Vanadium removal by metal (hydr)oxide adsorbents

Enhanced adsorption properties of zirconium modified chitosan-zeolite nanocomposites for vanadium ion removal

The novel hybrid adsorbents, which were composed of nanozeolite and nanochitosan (NZ@NCT) and nanozeolite-multi walled carbon nanotube and nanochitosan (CNZ@NCT) were produced by simple method. The adsorption capacity of synthesized nanocomposites towards vanadium (V) was compared with that of a clinoptilolite-nanochitosan nanocomposite (CPL@NCT) obtained from natural zeolite. Zirconium (Zr) was employed to modify prepared nanocomposites because Zr (IV) has a strong affinity towards oxyanions such as V. Zr-modified nanocomposites and their pristine nanocomposites were comparatively characterized by different techniques. Batch experiments were conducted to find out the influence of different experimental factors. The adsorption capacities of all prepared materials towards V ions decreased with temperature increasing from 298 to 348 K. The calculated values of the thermodynamic parameters ΔH and ΔG demonstrated that the adsorption was exothermic and spontaneous. The adsorption process was described by the Freundlich isotherm and pseudo-second order model. The V species loaded nanocomposites could be regenerated by 0.5 M HCl-1.0 M thiourea solution. The adsorption performance was not considerably influenced by the coexistence of the nickel ( Ni²⁺) but nitrate (NO₃^-) and sulfate (SO₄^2-) revealed slightly greater negative effects. The as-prepared nanocomposites can be used in three adsorption cycles without specific changing its adsorption efficiency.

Review of plant-vanadium physiological interactions, bioaccumulation, and bioremediation of vanadium-contaminated sites

Vanadium is a multivalent redox-sensitive metal that is widely distributed in the environment. Low levels of vanadium elevate plant height, root length, and biomass production due to enhanced chlorophyll biosynthesis, seed germination, essential element uptake, and nitrogen assimilation and utilization. However, high vanadium concentrations disrupt energy metabolism and matter cycling; inhibit key enzymes mediating energy production, protein synthesis, ion transportation, and other important physiological processes; and lead to growth retardation, root and shoot abnormalities, and even death of plants. The threshold level of toxicity is highly plant species-specific, and in most cases, the half maximal effective concentration (EC₅₀) of vanadium for plants grown under hydroponic conditions and in soil varies from 1 to 50 mg/L, and from 18 to 510 mg/kg, respectively. Plants such as Chinese green mustard, chickpea, and bunny cactus could accumulate high concentrations of vanadium in their tissues, and thus are suitable for decontaminating and reclaiming of vanadium-polluted soils on a large scale. Soil pH, organic matter, and the contents of iron and aluminum (hydr)oxides, phosphorus, calcium, and other coexisting elements affect the bioavailability, toxicity, and plant uptake of vanadium. Mediation of these conditions or properties in vanadium-contaminated soils could improve plant tolerance, accumulation, or exclusion, thereby enhancing phytoremediation efficiency. Phytoremediation with the assistance of soil amendments and microorganisms is a promising method for decontamination of vanadium polluted soils.

Aqueous Vanadate Removal by Iron(II)-Bearing Phases under Anoxic Conditions

Vanadium contamination is a growing environmental hazard worldwide. Aqueous vanadate (H_xV^VO₄^(3-x)-_(aq)) concentrations are often controlled by surface complexation with metal (oxyhydr)oxides in oxic environments. However, the geochemical behavior of this toxic redox-sensitive oxyanion in anoxic environments is poorly constrained. Here, we describe results of batch experiments to determine kinetics and mechanisms of aqueous H₂V^VO₄^- (100 μM) removal under anoxic conditions in suspensions (2.0 g L^-1) of magnetite, siderite, pyrite, and mackinawite. We present results of parallel experiments using ferrihydrite (2.0 g L^-1) and Fe²⁺_(aq) (200 μM) for comparison. Siderite and mackinawite reached near complete removal (46 μmol g^-1) of aqueous vanadate after 3 h and rates were generally consistent with ferrihydrite, whereas magnetite removed 18 μmol g^-1 of aqueous vanadate after 48 h and uptake by pyrite was limited. Removal during reaction with Fe²⁺_(aq) was observed after 8 h, concomitant with precipitation of secondary Fe phases. X-ray absorption spectroscopy revealed V(V) reduction to V(IV) and formation of bidentate corner-sharing surface complexes on magnetite and siderite, and with Fe²⁺_(aq) reaction products. These data also suggest that V(IV) is incorporated into the mackinawite structure. Overall, we demonstrate that Fe(II)-bearing phases can promote aqueous vanadate attenuation and, therefore, limit dissolved V concentrations in anoxic environments.

Removal of V(V) From Solution Using a Silica-Supported Primary Amine Resin: Batch Studies, Experimental Analysis, and Mathematical Modeling

Every year, a large quantity of vanadium-containing wastewater is discharged from industrial factories, resulting in severe environmental problems. In particular, V(V) is recognized as a potentially hazardous contaminant due to its high mobility and toxicity, and it has received considerable attention. In this study, a silica-supported primary amine resin (SiPAR) was prepared by in-situ polymerization, and the V(V) adsorption from the solution was examined. The as-prepared resin exhibited fast adsorption kinetics, and it could attain an equilibrium within 90 min for the V(V) solution concentration of 100 mg/L at an optimum pH of 4, whereas the commercial D302 resin required a treatment time of more than 3 h under the same conditions. Furthermore, the maximum adsorption capacity of the resin under optimum conditions for V(V) was calculated to be 70.57 mg/g. In addition, the kinetics and isotherm data were satisfactorily elucidated with the pseudo-second-order kinetics and Redlich–Peterson models, respectively. The silica-based resin exhibited an excellent selectivity for V(V), and the removal efficiency exceeded 97% in the presence of competitive anions at 100 mmol/L concentrations. The film mass-transfer coefficient (k_f) and V(V) pore diffusivity (D_p) onto the resins were estimated by mathematical modeling. In summary, this study provided a potential adsorbent for the efficient removal of V(V) from wastewater.

Highly selective adsorption of vanadium (V) by nano-hydrous zirconium oxide-modified anion exchange resin

Adsorption is widely used in removal of toxic vanadium (V) [V(V)] from water streams, and a fit-for-purpose adsorbent plays a vital role in this process. Herein HZrO@D201, an adsorbent with decoration of nanosized hydrous zirconium oxide (HZrO) on anion exchange resin D201, is fabricated for efficient V(V) removal. Compared to pristine D201, HZrO@D201 excelled in V(V) removal with a maximum adsorption capacity of 118.1 mg/g, due to potential formation of inner sphere complexation between V(V) and HZrO. HZrO@D201 could also functioned well in a wide pH range (3.00 to 9.00) and exhibited outstanding selective V(V) adsorption under the presence of competing anions (chloride, nitrate, sulfate, and phosphate). The adsorption thermodynamics was in accordance with the Langmuir model, while adsorption kinetics followed the Pseudo-Second-Order model. When treating actual vanadium contaminated groundwater from Panzhihua region (China), HZrO@D201 indicated a satisfactory lifespan in the column experiment for V(V) removal (2.41 times longer than D201), and the treated groundwater could meet the vanadium standard of drinking water source in China (less than 50 μg/L). Regeneration of HZrO@D201 was easily achievable with negligible capacity loss. Results from this work suggests a promising application potential of HZrO@D201 in vanadium pollution control.

Microbial vanadate and nitrate reductions coupled with anaerobic methane oxidation in groundwater

Vanadate contaminant in groundwater receives increasing attentions, but little is known on its biogeochemical transformation with gaseous electron donors. This study investigated bio-reduction of vanadate coupled with anaerobic methane oxidation and its relationship with nitrate reduction. Results showed 95.8 ± 3.1% of 1 mM vanadate was removed within 7 days using methane as the sole electron donor. Tetravalent vanadium compounds were the main reduction products, which precipitated naturally in groundwater environment. The introduction of nitrate inhibited vanadate reduction, though both were reduced in parallel. Accumulations of volatile fatty acids (VFAs) were observed from methane oxidation. Preliminary microbial community structure and metabolite analyses indicated that vanadate was likely reduced via Methylomonas coupled with methane oxidation or through synergistic relationships between methane oxidizing bacteria and heterotrophic vanadate reducers with VFAs served as the intermediates.

Adsorption and Desorption Performance and Mechanism of Tetracycline Hydrochloride by Activated Carbon-Based Adsorbents Derived from Sugar Cane Bagasse Activated with ZnCl2

Adsorption and desorption behaviors of tetracycline hydrochloride by activated carbon-based adsorbents derived from sugar cane bagasse modified with ZnCl₂ were investigated. The activated carbon was tested by SEM, EDX, BET, XRD, FTIR, and XPS. This activated carbon exhibited a high BET surface area of 831 m² g⁻¹ with the average pore diameter and pore volume reaching 2.52 nm and 0.45 m³ g⁻¹, respectively. The batch experimental results can be described by Freundlich equation, pseudo-second-order kinetics, and the intraparticle diffusion model, while the maximum adsorption capacity reached 239.6 mg g⁻¹ under 318 K. The effects of flow rate, bed height, initial concentration, and temperature were studied in fixed bed adsorption experiments, and adsorption data were fitted with six dynamic adsorption models. The results of characterizations and the batch experiments were analyzed to study the adsorption and desorption mechanisms. Tetracycline hydrochloride and activated carbon were bonded together by π–π interactions and cation–π bonds. Ethanol was used as an eluent which bonded with 10 hydrogen bond acceptors on tetracycline hydrochloride to form a complex by hydrogen bonding to achieve recycling.

Methane oxidation coupled to vanadate reduction in a membrane biofilm batch reactor under hypoxic condition

This study shows vanadate (V(V)) reduction in a methane (CH₄) based membrane biofilm batch reactor when the concentration of dissolved oxygen (O₂) was extremely low. V(IV) was the dominant products formed from V(V) bio-reduction, and majority of produced V(IV) transformed into precipitates with green color. Quantitative polymerase chain reaction and Illumina sequencing analysis showed that archaea methanosarcina were significantly enriched. Metagenomic predictive analysis further showed the enrichment of genes associated with reverse methanogenesis pathway, the key CH₄-activating mechanism for anaerobic methane oxidation (AnMO), as well as the enrichment of genes related to acetate synthesis, in archaea. The enrichment of aerobic methanotrophs Methylococcus and Methylomonas implied their role in CH₄ activation using trace level of O₂, or their participation in V(V) reduction.

Geochemical simulation of the stabilization process of vanadium-contaminated soil remediated with calcium oxide and ferrous sulfate

Vanadium (V)-contaminated soil poses health risks to plants, animals, and humans via both direct exposure and through the food chain. Stabilization treatment of metal-contaminated soil can chemically convert metal contaminants into less soluble, mobile, and toxic forms. However, the stabilization mechanisms of V-contaminated soil have not been thoroughly investigated. Therefore, we performed geochemical modeling of V-contaminated soil stabilized with the common binders calcium oxide (CaO) and ferrous sulfate (FeSO₄), as well as their mixture, using Visual MINTEQ software. The results were validated and exhibited good agreement with experimental results. For CaO, the formation of Ca₂V₂O₇(s) and Ca₃(VO₄)₂·4H₂O(s) under mild and strong alkaline conditions (pH = 8.0-11.5 and 11.5-12.5), respectively, were predicted as the main immobilization routes. For FeSO₄, there appeared to be three reaction routes, corresponding to approaches A, B, and C, during the stabilization process. In the simulation, approach C (adsorption of V(V) onto ferrihydrite) was undervalued, whereas approaches A (formation of Fe(VO₃)₂(s)) and B (reduction of V(V) into V(IV) to form V₂O₄(s) or adsorb onto soil organic matter) were overvalued. Among the three approaches, approach C had a dominant role and exhibited good agreement with the experimental results. Additionally, soil pH and the saturation index of precipitation had major roles in the stabilization process. The optimal pH ranges for the stabilization of V-contaminated soil using CaO and FeSO₄ were pH = 9.5-12.5 and pH = 4.0-5.0, respectively.

The mechanism for promoted oxygenation of V(IV) by goethite: Positive effect of surface hydroxyl groups

The most toxic and mobile form of vanadium (V) is V(V). Thus, the oxidation of V is a subject of considerable importance since the process may increase environmental risks of V. V(IV) is known to be stable when pH < 4.5. However, in this study, stable V(IV) was oxidized almost completely in goethite suspension within 60 min at pH 2.0 and pH 4.0, correspondingly, only 25%-30% and 15%-20% of V(IV) were oxidized in equimolar Fe³⁺ solution and the blank solution, respectively. The promoted oxidation of V(IV) by FeOOH is attributed to the formation of the complex, VO(OFe<)⁺ or VO(OFe<)₂. On the one hand, the formation of the complex caused higher pH in the interface of solid FeOOH and corresponding lower conditional potential of V(V)/V(IV) than those in bulk solutions, which facilitates the oxidation of V(IV). On the other hand, the surface group OFe < may serve as a medium that facilitating the electron transfer from V(IV) ions to dissolved oxygen molecules, also favoring the oxidation of V(IV). This study not only deepens our understanding of the transfer, transformation, and risk of V in environments, but also provides a reference to speculate the fate of similar elements in environments.

The Influence of Phosphate on the Adsorption-Desorption Kinetics of Vanadium in an Acidic Soil

Quantitative understanding of the mechanisms controlling the competitive retention and transport of V and phosphate on soils is essential for accurately evaluating the environmental risks of contaminants in the environment. Batch and stir-flow chamber experiments were performed to quantify the extent of kinetics of V and phosphate competitive retention in an acidic soil (Sharkey clay). In this study, a stir-flow model was used to describe tracer and competitive reactive solute adsorption, and desorption processes in soils. Based on optimized and predictive modeling results, a fully reversible-irreversible multi-reaction model successfully described the time-dependent competitive V and phosphate retention and transport process in Sharkey soil. Adsorption for V and phosphate were highly nonlinear and time dependent, where V binding affinities were stronger than those for phosphate. Results from batch experiments indicated that that the rate and extent (amount) of V released increased significantly in the presence of phosphate. Breakthrough curves for V, from stir-flow experiments, were asymmetrical and exhibited slow release or tailing, indicating that nonequilibrium retention on the surface of soil was the dominant mechanism of the time-dependent adsorption of V. Results of stir-flow experiments indicated that increased mobility of V was observed in the presence of phosphate caused by direct competition for available retention sites. In conclusion, increased addition of phosphate causes decreasing sorption capacity and increasing mobility of V and needs to be considered in modeling the fate and transport of V in soil.

Origin and Fate of Vanadium in the Hazeltine Creek Catchment following the 2014 Mount Polley Mine Tailings Spill in British Columbia, Canada

Results from the analysis of aqueous and solid-phase V speciation within samples collected from the Hazeltine Creek catchment affected by the August 2014 Mount Polley mine tailings dam failure in British Columbia, Canada, are presented. Electron microprobe and X-ray absorption near-edge structure (XANES) analysis found that V is present as V³⁺ substituted into magnetite and V³⁺ and V⁴⁺ substituted into titanite, both of which occur in the spilled Mount Polley tailings. Secondary Fe oxyhydroxides forming in inflow waters and on creek beds have V K-edge XANES spectra exhibiting E1/2 positions and pre-edge features consistent with the presence of V⁵⁺ species, suggesting sorption of this species on these secondary phases. PHREEQC modeling suggests that the stream waters mostly contain V⁵⁺ and the inflow and pore waters contain a mixture of V³⁺ and V⁵⁺. These data, and stream, inflow, and pore water chemical data, suggest that dissolution of V(III)-bearing magnetite, V(III)- and V(IV)-bearing titanite, V(V)-bearing Fe(-Al-Si-Mn) oxhydroxides, and V-bearing Al(OH)₃ and/or clay minerals may have occurred. In the circumneutral pH environment of Hazeltine Creek, elevated V concentrations are likely naturally attenuated by formation of V(V)-bearing secondary Fe oxyhydroxide, Al(OH)₃, or clay mineral colloids, suggesting that the V is not bioavailable. A conceptual model describing the origin and fate of V in Hazeltine Creek that is applicable to other river systems is presented.

Removal of Hazardous Oxyanions from the Environment Using Metal-Oxide-Based Materials

Scientific development has increased the awareness of water pollutant forms and has reawakened the need for its effective purification. Oxyanions are created by a variety of redox-sensitive metals and metalloids. These species are harmful to living matter due to their toxicity, nondegradibility, and mobility in aquatic environments. Among a variety of water treatment techniques, adsorption is one of the simplest, cheapest, and most effective. Since metal-oxide-based adsorbents poses a variety of functional groups onto their surface, they were widely applied in ions sorption. In this paper adsorption of harmful oxyanions by metal oxide-based materials according to literature survey was studied. Characteristic of oxyanions originating from As, V, B, W and Mo, their probable adsorption mechanisms and comparison of their sorption affinity for metal-oxide-based materials such as iron oxides, aluminum oxides, titanium dioxide, manganium dioxide, and various oxide minerals and their combinations are presented in this paper.

Immobilisation of geogenic arsenic and vanadium in iron-rich sediments and iron stone deposits

Determination of how geogenic arsenic (As) and vanadium (V) is mobilised from naturally-enriched soils and iron (Fe) stones is integral for understanding the potential risk to the environment from changed land use conditions. Thus, the association of As, V and Fe in As-enriched sediments and Fe stones in Tertiary sediments of Melbourne, Australia, was assessed using chemical extraction methods, micro focused X-ray fluorescence and X-ray absorption spectroscopy. We show that the selective association of As with Fe during Fe stone formation has resulted in As enrichment of up to 60 times the concentration of surrounding soils, and 1000 times higher than mean As concentrations in world soils. In both soil and Fe stones, As was distributed with goethite as arsenate and relatively immobile under oxic conditions. The presence of V on the outer edge of the assessed Fe stone provided evidence of differences in historical As and V solubility; that is, As was immobilised by Fe during an earlier stage of Fe stone formation than V.

Experimental and simulation results of the adsorption of Mo and V onto ferrihydrite

This study aims to highlight discrepancies between experimental and simulation linked to the mechanisms of Mo and V adsorption onto ferrihydrite (FHY) nanoparticles. We have measured adsorption capacities and uptake efficiencies and then fitted and compared these with outputs from various geochemical and adsorption models that were run as a function of pH, surface area (SA) and ferrihydrite particles size distributions. Our results revealed that the experimental data for the Mo system could be fitted very well, but this was not the case for the V system, when a model default value for the SA of FHY of 600 m² g⁻¹ was used. The discrepancy in the results for the V system can be explained by the lack of specific V species and/or associated constants in databases and variation in software versions, which change the outputted chemical species. Our comparative results also confirm that any experimental variables used as modelling inputs need to be checked carefully prior to any modelling exercises.

Facile Preparation of Iron-Manganese Oxide@Diatomite Composite for Effective Removal of Vanadium from Wastewater

Excess pentavalent vanadium(v) has severely degraded water quality and posed a huge threat to human health over the past several decades. Hence, it’s urgent and significant to explore a novel adsorbent which is low cost and efficient to treat vanadium pollution. In this work, a novel iron-manganese oxide@diatomite (MnFe2O4@DE) adsorbent with superior removal performance for simulated vanadium(v) wastewater was synthesised via a facile hydrothermal method. The as-prepared MnFe2O4@DE composite was characterised through different characterisation techniques. The results indicated that the MnFe2O4 nanoparticles were uniformly deposited on the surface of diatomite, resulting in a larger specific surface area and pore volume of the composite. In addition, the MnFe2O4@DE adsorbent exhibited the highest adsorption capacity for vanadium(v) (18.37mgg−1±0.5%), which was up to around 13.24 and 1.33 times as much as that of pure diatomite and MnFe2O4, respectively. This is mainly attributed to the enhanced specific surface area and pore volume. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis demonstrated vanadium(v) could be reduced to low valence vanadium with low toxicity by the MnFe2O4@DE composite which could exist as VO2+ and VO+ cations in solution. The adsorption process was better fitted with a pseudo-second-order kinetic model and Langmuir model, which is spontaneous and endothermic. Overall, the novel MnFe2O4@DE composite could be applied as a promising adsorbent in addressing vanadium pollution issues due to its properties of low cost, effectiveness, and environmental friendliness.

Removal of vanadium and palladium ions by adsorption onto magnetic chitosan nanoparticles

Chitosan (CS), synthesized from chitin chemically extracted from shrimp shells, was used for the synthesis of magnetic chitosan nanoparticles (Fe₃O₄-CSN), which makes the adsorbent easier to separate. Fe₃O₄-CSN was used for the removal of toxic metals such as vanadium (V(V)) and palladium (Pd(II)) ions from aqueous solutions. Influencing factors on the adsorption process such as pH, contact time, adsorbent dosage, and agitation speed were investigated. A competitive adsorption of V(V) and Pd(II) ions for the active sites was also studied. The monolayer maximum adsorption capacities (Q_m) of 186.6 and 192.3 mg/g were obtained for V(V) and Pd(II) ions, respectively. The pseudo-second-order equation gave the best fit for the kinetic data, implying that chemisorption was the determining step. Freundlich model yielded a much better fit than the other adsorption models assessed (Langmuir, Temkin and Dubinin-Radushkevich). Thus, the adsorption of V(V) and Pd(II) ions onto Fe₃O₄-CSN is a combination of physical and chemical adsorption, as based on the kinetics and equilibrium study. Generally, physical adsorption is the mechanism that governs the system, while chemical adsorption is the slowest adsorption step that takes place. Thermodynamic studies displayed that the adsorption process was exothermic and spontaneous. Removal efficiencies of 99.9% for V(V) and 92.3% for Pd(II) ions were achieved, implying that Fe₃O₄-CSN adsorbent had an excellent ability for the removal of the metal ions from real industrial wastewaters without remarkable matrix effect. Graphical abstract ᅟ.

Synchronous microbial vanadium (V) reduction and denitrification in groundwater using hydrogen as the sole electron donor

Groundwater co-contaminated by vanadium (V) (V(V)) and nitrate requires efficient remediation to prevent adverse environmental impacts. However, little is known about simultaneous bio-reductions of V(V) and nitrate supported by gaseous electron donors in aquifers. This study is among the first to examine microbial V(V) reduction and denitrification with hydrogen as the sole electron donor. V(V) removal efficiency of 91.0 ± 3.2% was achieved in test bioreactors within 7 d, with synchronous, complete removal of nitrate. V(V) was reduced to V(IV), which precipitated naturally under near-neutral conditions, and nitrate tended to be converted to nitrogen, both of which processes helped to purify the groundwater. Volatile fatty acids (VFAs) were produced from hydrogen oxidation. High-throughput 16S rRNA gene sequencing and metagenomic analyses revealed the evolutionary behavior of microbial communities and functional genes. The genera Dechloromonas and Hydrogenophaga promoted bio-reductions of V(V) and nitrate directly coupled to hydrogen oxidation. Enriched Geobacter and denitrifiers also indicated synergistic mechanism, with VFAs acting as organic carbon sources for heterotrophically functional bacteria while reducing V(V) and nitrate. These findings are likely to be useful in revealing biogeochemical fates of V(V) and nitrate in aquifer and developing technology for removing them simultaneously from groundwater.

Physiological and anthocyanin biosynthesis genes response induced by vanadium stress in mustard genotypes with distinct photosynthetic activity

The present study aimed to elucidate the photosynthetic performance, antioxidant enzyme activities, anthocyanin contents, anthocyanin biosynthetic gene expression, and vanadium uptake in mustard genotypes (purple and green) that differ in photosynthetic capacity under vanadium stress. The results indicated that vanadium significantly reduced photosynthetic activity in both genotypes. The activities of the antioxidant enzymes were increased significantly in response to vanadium in both genotypes, although the purple exhibited higher. The anthocyanin contents were also reduced under vanadium stress. The anthocyanin biosynthetic genes were highly expressed in the purple genotype, notably the genes TT8, F3H, and MYBL2 under vanadium stress. The results indicate that induction of TT8, F3H, and MYBL2 genes was associated with upregulation of the biosynthetic genes required for higher anthocyanin biosynthesis in purple compared with the green mustard. The roots accumulated higher vanadium than shoots in both mustard genotypes. The results indicate that the purple mustard had higher vanadium tolerance.

Autotrophic Vanadium(V) Bioreduction in Groundwater by Elemental Sulfur and Zerovalent Iron

Vanadium (V) is an emerging contaminant in groundwater that can adversely affect human health. Although bioremediation has been shown effective, little is known on autotrophic V(V) bioreduction in the context of oligotrophic characteristics of groundwater. In this study, we demonstrate that efficient V(V) bioreductions can be coupled with bio-oxidation of elemental sulfur (S(0)) or zerovalent iron (Fe(0)), and the V(V) removal efficiencies reached 97.5 ± 1.2% and 86.6 ± 2.5% within 120 h using S(0) and Fe(0), respectively. V(IV) is the main reduction product and precipitates naturally in near-neutral conditions. Microbial community, functional gene, and metabolites analyses reveal that synthetic metabolisms among autotrophs and heterotrophs played major roles in V(V) reduction using S(0) and Fe(0). These results demonstrate a new approach for V(V) contaminated groundwater remediation.

Release kinetics of vanadium from vanadium (III, IV and V) oxides: Effect of pH, temperature and oxide dose

Batch experiments were performed to derive the rate laws for the proton-promoted dissolution of the main vanadium (III, IV and V) oxides at pH 3.1-10.0. The release rates of vanadium are closely related to the aqueous pH, and several obvious differences were observed in the release behavior of vanadium from the dissolution of V₂O₅ and vanadium(III, IV) oxides. In the first 2hr, the release rates of vanadium from V₂O₃ were r=1.14·([H⁺])^0.269 at pH 3.0-6.0 and r=0.016·([H⁺])^-0.048 at pH 6.0-10.0; the release rates from VO₂ were r=0.362·([H⁺])^0.129 at pH 3.0-6.0 and r=0.017·([H⁺])^-0.097 at pH 6.0-10.0; and the release rates from V₂O₅ were r=0.131·([H⁺])^-0.104 at pH 3.1-10.0. The release rates of vanadium from the three oxides increased with increasing temperature, and the effect of temperature was different at pH 3.8, pH 6.0 and pH 7.7. The activation energies of vanadium (III, IV and V) oxides (33.4-87.5kJ/mol) were determined at pH 3.8, pH6.0 and pH 7.7, showing that the release of vanadium from dissolution of vanadium oxides follows a surface-controlled reaction mechanism. The release rates of vanadium increased with increasing vanadium oxides dose, albeit not proportionally. This study, as part of a broader study of the release behavior of vanadium, can help to elucidate the pollution problem of vanadium and to clarify the fate of vanadium in the environment.

Release kinetics of vanadium from vanadium titano-magnetite: The effects of pH, dissolved oxygen, temperature and foreign ions

As part of a broader study of the environmental geochemistry behavior of vanadium (V), the release kinetics of V from the dissolution of natural vanadium titano-magnetite under environmentally relevant conditions was investigated. In both the acidic and basic domains, the V release rate was found to be proportional to fractional powers of hydrogen ion and dissolved oxygen activities. The dependence of the rate on dissolved oxygen can also be described in terms of the Langmuir adsorption model. The empirical rate equation is given by: r [Formula: see text] where, α=0.099-0.265, k'=3.2×10^-6-1.7×10^-5, K=2.7×10⁴-3.9×10⁴mol/L in acid solution (pH4.1), and α=-0.494-(-0.527), k'=2.0×10⁴-2.5×10^-11, and K=4.1×10³-6.5×10³mol/L in basic solution (pH8.8) at 20°C. Based on the effect of temperature on the release rate of V, the activation energies of minerals at pH8.8 were determined to be 148-235kJ/mol, suggesting that the dissolution of vanadium titano-magnetite is a surface-controlled process. The presence of Na⁺, Ca²⁺, Mg²⁺, K⁺, NO₃^-, Cl^-, SO₄^2- and CO₃^2- was found to accelerate the V release rates. This study improves the understanding of both the V pollution risk in some mine areas and the fate of V in the environment.

Development, modification, and application of low-cost and available biochar derived from corn straw for the removal of vanadium(v) from aqueous solution and real contaminated groundwater

In this work, a low-cost and available material for use as a permeable reactive barrier (PRB) to prevent vanadium in groundwater from leaking into river water was developed. Three modified biochars were prepared from available corn straw pretreated with CsCl, Zn(ii), and Zr(iv) to enhance ion exchange capacity (IEC) and specific surface area, and were designated as Cs-BC, Zn-BC, and Zr-BC, respectively. These materials were characterized via IEC, N₂ adsorption–desorption, Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses. The Langmuir isotherm model could be applied for the best fit for the adsorption data of Cs-BC and Zr-BC, indicating that vanadium(v) sorption occurred in a monolayer. The vanadium(v) adsorption capacities of Cs-BC, Zn-BC, and Zr-BC were 41.07, 28.46, and 23.84 mg g⁻¹, respectively, which were 3.22–5.55 times higher than that of commercial activated carbon (AC) (7.40 mg g⁻¹), probably because of their higher IECs and specific surface areas after modification. In addition, no heavy metal leaching was found from the modified biochars during the adsorption processes when pH > 2. According to the FTIR and XRD patterns, the adsorption mechanism of Cs-BC and Zr-BC was ion exchange, whereas for Zn-BC, it was mainly surface precipitation and electrostatic attraction. The adsorption of vanadium(v) onto the modified biochars was independent of pH in the range of 4.0 to 8.0. Furthermore, the removal efficiency of the vanadium(v) in real contaminated groundwater from the catchment of the Chaobei River by Zn-BC reached 100% at a dose of 4 g L⁻¹. Hence, modified biochars are promising PRB filling materials for removing vanadium(v) from contaminated groundwater.

In this work, a low-cost and available material for use as a permeable reactive barrier (PRB) to prevent vanadium in groundwater from leaking into river water was developed.

Engineering metal (hydr)oxide sorbents for removal of arsenate and similar weak-acid oxyanion contaminants: A critical review with emphasis on factors governing sorption processes

To create an integrative foundation for engineering of the next generation inexpensive sorbent systems, this critical review addresses the existing knowledge gap in factor/performance relationships between weak-acid oxyanion contaminants and metal (hydr)oxide sorbents. In-depth understanding of fundamental thermodynamics and kinetics mechanisms, material fabrication, and analytical and characterization techniques, is necessary to engineer sorbent that exhibit high capacity, selectivity, stability, durability and mass transport of contaminants under a wide range of operating and water matrix conditions requirements. From the perspective of thermodynamics and kinetics, this critical review examines the factors affecting sorbent performances and analyzes the existing research to elucidate future directions aimed at developing novel sorbents for removal of weak-acid oxyanion contaminants from water. Only sorbents that allow construction of simple and inexpensive water treatment systems adapted to overcome fiscal and technological barriers burdening small communities could pave the road for providing inexpensive potable water to millions of people. Novel sorbents, which exhibit (1) poor performances in realistic operating and water matrix conditions and/or (2) do not comply with the purely driven economics factors of production scalability or cost expectations, are predestined to never be commercialized.

Reactive Transport of U and V from Abandoned Uranium Mine Wastes

The reactive transport of uranium (U) and vanadium(V) from abandoned mine wastes collected from the Blue Gap/Tachee Claim-28 mine site in Arizona was investigated by integrating flow-through column experiments with reactive transport modeling, and electron microscopy. The mine wastes were sequentially reacted in flow-through columns at pH 7.9 (10 mM HCO₃^-) and pH 3.4 (10 mM CH₃COOH) to evaluate the effect of environmentally relevant conditions encountered at Blue Gap/Tachee on the release of U and V. The reaction rate constants (k_m) for the dissolution of uranyl-vanadate (U-V) minerals predominant at Blue Gap/Tachee were obtained from simulations with the reactive transport software, PFLOTRAN. The estimated reaction rate constants were within 1 order of magnitude for pH 7.9 (k_m = 4.8 × 10^-13 mol cm^-2 s^-1) and pH 3.4 (k_m = 3.2 × 10^-13 mol cm^-2 s^-1). However, the estimated equilibrium constants (K_eq) for U-V bearing minerals were more than 6 orders of magnitude different for reaction at circumneutral pH (K_eq = 10^-38.65) compared to acidic pH (K_eq = 10^-44.81). These results coupled with electron microscopy data suggest that the release of U and V is affected by water pH and the crystalline structure of U-V bearing minerals. The findings from this investigation have important implications for risk exposure assessment, remediation, and resource recovery of U and V in locations where U-V-bearing minerals are abundant.

Properties of vanadium-loaded iron sorbent after alkali regeneration

The aim of this research was to investigate the regeneration and reuse of a commercial granular iron sorbent (mainly goethite) when used in vanadium removal. A regeneration rate of 3 M NaOH was the highest (85%) achieved, followed by 2 M NaOH (79%) and 1 M NaOH (68%). The breakthrough curves show that the regenerated material can be reused. The BET (Brunauer-Emmett-Teller) surface area increased by 35-38% and the total pore volume increased by 123-130% as a consequence of NaOH treatment. The results indicated that sodium hydroxide could be used for the regeneration of iron sorbent although the regeneration was incomplete. This may be explained by the fact that vanadium diffusion into pores is a significant sorption mechanism in addition to complex formation with surface functional groups. As a consequence, vanadium desorbability from pores is not as effective as the regeneration of surface sites. X-ray photoelectron spectroscopy analyses confirmed a very low vanadium content on the surface of the NaOH-treated iron sorbent.

Understanding the Reduction Kinetics of Aqueous Vanadium(V) and Transformation Products Using Rotating Ring-Disk Electrodes

Vanadium(V) is an emerging contaminant in the most recent Environmental Protection Agency's candidate contaminant list (CCL4). The redox chemistry of vanadium controls its occurrence in the aquatic environment, but the impact of vanadium(V) speciation on the redox properties remains largely unknown. This study utilized the rotating ring-disk electrode technique to examine the reduction kinetics of four pH- and concentration-dependent vanadium(V) species in the presence and the absence of phosphate. Results showed that the reduction of VO₂⁺, H_xV₄O_12+x^(4+x)- (V₄), and HVO₄^2- proceeded via a one-electron transfer, while that of Na_xH_yV₁₀O₂₈^(6-x-y)- (V₁₀) underwent a two-electron transfer. Koutecky-Levich and Tafel analyses showed that the intrinsic reduction rate constants followed the order of V₁₀ > VO₂⁺ > V₄ > HVO₄^2-. Ring-electrode collection efficiency indicated that the reduction product of V₁₀ was stable, while those of VO₂⁺, HVO₄^2-, and V₄ had short half-lives that ranged from milliseconds to seconds. With molar ratios of phosphate to vanadium(V) varying from 0 to 1, phosphate accelerated the reduction kinetics of V₁₀ and V₄ and enhanced the stability of the reduction products of VO₂⁺, V₄, and HVO₄^2-. This study suggests that phosphate complexation could enhance the reductive removal of vanadium(V) and inhibit the reoxidation of its reduction product in water treatment.

Assessing the role of bed sediments in the persistence of red mud pollution in a shallow lake (Kinghorn Loch, UK)

Red mud is a by-product of alumina production. Little is known about the long-term fate of red mud constituents in fresh waters or of the processes regulating recovery of fresh waters following pollution control. In 1983, red mud leachate was diverted away from Kinghorn Loch, UK, after many years of polluting this shallow and monomictic lake. We hypothesised that the redox-sensitive constituents of red mud leachate, phosphorus (P), arsenic (As) and vanadium (V), would persist in the Kinghorn Loch for many years following pollution control as a result of cycling between the lake bed sediment and the overlying water column. To test this hypothesis, we conducted a 12-month field campaign in Kinghorn Loch between May 2012 and April 2013 to quantify the seasonal cycling of P, As, and V in relation to environmental conditions (e.g., dissolved oxygen (DO) concentration, pH, redox chemistry and temperature) in the lake surface and bottom waters. To confirm the mechanisms for P, As and V release, a sediment core incubation experiment was conducted using lake sediment sampled in July 2012, in which DO concentrations were manipulated to create either oxic or anoxic conditions similar to the bed conditions found in the lake. The effects on P, As, and V concentrations and species in the water column were measured daily over an eight-day incubation period. Phosphate (PO₄-P) and dissolved As concentrations were significantly higher in the bottom waters (75.9 ± 30.2 μg L^-1 and 23.5 ± 1.83 μg L^-1, respectively) than in the surface waters (12.9 ± 1.50 μg L^-1 and 14.1 ± 2.20 μg L^-1, respectively) in Kinghorn Loch. Sediment release of As and P under anoxic conditions was confirmed by the incubation experiment and by the significant negative correlations between DO and P and As concentrations in the bottom waters of the lake. In contrast, the highest dissolved V concentrations occurred in the bottom waters of Kinghorn Loch under oxic conditions (15.0 ± 3.35 μg L^-1), with the release from the bed sediment apparently being controlled by a combination of competitive ion concentrations, pH and redox conditions.

Removal of vanadium from industrial wastewater using iron sorbents in batch and continuous flow pilot systems

This study investigated the removal of vanadium from real industrial wastewater by using six iron materials: commercial iron sorbent (CFH-12), commercial mineral sorbent (AQM), blast furnace sludge (BFS), steel converter sludge (SCS), ferrochrome slag (FeCr) and slag from a steel foundry (OKTO). Batch tests revealed that CFH-12 (ferric oxyhydroxide) removed vanadium most efficiently, which was explained by its high iron content and the amorphous form of the iron, and that the sorption followed the Langmuir isotherm. With a dosage of 10 g/l and an initial vanadium concentration of 58.2 mg/l, 91-94% removal rates for vanadium were achieved in the studied pH range (3-9). Other sorbents showed significantly lower efficiency than CFH-12, with the exception of BFS at acidic pH (93%). Based on the batch test results, CFH-12 was selected for a pilot study made on site. The pilot study demonstrated the feasibility of CFH-12 to remove vanadium at high temperature (80 °C) from concentrated industrial wastewater with fluctuating water quality (vanadium concentration varied from 51 to 83 mg/l, pH about 9 (at 25 °C)). Leaching of impurities (mainly S, Ca, Mg and K) into the effluent occurred during the first day, but subsequently good quality effluent was produced (e.g. <0.1 mg/l V). During the pilot study, the amorphous iron material of CFH-12 was crystallized into a hematite-like phase (Fe_1.67 H_0.99 O₃), and goethite (FeO(OH)) with a higher average pore diameter, probably due to the hot process conditions to which CFH-12 was exposed for over five days.

Current status and associated human health risk of vanadium in soil in China

A detailed assessment of vanadium contamination characteristics in China was conducted based on the first national soil pollution survey. The map overlay analysis was used to evaluate the contamination level of vanadium and the non-carcinogenic risk assessment model was calculated to quantify the vanadium exposure risks to human health. The results showed that, due to the drastically increased mining and smelting activities, 26.49% of soils were contaminated by vanadium scattered in southwest of China. According to Canadian soil quality guidelines, about 8.6% of the national soil pollution survey samples were polluted, and pose high non-carcinogenic risks to the public, especially to children living in the vicinity of heavily polluted mining areas. We propose the area near the boundary of Yunnan, Guizhou, Guangxi, and Sichuan provinces as priority control areas due to their higher geochemical background or higher health risks posed to the public. Finally, recommendations for management are proposed, including minimization of contaminant inputs, establishing stringent monitoring program, using phytoremediation, and strengthening the enforcement of relevant laws. Therefore, this study provides a comprehensive assessment of soil vanadium contamination in China, and the results will provide valuable information for China's soil vanadium management and risk avoidance.

Simultaneous microbial reduction of vanadium (V) and chromium (VI) by Shewanella loihica PV-4

Toxic vanadium (V) and chromium (VI) often co-exist in wastewater from vanadium ore smelting and their reductions by bacterial strain Shewanella loihica PV-4 is realized simultaneously. After 27-d operation, 71.3% of V(V) and 91.2% of Cr(VI) were removed respectively, with citrate as organic carbon source. Enhancement of Cr(VI) bioreduction was observed with the suppressed V(V) reduction. V(IV) and Cr(III), the main reduction products, precipitated inside the organisms and attached on cell surfaces. Both membrane components containing cytochrome c and cytoplasmic fractions containing soluble proteins as well as NADH may contribute to these microbial reductions. Most Cr(VI) were reduced extracellularly and V(V) tended to be reduced through intracellular process, as revealed by mapping the microbial surface and a line scan across the cell, performed by scanning transmission electron microscopy. This study provides an efficient alternative for controlling combined pollution caused by these two metals based on microbial technology.

Removal and recovery of vanadium from alkaline steel slag leachates with anion exchange resins

Leachable vanadium (V) from steel production residues poses a potential environmental hazard due to its mobility and toxicity under the highly alkaline pH conditions that characterise these leachates. This work aims to test the efficiency of anion exchange resins for vanadium removal and recovery from steel slag leachates at a representative average pH of 11.5. Kinetic studies were performed to understand the vanadium sorption process. The sorption kinetics were consistent with a pseudo-first order kinetic model. The isotherm data cannot differentiate between the Langmuir and Freundlich models. The maximum adsorption capacity (Langmuir value q_max) was 27 mg V g^-1 resin. In column anion exchange, breakthrough was only 14% of the influent concentration after passing 90 L of steel slag leachate with 2 mg L^-1 V through the column. When eluting the column 57-72% of vanadium was recovered from the resin with 2 M NaOH. Trials on the reuse of the anion exchange resin showed it could be reused 20 times without loss of efficacy, and on average 69% of V was recovered during regeneration. The results document for the first time the use of anion exchange resins to remove vanadium from steel slag leachate. As an environmental contaminant, removal of V from leachates may be an obligation for long-term management requirements of steel slag repositories. Vanadium removal coupled with the recovery can potentially be used to offset long-term legacy treatment costs.

Monitoring the clean-up operation of agricultural fields flooded with red mud in Hungary

In the course of the clean-up operation after the red mud inundation in 2010, red mud was removed from the soil surface in places where the layer was more than 5 cm deep. Before its removal, the red mud seeped into the soil. In 2012, soil samples were taken from depths of 0 to 20 and 20 to 40 cm on some of the affected areas. The parameters investigated were pH, organic matter, salt%, and the total and mobile fractions of various elements. The values recorded in 2012 were compared with those measured immediately after the removal of the red mud in 2010 and with the background and clean-up target concentrations. The pH values remained below the designated limit, while the salt content only exhibited values in the weakly salty range on areas at the greatest distance from the dam. In the central part of the inundated area, total Na contents above the 900 mg/kg target value were observed, but the Na content in the 0-20-cm layer generally exhibited a decrease due to leaching. The pH and As concentration also showed a decline on several areas compared with the values recorded in 2010. Total As and Co contents in excess of the target values were recorded on the lowest-lying part of the flooded area, probably because the finest red mud particles were deposited the furthest from the dam, where they seeped into the soil. Nevertheless, the mobility and plant availability of both elements remained moderate. The total contents of both Co and Mo, however, exhibited a significant rise compared with both the background value and the 2010 data. The monitoring of the cleaned-up areas showed that after a 2-year period element concentrations that exceeded the target values and could be attributed to the red mud pollution were only detectable on the lowest-lying areas.

Vanadium removal and recovery from bauxite residue leachates by ion exchange

Bauxite residue is an important by-product of the alumina industry, and current management practices do not allow their full valorisation, especially with regard to the recovery of critical metals. This work aims to test the efficiency of ion exchange resins for vanadium (V) removal and recovery from bauxite residue leachates at alkaline pH (11.5 and 13). As an environmental pollutant, removal of V from leachates may be an obligation of bauxite residue disposal areas (BRDA) long-term management requirements. Vanadium removal from the leachate can be coupled with the recovery, and potentially can be used to offset long-term legacy treatment costs in legacy sites. Kinetics studies were performed to understand the adsorption process. The rate kinetics for the V adsorption was consistent with the pseudo-first-order kinetic model, with a higher adsorption rate for pH 11.5 (1.2 min^-1). Adsorption isotherm data fitted better to Freundlich equations than to the Langmuir model. The maximum adsorption capacity (Langmuir value q _max) was greatest for pH 13 (9.8 mg V g^-1 resin). In column tests, breakthrough was reached at 70 bed volumes with the red mud leachate at pH 13, while no breakthrough was achieved with the effluent at pH 11.5. In regeneration, 42 and 76 % of V were eluted from the resin with 2 M NaOH from the red mud leachate at pH 13 and 11.5, respectively. Further optimization will be needed to upscale the treatment.

Application of banana peels nanosorbent for the removal of radioactive minerals from real mine water

Transformation of agricultural waste such as banana peels into a valuable sorbent material has been proven effective and efficient in wastewater treatment. Further, transformation into nanosorbent to enhance the removal capacity of actinides (uranium and thorium) from synthetic and real mine water is extensively investigated in this study. The nanosorbent samples before and after adsorption were characterised by X-ray diffraction (XRD), Fourier transform infra-red (FTIR), zetasizer nanoseries and scanning electron microscopy (SEM) while the amount of radioactive substances adsorbed was determined by inductively coupled plasma optical emission spectroscopy. Results revealed that there was a crystallite size and particle size reduction from 108 to 12 nm and <65,000 nm to <25 nm respectively as a function of milling time. Furthermore, appearance and disappearance of nanofibers via milling was noticed during structural analysis. The functional groups responsible for the banana peels capability to coordinate and remove metal ions were identified at absorption bands of 1730 cm^-1 (carboxylic groups) and 889 cm^-1 (amine groups) via FTIR analysis. Equilibrium isotherm results demonstrated that the adsorption process was endothermic for both uranium and thorium. The Langmuir maximum adsorption capacity was 27.1 mg g^-1, 34.13 mg g^-1 for uranium and 45.5 mg g^-1, 10.10 mg g^-1 for thorium in synthetic and real mine water, respectively. The results obtained indicate that nanostructured banana peels is a potential adsorbent for the removal of radioactive substances from aqueous solution and also from real mine water. However, the choice of this sorbent material for any application depends on the composition of the effluent to be treated.

Removal of vanadium from vanadium-containing wastewater by amino modified municipal sludge derived ceramic

In this work, an amino modified porous ceramic derived from municipal sludge was synthesized for the adsorption of vanadium (V) from wastewater. In this approach, a maximum vanadium (V) removal of 99.8% can be achieved by using 800 g adsorbent with a height of 800 mm when the initial concentration of vanadium (V) was 50 mg/L, pH was 4, flow rate was 5 L/h.

Polycyclic aromatic hydrocarbons (PAHs) removal by sorption: A review

Polycyclic aromatic hydrocarbons (PAHs) are organic micro pollutants which are persistent compounds in the environment due to their hydrophobic nature. Concerns over their adverse effects in human health and environment have resulted in extensive studies on various types of PAHs removal methods. Sorption is one of the widely used methods as PAHs possess a great sorptive ability into the solid media and their low aqueous solubility property. Several adsorbent media such as activated carbon, biochar, modified clay minerals have been largely used to remove PAHs from aqueous solution and to immobilise PAHs in the contaminated soils. According to the past studies, very high removal efficiency could be achieved using the adsorbents such as removal efficiency of activated carbon, biochar and modified clay mineral were 100%, 98.6% and >99%, respectively. PAHs removal efficiency or adsorption/absorption capacity largely depends on several parameters such as particle size of the adsorbent, pH, temperature, solubility, salinity including the production process of adsorbents. Although many studies have been carried out to remove PAHs using the sorption process, the findings have not been consolidated which potentially hinder to get the correct information for future study and to design the sorption method to remove PAHs. Therefore, this paper summarized the adsorbent media which have been used to remove PAHs especially from aqueous solutions including the factor affecting the sorption process reported in 142 literature published between 1934 and 2015.

Damage suffered by swamp morning glory (Ipomoea aquatica Forsk) exposed to vanadium (V)

To elucidate the physiological and morphological responses generated by vanadium (V) in plants, hydroponic culture experiments were performed with swamp morning glory (Ipomoea aquatica Forsk) exposed to 0 mg L(-1) to 2.50 mg L(-1) pentavalent V [V(V)] in Hoagland nutrient solutions. The concentration of chlorophyll a, chlorophyll b, and carotene peaked at a V(V) concentration of 0.05 mg L(-1) and gradually decreased at higher V(V) concentrations. Similarly, the plant biomass was stimulated at low levels of V(V) and was inhibited when V(V) concentrations exceeded 0.1 mg L(-1). Pentavalent V had negative effects on the uptake of phosphorus (P) by roots, shoots, and leaves. The biological absorption coefficients of V of the roots were higher than those of the aerial parts. Under low concentrations of V(V) exposure, the predominant species of V in the aerial parts was tetravalent V [V(IV)], whereas V(V) became more prevalent when concentrations of V(V) in the solution was higher than 0.50 mg L(-1). In the roots, however, the concentrations of V(V) were always higher than those of the V(IV), except in the control group. Organelles in the V(V)-treated leaves were distorted, and the periplasmic space became wider. These results indicate V(V) has concentration-dependent effects on the physiological properties of swamp morning glory, whereas the plant has the ability to develop self-protective function to adapt to the toxicity of V(V).

Impact of soil pH and organic matter on the chemical bioavailability of vanadium species: The underlying basis for risk assessment

The main objective of this study was to unravel the chemical reactions and processes dictating the potential bioavailability of vanadium (V). In environmental solutions V exists in two stable oxidation states, +IV and +V, of which + V is considered to be more toxic. In this study, the effect of speciation and soil pH on the chemical accessibility of V was investigated with two soils: 1) field soil rather rich in soil organic matter (SOM) and 2) coarse mineral soil low in SOM. Fresh soil samples treated with V(+V) (added as NaVO3) or V(+IV) (added as VOSO4) (pH adjusted to the range 4.0-6.9) were incubated for 3 months at 22 °C. The adsorption tendency of V species was explored by water extraction (Milli-Q water, 1:50 dw/V) and by sequential extraction (0.25 M KCl; 0.1 M KH2/K2HPO4; 0.1 M NaOH; 0.25 M H2SO4, 1:10 dw/V). The potential bioavailability of V was found to be dictated by soil properties. SOM reduced V(+V) to V(+IV) and acted as a sorbent for both species, which lowered the bioaccessibility of V. A high pH, in turn, favored the predominance of the V(+V) species and thus increased the chemical accessibility of V.

Microbial reduction and precipitation of vanadium (V) in groundwater by immobilized mixed anaerobic culture

Vanadium is an important contaminant impacted by natural and industrial activities. Vanadium (V) reduction efficiency as high as 87.0% was achieved by employing immobilized mixed anaerobic sludge as inoculated seed within 12h operation, while V(IV) was the main reduction product which precipitated instantly. Increasing initial V(V) concentration resulted in the decrease of V(V) removal efficiency, while this index increased first and then decreased with the increase of initial COD concentration, pH and conductivity. High-throughput 16S rRNA gene pyrosequencing analysis indicated the decreased microbial diversity. V(V) reduction was realized through dissimilatory reduction process by significantly enhanced Lactococcus and Enterobacter with oxidation of lactic and acetic acids from fermentative microorganisms such as the enriched Paludibacter and the newly appeared Acetobacterium, Oscillibacter. This study is helpful to detect new functional species for V(V) reduction and constitutes a step ahead in developing in situ bioremediations of vanadium contamination.