Jin-Yan Yang

Lithium refinery residue (LRR), generated during the sulfuric acid processing of spodumene, is dominated by aluminosilicate phases and contains residual lithium (Li). Although bioleaching has been applied to primary Li ores and spent lithium-ion batteries, its applicability to aluminosilicate-dominated LRR remains poorly understood. Here, Acidithiobacillus thiooxidans, Acidithiobacillus ferrooxidans, and a mixed culture of the two species were evaluated for Li bioleaching from LRR. Among the conditions tested, the A. thiooxidans system achieved a Li leaching efficiency of 26.7% at a pulp density of 5.0 g/L with the addition of 5.0 g/L elemental sulfur, and the A. ferrooxidans system achieved 27.3% with the addition of 11.2 g/L FeSO₄·7H₂O. The mixed culture, supplied with both 5.0 g/L elemental sulfur and 11.2 g/L FeSO₄·7H₂O, at an inoculum volume ratio of A. thiooxidans to A. ferrooxidans of 1:1 achieved the Li leaching efficiency of 36.9%, which was numerically 38.1% and 35.1% higher than the values obtained in the A. thiooxidans and A. ferrooxidans treatments, respectively. Trends in pH and oxidation-reduction potential, decreases in dissolved Fe(II) and Fe(III), and increased Fe/S surface signals in the dried residue showed that Li release occurred concurrently with acidification, changes in dissolved Fe concentrations, and Fe- and S-associated changes in the bioleaching system. These findings provide evidence for Li bioleaching from LRR using an Fe/S-supplemented mixed culture under low-pulp-density laboratory conditions.

Vanadium (V), a toxic element with multiple valence states, is widely distributed in the earth's crust and can be released into the environment through various human activities, posing potential health risks to humans. Understanding the bioaccessibility of V is crucial for assessing its potential toxicity and health risks. This study investigated the bioaccessibility of V via respiratory inhalation and dermal contact using in vitro biomimetic simulations. Results showed significant variations in V bioaccessibility among different sample types, V valence states, and exposure pathways. For respiratory exposure, in lung epithelial cell gap fluid, the bioaccessibility of V(IV) and V(V) in vanadium-titanium concentrate was 21.10% and 49.67%, respectively, and in lung macrophage lysosomal fluid simulations was 25.00% and 32.69%.The vanadium-titanium concentrate exhibited higher bioaccessibility of V than the soils and the dusts in both lung epithelial cell gap fluid and lung macrophage lysosomal fluid simulations. In dermal exposure simulations, V bioaccessibility was relatively low and varied with the composition of the simulated sweat solutions. The bioaccessibility of both V(IV) and V(V) in simulated sweat BS-1 solution (pH = 6.5) was the highest (3.70-4.91%), followed by in BS-2 (pH = 4.7) at 2.93-4.30%, while in BS-3 (pH = 5.5) was the lowest (2.16-4.99%). This study demonstrates significant variations in V bioaccessibility across different exposure pathway and matrix. These findings provide insights for health risk assessments of V contamination.

Chromium (Cr) contamination originating from the tanning industry presents a significant threat to soil and groundwater. Traditional static risk assessment models often lack the capacity to account for the dynamic evolution of risks due to oversights in hydrogeological processes, changes in Cr speciation, and uncertainties in parameters. In this study, an integrated analytical framework combining contaminant transport models with Bayesian networks was proposed to investigate the dynamic health risks associated with Cr exposure at 10 tannery sites in China. Key parameters were derived from laboratory experiments and field studies, enabling analysis of the dynamic changes and health risks associated with Cr pollution. By integrating solute transport with chemical equilibrium models, the dynamic changes in Cr speciation were simulated. Additionally, a Bayesian network model incorporating 43 variables was used to address multi-parameter uncertainty. Results indicated that Type III sites (Inadequate landfills) exhibited high and most persistent carcinogenic risk of Cr exposure (CR = 1.0 × 10⁻⁵ at 6000 days, 10 times above threshold), while Type II sites (legacy tanneries) had the highest short-term carcinogenic risk (CR = 1.0 × 10⁻² at day 100). Risk levels in Type I sites (modernized tanneries) were acceptable. Sensitivity analysis revealed that groundwater Cr(VI) concentration was the dominant driver of the human health risk, followed by groundwater flow velocity and hydraulic gradient. These findings highlight the importance of considering Cr speciation dynamics and key influencing parameters in dynamic risk management, emphasizing the need for process-based assessments to effectively manage Cr pollution at tannery sites.

Bamboo powder waste generated from bamboo processing serves as an ideal feedstock for biochar (BC). This study employed potassium hydroxide (KOH) to modify biochar derived from bamboo powder waste, activating it at different temperatures (700 °C, 800 °C, and 900 °C) to yield samples designated KBC-700, KBC-800, and KBC-900, respectively. The physicochemical properties and pore structures of the modified biochar were characterized using SEM, specific surface area and pore size analysis, FT-IR, Raman spectroscopy, XRD, and zeta potential measurements. The adsorption performance of the modified biochar toward PFOA was investigated using kinetic and thermodynamic models, examining the effects of the solution pH, adsorbent dosage, and temperature. Results indicate that KBC-900 exhibits a significantly enhanced specific surface area (up to 2924.7 m² g⁻¹), reduced surface oxygen-containing functional groups, increased carbon skeleton aromatization, and expanded mesoporous channels. Under initial conditions of pH = 3 and reaction temperature of 298 K, KBC-900 achieved a PFOA adsorption capacity of 366.7 mg g⁻¹ with a removal efficiency of 91.67%. The adsorption process conformed to pseudo-first-order and pseudo-second-order kinetic models as well as the Freundlich model. The adsorption equilibrium was reached within 12 h, indicating multi-layer adsorption dominated by chemisorption on a heterogeneous surface. Thermodynamic parameters indicate the adsorption reaction is an exothermic process. After five cycles of regeneration, KBC-900 maintained a removal efficiency of 75.69%. This study provides an efficient and reliable solution for removing PFOA from water.

Vanadium(V) is a primary pollutant in vanadium-titanium magnetite tailings, with its geochemical behavior strongly shaped by redox dynamics. To date, how Fe transformations and organic acids regulate V mobilization and sequestration in tailings under repeated redox fluctuations has not yet been sufficiently studied. Here, we examined the coupled effects of Fe (hydr)oxides and oxalic acid (OA) on V transformation and (im)mobilization in vanadium-titanium magnetite tailings over 56 days across four redox cycles. Under anoxic conditions, OA promoted the dissolution of Fe (hydr)oxides, releasing substantial dissolved Fe(II) and comobilizing V. During subsequent redox cycles, progressive crystallization of secondary Fe phases (e.g., hematite) markedly immobilized V. Oxalic acid not only mediated Fe transformation but also facilitated redox-driven V(V) reduction and redistribution among acid-soluble, reducible, oxidizable, and residual fractions. In moderate (0.5 mM) and high (5.0 mM) V treatments, OA significantly promoted V immobilization by shifting acid-soluble V into the reducible fraction, particularly under anoxic conditions in the moderate case at the end of the experiment. These findings highlight the dual role of OA in promoting short-term V mobilization while enhancing its long-term sequestration through Fe (hydr)oxides transformations over repeated redox cycling, providing new insights into redox-driven stabilization strategies for V-bearing tailings.

Microplastics (MPs) are widely present in soils, often co-contaminated with heavy metals (HMs), complicating the assessment of their adsorption performance. This study prepared environmental-simulating microplastics (EMPs) and compared their Cd/Cr adsorption–desorption properties with five commercial MPs in artificial soil solutions. Aging treatments altered the physicochemical characteristics of MP surfaces, increasing oxygen-containing functional groups and forming smaller particles. These changes enhanced HM adsorption, with EMPs showing higher adsorption capacities for Cd and Cr than the five single-type commercial MPs. Among the commercial MPs, degradable polylactic acid (PLA) showed the highest maximum adsorption capacities for Cd (4.52 mg g⁻¹) and Cr (3.78 mg g⁻¹) at elevated concentrations, indicating its greater potential for HM transport. Adsorption kinetics revealed that surface chemisorption and intraparticle diffusion were the key rate-limiting steps in the MP–Cd/Cr adsorption processes. Desorption of Cd was more pronounced than that of Cr, indicating higher activity of Cd on MP surfaces. Higher HM accumulation factors of aged MPs (Cd: 3.49–8.24%, Cr: 1.95–7.82%) suggest their potential to accumulate and immobilize soil HMs. The EMPs exhibited the highest accumulation factors, implying a greater impact of mixed MPs on soil total and bioavailable Cd/Cr concentrations than single-type MPs. These findings offer new insights into the interactions between pollutants in soils co-contaminated with mixed MPs and HMs.

Zinc hydrometallurgy sites are critical hotspots for combined toxic metal(loid)s (TMs) pollution, yet the integration of spatial heterogeneity and migration dynamics into source apportionment remains underexplored. This study investigated the concentrations, speciation, and spatial distribution of nine TMs (As, Cd, Cu, Hg, Mn, Ni, Pb, Sb, Zn) in soils at an abandoned zinc smelter in southwest China. Multivariate statistical methods and the Positive matrix factorization (PMF) model were applied to disentangle primary sources and secondary redistribution. Spatial analysis revealed that As, Cd, Cu, Pb, Sb, and Zn shared similar contamination patterns, concentrated in slag storage and comprehensive recovery areas, whereas Hg and Mn exhibited distinct hotspots near sulfuric acid production and electrolysis zones. Vertical migration was most pronounced for Cd and Zn (> 8 m depth), followed by Hg and Mn (4–8 m), while As, Cu, Pb, and Sb were restricted to 0–4 m due to adsorption in clay-rich layers. Speciation analysis indicated high mobility of Cd and Zn (acid-soluble fraction: 66.96 and 52.10%, respectively), contrasting with reducible Pb and Mn (51.59 and 48.32%) and residual As, Hg, Ni, Sb (60.74–76.64%). The results from PMF model identified aqueous-phase (Cd, Zn, Mn) and solid-phase (As, Cu, Pb, Sb) migration pathways, validated by spatial correlations with topography and functional zones. Aqueous-phase contributions dominated low-lying areas, while solid-phase contributions aligned with elevated regions, reflecting topography-driven redistribution. This study advances source apportionment of TM in soil by unifying spatial heterogeneity, speciation dynamics, and receptor modeling, offering a framework for targeted risk assessment and remediation of industrial sites.