction between methacrylic acid and TiO2, promoting the formation of specific binding sites and presenting a good imprinting factor. The results showed that the MIP with 5% TiO2 had the highest adsorption and retention capacity, attributed to the imprinting effect and the reduced interference from TiO2. The surface of the MIPs is heterogeneous, as it was indicated by the Freundlich isotherm model. The KF for the MIP with 25% of TiO2 was higher than for the materials with 5%; values for the MIP/TiO2 5% and the NIP/TiO2 5% KF were 4.808 and 4.163 (mg/g)(L/mg)1/n respectively, while for the MIP/TiO2 25% was 6.542 (mg/g)(L/mg)1/n and for the NIP/TiO2 25% it was 2.736 (mg/g)(L/mg)1/n. Kinetic studies followed the pseudo-second-order model, suggesting more active binding sites in MIPs. Photocatalytic experiments achieved 60% degradation, demonstrating the degradation performance of MIPs; however, this behavior is restricted by the slow degradation of NPX. The materials were evaluated using a water sample (Querétaro River, México); the sample was preconcentrated and analyzed, detecting a concentration of 0.332 mg/L of NPX. This finding highlights the MIPs’ potential application in environmental monitoring and treatment; nevertheless, due to the recalcitrant nature of NPX, MIPs should be used along with other advanced treatment methods to achieve effective removal.

Separations doi: 10.3390/separations13040120

Authors: Mengmeng Jia Mengchen Shi Yi Wang Xiaofeng Fang

The efficient removal of dyes and separation from dissolved salts are crucial for the recovery of valuable resources from saline textile wastewater. In this study, hollow fiber membranes were fabricated using the non-solvent-induced phase separation (NIPS) method and then improved with a dual-coating process to create effective nanofiltration (NF) membranes. First, hollow fiber substrates with Fe3+ were fabricated using NIPS. Subsequently, the inner surface of the membrane was coated with phytic acid (PA) and polyethyleneimine (PEI), which increased the thickness of the separation layer and reduced the size of the surface pores, thereby improving the separation efficiency. The loose NF membrane exhibited superior water permeance (pure water permeability of 280 L·m−2·h−1·bar−1) and, with dye rejection rates consistently exceeding 95%, also remarkable dye/salt selectivity (with separation factors of CR/NaCl: 64.08, CR/Na2SO4: 21.21, CBB/NaCl: 14.75, and CBB/Na2SO4: 10.74). The flux recovery of the membrane was over 80% for humic acid, and the membrane exhibited favorable stability under acidic and alkaline conditions, confirming its excellent antifouling and stability performance. In conclusion, this study presents a straightforward and effective approach for fabricating hollow fiber loose NF membranes, underscoring their potential for treating hypersaline wastewater and resource recovery.

Separations doi: 10.3390/separations13040119

Authors: Hancheng Mao Shengdong Wang Muyao Lu Haibei Wang Denggao Zhang

This study presents a combined process of sulfide precipitation followed by hydrogen peroxide leaching for rhenium recovery from copper smelting waste acid under ambient temperature and pressure. The process first removed copper through selective sulfide precipitation, then achieved co-precipitation of rhenium and arsenic to obtain a rhenium-rich precipitate. Subsequently, exploration of rhenium-containing precipitate leaching using H2O2 solution was conducted under isothermal conditions at 20 °C. The effects of H2O2 concentration, liquid-to-solid ratio, acidity, and leaching time rhenium extraction efficiency were examined systematically. The optimal leaching conditions were determined as: H2O2 concentration of 150 g/L, liquid-to-solid ratio of 5:1 mL/g, stirring speed of 350 r/min, and leaching time of 30 min. Under these conditions, the leaching conversions of rhenium and arsenic reached 96.0% and 93.8%, respectively. Through characterization of precipitate and leaching residue using ICP, SEM-EDS, XRD, and XPS analyses, the process and related reactions were elucidated. Results demonstrated that low-valence rhenium oxides and sulfides serve as the main reactive species during H2O2 leaching, whereas organic sulfur, high-valence oxides, and copper sulfide remained stable and resistant to leaching. Selective precipitation of copper effectively eliminated insoluble metal sulfides from rhenium-containing precipitates, thereby enabling efficient separation of rhenium under mild conditions.

Separations doi: 10.3390/separations13040118

Authors: Fang Li Yuping Fan Yuanpeng Fu Xiaomin Ma Xianshu Dong Yangge Zhu Wei Xiao Wenjie Fang

Fluorapatite is a typical phosphate rock resource. Fluorapatite tends to generate fine mud agglomeration, which induces dehydration challenges owing to its inherently fine particle size and negative surface charge. In this paper, phosphate tailings slurries from a phosphate mine in Hubei Province, China, were selected as the research object, and flocculation–dehydration experiments were conducted using anionic, cationic, and nonionic polyacrylamide (PAM) flocculants. The results show that the maximum settling velocity is 51 mm/s and the moisture content of filter cake is 41.54%, which were obtained when the unit consumption of cationic flocculant with molecular weight 12 million was 1000 g/t. The mechanism of sedimentation and dehydration was studied by infrared spectroscopy and a particle size analyzer. The results showed that polyacrylamide was effectively adsorbed on the mineral surface, and the size of flocs increased significantly. Finally, the mechanism of sedimentation and dehydration was proposed. It has important guiding significance for the efficient solid–liquid separation and water circulation of fluorapatite mineral processing wastewater.

Separations doi: 10.3390/separations13040117

Authors: Jun Zhang Ming Shao Minghan Zhou Lin Zhang Yingguang Zuo Lijun Wang Yadong Zhang

The paper utilizes the synergy of vibration and hot air flow to form a composite force field, and low-quality fine coal with viscous moisture is subjected to ash removal. The vibration signals of the bed surface at different positions are collected online using an accelerometer, and the dominant force affecting the vibration behavior of the bed is analyzed using signal time-domain analysis. By examining the impact of the synergy between vibration and airflow on the ash removal effect of low-quality, viscous moisture coal, the response of the drying and sorting behavior of low-quality fine coal to this synergy is elucidated. Based on the study of the experimental results of dehydration and ash removal of −6 + 1 mm fine coal, under the synergy of temperature and load force field, when the air flow temperature is 90 °C, v = 0.65 m/s, and f = 20 Hz, the collision force range between particles is 120 nN–370 N, which is different from that between particles. The liquid bridge force is large, which can achieve the fracture of liquid bridges between particles and strengthen the loose fluidization of particles. In addition, based on the study of the vibration characteristics of the bed surface at different positions, the vibration along the y-axis direction plays a dominant role in the density segregation behavior of the bed particles. With the increase in gas velocity and vibration frequency, the ash content of the selected clean coal exhibits a trend of first decreasing and then increasing. At the same time, the ash segregation degree initially increases and then decreases. Moreover, under the conditions of v = 0.65 m/s and f = 20 Hz, the separation effect of fine coal is the best. The separation accuracy E values of 1–6 mm without fine particles are 0.06 g/cm3, and the ash content of the clean coal is 12.55%.

Separations doi: 10.3390/separations13040116

Authors: Hideo Maruyama

Surface-modified waste scallop shells were investigated as a solid flocculant for removing suspended particles, and a light transmission method was examined as a simple approach for evaluating flocculation behavior. Kaolin suspensions (3, 5, 10 g/L, pH 6.95–7.05) were used as model wastewater. Temporal changes in transmitted light intensity were monitored using a white LED–sensor optical system after agitation of the suspension was stopped. The transmitted light intensity, I, was normalized by the intensity measured for particle-free water (I0), and an optical extinction index, A = −log10(I/I0), was used to describe the attenuation of light in the suspension. An apparent clarification rate (rate of change in optical extinction), v, was defined from the initial decrease in the optical extinction index and used as an operational kinetic parameter for comparing flocculation behavior under identical conditions. The results showed that the surface-modified scallop shell particles exhibited measurable flocculation activity toward kaolin suspensions, although the performance was lower than that of commercial polymer flocculants. The optical transmission method enabled continuous monitoring of the flocculation process and provided a practical index for comparing the flocculation performance of different materials.

Separations doi: 10.3390/separations13040115

Authors: Jing Chang Bianbian Guo Guoyu Bai Xinyuan Zhang Hang Zhang Wei Zhao Zhen Li

Intelligent dosing in coal slime water treatment remains a challenge due to the lack of real-time and solid hardware-based measurement of key microscopic parameters governing the settling process, particularly zeta potential. This study proposes a soft-sensor method using Sparrow Search Algorithm-optimized Extreme Learning Machine (SSA-ELM) to simultaneously predict four critical settling process parameters: settling velocity, supernatant turbidity, sediment layer height, and zeta potential. Key variables influencing the coal slime water settling process, including coal slime water concentration, fines content, water hardness, pH, and chemical dosage, were investigated, and the experimental data were used as inputs for the development of the prediction model. The prediction performance of the proposed SSA-ELM model was evaluated against standard ELM and SSA-optimized Back Propagation (BP) models. The results demonstrate that the SSA-ELM model achieved superior prediction accuracy for all parameters, with R2 values ranging from 0.95 to 0.98, while maintaining favorable computational efficiency. This study establishes a method for virtual measurement of zeta potential, providing a crucial data foundation for developing mechanism-driven, intelligent dosing systems aimed at precise intelligent control and reduced chemical consumption for coal preparation plants.

Separations doi: 10.3390/separations13040114

Authors: Haoqian Yan Guifeng Zhang Li Ma

This study aims to achieve the efficient preparation of sunflower calathide flavonoids (SCF) through optimized processes and to elucidate their composition and bioactivity. Total flavonoids were prepared by optimizing the ultra-high-pressure extraction (UHPE) process using a combination of single-factor experiments and response surface methodology, followed by purification and enrichment via macroporous resin. The components were identified with UPLC-QTOF-MS/MS technology, and their antioxidant activity and inhibitory capacity against xanthine oxidase (XOD) were systematically evaluated. The optimal extraction conditions were determined as follows: an extraction pressure of 290 MPa, a holding time of 8 min, an ethanol concentration of 67%, and a solid-to-liquid ratio of 1:14 g/mL. Under these conditions, the total flavonoid extraction yield reached 13.52 mg/g, which was further enriched to 16.74 mg/g after purification by macroporous resin. A total of 32 flavonoid compounds were identified, and the purified extract exhibited stronger free radical scavenging ability, total reducing power, ferric ion reducing activity, and XOD inhibitory effect compared to the unpurified extract. The combination of UHPE with macroporous resin separation technology effectively enriches SCF, and the resulting extract possesses both antioxidant and xanthine oxidase inhibitory activities, providing a theoretical basis and technical support for its industrial production and application.

Separations doi: 10.3390/separations13040113

Authors: Weinan Wang Xu Hou Jiahao Pan Wei Shi Xiaolu Ye

Flip-flow screens are widely used for the efficient separations of wet fine materials. To explore the separation characteristics of the particle and screen plate in the flip-flow screening process, a flip-flow plate impact experimental system was built. The experimental system was based on a spherical inertial measurement device and a semi-industrial flip-flow screen system. In this study, we first derive the impact mechanics equation of the flip-flow screen plate on the particle and analyze the influence of the main parameters on the maximum impact force. Subsequently, we investigated the kinematic characteristics of the particle impacted by the screen plate at different moving positions, the variation of the centerline acceleration mechanism, and determined the angular velocity in the collision process. Additionally, we further clarified the alteration in the rules of translational and rotational kinetic energy of the particles in the collision process. This study addresses a research gap in the phenomenological modelling of particulate screening process. At the same time, it provides theoretical support for the accurate control of the flip-flow screening process.

Separations doi: 10.3390/separations13040112

Authors: Qinhan Ye Pei Zhao Xuan Xia Yang Xiao Xinhong Qiu

Two mineral-based solid residues, namely coal gangue (CG) and phosphorus tailings (PT), two of the largest solid waste streams in the mining industry, were used as the sole metal feedstocks to fabricate a novel MgCaFeAl layered double hydroxide (LDH-GT) via a 700 °C calcination, acid leaching and hydrothermal coprecipitation route, with simultaneous synthesis of white carbon black from the reaction byproducts. Under optimized conditions (total metal load is 150 mg kg−1, LDH-GT dose is 0.09 g, pH from 6 to 7), the synthesized material achieved concurrent immobilization efficiencies of 76.28%, 99.96%, and 99.95% for Cr (VI), Cd (II) and Ni (II), respectively, within a 24 h reaction period. TCLP leachability decreased by 82 to 91% relative to the untreated soil. After three wetting, drying and freeze–thaw cycles, the leached concentrations of all three metals remained below 0.3 mg L−1, confirming excellent long-term stability. Mechanistic analyses revealed that Cr (VI) was mainly sequestered through interlayer anion exchange and surface complexation, whereas Cd (II) and Ni (II) were immobilized via isomorphic substitution into the LDH lattice, precipitation as carbonates, and incorporation into Fe/Mn oxides. A 7-day mung bean bioassay showed that LDH-GT amendment increased seed germination from 50% to 73%, enhanced root and shoot biomass by 1.1- to 1.6-fold, and decreased plant Cr, Cd, and Ni contents by over 80%. The 16S rRNA sequencing further demonstrated that LDH-GT reversed the decline in microbial α diversity induced by heavy metal stress, restored aerobic chemoheterotrophic and sulfur cycling functional guilds, and reduced pathogenic signatures. This study provides the demonstration of a waste-to-resource LDH that achieves efficient, durable remediation of multi-metal-contaminated soils, offering a scalable route for coupling solid waste valorization with in situ site restoration.

Separations doi: 10.3390/separations13040111

Authors: Xiaoxiao Cai Hao Lu

As an efficient solid–liquid separation device, the hydrocyclone is widely applied in various industrial fields such as coal preparation and oil impurity removal, and its classification performance directly determines the efficiency of industrial separation operations., As the core separation zone of the hydrocyclone, the cone segment, its structure and the number of cone angles directly affect the flow field distribution characteristics and particle classification performance of the hydrocyclone. To reveal the regulation mechanism of the combined cone angles on the classification performance of hydrocyclones, numerical analysis and experimental verification methods were adopted to investigate the internal flow field and classification performance of hydrocyclones under different cone angle combinations. The evolution laws of velocity field, pressure field, turbulence characteristics, and particle classification effect under different configurations were systematically explored. The results show that the basic characteristics of the core flow field of the hydrocyclone do not change essentially with the increase in the number of cone segments, but the amplitude, distribution, and stability of flow field parameters are significantly regulated. The three-cone configuration achieves the optimal flow field synergy effect: the amplitude of the high turbulence intensity zone is lower and concentrated near the central axis; the zero-velocity envelope surface is stably maintained at approximately 8 mm in the core separation zone; and the full axial fluctuation of the air core is gentle, which effectively inhibits random particle diffusion and flow pattern mixing. In terms of separation performance, the three-cone configuration exhibits the highest classification efficiency in the core range of sub-coarse particles (10~30 μm), with the cut size (approximately 17.5 μm) in a reasonable range, the steepness index reaching a peak value (approximately 0.55), and the pressure drop (approximately 1.8 × 105 Pa) and split ratio (2.8%) achieving synergistic optimization, balancing separation accuracy and energy consumption control. The single-cone configuration causes flow field disturbance due to the one-time contraction of the flow channel, while the four-cone configuration falls into the dilemma of “high pressure drop–marginal performance gain”, and neither achieves optimal performance. The regulation law of the number of cone segments revealed in this study provides a scientific basis for the structural optimization and engineering application of multi-cone hydrocyclones, and is of great significance for improving the particle classification efficiency in fields such as wastewater treatment and mineral processing.

Separations doi: 10.3390/separations13040110

Authors: Yan Fang Yi Nan Xijie Tian Junyu Zhang Xiaojuan Chen Juan Song Haizhen Liang Baiping Ma

Traditional Chinese prescriptions are characterized by complex chemical constituents and wide variations in constituent content, which pose a substantial challenge to their comprehensive characterization. As a classic traditional Chinese prescription known for its heat-clearing and detoxifying properties, Huangqintang Decoction (HQD) is composed of Scutellariae Radix, Paeoniae Radix Rubra, Glycyrrhizae Radix et Rhizoma, and Jujubae Fructus. In this study, we developed an off-line two-dimensional liquid chromatography that addressed the limitations of traditional analysis of unfractionated extracts, such as restricted peak capacity, which often obscured trace components. By coupling with ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF/MS), this study successfully performed rapid identification or characterization of the complete chemical profile of HQD. Notably, beyond high-throughput identification, this approach leveraged characteristic fragment ions and reversed-phase chromatographic behaviors to differentiate some isomers of flavonoid glycosides and triterpenoid saponins, demonstrating its depth in structural identification. Flavonoid glycoside isomers were distinguished by diagnostic neutral losses, while flavanones and chalcones were characterized by retro-Diels–Alder (RDA) and β-rearrangement, respectively. Isomers of triterpenoid saponins were inferred from aglycone-specific pathways alongside RDA cleavages. Ultimately, a total of 192 compounds were identified, including 88 flavonoids, 80 triterpenoids, 7 monoterpene glycosides, 3 fatty acid amides, 3 phenylethanoid glycosides, 4 coumarins, 3 saccharides, 1 organic acid, and 3 others. This study demonstrated that the off-line two-dimensional liquid chromatography analysis strategy significantly enhanced chromatographic resolution and expanded the coverage of trace components. It presented an effective strategy for comprehensive compound identification in complex traditional Chinese medicine prescriptions.

Separations doi: 10.3390/separations13040109

Authors: Panpan Chu Qihan Wang Fan Yang Guangpeng Chen Wangzhiyuan He Hao Pan Liting Fan Xiaojian Yang Jinpeng Shi Shaolong Wan

The selective removal of HCl from industrial HCl/SiF4 mixtures was investigated using a series of alcohol-based and deep eutectic solvents (DESs). Among them, glycerol (GL) exhibited superior selectivity for HCl despite a moderate total capacity. Absorption at 60 °C ensured stable operation with minimal foaming. Desorption analysis revealed that both HCl and SiF4 underwent partial irreversible absorption under N2 stripping, while staged vacuum desorption enabled efficient and selective recovery—SiF4 was fully removed at 70 °C and 6 kPa, followed by nearly complete HCl desorption at 90 °C. Cyclic tests confirmed excellent solvent stability and rapid regeneration, with complete desorption achieved within 10–15 min. A conceptual process was proposed based on these findings, demonstrating a practical and energy-efficient route for selective HCl recovery from acid–gas mixtures.

Separations doi: 10.3390/separations13040108

Authors: Xue Yu Zihan Zhai Qiangcheng Zeng Jiajia Chen Jiayi Wang Wei Zhao Jinling Liang Guoxiu Han

This study presents a novel, integrated membrane–resin hybrid platform for the high-efficiency purification of N-acetylneuraminic acid (sialic acid, NANA) from complex microbial fermentation broths. By synergistically combining four sequential stages—ceramic microfiltration (50 nm), ultrafiltration (3 kDa), nanofiltration (150 Da), and dual-resin purification (macroporous adsorption + cation-exchange)—the process achieves stepwise removal of cells, proteins, pigments, monovalent salts, and divalent metal ions without using organic solvents or high-salt buffers. Critically, each stage demonstrates high target recovery: 76.2% (CM), 67.3% (UF), and 77.5% (NF), with near-quantitative retention (>95%) during resin treatment due to NANA’s low hydrophobicity and electrostatic repulsion at pH 6.8. Following optimised acidification crystallisation (acetic acid dosage = 3 × concentrate volume; sialic acid concentrate concentration = 333.49 g/L), the final product reaches 97.9% purity with a crystalline yield of 78.6%. This scalable, green purification strategy eliminates major bottlenecks in downstream processing and enables industrial-scale production of pharmaceutical-grade sialic acid, with broad applicability to other high-value acidic biomolecules.

Separations doi: 10.3390/separations13040107

Authors: Shengbing Xiao Lixin Li

Mine water treatment remains a long-term challenge due to high suspended solids, wide particle size distributions, and inflow variability, all of which stress solid–liquid separation systems. Hydrocyclones and filtration often fail not from insufficient capacity, but from the inability to handle dynamic influent behavior. This review integrates existing studies and reinterprets mine water treatment as a system performance issue, focusing on maintaining operability under fluctuating conditions. Evidence shows that high-solids mine water behaves as a concentrated multiphase flow, where particle interactions and flow changes lead to gradual shifts in separation behavior. For example, hydrocyclone efficiency ranges from 85 to 95%, and pressure drop increases by 0.5–5 kPa/h under continuous operation. Wear, clogging, and flow redistribution develop together, impacting the operational window of integrated treatment units. Key gaps remain in system performance under fluctuating loads and reliable performance under high-solids loading. The complexity of these interactions often leads to significant operational risk and performance variability in real-world conditions. Future research should focus on dynamic control strategies, multi-stage pre-separation, and advanced filtration designs to enhance system performance, long-term stability, and adaptability in real mining environments. Emerging technologies and new system configurations may further improve efficiency and reduce operational failure risks under extreme conditions.

Separations doi: 10.3390/separations13040106

Authors: Cristiane Nunes da Silva Camilla Ribeiro Ferreira Bernardo Dias Ribeiro Filipe Smith Buarque

Spent coffee grounds (SCGs) are an abundant agro-industrial residue with high potential as a source of phenolic compounds and proteins. This study evaluated the extraction of these value-added fractions using hydrophilic and hydrophobic eutectic solvents, applied either alone or combined with enzyme-assisted extraction. A total of 31 hydrophobic eutectic solvents (HESs), nine hydrophilic deep eutectic solvents (DESs), and five conventional solvents were screened for phenolic recovery. Extraction performance was strongly formulation-dependent, with hydrophobic systems showing the highest phenolic yields. HES 4 (camphor:oleic acid) was the best-performing solvent, reaching 1279.49 ± 2.31 mg GAE L−1, followed by borneol:oleic acid (1133.92 ± 5.29 mg GAE L−1). Enzyme addition did not enhance phenolic extraction; the highest values under enzymatic conditions were 896.12 ± 4.80 mg GAE L−1 for HES 4 + Cellic® CTec2 and 819.84 ± 2.66 mg GAE L−1 for HES 4 + Viscozyme®. In contrast, protein extraction increased remarkably with enzyme supplementation, particularly with Cellic® CTec2. The highest protein recovery was obtained with HES 4 + Cellic® CTec2 (1608.74 ± 3.32 mg·L−1), compared with 506.37 ± 5.20 mg·L−1 for neat HES 4. In general, neat HESs were more suitable for phenolic recovery, whereas HESs combined with Cellic® CTec2 were more effective for protein extraction.

Separations doi: 10.3390/separations13040105

Authors: Xiu Wang Xiao-Juan Chen Qing Sun Juan Song Hai-Zhen Liang Bai-Ping Ma

Fufang Yinhua Jiedu Granules (FFYHG) is usually applied to treat influenza and the common cold. However, there is no available report concerning the effects of chemical constituents in FFYHG on antiviral activity. In our study, four new terpenoid derivatives (1–4) and seventeen known compounds were isolated from FFYHG. Their structures and absolute configurations were determined by various techniques, including high-resolution mass spectrometry analysis, 1/2-dimensional (1D/2D) nuclear magnetic resonance (NMR) analysis, comparative electronic circular dichroism (ECD) studies (experiment vs. calculation), and acid hydrolysis. In addition, the inhibitory effects of twenty-one isolated compounds against influenza A viruses (H1N1) including A/California/07/2009 (CA07) and A/WSN/1933 (WSN) strains were evaluated in vitro, and compound 4 exhibited a moderate inhibitory effect on CA07 strain, with a half maximal inhibitory concentration (IC50) value of 37.10 ± 1.35 μM. This study enhanced the understanding of the active ingredients in FFYHG against influenza virus, providing a foundation for further research on the material basis and quality control of FFYHG.

Separations doi: 10.3390/separations13040104

Authors: Tingting Ren Hongxiang Zhu Zongqiang Zhu Jian Tan Qiqi Qin

In this work, iron–phosphorus-based composite biochar (FPBC) was prepared by modification with the leachate of spent LiFePO4 batteries. The effects of solution pH, dosage, adsorption time, initial concentration, and temperature on the adsorption performance of FPBC were investigated by batch adsorption experiments with Pb(II) and Sb(III) as the target pollutants, and the adsorption mechanism was explored using SEM, BET, XPS, FTIR and XRD characterization. The results indicated that as the initial pH of the solution increased, the removal efficiency of FPBC for Pb(II) gradually increased, while the removal efficiency for Sb(III) remained largely unchanged. The removal of Pb(II) and Sb(III) by FPBC fitted the pseudo-second-order kinetic model and the three-step intraparticle diffusion model, indicating that their removal was primarily controlled by chemical adsorption. Isothermal adsorption studies revealed that FPBC adsorption of Pb(II) better fitted the Langmuir and D-R models, suggesting a monolayer-dominated adsorption process. In contrast, adsorption of Sb(III) fitted the Langmuir, Freundlich, and Temkin models, suggesting a combination of monolayer and multilayer adsorption characteristics. The maximum adsorption capacities of FPBC for Pb(II) and Sb(III) were 312.54 mg·g−1 and 219.20 mg·g−1 at 30 °C, which were approximately 12.85 and 3.37 times those of commercial corn stalk biochar (BC). Thermodynamic analysis confirmed that the removal of Pb(II) and Sb(III) by FPBC was a spontaneous and endothermic process. In addition, FPBC demonstrated strong selective adsorption of Pb(II) in the binary co-adsorption system of Pb(II) and Sb(III). Mechanism studies indicated that Pb(II) removal primarily occurred through co-precipitation, complexation, ion exchange, and electrostatic adsorption, while Sb(III) was mainly adsorbed by FPBC via redox reactions and complexation. Therefore, this work not only provides a low-cost, high-performance adsorbent for the remediation of water contaminated with Pb(II) and Sb(III), but also opens up new avenues for the resource recovery of the leachate of spent LiFePO4 batteries.

Separations doi: 10.3390/separations13040103

Authors: Mara Junqueira Carneiro Alexandre Augusto Borghi Guilherme Perez Pinheiro Ana Lucia Tasca Gois Ruiz Daniela Mizobutti Elaine Minatel Lisieux Santana Juliao Svetlana Ignatova Peter Hewitson Alexandra Christine Helena Frankland Sawaya

The chemical composition of natural products is complex and the investigation of bioactivities of compounds of interest demands their isolation. S. terebinthifolia Raddi is a tree belonging to the Anacardiaceae family and is used in Brazilian folk medicine; its fruit (pink peppers) are used in cooking and its bark in phytomedicine. Extracts of other parts of this plant contain a plethora of components and merit further studies. Countercurrent chromatography (CCC) is frequently employed with natural products due to the high sample recovery rate. The objective of this work was to determine the best solvent system (SS) to fraction the ethanol extracts of leaves, flowers and fruit of Schinus terebinthifolia by CCC and isolate compounds of interest and elucidate their structures through nuclear magnetic resonance (NMR) and mass spectrometry (MS). In addition, antiproliferative, potential cell regeneration and antioxidant activities of the fractions of interest were evaluated. In the present work, three compounds were isolated; two were identified as anacardic acids [(6-(8′, 11′-heptadecadienyl)-salicylic acid and 6-(8′-heptadecenyl)-salicylic acid], as well as (Z)-masticadienoic acid. These compounds showed antiproliferative and potential cell regeneration activities as well as varying degrees of antioxidant capacity. Although these compounds present potential therapeutic activity, more studies are necessary to confirm their safety.