Search Results (1,711)

Achieving sustainable land restoration in southern Chinese ionic rare earth mining areas remains a significant challenge due to the extended duration and low efficiency of conventional remediation approaches. Although the hyperaccumulator Dicranopteris pedata possesses a remarkable capacity for rare earth element (REE) enrichment, a significant knowledge gap exists regarding how to effectively combine exogenous organic acids with agronomic practices like clipping to enhance its remediation efficiency in an environmentally sustainable manner. Crucially, the potential environmental risks associated with such synergistic strategies have not been systematically evaluated, hindering their practical application. To address this, our study focused on Dicranopteris pedata and employed integrated pot and soil column leaching experiments to systematically analyze the effects of different concentrations of citric acid and tartaric acid on REE migration and transformation within the soil–plant system. The results demonstrated that exogenous organic acids significantly reduced soil pH and promoted the conversion of REEs from the residual to the exchangeable fraction. Specifically, the 20 mmol·kg⁻¹ citric acid treatment increased the proportion of exchangeable REEs by 43.46%. Furthermore, organic acid treatments significantly altered the REE uptake patterns in Dicranopteris pedata, inhibiting the translocation and accumulation of REEs in the aboveground tissues. Soil column leaching experiments revealed that citric acid drove the migration of REEs to deeper soil layers, with the concentration peaking at 288.33 mg·kg⁻¹ at a depth of 6–8 cm; concomitantly, the REE content in the leachate reached its maximum on the 5th day. This study demonstrates that the combined application of 20 mmol·kg⁻¹ citric acid and 100% clipping management increased the annual REE accumulation in Dicranopteris pedata to 4.85 g·m⁻², thereby significantly shortening the theoretical remediation period from 25.0 years in the control to 12.1 years. Soil column leaching experiments indicated no significant secondary pollution risk associated with this strategy. These findings provide a feasible, low-risk, and sustainable technical strategy for the synergistically enhanced remediation of REE-contaminated soils, offering a promising path for ecological restoration and sustainable land management in degraded mining ecosystems. Full article

Currently, water pollution is one of the major global environmental sustainability and public health issues that requires efficient and viable remediation technologies, as existing decontamination methods face limitations. In this sense, this review aims to highlight the potential of multifunctional aerogel-based magnetic nanocomposites as a novel strategy for water decontamination by integrating magnetic nanostructures into aerogel matrices that promote high adsorption capacity, selective catalysis, and facile magnetic recovery. In this regard, providing a comprehensive analysis of their functional design, contaminant-removal mechanisms, and multifunctional performance is crucial for developing and optimizing a system capable of addressing complex pollutants through multiple mechanisms (e.g., adsorption, photocatalysis, and reductive pathways). However, ecotoxicological evaluations focus on the potential for nanoparticles to leach, induce oxidative stress, and cause aquatic toxicity, supporting the development of strategies that comply with safety principles. Additionally, this review examines the aerogels’ capabilities for regeneration, operational stability, and scalability across repeated-use cycles, as well as their potential for real-world wastewater applications. Moreover, future directions for these aerogels include the development of smart, stimuli-responsive aerogels, machine-learning-based modeling, and the use of green synthesis approaches to enable sustainable water remediation strategies. Full article

Oxalic acid serves as an environmentally benign leaching agent, exhibiting strong reducing and complexing capabilities. In the oxalic acid leachate derived from vanadium-bearing shale, aluminum ions are present as major impurities. Achieving efficient and deep separation of vanadium from aluminum remains a key technical challenge. This study investigates the selective separation of vanadium and aluminum from oxalic acid leaching solutions using solvent extraction with Aliquat 336, supported by density functional theory (DFT) calculations. Experimental results demonstrate that, under optimized conditions, Aliquat 336 enables effective separation of vanadium from aluminum. DFT analysis elucidates the molecular-level interaction mechanism, revealing that the binding affinity of Aliquat 336 for [VO(C₂O₄)₂]²⁻ (ΔG = −287.96 kJ/mol) is significantly stronger than for [Al(C₂O₄)₂]⁻ (ΔG = −186.68 kJ/mol). These results provide a solid thermodynamic basis for the observed selectivity and establish a robust theoretical framework for developing high-efficiency separation processes. This work thus clarifies, for the first time, the mechanistic foundation of vanadium–aluminum separation in oxalic acid systems. Full article

In this work, a method for leaching black mass from spent Li batteries using oxalic acid was developed and experimentally verified with the objective of selectively separating lithium and cobalt. Oxalic acid proved to be an efficient and selective leaching agent. Under 1 M C₂H₂O₄, 120 min, L:S = 20, 80 °C and 300 rpm, a lithium yield of 90% was achieved, while cobalt dissolution remained low at 1.57%. Subsequently, cobalt spontaneously precipitated from the leachate within several hours, and the solid phase was fully separated after 24 h. The leachate contained minor amounts of accompanying metals, with dissolution yields of 0.5% Mn, 8% Fe and 1.4% Cu. These impurities were removed from the leachate by controlled pH adjustment using NaOH at ambient temperature and 450 rpm, with complete precipitation at pH 12. This procedure generated a purified lithium-rich leachate, which was converted into lithium oxalate by crystallisation at 105 °C. Subsequent calcination of the resulting solid at 450 °C for 30 min produced Li₂CO₃ with a purity of 91%. Based on the experimental findings, a conceptual technological process for selective lithium leaching using oxalic acid was proposed, demonstrating the potential of this method for sustainable lithium recovery. Full article

The accelerating global demand for sustainable energy, driven by population growth, industrialization, and environmental concerns, has intensified the search for renewable alternatives to fossil fuels. Biofuels, including bioethanol, biodiesel, biogas, and biohydrogen, offer a viable and practical pathway to reducing net carbon dioxide (CO₂) emissions. Yet, their large-scale production remains constrained by biomass recalcitrance, high pretreatment costs, and the enzyme-intensive nature of conversion processes. Recent advances in enzyme immobilization using magnetic nanoparticles (MNPs), covalent organic frameworks, metal–organic frameworks, and biochar have significantly improved enzyme stability, recyclability, and catalytic efficiency. Complementary strategies such as cross-linked enzyme aggregates, carrier-free immobilization, and site-specific attachment further reduce enzyme leaching and operational costs, particularly in lipase-mediated biodiesel synthesis. In addition to biocatalysis, nanozymes—nanomaterials exhibiting enzyme-like activity—are emerging as robust co-catalysts for biomass degradation and upgrading, although challenges in selectivity and environmental safety persist. Green synthesis approaches employing plant extracts, microbes, and agro-industrial wastes are increasingly adopted to produce eco-friendly nanomaterials and bio-derived supports aligned with circular economy principles. These functionalized materials have demonstrated promising performance in esterification, transesterification, and catalytic routes for biohydrogen generation. Technoeconomic and lifecycle assessments emphasize the need to balance catalyst complexity with environmental and economic sustainability. Multifunctional catalysts, process intensification strategies, and engineered thermostable enzymes are improving productivity. Looking forward, pilot-scale validation of green-synthesized nano- and biomaterials, coupled with appropriate regulatory frameworks, will be critical for real-world deployment. Full article

Wooden waste railroad ties preserved with coal tar creosote oil represent a specific source of polluting substances. The aim of this study was to investigate and compare extraction capacity due to solvent extraction of fifteen frequently used organic solvents for the purpose of decontamination treatment of waste wooden railroad ties, while recovering wood for reuse. Pure organic solvents, ethanol 96%, propan-2-ol, deionized water, dichloromethane, acetone, n-hexane, mixture n-hexane/acetone (V/V = 1/1), cyclohexane, methanol, N,N-dimethyl formamide, toluene, ethyl acetate, acetonitrile, amyl acetate, medical gasoline, n-pentane and n-butyl acetate were for leaching pollutants from waste railroad ties. The highest extraction capacity was achieved using dichloromethane, where 7.50 to 7.89 wt.% of total sixteen polycyclic aromatic hydrocarbons were extracted from waste railroad tie chips. The most promising solvents for the treatment exhibited extraction efficiency which decreases in a series dichloromethane > n-hexane/acetone > acetone > methanol > ethanol 96% > propan-2-ol > cyclohexane > toluene > n-hexane. Solvent extraction represents a novel approach for treatment of wooden waste railroad ties. The experiments are based on the search for a management process for the treatment of wood waste railroad ties that is simple, low energy consumption, efficient and could potentially be applied for large scale. Full article

Biochar is known to enhance soil potassium (K) availability and promote plant K uptake; however, its influence on the transformation pathways of fertilizer potassium and the mechanisms regulating crop potassium accumulation remains insufficiently understood. This study conducted a pot experiment using three soil types—Albic, Brown, and Sandy soils—with different biochar application rates (0, 10, and 20 g·kg⁻¹) in combination with potassium fertilizer, to systematically evaluate the regulation of soil K forms, K fertilizer transformation rates, K use efficiency, and K uptake and accumulation in soybeans. The results demonstrated that the combined application of biochar and K fertilizer significantly increased the contents of available, water-soluble, exchangeable, and non-exchangeable K across all three soils. At the highest biochar application rate (20 g·kg⁻¹), available K increased by 15.37%, 16.78%, and 11.77% in the Albic, Sandy, and Brown soils, respectively, compared to the control. Furthermore, biochar altered the transformation pathways of fertilizer K; it consistently reduced the conversion rate of fertilizer K into exchangeable K across all soils, redirecting it toward the water-soluble and non-exchangeable K pools, thus functioning as a potassium “scheduling center”. Adsorption–desorption experiments revealed that biochar exhibits a strong multilayer adsorption capacity for K ions, with most of the adsorbed K not easily desorbed, providing mechanistic support for the observed shift in transformation pathways. In terms of K use efficiency, biochar reduced the K of agronomic efficiency (KAE) due to a “dilution effect” from its inherent K content. Under the high application rate (20 g·kg⁻¹), the KAE decreased by 11.79% in Albic soil, 88.48% in Sandy soil, and 71.73% in Brown soil, while significantly increasing the partial factor productivity of K (PFPK) and apparent recovery efficiency of K (AREK). Ultimately, the co-application of biochar and K fertilizer significantly enhanced total K accumulation and seed yield in soybeans by increasing K concentrations in various plant parts and promoting dry matter accumulation. At the biochar application rate of 20 g·kg⁻¹, the potassium accumulation and soybean yield under biochar treatment reached maximum increases of 70.77% (in Brown soil) and 42.63% (in Albic soil), respectively. This study demonstrates that biochar can synergistically reduce potassium (K) leaching and improve fertilizer use efficiency by regulating K transformation pathways. This provides a practical guideline for utilizing biochar as a dual-function amendment, which acts as both a supplemental K source and a soil conditioner, thereby supporting the development of more sustainable potassium management practices in diverse cropping systems. Full article

Rational nitrogen applications can not only improve nutrient use efficiency, but also reduce environmental pollution caused by nitrogen leaching. To explore reasonable nitrogen application strategies for synergistically enhancing alfalfa production and ecological benefits, this study calibrated and validated the APSIM–Lucerne model based on field experiments conducted from 2021 to 2023. The effects of nitrogen application levels of 0, 80, 120, 140, 160, 180, 200, and 240 kg/ha on alfalfa yield, soil NO₃⁻–N and NH₄⁺–N residues, and nitrogen use efficiency under dry, normal, and wet years were simulated. The results indicate: (1) The calibrated APSIM–Lucerne model effectively simulates alfalfa yield and soil nitrogen residuals (R² ranging from 0.67 to 0.91, NRMSE between 6.55% and 24.03%). (2) Increased nitrogen application significantly elevates soil nitrogen residue, yet alfalfa yield follows a pattern of initial increase followed by decline, with nitrogen fertilizer use efficiency continuously decreasing. Under identical nitrogen application rates, the wet year type proves more advantageous for achieving high yields, low nitrogen residue, and high nitrogen fertilizer use efficiency. (3) The nitrogen application thresholds for achieving increased alfalfa yields and high efficiency during dry years, normal years, and wet years are 107–140 kg/ha, 135–160 kg/ha, and 150–183 kg/ha, respectively. Full article

To facilitate the large-scale recycling of phosphogypsum (PG) as a construction material and mitigate the environmental safety concerns associated with its stockpiling or discharge, this study proposes an innovative approach. The method employs modified (acid-treated) basalt fibers (MBF) synergistically combined with microbially induced carbonate precipitation (MICP) technology for PG solidification. This synergistic MBF–MICP treatment not only enhances the strength and further improves the toughness of the solidified PG but also effectively immobilizes heavy metals within the PG matrix. Bacterial attachment tests conducted on fibers subjected to various pretreatment conditions revealed that the maximum bacterial adhesion occurred on fibers treated with a 1 mol/L acid concentration for 2 h at 40 °C. However, MICP mineralization experiments performed on these pretreated fibers determined the optimal pretreatment conditions for mineralization efficiency to be an acid concentration of 0.93 mol/L, a treatment duration of 0.96 h, and a temperature of 30 °C. Unconfined compressive strength (UCS) tests and calcium carbonate content measurements identified the optimal reinforcement parameters for MBF–MICP-solidified PG as a fiber length of 9 mm and a fiber dosage of 0.4%. Furthermore, comparative analysis demonstrated that the UCS and toughness of MBF–MICP-solidified PG were superior to those of bio-cemented PG specimens treated with unmodified fibers or without any fiber reinforcement. It was found by scanning electron microscopy that there was an obvious phosphogypsum particle-fiber-calcium carbonate precipitation interface in the sample, and the fiber had a bridging effect. Finally, heavy metal leaching tests conducted on the solidified PG confirmed that the leached heavy metal concentrations were below the detection limit, complying with national discharge standards. Full article

Fly ash (FA), a major by-product of coal combustion, has long been regarded as a challenging industrial solid waste. Its inherent abundance of alkaline-earth oxides positioned it as a promising candidate for CO₂ sequestration through mineral carbonation. This study systematically investigated the effects of key operational parameters, including time, stirring rate, ultrasonic treatment, and solid-to-liquid ratio, on the leaching efficiency of calcium ions and subsequent CO₂ fixation. Ultrasonic treatment, a solid-to-liquid ratio of 1:7, a stirring speed of 600 rpm, and 7% monoethanolamine (MEA) collectively enhanced the calcium leaching efficiency (χ_e) to 16.7%, thereby supplying a substantial reservoir of calcium ions for CO₂ fixation. Additionally, the CO₂ injection into fly ash slurry and the slurry spraying into CO₂ gas were investigated to optimize reactor configurations. The latter method demonstrated superior performance, attaining a CO₂ fixation efficiency of 7.23%. This corresponds to a carbonation conversion efficiency (ηc) of approximately 44.5%, indicating that nearly half of the leached calcium ions were successfully converted into stable carbonates. Advanced characterization techniques (SEM-EDS, XRD, FTIR) confirmed the formation of stable carbonates and highlighted the role of additives in enhancing reactivity. The environmental benefit of this approach is addressing fly ash wastes and transforming fly ash into a CO₂ fixation material. These findings provided critical insights for calcium leaching and CO₂ fixation of fly ash. Full article

Coal-based humic acid waste residue is a solid waste generated during the production of humic acid products. The extraction of coal-based humin (NHM) from such residues presents an effective approach for solid waste resource recovery. In this study, a novel calcium-based humin (Ca-NHM) was synthesized via a low-temperature-assisted method. The material was characterized and its cadmium passivation mechanism was investigated using scanning electron microscopy (SEM), zeta potential analysis (Zeta), carbon nuclear magnetic resonance (¹³C-CPMAS-NMR), and X-ray photoelectron spectroscopy (XPS). Soil incubation experiments were conducted to determine the actual cadmium adsorption capacity of coal-based humin in soils and to evaluate the stability of cadmium passivation. Plant cultivation experiments were carried out to verify the effects of coal-based humin on migration and transformation in soil, as well as on cadmium bioefficiency. The results showed that Ca-NHM passivated soil cadmium through multiple mechanisms such as ion exchange, electrostatic adsorption, complexation reactions, and physical adsorption. Compared with NHM, Ca-NHM exhibited a 69.71% increase in passivation efficiency, and a 2.44% reduction in cadmium leaching concentration. In Ca-NHM treatments, the above- and below-ground biomass of pakchoi increased by 18.06%, and 80.95%, respectively, relative to the control group. Furthermore, Ca-NHM enhanced the cadmium resistance of pakchoi, reduced the enrichment coefficient, activity coefficient, and activity-to-stability ratio in the above-ground portion of pakchoi, and maintained a transfer coefficient below 1, thereby alleviating cadmium toxicity. In summary, this study provides a theoretical foundation for understanding the mechanisms by which coal-based humin mitigates cadmium toxicity in pakchoi. Full article

Growing demand for rare earth elements (REEs) necessitates the development of efficient recycling strategies from secondary sources. This work presents a complete hydrometallurgical process for recovering yttrium (Y) from spent fluorescent lamps, emphasizing the efficient coupling of a conventional acid leaching with a solid–liquid extraction system. Multi-stage sulfuric acid leaching (2 M, 65 °C, an S/L ratio of 0.25 g/L) achieved a cumulative yttrium dissolution of 71.11% over four stages, with individual stage recoveries (based on initial yttrium content) of 44.2%, 21.56%, 7.19%, and 0.68%. Kinetic and spectroscopic analyses (FTIR, SEM-EDS) revealed that the leaching rate is controlled by diffusion through an in situ formed sulfate-rich layer (CaSO₄, Na₂SO₄), as described by the Z-L-T (Zhuravlev–Leshokin–Templeman) model (Ea = 35.5 kJ mol⁻¹). The resulting leachate was subjected to solid–liquid extraction using Amberlite XAD-7 resin impregnated with D₂EHPA. Under optimal conditions, the extraction process was highly efficient, yielding over 99% yttrium recovery at an optimal pH of 0.75 with a low resin dosage of 0.1 g/L. Furthermore, the solvent-impregnated resins exhibited excellent reusability over five consecutive extraction–stripping cycles, maintaining a single-cycle stripping efficiency above 70% and a cumulative recovery exceeding 97%. This study validates the technical feasibility of an integrated leach–extract–strip process based on impregnated resins as an alternative approach for yttrium recycling from electronic waste, potentially supporting the development of a circular economy. Full article

The conventional method of flue gas desulfurization gypsum (FGDG) application, i.e., blending with flood irrigation, is hindered by low water efficiency and significant amendment loss due to runoff and uncontrolled leaching, particularly in arid and semi-arid regions in which water scarcity is a major constraint. This study aimed to evaluate a novel integration of FGDG band application with drip irrigation to enhance targeting and resource efficiency. A laboratory-scale experiment investigated the effects of two FGDG application methods (band and blend application) and drip rates (0.3 and 0.6 L h⁻¹) on soil water movement and chemical properties. Band application significantly accelerated initial wetting front advancement by up to 44.9 cm h⁻¹ near the emitter and sustained horizontal propagation, while blend application promoted a more uniform water distribution. Chemically, band application created localized zones of reduced pH (7.57–8.62) and elevated water-soluble Ca²⁺ (up to 492.2 mmol kg⁻¹), facilitating a 79.1% reduction in exchangeable Na⁺ near the emitter. In contrast, blend application resulted in broader but shallower amendment distribution, reducing exchangeable sodium percentage uniformly to 1.99–4.16% across the soil profile. The combination of banded FGDG and drip irrigation achieves targeted amelioration, with superior Na⁺/Ca²⁺ exchange and favorable moisture dynamics resulting from the synergy between amendment placement and water delivery. This approach is a viable strategy for precision reclamation in arid regions. Full article

Developing sustainable and molecularly selective adsorbents for heavy-metal removal remains a critical challenge in water purification. Herein, we report a green molecular-engineering approach for fabricating aza-crown ether functionalized sodium alginate aerogels (ACSA) capable of highly selective Cu²⁺ capture. The aerogels were synthesized via saccharide-ring oxidation, Cu²⁺-templated self-assembly, and reductive amination, enabling the covalent integration of aza-crown ether motifs within a hierarchically porous biopolymer matrix. Structural analyses (FTIR, ¹³C NMR, XPS, SEM, TGA) confirmed the in situ formation of macrocyclic N/O coordination sites. Owing to their interconnected porosity and chemically stable framework, ACSA exhibited rapid sorption kinetics following a pseudo-second-order model (R² = 0.999) and a Langmuir maximum adsorption capacity of 150.82 mg·g⁻¹. The material displayed remarkable Cu²⁺ selectivity over Zn²⁺, Cd²⁺, and Ni²⁺, arising from the precise alignment between Cu²⁺ ionic radius (0.73 Å) and crown-cavity dimensions, synergistic N/O chelation, and Jahn-Teller stabilization. Over four regeneration cycles, ACSA retained more than 80% of its original adsorption capacity, confirming excellent durability and reusability. This saccharide-ring modification strategy eliminates crown-ether leaching and weak anchoring, offering a scalable and environmentally benign route to bio-based adsorbents that combine molecular recognition with structural stability for efficient Cu²⁺ remediation and beyond. Full article

This study investigated the effect of mechanical activation on the physicochemical properties of lepidolite and the leaching behavior of mechanically activated samples in sulfuric acid (H₂SO₄). Lepidolite was mechanically activated using a high-energy planetary ball mill (PBM) at 400 RPM with a 20:1 ball-to-feed weight ratio (BFR, g:g) and the samples activated for different durations were characterized for amorphous phase content, particle size, and morphology using various solid analyses. X-ray diffraction (XRD) revealed the progressive amorphization of lepidolite, with the amorphous fraction increased from 34.1% (unactivated) to 81.4% after 60 min of mechanical activation. Scanning electron microscopy (SEM) showed that mechanically activated particles became fluffy and rounded, whereas unactivated particles retained lamellar and angular shapes. The reactivity of minerals after mechanical activation was evaluated through a 2 M H₂SO₄ leaching test at different leaching temperatures (25–80 °C) and time periods (30–180 min). Although the leaching efficiencies of Li and Al slightly improved at higher leaching temperatures and longer leaching times, the leaching of these metals was primarily governed by the mechanical activation time. The highest Li and Al leaching efficiencies—87.0% for Li and 79.4% for Al—were obtained from lepidolite that was mechanically activated for 60 min under leaching conditions of 80 °C and a 10% (w/v) solid/liquid (S/L) ratio for 30 min. The elemental mapping images of leaching feed and residue produced via energy dispersive spectroscopy (EDS) indicated that unactivated particles in the leaching residue had much higher metal content than mechanically activated particles. Kinetic analysis further suggested that leaching predominantly occurs at mechanically activated sites and the apparent activation energies calculated in this study (<3.1 kJ·mol⁻¹) indicate diffusion-controlled behavior with weak temperature dependence. This result confirmed that mechanical activation significantly improves reactivity and that the residual unleached fraction can be attributed to unactivated particles. Full article