Separations

15 pages, 1486 KB

Open AccessArticle

Study on the Flow Field Characteristics and Particle Motion Behavior in the Cylindrical Hydrocyclone

by Duanxu Hou, Haihao Wang, Daqing Hou, Hongying Zhu, Hongrun Song, Jingyan Zhang and Qingguo Shao

Separations 2026, 13(5), 155; https://doi.org/10.3390/separations13050155 - 21 May 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Advances in Technologies Used for Mineral Separation)

12 pages, 1407 KB

Open AccessArticle

Enhanced Separation of Am(III) and Cm(III) from Nitrate Solution by Bis(isobutylphenyl)dithiophosphinic Acid

by Qiaorui Sui, Xuan Hao, Jiale Li, Jin Zhou and Suliang Yang

Separations 2026, 13(5), 154; https://doi.org/10.3390/separations13050154 - 21 May 2026

Abstract

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 ³¹ [...] Read more.

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 (pH_1/2 = 3.39 for Am(III) and 3.64 for Cm(III)) and a notably improved separation factor for Am(III) over Cm(III) (SF_{Am(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. Full article

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19 pages, 5353 KB

Open AccessArticle

Trimethylsilane-Grafted Low-Rank Coal-Based Activated Coke for Hydrophobic Adsorption of Indole and Diethyl Phthalate from Wastewater

by Shaomeng Huang, Junhan Huyan, Xinyuan Li and Haiting Zhang

Separations 2026, 13(5), 153; https://doi.org/10.3390/separations13050153 - 20 May 2026

Abstract

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 [...] Read more.

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. Full article

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25 pages, 3657 KB

Open AccessArticle

Vapor–Liquid Equilibrium and Design of Energy-Efficient High-Vacuum Pressure-Swing Distillation for Bio-Based Alcohol/Alkane Separation

by Chunli Li, Tianzhu Ma, Yuze Sun, Kaile Shi, Wen Liu, Rui Wang and Jiapeng Liu

Separations 2026, 13(5), 152; https://doi.org/10.3390/separations13050152 - 18 May 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Section Separation Engineering)

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16 pages, 5280 KB

Open AccessArticle

The Effects of Outlet Diameter on Particle Movement and Separation Performance of the Cylindrical Hydrocyclone

by Duanxu Hou, Haihao Wang, Daqing Hou, Hongying Zhu, Hongrun Song, Honghe Deng and Qingguo Shao

Separations 2026, 13(5), 151; https://doi.org/10.3390/separations13050151 - 17 May 2026

Abstract

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 [...] Read more.

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 D_u = 0.075 D and D_o ≥ 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 D_u = 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. Full article

(This article belongs to the Special Issue Advances in Technologies Used for Mineral Separation)

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22 pages, 8586 KB

Open AccessArticle

Effects of Hydrocarbons and Ionic Impurities on Foaming and Purification of UDS Desulfurization Solvent

by Haiyang Wen, Qiyue Zhao, Yaolin Wang, Zhenwu Jiang, Yupeng Cui, Mengna Xu, Chuanlei Liu and Hui Sun

Separations 2026, 13(5), 150; https://doi.org/10.3390/separations13050150 - 16 May 2026

Abstract

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 [...] Read more.

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 q_0–12 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. Full article

(This article belongs to the Topic Application of Chromatography-Mass Spectrometry and Related Techniques, 2nd Edition)

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31 pages, 3295 KB

Open AccessReview

Determinants of CH₄ Selective Adsorption and Separation Performance in Coal Mine Gas Under High-Humidity and Multi-Component Conditions: A Review

by Ruguo Dong, Yongli Liu and Lixin Li

Separations 2026, 13(5), 149; https://doi.org/10.3390/separations13050149 - 15 May 2026

Abstract

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 [...] Read more.

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. Full article

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14 pages, 7683 KB

Open AccessArticle

A Facile Strategy to Construct Structured Mg-Gallate Adsorbent for Post-Combustion CO₂ Capture Under 80% RH

by Siyu Wang, Junyang Du, Junsu Jin and Jianguo Mi

Separations 2026, 13(5), 148; https://doi.org/10.3390/separations13050148 - 14 May 2026

Abstract

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 [...] Read more.

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. Full article

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16 pages, 1013 KB

Open AccessArticle

A Method for Separation of Elemental Sulfur from Organic Polysulfides in Their Mixtures

by Irina Zweig and Alexey Kamyshny, Jr.

Separations 2026, 13(5), 147; https://doi.org/10.3390/separations13050147 - 13 May 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Section Environmental Separations)

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24 pages, 5974 KB

Open AccessArticle

Multidimensional Quality Evaluation of Drying Methods on the Bioactive Components and Antioxidant Activity of Astragalus membranaceus var. mongholicus Slices

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

Separations 2026, 13(5), 146; https://doi.org/10.3390/separations13050146 - 11 May 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Extraction, Purification and Functional Substances of Natural Products and Plants)

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Graphical abstract

13 pages, 10037 KB

Open AccessArticle

Direct Analysis of Silk Dyes from the Murong Zhi Tomb from the Tang Dynasty Using Desorption Electrospray Ionization High-Resolution Mass-Spectrometry Imaging (DESI-MSI)

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

Separations 2026, 13(5), 145; https://doi.org/10.3390/separations13050145 - 9 May 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Topic Innovative Analytical Approaches for Natural Products and Pharmaceuticals in Complex Matrices)

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20 pages, 931 KB

Open AccessEditorial

The Evolution of Chromatography in Greece: A Historical Perspective

by Victoria Samanidou

Separations 2026, 13(5), 144; https://doi.org/10.3390/separations13050144 - 9 May 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Collection CEGSS Yesterday, Today and Tomorrow)

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29 pages, 4008 KB

Open AccessArticle

Simultaneous Optimization of Polyphenol Content and Antioxidant Capacity of Extracts from Habanero Pepper Leaves Obtained with Green Technologies: NADES and Ultrasound

by Yajaira Cecilia Torruco-Ortiz, Kevin Alejandro Avilés-Betanzos, Manuel Octavio Ramírez-Sucre and Ingrid Mayanin Rodríguez-Buenfil

Separations 2026, 13(5), 143; https://doi.org/10.3390/separations13050143 - 9 May 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Novel Solvents and Methods for Extraction of Chemicals)

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21 pages, 4445 KB

Open AccessArticle

Selective Adsorption and Dynamic Fractionated Separation of Mixed Rare Earth Elements by a Silane-Grafted Aminophosphonate D152 Resin

by Mixuan Huan, Wenhan Sun, Chunlin He, Xiaohao Pu, Mingzhou Li, Huawu Mo and Mingyue Fei

Separations 2026, 13(5), 142; https://doi.org/10.3390/separations13050142 - 7 May 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Section Separation Engineering)

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22 pages, 4114 KB

Open AccessArticle

Enhancement of the Wastewater Treatment Process of a PETRO System by Natural and Commercial Coagulants

by Phillimon Tlamelo Odirile and Nkgopolang Matthews Boima

Separations 2026, 13(5), 141; https://doi.org/10.3390/separations13050141 - 5 May 2026

Abstract

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) [...] Read more.

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. Full article

(This article belongs to the Special Issue Separation Techniques for Wastewater Treatment)

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22 pages, 11231 KB

Open AccessArticle

Resource Recovery from High-Salinity Rare Earth Metallurgy Wastewater by Coupling Electrolysis and Membrane Processes

by Yanxin Xie, Jiuyang Lin, Yinhua Wan, Chao Wang, Kaibo Hu, Wenjing Yuan, Ning Li and Xuewei Li

Separations 2026, 13(5), 140; https://doi.org/10.3390/separations13050140 - 2 May 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Electrochemical Separation and Recovery Technology in Wastewater Treatment)

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18 pages, 1103 KB

Open AccessReview

A Review on the Extraction, Purification, and Biological Activities of Polysaccharides from Elaeagnus angustifolia Fruits

by Xinhan Fan and Wei Wang

Separations 2026, 13(5), 139; https://doi.org/10.3390/separations13050139 - 1 May 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Design and Optimization of Extraction/Separation Processes for Natural Products)

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19 pages, 4777 KB

Open AccessArticle

A Novel Hybrid Adsorbent Based on Fly Ash and Waste Flax Fibers for Efficient Separation of Rare Earth Ions from Water

by Tijana Radojičić, Katarina Trivunac, Marina Maletić, Ivona Janković-Častvan, Miloš Simić, Ana Kalijadis and Marija Vukčević

Separations 2026, 13(5), 138; https://doi.org/10.3390/separations13050138 - 1 May 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Recent Advances in Rare Earth Separation and Extraction)

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18 pages, 2677 KB

Open AccessArticle

Selective Recovery of Gold Using Two Sea Algae (Ulva lactuca and Ulva pertusa) with or Without Concentrated Sulfuric Acid Treatment

by Jhapindra Adhikari, Gehui Pang, Shintaro Morisada, Hidetaka Kawakita, Keisuke Ohto, Mikihide Demura and Kazuya Urata

Separations 2026, 13(5), 137; https://doi.org/10.3390/separations13050137 - 30 Apr 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Section Materials in Separation Science)

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