Search Results (377)

Vanadium-bearing steel slag has attracted considerable attention as a secondary source of vanadium. Pre-decalcified vanadium-bearing steel slag served as the feedstock to evaluate vanadium leaching under microwave irradiation and conventional water-bath heating by varying sulfuric acid concentration, temperature, leaching time, and liquid-to-solid ratio. The leaching performance was further evaluated through countercurrent leaching experiments, and kinetic analysis was conducted to investigate the rate-controlling behavior. The results demonstrated that the optimum leaching conditions under microwave irradiation were a liquid-to-solid ratio of 8 mL·g⁻¹, a leaching time of 60 min, a sulfuric acid concentration of 15%, and a temperature of 70 °C, yielding a vanadium leaching rate of 74.43%. Multistage leachate reuse increased the normalized V enrichment index from 74.43% after the initial single-stage leaching to 89.93% after two reuse stages, with only a limited further increase thereafter. Kinetic analysis indicated a constant-particle-size shrinking-core mechanism for vanadium leaching. Sulfuric acid concentration exhibited an apparent reaction order of 1.80, and the apparent activation energy was 57.20 kJ·mol⁻¹. Internal diffusion was identified as the predominant rate-controlling step, while the contribution of the interfacial chemical reaction could not be neglected. Microwave irradiation enhanced vanadium extraction through volumetric and selective heating effects, potentially promoting structural disruption of the pre-decalcified slag and facilitating leaching agent diffusion into the particle interior. These findings provide an effective hydrometallurgical strategy for sustainable vanadium recovery from industrial solid waste. Full article

Phosphorus (P) leaching from dryland from purple soils poses a significant risk to water quality, yet effective mitigation strategies and their underlying microbial mechanisms remain poorly understood. This study aimed to evaluate the efficacy of biochar (B), a silicon-based conditioner (Si), and their combination (BSi) in controlling P leaching, hypothesizing that B would immobilize P while Si would mobilize it. The indoor soil column leaching experiments were conducted with four treatments (CK, B, Si, BSi), measuring leachate P fractions and soil P forms, and employed metagenomic sequencing combined with partial least-squares path modeling (PLS-PM) and Bayesian structural equation modeling (BSEM) to explore microbial functional mechanisms. Results showed that B alone reduced cumulative leaching of inorganic P (IP), organic P (OP), and total P (TP) by a range of 5.4–6.3%, while increasing available phosphorus (Olsen-P) by 39.4% in the surface layer. Si and BSi promoted leaching, with BSi reducing available P sharply, despite raising TP. Metagenomic analysis revealed that B suppressed subsurface IP solubilization genes (e.g., gcd, ppx) and optimized OP mineralization, whereas Si inhibited mineralization via reducing key microbial taxa. BSEM further identified water-soluble P (Water-P) and total nitrogen (TN) as direct positive drivers of inorganic P dissolution. Collectively, the key biological mechanisms for leaching reduction involve inhibiting subsurface IP solubilization, optimizing surface OP mineralization, and enhancing P transport/starvation responses. Collectively, biochar applied alone offers the optimal balance between P retention and crop-available P supply in dryland purple soils, and provides mechanistic insights—through functional gene profiling—that can inform the design of more sustainable P fertilization and leaching control practices. Full article

The growing adoption of lithium iron phosphate (LiFePO₄, LFP) batteries in renewable energy storage systems is expected to generate substantial volumes of end-of-life batteries, presenting both waste-management challenges and opportunities for critical-mineral recovery. Although lithium recovery from spent LFP batteries has been widely investigated, many hydrometallurgical processes employ strong inorganic acids, external heating, and finely ground feed material. Comparatively few studies have specifically examined selective lithium recovery from end-of-life LFP batteries used in stationary solar-energy-storage systems. This study investigated the selective recovery of lithium from spent solar-energy-storage LFP batteries using an acetic acid–hydrogen peroxide leaching system. Cathode active material (CAM) recovered from spent batteries was characterized and subjected to scouting and OFAT optimization experiments. The optimized conditions comprised 100% stoichiometric acetic acid addition, 275% stoichiometric H₂O₂ addition, an initial ambient temperature, a pulp density of 20% (w/w) solids, a residence time of 1 h, and unmilled CAM with 85% (w/w) passing 850 µm. Three independent confirmatory experiments achieved mean leaching efficiencies of 95.382 ± 0.109% for Li, 0.089 ± 0.008% for Fe, and 0.009 ± 0.002% for P. XRD analysis identified heterosite (FePO₄) as the dominant crystalline phase in the residue, with semi-quantitative analysis indicating an approximate phase proportion of 96%, supporting the selective delithiation of the LFP structure. The process produced a lithium-rich leachate and an FePO₄-rich residue under mild operating conditions without external heating or additional grinding. These findings demonstrate the potential of the acetic–H₂O₂ system for the selective hydrometallurgical recovery of lithium from spent LFP batteries. Full article

Hydrothermal hydrolysis of TiOSO₄ is a critical step in recovering titanium from sulfuric-acid leachates derived from titanium-bearing blast furnace slag (TBFS). This research examined the effects of Mg, Al, and Fe impurities on TiOSO₄ hydrolysis and assessed modified coal gasification slag (m-CGS) as a substrate for TiO₂ deposition. Mg, Al, and Fe sulfates suppressed Ti hydrolysis but yielded smaller, more highly dispersed metatitanic acid particles; at comparable hydrolysis ratios, the mean particle size decreased from 305 to 143 nm. Thermodynamic calculations indicated that the additional sulfate reduced the [TiO²⁺][OH⁻]² concentration product and the theoretical hydrolysis ratio. In contrast, m-CGS accelerated hydrolysis, particularly at lower temperatures. The lower Avrami exponents observed upon the addition of m-CGS indicated an increased contribution of heterogeneous particle growth. Particle size distribution analysis and TEM-EDS confirmed Ti deposition on the m-CGS surfaces. These results support direct TiO₂ deposition from impurity-bearing TiOSO₄ solutions as a route to the integrated utilization of TBFS and CGS. Full article

Upon entering aquatic ecosystems, coal fly ash (CFA) particles and their leachates distribute across all environmental compartments, from surface water to benthic sediments, rendering them accessible to aquatic organisms spanning multiple trophic levels. Although CFA is widely classified as non-hazardous waste, a growing body of toxicological evidence demonstrates its capacity to induce significant adverse biological effects. This discrepancy between laboratory-demonstrated toxicity and its current non-hazardous regulatory status highlights a critical knowledge gap in risk assessment frameworks and testing philosophies. Herein, we provide a comprehensive review of CFA characterization techniques, leaching methodologies and their environmental relevance, and the aquatic ecotoxicity of both particulates and leachates to primary, secondary, and tertiary consumers. Based on the findings from the review, we propose four paradigm shifts to more accurately characterize CFA ecotoxicological risks: from standardized leaching protocols to application-specific and maximum leachability tests, from single-species assays to multi-trophic-level bioassays, from single-metal analysis to comprehensive, whole-matrix testing that integrates particulate and dissolved fractions, and from standardizing the reporting of CFA provenance, coal types, and combustion conditions to meaningful meta-analyses and cross-study comparisons. It is believed that these suggestions will substantially advance the realistic ecotoxicological assessment of CFA and bridge the gap between laboratory toxicity data and regulatory classification. Full article

In vegetable production, excessive nitrogen fertilizer application leads to extremely low NUE and substantial reactive nitrogen losses. Given the abundant rainfall and the high residual soil nitrogen in soil after harvest, there is a pronounced risk of nitrate leaching during the summer fallow period. This study conducted a meta-analysis to systematically evaluate the effects of catch crops on nitrogen loss and soil nitrogen accumulation during the summer fallow season. The results showed that catch crops significantly reduced total N leaching loss by 58.10% through decreasing leachate volume by 24.54% and reducing leachate concentrations of TDN (43.36%), NO₃⁻–N (34.47%), and NH₄⁺–N (56.05%), respectively. Catch crops reduced soil NO₃⁻–N storage by 36.28% and SIN storage by 40.61%, while increasing SON storage by 69.79% and MBN by 21.47%, thereby achieving a transformation from readily available mineral N to more stable organic N. Catch crops also enhanced ammonification, mineralization, and nitrification by 126%, 142%, and 42%, respectively, and altered the microbial community structure. The effectiveness of catch crops varied significantly among taxa: Poaceae exhibited the best overall performance, the genus Zea (especially sweet corn) showed the most comprehensive performance in integrated N control, while Fabaceae increased soil NH₄⁺-N. Environmental factors, including soil depth, pH, organic matter, total nitrogen, initial NO₃⁻–N, rainfall, and soil texture, collectively regulated the effectiveness of catch crops. In summary, a rational selection of catch crop species tailored to site-specific soil and environmental conditions can effectively reduce nitrogen leaching during the summer fallow period and support precision nitrogen management. Full article

A large amount of germanium-containing waste is generated during optical fiber preform production, representing a critical secondary germanium resource. To address recovery challenges from low germanium content, high silicon content and complex occurrence states in optical fiber solid waste, this study proposes a short-flow clean hydrometallurgical process based on low-modulus alkaline leaching coupled with direct adsorption using customized meglumine resin. Results show that under low-modulus (M = 1) strong alkaline conditions, the system achieved a maximum germanium release concentration of 331.25 mg/L and exhibited excellent anti-gelation stability. The self-synthesized alkali-resistant NMG resin was applied for direct adsorption in raw M = 1 leachate without pH adjustment. The adsorption process follows pseudo-second-order kinetics and the Langmuir isotherm, with a maximum theoretical adsorption capacity of 3.529 mg/g. Spectral analysis indicates that the ortho-cis-diol groups of the resin can specifically chelate with germanate, overcoming competitive interference from strong alkali and high silicon. This process provides a theoretical basis for the green recycling of high-silicon germanium-containing secondary resources. Full article

Mine leachate and saline industrial wastewater streams are often treated as liabilities to be remediated or disposed of. These flows often contain substantial water and dissolved mineral resources that can be reclaimed. In this work, a waste-heat-assisted falling-film evaporation reactor was developed and assessed for application as a pre-concentration step before water and mineral recovery processes. Two case studies were considered: synthetic saline wastewater containing 80 g/L Na₂SO₄ and 70 g/L NaCl for salt recovery, and iron-rich mine water containing approximately 4000 mg/L Fe²⁺, 95 mg/L Fe³⁺, and 13,000 mg/L acidity as CaCO₃ for downstream pigment and magnetite recovery. Saline water or mine leachate flows down a bank of vertical conduit pipes as a thin film while air flows through the pipe cores. Heat is transferred to the system from industrial waste gas externally. Psychrometric relationships, heat transfer, energy balances, and techno-economic analysis were used to assess the impact of air temperature, conduit diameter, column height, pipe material, and waste-gas temperature on overall reactor performance. Experiments were carried out to confirm expected psychrometric operation and establish appropriate operating temperatures while confirming the impact of conduit geometry on heat-transfer characteristics. A benchmark case of design evaporation rate equal to 100 L/h was chosen for comparison of all tests. Dry air operation was shown to be technically possible but severely limited by the moisture capacity of air; at 26 °C and 101.3 kPa, approximately 205,000 m³/h of air was required. When using industrial waste heat, the operation changed from psychrometric/mass-transfer-limited to heat-transfer-controlled. Using waste gas entering at 144 °C and exiting at 80 °C reduced airflow requirements to approximately 880 m³/h, allowing a much more compact reactor design with approximately 635 (12 mm diameter) conduit pipes. Relative to the 40 °C air benchmark, electrical power was reduced from approximately 24.7 kW to 2.9 kW, and screening-level reactor cost by ~84%. Findings demonstrated that appropriate waste heat enables the application of evaporation if there is sufficient local heat flux. Smaller conduit diameters, sufficient column height, and greater waste-gas inlet temperatures were all beneficial. Choice of material required trade-offs between heat-transfer coefficient, corrosion, and material cost. Full article

Landfill leachate circuits that operate without discharge, by recirculating aerated leachate onto the waste mass, are widespread in South-East Europe, yet their long-term behaviour is rarely documented with sample-level data. This study reports a six-year (2020–2025) seasonal monitoring campaign at a sanitary landfill in northern Serbia (alluvial aquifer of the Sava River, transboundary Danube basin) and re-examines it with a transparent multivariate protocol. Seventy-two leachate samples (collection well, aeration lagoon, sedimentation lagoon; n = 24 each, 30 parameters), 28 realised surface-water campaigns, and six years of groundwater summaries were evaluated by principal component analysis/factor analysis (PCA/FA, Varimax normalized), hierarchical cluster analysis, PERMANOVA, non-parametric paired tests and, for benchmarking, supervised machine learning. The pooled leachate model (n = 72; 21 variables; KMO = 0.700; Bartlett χ² = 956, p < 0.001) retained four factors by parallel analysis, explaining 61.6% of total variance; after rotation the factors accounted for 27.7%, 14.3%, 10.4%, and 9.3%. Factor 1 grouped organic load with particle-reactive metals (COD, BOD₅, Fe, Ni, Cr, As, Zn), Factor 2 a reduced sulfur–fluoride–BTEX signature, Factor 3 temperature-driven nitritation, and Factor 4 a nitrate–manganese redox contrast. Crucially, paired campaign-by-campaign comparison showed no removal of the dominant pollutants along the circuit. Median COD, BOD₅ and NH₄-N were not lower in the sedimentation lagoon than in the collection well, while pH rose from 8.08 to 8.75 (p < 0.001); only Cu, Pb, NO₃-N, and NO₂-N decreased significantly. The circuit therefore homogenises and concentrates dissolved load rather than removing it. Downstream surface water was significantly enriched in electrical conductivity (+110 µS/cm), total dissolved solids, NH₄-N, and NO₂-N relative to upstream (Wilcoxon, p < 0.05), and groundwater showed episodic conductivity up to 12,760 µS/cm and NH₄-N up to 102 mg/L. Cytotoxicity (MTT) confirmed biological relevance, with MRC-5 viability falling to 37% after 24 h exposure to 50 vol.% groundwater (Pw3) versus 60% in A549 cells. A random-forest classifier separated circuit units far better than PCA-based discrimination (76.4% versus 54.2% cross-validated accuracy) and distinguished the 2020–2021 pandemic period from 2022–2025 with 94.2% accuracy, a period effect also confirmed by PERMANOVA (R² = 7.2%, p < 0.001). The results indicate that closed-loop recirculation without an engineered discharge barrier transfers, rather than eliminates, contaminant load, and that after-care of such systems requires mass-balance monitoring and polishing treatment. Full article

Effective iron removal from highly acidic leachates without neutralizer addition is a long-standing challenge in hydrometallurgy. For Cu-Co-bearing pyrite cinder, we demonstrate that a cyclic leaching process achieves this outcome. Operating entirely without neutralizers, the process consumed 96% of residual acid, enriched Cu and Co 4.76- and 3.88-fold, and removed 48.2% of iron, all while maintaining pH below 1.5 across four closed-loop cycles. Thermodynamic analysis reveals that Fe³⁺-${\mathrm{SO}}_4^{2-}$ complexation suppresses free Fe³⁺ to approximately 10⁻⁸ mol/L, ruling out conventional hydrolytic precipitation and directing precipitation towards schwertmannite-type basic ferric sulfate (Fe₈O₈(OH)₆SO₄). The formation of this sulfate-bearing Fe precipitate is consistent with the thermodynamic analysis, the iron mass balance, and a 176% increase in solid-phase sulfur. This neutralizer-free strategy offers a sustainable paradigm for recovering critical metals from iron-rich secondary resources. Full article

The leaching behavior of bisphenol A (BPA) remains a significant environmental concern. Despite EU regulatory restrictions and the World Health Organization (WHO) establishing precautionary values for human exposure to this monomer, BPA is still widely used in polymer-based products, including materials for sewer rehabilitation. Standard leaching assessments typically employ deionized water, although natural waters represent actual field conditions. This study investigates the release of BPA and its substitute, bisphenol F (BPF), from an epoxy resin system and a vinyl ester resin system. Sample discs (0.5 cm in height and 11 cm in diameter) were subjected to dynamic surface leaching tests using groundwater and tap water as leaching media. Eluate replacement intervals followed the standardized Dynamic Surface Leaching Test (DSLT; EN 16637-2), marking the first application of natural waters within this standardized test procedure. The detection limit for the gas chromatography analyses was 0.001 µg/L. Compared with the deionized water prescribed by the standard, natural waters resulted in significantly higher cumulative releases of BPA and BPF, with cumulative BPA release increasing by factors of 5.2–9.2 to a maximum of 0.412 mg/m². These findings indicate that the standardized 64-day DSLT may underestimate environmentally relevant emissions and that permissible cumulative release values, derived from modeling and regulatory thresholds, may not be maintained under environmentally relevant conditions. GC–MS screening and the Umu test showed no evidence of genotoxic effects in the leachates. Exploratory analysis suggested a positive relationship between BPA release and pH (R² = 0.79). Overall, the results demonstrate that the choice of leaching medium strongly influences measured emissions and should therefore be reconsidered in assessment frameworks for polymer-based construction materials to better reflect environmentally relevant conditions. Full article

Municipal solid waste landfill leachate represents one of the most environmentally challenging liquid effluents in modern waste management; however, its high nitrogen and phosphorus content renders it a potentially valuable nutrient source for microalgal phycoremediation. Here, Chlorella sp. and Scenedesmus sp. were cultivated for 15 days in CHU-10 standard medium and 50% (v/v) municipal landfill leachate from Nauta, Peru, and characterized across 33 biochemical variables, 14 physicochemical parameters, and 32 metal ions and trace elements. A sequential competitive multivariate pipeline comprising principal component analysis (PCA), hierarchical cluster analysis (HCA), permutational multivariate analysis of variance (PERMANOVA), and linear discriminant analysis (LDA) was applied to both the biochemical and bioremediation datasets. Leachate supplementation increased peak biomass density by 26.6–28.3% and elevated total protein by 56.9% in Chlorella sp. and 73.4% in Scenedesmus sp., while reducing total lipids by 37–46% and suppressing polyunsaturated fatty acid production. Both species achieved net biological removal efficiencies (NBRE) exceeding 86% for ammonium and ammonia; toxic elements, including Cd (~96%), Al (~92%), As (~90%), and Pb (~90%), were removed at higher NBRE than macro- and micronutrient categories. LDA achieved 100% leave-one-out cross-validation accuracy for species classification from both physicochemical and 32-element NBRE profiles. These findings indicate two complementary valorization directions, contingent on further biomass safety verification: leachate-grown Scenedesmus sp. shows a favorable combination of protein enrichment and nutrient removal for single-cell protein production integrated with bioremediation, while Chlorella sp. in standard medium shows a more favorable fatty acid profile for nutraceutical applications. Because leachate-grown biomass also accumulates inorganic and trace-element constituents from the medium, its suitability for protein or nutraceutical use requires direct heavy-metal characterization of the harvested biomass, independent of the demonstrated removal efficiency from the liquid phase. Full article

Tomato production is highly affected by salt stress conditions, especially under protected cultivation systems using low-quality irrigation water. This study assessed the effects of increasing electrical conductivity (EC) levels of the nutrient solution (2, 4, 6, and 8 dS m⁻¹) on growth, biomass distribution, RGB-based spectral indices, physiological traits, petiole sap composition, and leachate chemistry in tomato plants (Solanum lycopersicum cv. Tiny Tim) cultivated in containers within a bamboo nethouse under tropical conditions. The results obtained reported that increasing salinity significantly reduced fresh and dry biomass (61.72 and 61.55% respectively) across all plant organs, with fruits showing the highest sensitivity. Leaf area index (LAI), SPAD values, leaf nitrogen (N) concentration, leaf relative humidity (LRH), and water uptake also declined progressively under saline conditions. In contrast, root and leaf biomass allocation increased under the highest salinity level. Spectral analyses reported reductions in red and blue RGB components and normalized red and blue index values, while normalized green index increased under higher salinity levels. Petiole sap analysis showed a progressive accumulation of sodium (Na⁺) and chloride (Cl⁻) together with reductions in nitrate (NO₃⁻-N) and potassium (K⁺) concentrations, particularly during the reproductive stage. In contrast, °Brix, calcium (Ca²⁺), and phosphorus (P) concentrations increased under salinity, particularly during the reproductive stage. Leachate analyses confirmed salt accumulation in the substrate and reduced plant water uptake. Overall, petiole sap analysis and RGB-based spectral indices provide a rapid, non-destructive, and cost-effective tool for the early detection of salinity stress in tomato, enabling timely irrigation and fertigation adjustments to improve crop performance and resource-use efficiency under saline conditions. Full article

Landfilling remains a widely used method for municipal solid waste disposal but may pose long-term risks to soil and groundwater. To address the fragmented management of landfill-related environmental information, this study developed a geographic information system (GIS)-based “One Map” framework that integrates landfill facilities, hydrogeological information, environmental monitoring data, pollutant indicators, and sensitive receptors into a unified spatial database. The framework links spatial features with attribute information and supports visualization, multi-criteria queries, statistical analysis, groundwater-quality assessment, and the preliminary screening of potentially undetected environmental risks. A municipal solid waste landfill in Xichuan County, Nanyang City, China, was selected as a case study, and groundwater quality was evaluated using the single-factor pollution index and Nemerow comprehensive pollution index. No Class III standard exceedance was identified at the five monitoring wells during the sampling event; however, the available hydrogeological and operational data were insufficient to attribute differences among wells to landfill-derived contaminant transport. The primary contribution is not a new GIS engine, but a landfill-specific data model and workflow that integrate fragmented survey outputs into a spatial decision-support environment. Because the case study comprises five wells and a single monitoring campaign, the findings represent a point-specific workflow demonstration rather than temporal or regional validation. Interpretation followed a source–pathway–receptor framework, but source attribution remained constrained by the absence of contemporaneous hydraulic-head data, a verified operational chronology, and quantitative leachate-management records. Repeated monitoring, an upgradient baseline, and a denser well network are required for stronger environmental inference. Full article

Background: Drilling slurry, a waste material generated during natural gas extraction, requires careful chemical characterization to determine its environmental hazard classification and inform appropriate management strategies. Methods: This study characterizes the drilling fluid used as raw material and the resulting drilling slurry waste, using a case study sample from the Buzău extraction area (Well 1 Florica, S.N.G.N. Romgaz S.A.), including total composition analysis, three-stage leaching tests, linear regression of leaching kinetics, and standardized geoaccumulation indices (Igeo, CF, PLI). Results: Total composition analysis confirmed low heavy metal concentrations (Cd = 0.02, Cr = 0.05, Pb = 0.64, Zn = 2.82 mg/kg dry matter). All leachate parameters remained below non-hazardous waste thresholds (Order No. 95/2005), with safety factors of 20–100× for regulated metals and 1.2–2.7× for chlorides, sulphates, and dissolved organic carbon. Standardized pollution indices confirmed Class 0 (unpolluted) status for all five metals, with a composite Pollution Load Index of 0.0124. Leaching regression analysis revealed dissolution-controlled release for chlorides, sulphates, and zinc (R² > 0.93) versus matrix-retention behavior for copper, nickel, cadmium, and chromium. Comparative analysis showed horizontal drilling generates approximately 146% more waste volume than conventional vertical drilling (170 m³ versus 69 m³ at 2100 m depth). Conclusions: The analyzed drilling slurry meets non-hazardous waste classification with substantial safety margins, corroborated by three independent analytical frameworks. Waste minimization strategies and biodegradable fluid substitution offer practical pathways to reduce the environmental footprint of natural gas drilling operations. Full article