Vanadium removal by metal (hydr)oxide adsorbents

Utilization of phosphoric acid-modified biochar to reduce vanadium leaching potential and bioavailability in soil

Remediating vanadium (V) polluted soil has garnered widespread attention over the past decade. Yet, few research projects have investigated the stabilization of soil V using modified biochar, so the effects and interacting mechanisms between soil properties and modified biochar for V immobilization and stabilization remain unclear. Hence, this gap is addressed by determining the leaching behavior and mechanisms of soil V on different dosages of phosphoric acid (H3PO4) impregnated biochar (MLBC, 0.5%-4%). The applicability and durability in soil V immobilization was investigated under acid precipitation. The MLBC effect on V bioavailability and mobility was assessed first by CaCl2, Toxicity Characteristic Leaching Procedure (TCLP) and Synthetic Precipitation Leaching Procedure (SPLP) extractions in different periods. The V concentrations significantly reduced in CaCl2, TCLP, and SPLP extract with MLBC at each dosage (30 d), while slight to significant increase in SPLP and TCLP extract V was recorded in a long-term incubation (90 d). Column leaching test further demonstrated the high durability of 4% MLBC in V stabilization under continuous acid exposure. Compared to the control (no-biochar), the accumulated V content in the leaching solution significantly decreased in MLBC-amended soil. Acid soluble fraction of V showed significant negative correlation with both soil organic matter (SOM) and available P, which was positively correlated with pH, suggested that pH, available P and SOM were key factors affecting the bioavailability of V in soil. Moreover, combining with the characterization results of MLBC and amended soil, the results revealed that H3PO4 modified biochar played a vital role on V immobilization and soil improvement by forming electrostatic adsorption, ion exchange, redox reaction or complexation with the increase of functional groups. These revealed an efficient and steady development of soil quality and treatment for soil V contamination, under MLBC operation to soil polluted with exogenous V.

Vanadium in the Environment: Biogeochemistry and Bioremediation

Vanadium(V) is a highly toxic multivalent, redox-sensitive element. It is widely distributed in the environment and employed in various industrial applications. Interactions between V and (micro)organisms have recently garnered considerable attention. This Review discusses the biogeochemical cycling of V and its corresponding bioremediation strategies. Anthropogenic activities have resulted in elevated environmental V concentrations compared to natural emissions. The global distributions of V in the atmosphere, soils, water bodies, and sediments are outlined here, with notable prevalence in Europe. Soluble V(V) predominantly exists in the environment and exhibits high mobility and chemical reactivity. The transport of V within environmental media and across food chains is also discussed. Microbially mediated V transformation is evaluated to shed light on the primary mechanisms underlying microbial V(V) reduction, namely electron transfer and enzymatic catalysis. Additionally, this Review highlights bioremediation strategies by exploring their geochemical influences and technical implementation methods. The identified knowledge gaps include the particulate speciation of V and its associated environmental behaviors as well as the biogeochemical processes of V in marine environments. Finally, challenges for future research are reported, including the screening of V hyperaccumulators and V(V)-reducing microbes and field tests for bioremediation approaches.

Soil amendments for vanadium remediation: a review of remediation of vanadium in soil through chemical stabilization and bioremediation

Immobilization of vanadium (V) in soils is one option to prevent groundwater contamination and plant uptake. Phytoremediation, microbial remediation, and chemical stabilization using soil amendments are among the leading environmentally friendly and economically feasible techniques in V remediation. Soil amendments were used to reduce V mobility by immobilizing it in the soil matrix through chemical stabilization, while bioremediation methods such as phytoremediation and microbial remediation were used to remove V from contaminated soils. Vanadium exists in several species and among them V5+ species are the most prevalent, toxic, and soluble form and present as a negatively charged ion (H2VO4- and HVO42-) in oxic soils above pH 4. Amendments used for chemical stabilization can change the physicochemical properties enhancing immobility of V in soil. The pH of the soil environment, point of zero charge of the colloid surface, and redox conditions are some of the most important factors that determine the efficiency of the amendment. Commonly used amendments for chemical stabilization include biochar, zeolites, organic acids, various clay minerals and oxides of elements such as iron, titanium, manganese, and aluminum. For bioremediation, chelating agents and microbial communities are used to mobilize V to enhance phyto-or microbial-extraction procedures. The objectives of this review were to discuss remediation methods of V while considering V speciation and toxicity in soil, and soil amendment application for V removal from soil. The information compiled in this review can guide further research on soil amendments for optimal V remediation in largely contaminated industrial sites.

MXenes and MXene-based materials for removal of pharmaceutical compounds from wastewater: Critical review

The rapid increase in the global population and its ever-rising standards of living are imposing a huge burden on global resources. Apart from the rising energy needs, the demand for freshwater is correspondingly increasing. A population of around 3.8 billion people will face water scarcity by 2030, as per the reports of the World Water Council. This may be due to global climate change and the deficiency in the treatment of wastewater. Conventional wastewater treatment technologies fail to completely remove several emerging contaminants, especially those containing pharmaceutical compounds. Hence, leading to an increase in the concentration of harmful chemicals in the human food chain and the proliferation of several diseases. MXenes are transition metal carbide/nitride ceramics that primarily structure the leading 2D material group. MXenes act as novel nanomaterials for wastewater treatment due to their high surface area, excellent adsorption properties, and unique physicochemical properties, such as high electrical conductivity and hydrophilicity. MXenes are highly hydrophilic and covered with active functional groups (i.e., hydroxyl, oxygen, fluorine, etc.), which makes them efficient adsorbents for a wide range of species and promising candidates for environmental remediation and water treatment. This work concludes that the scaling up process of MXene-based materials for water treatment is currently of high cost. The up-to-date applications are still limited because MXenes are currently produced mainly in the laboratory with limited yield. It is recommended to direct research efforts towards lower synthesis cost procedures coupled with the use of more environmentally friendly materials to avoid secondary contamination.

Silanized fiberglass modified by carbon dots as novel and impressive adsorbent for aqueous heavy metal ion removal

This work discusses the application of a silanized fiberglass (SFG) modified by carbon dots (CDs) as an effective adsorbent for up-taking some heavy metal ions including lead (Pb²⁺), chromium (Cr³⁺), cadmium (Cd²⁺), cobalt (Co²⁺), and nickel (Ni²⁺) as pollutant in the aqueous solution by batch method. Removal tests were carried out after optimization of pH, contact time, initial concentration of metal ions, and CDs amount. The SFG modified with CDs (CDs-SFG) was applied for the removal of 10 ppm of each metal ion solution after 100 min and the corresponding results showed the removal efficiencies of 100, 93.2, 91.8, 90, and 88.3% for Pb²⁺, Cd²⁺, Cr³⁺, Co²⁺, and Ni²⁺, respectively. The adsorption capacity of CDs-SFG in the metal ion mixed solution was also evaluated, and the results indicated the same trend in the adsorption capacity for metal ions in the mixed solution, though with lower absolute values compared to the single metal solutions. Moreover, the selectivity of this adsorbent for the adsorption of Pb²⁺ was almost twice of other tested metal ions. The regeneration of the CDs-SFG showed that its adsorption capacity after five cycles was reduced about 3.9, 6.0, 6.8, 6.7, and 8.0% for Pb²⁺, Cd²⁺, Cr³⁺, Co²⁺, and Ni²⁺, respectively. Finally, the applicability of the CDs-SFG adsorbent was examined with the analysis of the metal ions in water and wastewater samples.

Watershed seasonality regulating vanadium concentrations and ecological risks in the coastal aquatic habitats of the northwest Pacific

Vanadium is a component of different natural and industrial products and a widely used metal, which, nonetheless, has only garnered attention in recent years owing to its potential risks. Six sampling trips were conducted over different seasons and years, collecting 108 samples from rivers and 232 from the bays and analyzed using high-precision inductively coupled plasma mass spectrometry. This study investigated the sources, spatiotemporal characteristics, and risks of vanadium in the aquatic ecosystems of two typical bays of the Northwest Pacific that have strong links with vanadium-related industries. Likewise, the health and ecological risks were assessed using probabilistic and deterministic approaches. Overall, vanadium concentrations were higher in Jiaozhou Bay (JZB: 0.41-52.7 μg L^-1) than in Laizhou Bay (LZB: 0.39-17.27 μg L^-1), with concentrations higher than the majority of the worldwide studies. Vanadium-realted industries significantly impacted (p < 0.05) the metal concentrations in the rivers with 54.22% (40.73-150%) and 54.45% (27.66%-68.87%) greater concentrations in JZB and LZB rivers. In addition, vanadium exhibited significant seasonal variation, and higher values were quantified during the monsoon period at LZB owing to the greater catchment area. Impacted by smaller freshwater inputs, the post-monsoon period had substantial impacts on JZB, and vanadium in the rivers and bays was significantly higher during the winter. Despite some concentrations being higher than that indicated in the drinking water guidelines established by China, vanadium presents low to null risks to the population as per both approaches. Last, species with limited resilience are likely to face medium to high risks, with an incidence of 65-93% using the probabilistic method and 52-97% using the deterministic assessment.

Soil covering measure mitigates vanadium loss during short-term simulated rainfall in the vanadium titano-magnetite tailings reservoir

Soil covering is an operative measure to decline pollutant release in tailings reservoirs and promote vegetation restoration, yet urgent research still needs to probe into pollutant leaching and migration in the artifact technology under extreme precipitation. Here, a soil column leaching experiment was designed to explore the migration and behaviors of vanadium (V) in the system of vanadium titano-magnetite tailings (VTMTs) covered by soils with different depths (5 cm, 10 cm, and 15 cm). Chemical fractions of V in the VTMTs and covered soils were analyzed to decipher the mechanisms underlying the V migration. We found a limited V leaching (0.26-0.52 μg/L, <0.01% of total V) in the columns during the experiments, and V in the VTMTs was not apt to be leached or migrate upward to the overlying soils. The soil volumes overlaid had nonsignificant effect on the V behaviors in the VTMTs (P > 0.05), because of the dominant and stable residual V (96.4% of total V) in the tailings. Although acid soluble V might be transformed to oxidizable V, it was resupplied by the fractions of weak-bound V in the solid phases during the leaching experiments. The mineral metal (hydr)oxides (e.g., aluminum, iron) determined the V behaviors in the VTMTs via absorption effect, and the high affinity of V to organic matters probably prevented its migration throughout the overlying soils. The results indicate that soil covering measure in the VTMTs reservoirs effectively reduces V migration or release from the tailings through leaching or upward migration, which provides a significant guidance for vegetation restoration in V-rich tailings reservoirs.

Study on release and occurrence of typical metals in corrosion products of drinking water distribution systems under stagnation conditions

Metal contaminants in corrosion products of drinking water distribution systems (DWDS) can be released into potable water under specific conditions, thereby polluting drinking water and posing a health risk. Under stagnation conditions, the release characteristics, occurring forms, and environmental risks of ten metals were determined in loose and tubercle scale solids of an unlined cast iron pipe with a long service history, before and after immersion. Most Al, As, Cr, Fe, and V in corrosion scales existed in the residual fraction, with the released concentration and pollution risk being low. Since more than 59% of Ca in pipe scales existed in the exchangeable fraction, Ca release was high. Although the Pb and Cd content of corrosion solids was low, a high proportion of Pb and Cd was present in non-residual fractions with high mobility. Sudden severe Pb or Cd pollution events in DWDS could result in high pollution and environmental risk levels. The total content and released amount of Mn and Zn in corrosion scales were both high. Therefore, while special attention should be paid to Mn and Zn, Pb and Cd also present a high risk in pipe scales, despite their low concentrations. During stagnation immersion, metal release from powdered pipe scales occurred via the processes of mass release, re-adsorption into scales, and slow release until equilibrium was reached. The levels of metal re-adsorption into scales were much higher than the concentrations dissolved into bulk water. However, the amount of metal re-adsorption into tubercle scale blocks was less. Importantly, these findings highlight that during DWDS operation, the sudden release of metal pollutants caused by pipe scale breakage should be avoided.

Photo-induced reduction of vanadium in vanadium-containing iron/manganese oxide agglomerates by oxalic acid

The stockpiling of vanadium-containing tailings allows vanadium to migrate into the surrounding area, resulting in toxic metal contamination. By using the vanadium-bearing iron/manganese (Fe/Mn) oxide agglomerates as the simulated tailings, the feasibility of photo-induced reduction of vanadium by oxalic acid was investigated. Batch effects of the available light and the reducing agents on agglomerates were investigated. Results showed that oxalic acid (5 mmol L^-1) can convert V(V) to V(IV) and convert Fe(III) released from the Fe/Mn oxide agglomerates to Fe(II) under both light and dark conditions. After 45 d of reaction in the dark, oxalic acid converted 33.54% Fe(III) and 100% V(V) in the leachate into Fe(II) and V(IV). The Fenton reaction occurred by light irradiation significantly increased the redox potential in the solution, and also caused V(IV) to be oxidized. Overall, oxalic acid can rapidly reduce V(V) to V(IV), but sunlight may have an inhibitory effect on the reduction reaction. Present study can deepen the understanding of the mechanism for valence transformation of elements in minerals by sunlight, and can help in implementing tailings treatment and environmental remediation by using oxalic acid and avoiding light.

Vanadium (V) Adsorption from Aqueous Solutions Using Xerogel on the Basis of Silica and Iron Oxide Matrix

Vanadium is considered a strategic metal with wide applications in various industries due to its unique chemical and physical properties. On the basis of these considerations, the recovery of vanadium (V) is mandatory because of the lack of raw materials. Various methods are used to recover vanadium (V) from used aqueous solutions. This study develops a clean and effective process for the recovery of vanadium (V) by using the adsorption method. At the same time, this study synthesizes a material starting from silica matrices and iron oxides, which is used as an adsorbent material. To show the phase composition, the obtained material is characterized by X-ray diffraction showing that the material is present in the amorphous phase, with a crystal size of 20 nm. However, the morphological texture of the material is determined by the N₂ adsorption-desorption method, proving that the adsorbent material has a high surface area of 305 m²/g with a total pore volume of 1.55 cm³/g. To determine the efficiency of the SiO₂Fe_xO_y material for the recovery of vanadium through the adsorption process, the role of specific parameters, such as the L-to-V ratio, pH, contact time, temperature, and initial vanadium concentration, must be evaluated. The adsorption process mechanism was established through kinetic, thermodynamic, and equilibrium studies. In our case, the process is physical, endothermic, spontaneous, and takes place at the interface of SiO₂Fe_xO_y with V₂O₅. Following equilibrium studies, the maximum adsorption capacity of the SiO₂Fe_xO_y material was 58.8 mg (V)/g of material.

Insight into the removal of vanadium ions from model and real wastewaters using surface grafted zirconia-based adsorbents: Batch experiments, equilibrium and mechanism study

This study concerns the fabrication of CTAB- and N,N-dimethyltetradecylamine-grafted zirconia and evaluation of their ability to adsorb vanadium ions. The effectiveness of ZrO₂ functionalization and the different nature of the modifiers used were confirmed by differences in the porosity (ZrO₂: S_BET = 347 m²/g; ZrO₂-CTAB: S_BET = 375 m²/g, ZrO₂-NH⁺: S_BET = 155 m²/g), types of functional groups, and isoelectric points (the ZrO₂ and CTAB-modified samples have IEPs = 3.8 and 3.9, ZrO₂-NH⁺ has IEP = 7.1) of the prepared adsorbents. The designed materials were tested in batch adsorption experiments involving the removal of vanadium ions from model wastewaters at various process parameters, among which pH proved to be the most important. Based on equilibrium and kinetic evaluations, it was proved that the sorption of V(V) ions followed pseudo-second-order and intraparticle diffusion models, and the data were better fitted to the Langmuir model, suggesting the following order of the sorbents in terms of favorability for V(V) ion adsorption: ZrO₂-NH⁺ > ZrO₂ > ZrO₂-CTAB. The estimated maximum monolayer capacity of ZrO₂-NH⁺ for V(V) (87.72 mg/g) was the highest among the tested materials. Additionally, it was confirmed that adsorption of V(V) ions onto synthesized materials is a heterogeneous, exothermic, and spontaneous reaction, as evidenced by the calculated values of thermodynamic parameters. The key goals included the transfer of experimental findings obtained using model solutions to the adsorption of V(V) ions from solutions arising from the leaching process of spent catalysts. The highest adsorption efficiencies of 70.8% and 47.5% were recorded for the ZrO₂-NH⁺ material in acidic solution; this may be related to the protonization of -NH⁺ groups, which favors the sorption of V(V) ions. Based on desorption tests as well as the results of infrared and X-ray photoelectron spectroscopy, irrespective of the process conditions, the physical nature of the adsorbent/adsorbate interaction was confirmed.

Adsorption/desorption of naphthalene and phenanthrene in a binary competitive system in the riparian zone

Polycyclic aromatic hydrocarbons (PAHs) such as naphthalene (Nap) and phenanthrene (Phe) are organic pollutants that are of concern because of their environmental toxicity. Adsorption is a promising process for the removal of Nap and Phe from water and soil. The riparian zone between a river and a riparian aquifer, which is rich in adsorption medium, may be important for PAH remediation. Nap and Phe may be removed from the surface water through adsorption by the media in the riparian zone. However, there is still a lack of the removal patterns and mechanisms of media in the riparian zone to remediate water contaminated by Nap and Phe simultaneously. In this study, focusing on the typical PAHs (Nap and Phe) as target pollutants, batch static adsorption and desorption experiments of Nap and Phe were carried out to explore the competitive adsorption mechanisms of Nap and Phe in the binary system. Batch dynamic adsorption experiments were conducted to ascertain the adsorption regulation of Nap and Phe in sediments during the recharge of groundwater by river water in a riparian zone. The static adsorption experiment results showed that competitive adsorption of Nap and Phe occurred, and a mutual inhibitory effect of Nap and Phe adsorption was observed in the binary system. Phe had a stronger inhibitory effect on Nap, Phe was preferentially adsorbed on the medium in binary adsorption. The results of batch dynamic experiments showed that, in terms of adsorption, the riparian zone in the study area showed stronger performance for removal of Phe than Nap. The results of this paper could be useful for alleviating Nap and Phe pollution of groundwater and developing treatment protocols for groundwater exposed to Nap and Phe.

Characteristics of vanadium release from layered steel pipe scales to bulk, steady, and occluded water in drinking water distribution systems

The release of vanadium (V) from drinking water distribution systems (DWDS) can endanger water quality and human health. Therefore, in this study, the physicochemical characteristics of old steel pipe scales were analyzed, and dynamic pipeline devices were constructed. Subsequently, static release experiments were conducted to find an optimum scale-water ratio and investigate the release behaviors of V in lumpy pipe scales. Besides, the release behaviors of V from layered pipe scales to bulk, steady, and occluded water under the combined effect of multiple water quality conditions were studied for the first time. Computational fluid dynamics (CFD) was adopted to explain the release behaviors of V in the dynamic pipeline. Results revealed that the adsorption performance of the layered scales decreased in the order of surface layer > porous core layer > hard shell-like layer. The release behaviors of V in the lumpy pipe scales were mainly divided into rapid desorption and colloidal agglomeration stages. The Double constant and Weber-Morris models can suitably describe release stage I (R² > 0.919) and release stage II (R² > 0.948), respectively. Notably, the release of V was aggravated by low pH, high temperature, and high SO₄^2- concentration, and the release amount of V in the pipeline was more significant than the layered pipe scales. Steady water in the gaps of scales contained more V than bulk water, and the malignant occluded water encased in scales contained relatively low V concentrations. In short, the main mechanism of V release was competitive adsorption in the early stage, and pH was the main influencing factor in the later stage. The above results are of great significance for revealing the release behaviors of V and reducing its release in DWDS.

A high-efficient and recyclable aged nanoscale zero-valent iron compound for V5+ removal from wastewater: Characterization, performance and mechanism

An effective complex of nanoscale zero-valent iron (NZVI) supported on zirconium 1,4-dicarboxybenzene metals-organic frameworks (UIO-66) with strong oxidation resistance was synthesized (NZVI@UIO-66) for V⁵⁺ removal from wastewater. The results demonstrated that NZVI was successfully loaded on UIO-66 with a uniform dispersion, and then the composite was aged in the air which was named A-NZVI@UIO-66. V⁵⁺ could be removed quickly and completely using A-NZVI@UIO-66 in a wider pH range except for the pH = 1 condition. The reaction between A-NZVI@UIO-66 and V⁵⁺ was an endothermic process. Freundlich model with a better-fitted value showed the adsorption of V⁵⁺ on A-NZVI@UIO-66 was multi-layer heterogeneous adsorption and the adsorbed amount of V⁵⁺ was 397.23 mg V/g NZVI. Nitrate had a competitive inhibition on V⁵⁺ removal by A-NZVI@UIO-66. Mechanisms of vanadium elimination from the aqueous phase by A-NZVI@UIO-66 included physical adsorption, reduction, and complex co-precipitation, particularly the reduction dominated. The subsistent Zr-O bond in A-NZVI@UIO-66 provided a possible double reaction path by playing an electron donor, storage, or conductor role. After acid leaching, A-NZVI@UIO-66 represented good reusability in the removal of V⁵⁺ from the practical mine sewage.

Soil indigenous microorganisms alleviate soluble vanadium release from industrial dusts

Vanadium-bearing dusts from industrial processes release abundant toxic vanadium, posing imminent ecological and human health concerns. Although the precipitation of these dusts has been recognized as the main source of soil vanadium pollution, little is known regarding the interrelationships between industrial dusts and soil inherent compositions. In this study, the interactions between dusts from vanadium smelting and soil indigenous microorganisms were investigated. Soluble vanadium (V) [V(V)] released from industrial dusts was reduced by 41.5 ± 0.39% with soil addition, compared to water leaching. Reducible fraction accounted for the highest proportion (55.1 ± 1.73%) of vanadium speciation in the resultant soils, while residual vanadium fraction increased to 83.7 ± 3.22% in the leached dusts. Functional genera (e.g., Aliihoeflea, Actinotalea) that transformed V(V) to insoluble vanadium (IV) alleviated dissolved vanadium release. Nitrate/nitrite reduction and glutathione metabolisms contributed to V(V) immobilization primarily. Structural equation model analysis indicated that V(V) reducers had significant negative impacts on soluble V(V) in the leachate. This first-attempt study highlights the importance of soil microorganisms in immobilizing vanadium from industrial dusts, which is helpful to develop novel strategies to reduce their environmental risks associated to vanadium smelting process.

Efficient Vanadate Removal by Mg-Fe-Ti Layered Double Hydroxide

A series of novel layered double hydroxides (Mg-Fe-Ti-LDHs) containing Mg2+, Fe3+ and Ti4+ were prepared. The adsorption performance of Mg-Fe-Ti-LDHs on vanadate in aqueous solution was investigated and the effects of various factors on the adsorption process were examined, including initial vanadate concentration, adsorbent dosage, contact time, solution pH and coexisting ions. A preliminary discussion of the adsorption mechanism of vanadate was also presented. Results show that the adsorption efficiency of vanadate increased with the introduction of Ti4+ into the laminate of LDHs materials. The adsorption capacity of the materials also differed for different anion intercalated layers, and the Mg-Fe-Ti-LDHs with Cl− intercalation showed higher vanadate removal compared to the CO32− intercalated layer. Furthermore, Mg-Fe-Ti-CLDH showed higher vanadate removal compared to pre-calcination. The adsorption experimental data of vanadate on Mg-Fe-Ti-LDHs were consistent with the Langmuir adsorption isotherm model and the adsorption kinetics followed a pseudo-second order kinetic model. The pH of the solution significantly affected the vanadate removal efficiency. Meanwhile, coexisting ions PO43−, SO42− and NO3− exerted a significant influence on vanadate adsorption, the magnitude of the influence was related to the valence state of the coexisting anions. The possible adsorption mechanisms can be attributed to ion exchange and layered ligand exchange processes. The good adsorption capacity of Mg-Fe-Ti-LDHs on vanadate broadens the application area of functional materials of LDHs.

A Clean Method for Vanadium (V) Reduction with Oxalic Acid

Water pollution deteriorates ecosystems and is a great threat to the environment. The environmental benefits of wastewater treatment are extremely important to minimize pollutants. Here, the oxalic acid used as reductant was used to treat the wastewater which contained high concentration of vanadium (V). Nearly 100% of vanadium was efficiently reduced at selected reaction conditions. The optimization results simulated by response surface methodology (RSM) analysis indicated the parameters all had significant effects on the reduction process, and followed the order: dosage of oxalic acid > reaction temperature > reaction time > initial pH of vanadium-containing wastewater. The reduction behavior analysis indicated that the pseudo first-order kinetics model could describe well the reduction process with Ea = 42.14 kJ/mol, and was described by the equation as followed: −LnC=K0·[pH]0.1016·[n(O)/n(V)]2.4569·[T]2.2588·exp(−42.14/T)·t.

Biosorption of V(V) onto Lantana camara biochar modified by H3PO4: Characteristics, mechanism, and regenerative capacity

Biochar has been widely recognized as an environmentally efficient adsorbent for removing heavy metals. However, considering the weak adsorption performance of the original biochar to the oxygen-containing anion, the adsorption of vanadium by biochar has rarely been investigated. This study proposes that H₃PO₄ activated biochar made from an invasive plant species growing near mines is a novel material to be investigated for V(V) recovery and reuse. As a noxious, invasive plant, Lantana camara L. (LC) has become widely naturalized around the world. Biochar was prepared from LC by pyrolysis at different conditions (200 °C, 350 °C, 500 °C, and 650 °C). The adsorption effect of biochar with and without P pretreatment on V(V) in aqueous solution was compared. The results show that biochar prepared from LC impregnated with H₃PO₄ (MLBC) had the highest adsorption capacity at 500 °C, and the maximal adsorption capacity fitted by Langmuir model was 77.38 mg g^-1, which was considerably higher than that of untreated biochar (LBC, 5.89 mg g^-1). The adsorption procedure was substantially fitted by the Langmuir isotherm and the pseudo-second-order kinetic. Additionally, the interaction of V(V) on MLBC is pH-dependent, and slightly acidic conditions are more favorable for adsorption. The characterization results indicated that electrostatic interaction, complexation reaction, and redox reaction were the primary mechanisms. After three cycles of adsorption, the final maximal adsorption capacity of MLBC remained at 76.03% of that of the virgin sample, demonstrating that MLBC had a recyclable capability to eliminate and restore V(V) from aqueous solutions.

Effect of vanadium on Lactuca sativa L. growth and associated health risk for human due to consumption of the vegetable

Elevated vanadium in the environment adversely affects organisms, including plants, animals, and humans. Plants act as the main conduit for environmental vanadium to enter the food chain, and simultaneously their growth response characteristics reflect vanadium toxicity efficacy for plants. The aim of the present study is to investigate lettuce (Lactuca sativa L.) growth involving morphological change, physiological adjustment, vanadium accumulation under vanadium stress, and the potential health risk (expressed as health risk index (HRI)) of adults and children who consume it. Lettuce was grown in nutrient solution with 0, 0.1, 0.5, 2.0, and 4.0 mg L-1 of pentavalent vanadium [V(V)]. Results showed that 0.1 mg L-1 V did not significantly affect lettuce growth versus control, and marked depression arose at ≥ 0.5 mg L-1 V. Foliar proline increased rapidly at ≥ 0.5 mg L-1 V. No striking change emerged in leaf cell membrane permeability at all treatments. V(V) and total vanadium concentration in plant tissues were ordered as root > stem > leaf, while tetravalent vanadium [V(IV)] was leaf > root > stem. No health risk (HRI < 1) exists for adults and children who consume lettuce at control treatment. However, the health risk occurs (HRI ˃ 1) when they both ingest the seedlings exposed to ≥ 0.1 mg L-1 V, and the risk overall markedly increases with increasing vanadium. Therefore, enough attention needs to be paid to the human health associated with the ingestion of vegetables like lettuce grown in substrata contaminated by vanadium.

Application of Ion Exchangers with the N-Methyl-D-Glucamine Groups in the V(V) Ions Adsorption Process

The adsorption capacities of ion exchangers with N-methyl-D-glucamine (NMDG) groups (Amberlite IRA 743, Lewatit MK 51, Purolite S110 and Purolite S108) relative to V(V) ions were tested in a batch system, taking into account the influence of various parameters, such as the adsorbent mass (0.05-0.20 g), phase contact time (1-240 min), initial concentration (10-150 mg/L), and temperature (293-333 K), as well as in a column system where the variable operating parameters were initial concentration (50, 100 mg/L), bed volume (10, 100 mL) and flow rate (0.6, 6 mL/min). Pseudo-first order, pseudo-second order, intraparticle diffusion and Boyd models were used to describe the kinetic studies. The best fit was obtained for the pseudo-second order model. The Langmuir, Freundlich and Temkin adsorption models were used to describe the equilibrium data to acquire better knowledge about the adsorption mechanism. The thermodynamic parameters were also calculated, which showed that the studied processes are endothermic, spontaneous and thermodynamically favorable. The physicochemical properties of the ion exchangers were characterized by nitrogen adsorption/desorption analyses, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photo electron spectroscopy (XPS). The point of zero charge (pH_PZC) was also determined.

On the Potential of a Poly(vinylidenefluoride-co-hexafluoropropylene) Polymer Inclusion Membrane Containing Aliquat® 336 and Dibutyl Phthalate for V(V) Extraction from Sulfate Solutions

A polymer inclusion membrane (PIM) composed of 50 wt% base polymer poly(vinylidenefluoride-co-hexafluoropropylene), 40 wt% extractant Aliquat^® 336, and 10 wt% dibutyl phthalate as plasticizer/modifier provided the efficient extraction of vanadium(V) (initial concentration 50 mg L⁻¹) from 0.1 M sulfate solutions (pH 2.5). The average mass and thickness of the PIMs (diameter 3.5 cm) were 0.057 g and 46 μm, respectively. It was suggested that V(V) was extracted as VO₂SO₄⁻ via an anion exchange mechanism. The maximum PIM capacity was estimated to be ~56 mg of V(V)/g for the PIM. Quantitative back-extraction was achieved with a 50 mL solution of 6 M H₂SO₄/1 v/v% of H₂O₂. It was assumed that the back-extraction process involved the oxidation of VO₂⁺ to VO(O₂)⁺ by H₂O₂. The newly developed PIM, with the optimized composition mentioned above, exhibited an excellent selectivity for V(V) in the presence of metallic species present in digests of spent alumina hydrodesulfurization catalysts. Co-extraction of Mo(VI) with V(V) was eliminated by its selective extraction at pH 1.1. Characterization of the optimized PIM was performed by contact angle measurements, atomic-force microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis/derivatives thermogravimetric analysis and stress–strain measurements. Replacement of dibutyl phthalate with 2-nitrophenyloctyl ether improved the stability of the studied PIMs.

Recent advances in removal techniques of vanadium from water: A comprehensive review

In recent years, with the development of economy and industry, water contaminated with heavy metal has become a global environmental problem. Vanadium (V) is an emerging contaminant reported in wastewater along with the increasing mining, smelting and recovering of vanadium ores and application in many fields as a significant national strategy resource. The increasing attention has been paid to the separations of V from water due to its potential toxic to animals and human beings. In the present study, the most common V removal techniques including adsorption, microbiological treatment, chemical precipitation, solvent extraction, electrokinetic remediation, photocatalysis, coagulation and membrane filtration are presented with discussion of their advantages, limitations and the recent achievements. Several major influencing factors and mechanisms of various processes have been briefly analyzed. Some research perspectives are proposed for improving the capacities to remove V from water. The core objective of this review is to provide comprehensive information or database for the superior approach for V removal.

Vanadium pollution and health risks in marine ecosystems: Anthropogenic sources over natural contributions

Vanadium has been classified as a potentially toxic metal and has been given limited attention in comparison to similar trace metals. Similarly, worldwide and continental vanadium pollution and risks remain contested. Here, we synthesized the worldwide concentration of vanadium in marine ecosystems with the relevant ecological and human health risks. We found that vanadium in biota and seawater collected from Asia shows significant increases over the temporal analysis, with rates similar to those reported for vanadium consumption and production. Furthermore, invertebrates have a higher concentration of vanadium than fishes. Similarly, we demonstrate that sediments classified as polluted have concentrations that are not directly correlated with the highest concentrations across continents. Finally, ecological risks were higher from seawater, with potential impacts to 55% of aquatic species in Asia estimated from chronic species sensitivity distribution (SSD). The concentration endangering only 5% of seawater species (HC5) was estimated as 1.13 (0.05-21.19) μg L^-1. Estimated daily intakes revealed that overall, there are none to low health risks from aquatic product consumption, yet high risks are plausible to children with consumption patterns in the 95th percentile.

The role of available phosphorous in vanadate decontamination by soil indigenous microbial consortia

Indigenous microbial consortia are closely associated with soil inherent components including nutrients and minerals. Although indigenous microbial consortia present great prospects for bioremediation of vanadate [V(V)] contaminated soil, influences of some key components, such as available phosphorus (AP), on V(V) biodetoxification are poorly understood. In this study, surface soils sampled from five representative vanadium smelter sites were employed as inocula without pretreatment. V(V) removal efficiency ranged from 81.7 ± 1.4% to 99.5 ± 0.2% in batch experiment, and the maximum V(V) removal rates were positively correlated with AP contents. Long-term V(V) removal was achieved under fluctuant hydrodynamic and hydrochemical conditions in column experiment. Geobacter and Bacillus, which were found in both original soils and bioreactors, catalytically reduced V(V) to insoluble tetravalent vanadium. Phosphate-solubilizing bacterium affiliated to Gemmatimonadaceae were also identified abundantly. Microbial functional characterization indicated the enrichment of phosphate ABC transporter, which could accelerate V(V) transfer into intercellular space for efficient reduction due to the structural similarity of V(V) and phosphate. This study reveals the critical role of AP in microbial V(V) decontamination and provides promising strategy for in situ bioremediation of V(V) polluted soil.

Application of layered double hydroxide enriched with electron rich sulfide moieties (S2O42-) for efficient and selective removal of vanadium (V) from diverse aqueous medium

The preparation of an adsorbent with highest efficiency, selectivity and stability is usually a challenging task. Herein, we prepared a thio functionalized layered double hydroxide (LDH) denoted as S₂O₄ LDH by intercalating a strong reducing agent (S₂O₄^2-) in the interlayers of trimetallic LDH and was applied to capture vanadium (V(V)) oxyanions from aqueous medium of diverse conditions. The successful preparation of the adsorbent was first confirmed using XRD, FTIR, EDX and CHS analyses. The results revealed that the modified LDH showed excellent performance at a wider pH range which can avoid the tedious work of adjusting pH in actual industrial wastewater treatment. The adsorption capacity was increased with temperature and obtained 379.55 mg/g at 323 K comparing to 112.3 mg/g at 293 K. The adsorption isotherm was better fitted to Langmuir model which suggested monolayer adsorption behavior. At lower temperature (293 K), the sorption kinetics were fitted to a pseudo-first order reaction model which implied physisorption reaction while at higher temperatures (303 and 323 K), the reaction order fitted to pseudo-second order reaction model which highlighted the chemisorption reaction mechanism. As confirmed using XRD, FTIR, EDX and XPS instrumental techniques, the dominant removal mechanism of V(V) involved ion-exchange and partial reduction reactions to nontoxic and less soluble V(IV) and V(III) species due to the low valent sulfur group and followed adsorption in S₂O₄ LDH. The prepared adsorbent showed very good selectivity towards V(V) in the presence of different co-existing ions both in synthetic wastewater and spiked real water samples. This novel adsorbent also exhibited high recyclability and obtained >90.0% removal of V(V) after four consecutive adsorption-desorption cycles due to the unique memory effect of the LDH. We believe that this strategy provides a new direction to find highly efficient and selective materials for capturing vanadium ions from wastewater of diverse conditions.

Profiling of Microbial Communities in the Sediments of Jinsha River Watershed Exposed to Different Levels of Impacts by the Vanadium Industry, Panzhihua, China

The mining, smelting, manufacturing, and disposal of vanadium (V) and associated products have caused serious environmental problems. Although the microbial ecology in V-contaminated soils has been intensively studied, the impacted watershed ecosystems have not been systematically investigated. In this study, geochemistry and microbial structure were analyzed along ~30 km of the Jinsha River and its two tributaries across the industrial areas in Panzhihua, one of the primary V mining and production cities in China. Geochemical analyses showed different levels of contamination by metals and metalloids in the sediments, with high degrees of contamination observed in one of the tributaries close to the industrial park. Analyses of the V4 hypervariable region of 16S rRNA genes of the microbial communities in the sediments showed significant decrease in microbial diversity and microbial structure in response to the environmental gradient (e.g., heavy metals, total sulfur, and total nitrogen). Strong association of the taxa (e.g., Thauera, Algoriphagus, Denitromonas, and Fontibacter species) with the metals suggested selection for these potential metal-resistant and/or metabolizing populations. Further co-occurrence network analysis showed that many identified potential metal-mediating species were among the keystone taxa that were closely associated in the same module, suggesting their strong inter-species interactions but relative independence from other microorganisms in the hydrodynamic ecosystems. This study provided new insight into the microbe-environment interactions in watershed ecosystems differently impacted by the V industries. Some of the phylotypes identified in the highly contaminated samples exhibited potential for bioremediation of toxic metals (e.g., V and Cr).

Contemporary Techniques for Remediating Endocrine-Disrupting Compounds in Various Water Sources: Advances in Treatment Methods and Their Limitations

Over the years, the persistent occurrence of superfluous endocrine-disrupting compounds (EDCs) (sub µg L⁻¹) in water has led to serious health disorders in human and aquatic lives, as well as undermined the water quality. At present, there are no generally accepted regulatory discharge limits for the EDCs to avert their possible negative impacts. Moreover, the conventional treatment processes have reportedly failed to remove the persistent EDC pollutants, and this has led researchers to develop alternative treatment methods. Comprehensive information on the recent advances in the existing novel treatment processes and their peculiar limitations is still lacking. In this regard, the various treatment methods for the removal of EDCs are critically studied and reported in this paper. Initially, the occurrences of the EDCs and their attributed effects on humans, aquatic life, and wildlife are systematically reviewed, as well as the applied treatments. The most noticeable advances in the treatment methods include adsorption, catalytic degradation, ozonation, membrane separation, and advanced oxidation processes (AOP), as well as hybrid processes. The recent advances in the treatment technologies available for the elimination of EDCs from various water resources alongside with their associated drawbacks are discussed critically. Besides, the application of hybrid adsorption–membrane treatment using several novel nano-precursors is carefully reviewed. The operating factors influencing the EDCs’ remediations via adsorption is also briefly examined. Interestingly, research findings have indicated that some of the contemporary techniques could achieve more than 99% EDCs removal.

Growth Responses and Accumulation of Vanadium in Alfalfa, Milkvetch Root, and Swamp Morning Glory and Their Potential in Phytoremediation

Pot experiments with alfalfa, milkvetch root and swamp morning glory were conducted to elucidate the effect of soil vanadium (V) on plant growth and to evaluate their phytoremediation potential under V(V) exposure. Based on biomass analysis, swamp morning glory showed higher tolerance than alfalfa and milkvetch root in response to different soil V(V) levels. The accumulation of V in plants increased with the increasing soil V and the V concentration in roots was 1.95-4.31 times that in shoots. After planting, soil total V, V(V), bioavailable V and water-soluble V all reduced, and the decreases in bioavailable V and V(V) showed significant. The decreased percentage of V(V) in total V in soils demonstrated that the planting process may stimulate the mechanism of V(V) reduction to V(IV). Therefore, the three tested plants, particularly swamp morning glory can be promising phytostabilizers applied to V phytoremediation practices.

Vanadium removal by cationized sawdust produced through iodomethane quaternization of triethanolamine grafted raw material

In this study, two-step surface modification of sawdust using triethanolamine (at 180 °C) and iodomethane (at 42 °C) was performed to produce a novel quaternized biosorbent, TEA-I-SD. The characterization studies revealed significant morphological changes in the sawdust and successful quaternization with a nitrogen content of 5.75%. The highest vanadium removal (96.2%) was achieved at pH 4 (dosage 1 g/L, initial vanadium concentration 19.1 mg/L). Equilibrium was achieved within 8 h of contact time and the adsorption kinetics were well fitted with the pseudo-second-order model. Both film diffusion and intra-particle diffusion contributed to the adsorption process, while the latter was the rate-limiting step. The maximum vanadium adsorption capacity of TEA-I-SD (35.0 mg/g, pH 4) was close to the theoretical value obtained from the Langmuir model. The best fit was achieved with the Redlich-Peterson model, exhibiting a monolayer adsorption phenomenon. Tests with real mine water containing 11 mg/L of vanadium also confirmed its high removal (91.3%, dosage 1 g/L) using TEA-I-SD at pH 4. The TEA-I-SD could be reused three times without significant capacity loss after regeneration, although the desorption efficiency was rather low (synthetic solution: 38.5-40.5% and mine water: 26.2-43.1%).

Pilot-scale field study for vanadium removal from mining-influenced waters using an iron-based sorbent

This study investigated the removal of vanadium from mining waters at a closed mine site (Mustavaara, Finland) using granular ferric oxyhydroxide (CFH-12) on pilot scale. Two filter systems, pilot A and pilot B, were placed in different streams, where the influent in pilot A contained a higher and very variable vanadium concentration (6.46-99.1 mg/L), while the pilot B treated influent had lower vanadium concentrations (0.443-2.33 mg/L). The operation periods were 51 days for pilot A and 127 days for pilot B. Water quality analyses revealed that vanadium was efficiently captured in the filter system in both pilots. X-ray fluorescence analysis revealed that the filter beds were not fully saturated with vanadium. X-ray photoelectron spectroscopy confirmed that oxidised vanadium (5⁺) existed in the used CFH-12 and the carbon content in the used material had increased due to the adsorbed organic compounds. For comparison, lab-scale coagulation experiments were conducted using ferric sulphate for the influent of pilot A (the sampled batch contained 15.9 mg/L V). The optimum coagulant dosage was 350 mg/L (>93% vanadium removal) at the original pH (7.8-7.9) of the influent, whereas the required coagulant amount decreased when the influent pH was adjusted to 4.6-4.8.

Development of functional lignin-based spherical particles for the removal of vanadium(V) from an aqueous system

A new type of functional lignin-based spherical particles (L-CTAB) prepared with the use of hexadecyltrimethylammonium bromide (CTAB) was applied as an effective biosorbent for removing vanadium(V) ions. The porous structure, characteristic functional groups, electrokinetic stability, morphology and size of the L-CTAB particles were examined. The conditions of removal were also investigated, including pH (2-12), sorbent mass (0.1-0.5 g), concentration (10-100 mg/dm3), phase contact time (1-240 min) and temperature (293-333 K). At pH 5.0 the maximum sorption percentage (%S) of V(V) was 45%, while at pH 2.0 it was 32%. The maximum sorption capacity of V(V) for L-CTAB was found to be 10.79 mg/g. The kinetic data indicate that the sorption followed the pseudo-second-order and film diffusion models. Sorption equilibrium for V(V) ions removal by L-CTAB was reached after 60 min at the initial concentrations 10 and 50 mg/dm³. It has been shown that the adsorption of V(V) ions on the surface of L-CTAB is a heterogeneous, endothermic and spontaneous reaction, as evidenced by the calculated values of thermodynamic parameters - free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) - for the tested systems at different temperatures. HCl solutions, used as an L-CTAB regeneration agent, quantitatively eluted V(V) ions.

Determination of Vanadium Isotope Compositions in Carbonates Using an Fe Coprecipitation Method and MC-ICP-MS

Vanadium isotope compositions (δ(⁵¹V)) in marine carbonates are a potential proxy to trace global redox states of ancient oceans. Although high-precision δ(⁵¹V) analyses are available for many geological materials, carbonate-hosted δ(⁵¹V) data have not been reported yet due to extremely high matrix elements and low V contents (generally below 10 μg g^-1). In this study, we developed an Fe coprecipitation method combined with an Fe column to preconcentrate V from the major matrix elements and subsequent four-step chromatographic procedures to further purify V in carbonates. The δ(⁵¹V) values were measured using a sample-standard bracketing method by MC-ICP-MS. The robustness of this method was assessed by analyzing element-doped and matrix-spiked synthetic carbonate solutions containing an in-house δ(⁵¹V) standard, USTC-V. The mean δ(⁵¹V) value of the synthetic carbonate solutions (0.06 ± 0.08‰; 2SD, n = 33) is in good agreement with the recommended value of the USTC-V relative to the Oxford AA solution (0.07 ± 0.08‰; 2SD, n = 347). In addition, the consistency in the δ(⁵¹V) value of the igneous carbonatite standard, COQ-1, which was processed in parallel with the whole purification (-0.48 ± 0.04‰; 2SD, n = 3) and a four-step chromatographic procedure (-0.43 ± 0.08‰; 2SD, n = 3), further validates the robustness of our method. For the first time, we obtained δ(⁵¹V) values of four carbonate reference materials: JDo-1, -0.56 ± 0.09‰ (2SD, n = 27); JLs-1, -0.61 ± 0.14‰ (2SD, n = 33); GBW07217a, -0.79 ± 0.09‰ (2SD, n = 6); GBW07214a, -0.51 ± 0.13‰ (2SD, n = 48). The long-term external precision of carbonate-hosted δ(⁵¹V) analyses is better than ±0.14‰ (2SD). Our method can be applied to measure carbonate-hosted δ(⁵¹V) to trace the evolution in global marine redox states throughout the Earth's history.

Sorption and Desorption of Vanadate, Arsenate and Chromate by Two Volcanic Soils of Equatorial Africa

Sorption of oxyanions by soils and mineral surfaces is of interest due to their role as nutrients or pollutants. Volcanic soils are variable charge soils, rich in active forms of aluminum and iron, and capable of sorbing anions. Sorption and desorption of vanadate, arsenate, and chromate by two African andosols was studied in laboratory experiments. Sorption isotherms were determined by equilibrating at 293 K soil samples with oxyanion solutions of concentrations between 0 and 100 mg L−1 V, As, or Cr, equivalent to 0−2.0 mmol V L−1, 0−1.3 mmol As L−1, and 0−1.9 mmol Cr L−1, in NaNO3; V, As, or Cr were determined by ICP-mass spectrometry in the equilibrium solution. After sorption, the soil samples were equilibrated with 0.02 M NaNO3 to study desorption. The isotherms were adjusted to mathematical models. After desorption with NaNO3, desorption experiments were carried out with a 1 mM phosphate. The sorption of vanadate and arsenate was greater than 90% of the amount added, while the chromate sorption was much lower (19–97%). The sorption by the Silandic Andosol is attributed to non-crystalline Fe and Al, while in the Vitric Andosol, crystalline iron species play a relevant role. The V and Cr sorption isotherms fitted to the Freundlich model, while the As sorption isotherms conformed to the Temkin model. For the highest concentrations of oxyanions in the equilibrating solution, the sorbed concentrations were 37–38 mmol V kg−1, 25 mmol As kg−1, and 7.2–8.8 mmol Cr kg−1. The desorption was low for V and As and high for Cr. The comparison of the sorption and desorption isotherms reveals a pronounced hysteresis for V in both andosols and for Cr in the Silandic Andosol. Phosphate induced almost no V desorption, moderate As desorption, and considerable Cr desorption.

Accumulation of vanadium and arsenic by cast iron pipe scales under drinking water conditions: A batch study

Metal pollutants accumulation in the scales of drinking water distribution systems presents a potential threat to water quality. Therefore, a study was carried out on the accumulation of V(V) and As(V) by cast iron pipe scales. The accumulation of V(V) and As(V) by scales and the effects of scale dosage, pH, temperature, and anion content on the accumulation process were assessed. Results showed that scales could rapidly accumulate V(V) and As(V), with maximum accumulation amounts of 3.94 mg/g and 3.90 mg/g, respectively. An increase in pH (from 3.0 to 9.0) and sulfate concentration (from 0 to 250 mg/L) decreased V(V) and As(V) accumulation by scales. Increased chloride ion concentrations (from 0 to 250 mg/L) reduced the amount of As(V) accumulated, while increasing the amount of V(V) accumulated. The V(V) and As(V) accumulation kinetics were well described by the Elovich model, with thermodynamic and accumulation isotherms showing that the accumulation process occurred via an entropic endothermic reaction. The mechanisms of accumulation of V(V) and As(V) by the scales include surface complexation, ligand exchange, electrostatic attraction and repulsion, and competitive adsorption.

A global systematic review, meta-analysis, and risk assessment of the concentration of vanadium in drinking water resources

The presence of toxic metals such as vanadium in water resources has attracted considerable attention as a new concern in international health. Systematic review and meta-analysis were performed to assess the concentration of vanadium in water resources along with the relevant ecological risk assessment. Databases of Scopus, PubMed, and Embase were investigated to retrieve the related articles from January 01, 1974 to December 25, 2019. Twenty-eight articles containing 152 samples from 24 countries were included. Furthermore, the meta-analysis was conducted by the approach of z-score to estimate differences in the effect size. In addition, the mean of concentrations of vanadium was applied to calculate the risk assessment only to the water surface and choose the maximum environmental concentration (MEC) for demonstrate a worst-case scenario. Here, the risk assessment approach was used to show that the MEC of vanadium confirm the risk it for aquatic ecosystems, being fish (e.g., Danio rerio) our model organism due to their sensibility. According to findings, the MEC of vanadium in surface water varied from 0.010 μg L^-1 (USA) and 68 μg L^-1 (China), with an overall mean of 6.21 ± 13.3 μg L^-1 (mean ± standard deviation). The ecological risk assessment demonstrated that people living in some countries such as China and Japan were at an adverse ecological risk of vanadium in the water resources. Hence, essential control plans besides adequate removal techniques must be implemented for significant deracination of heavy metals like vanadium.

Ultrasonic-assisted synthesis of SiO2 nanoparticles and SiO2/chitosan/Fe nanocomposite and their application for vanadium adsorption from aqueous solution

The husk of brown rice, as a source of silica, was applied to synthesize natural SiO₂ nanoparticles via sonochemical method. SiO₂/CH/Fe nanocomposite was synthesized from SiO₂, chitosan (prepared from shrimp shells via sonochemical method), and iron functional groups and detected using BET, EDX-SEM, and FTIR techniques. These natural-based nanostructures (SiO₂ and SiO₂/CH/Fe) have been applied for vanadium adsorption. The influences of initial pH, initial concentration, and adsorption time were studied via a batch process. The analysis of the kinetics data indicated that the chemical adsorption is predominant. The analysis of the equilibrium data indicated the single layer and exothermic adsorption process. The mono-layer adsorption capacity of SiO₂/CH/Fe was 199.540 mg g^-1. The performance of SiO₂/CH/Fe in a continuous column system was investigated in four adsorption and desorption cycles. Results showed that SiO₂/CH/Fe nanocomposite synthesized with the sonochemical method is a candidate with high adsorption ability for use as an industrial adsorbent.

Sulfur-based Mixotrophic Vanadium (V) Bio-reduction towards Lower Organic Requirement and Sulfate Accumulation

Although remediation of toxic vanadium (V) [V(V)] pollution can be achieved through either heterotrophic or sulfur-based autotrophic microbial reduction, these processes would require a large amount of organic carbons or generate excessive sulfate. This study reported that by using mixotrophic V(V) bio-reduction with acetate and elemental sulfur [S(0)] as joint electron donors, V(V) removal performance was enhanced due to cooccurrence of heterotrophic and autotrophic activities. Deposited vanadium (IV) was identified as the main reduction product by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Based on 16S rRNA gene amplicon sequencing, qPCR and genus-specific reverse transcription qPCR, it was observed that V(V) was likely detoxified by heterotrophic V(V) reducers (e.g., Syntrophobacter, Spirochaeta and Geobacter). Cytochrome c, intracellular nicotinamide adenine dinucleotide and extracellular polymeric substances were involved in V(V) reduction and binding. Organic metabolites synthesized by autotrophs (e.g., Thioclava) with energy from S(0) oxidation might compensate electron donors for heterotrophic V(V) and sulfate reducers. Less sulfate was accumulated presumably due to activities of sulfur-respiring genera (e.g., Desulfurella). This study demonstrates mixotrophic microbial V(V) reduction can save organic dosage and avoid excessive sulfate accumulation, which will be beneficial to bioremediation of V(V) contamination.

Growth responses, accumulation, translocation and distribution of vanadium in tobacco and its potential in phytoremediation

The metal tolerance mechanism of plants is of great importance to explore the plant-based clean-up of environmental substrata contaminated by heavy metals. Indoor experiment of tobacco (Nicotiana tabacum L.) seedlings growing hydroponically in nutrient solution containing 0, 0.1, 0.5, 2.0, and 4.0 mg L-1 V was conducted. The results indicated that plant overall growth performance was significantly affected at ≥ 2.0 mg L-1 V. Oxidative stress degree as indicated by foliar O2-· and H2O2 content intensified markedly at ≥ 0.5 mg L-1 V treatments. In response, the plant activated its enzyme and non-enzyme protecting mechanism to cope with oxidative stress inflicted by vanadium. The activities of antioxidant enzymes, including SOD, POD, CAT, APX, and the concentration of non-enzyme antioxidants, e.g., AsA and GSH were all conspicuously (p < 0.5 or p < 0.1) enhanced at ≥ 0.5 mg L-1 V treatments. Vanadium accumulated in leaves, stems, and roots increased with increasing vanadium level. The majority of the absorbed vanadium retained in plant root, and minor portions were transferred to aerial parts. Vanadium concentration in plant tissues ordered as root ˃ stem ˃ leaf. Translocation factors (TF) in vanadium-treated tobaccos (TF « 1) were significantly lower than that of control (TF ˃ 1). In conclusion, although vanadium at ≥ 2.0 mg L-1 inhibited plant growth, tobacco exhibited a relatively good vanadium tolerance through self-adaptive regulation and has the potential as a phytostabilizer in decontaminating the environment contaminated by vanadium.

Predicting breakthrough of vanadium in fixed-bed absorbent columns with complex groundwater chemistries: A multi-component granular ferric hydroxide-vanadate-arsenate-phosphate-silicic acid system

Granular ferric hydroxide (GFH) is often used for fixed bed adsorbent (FBA) columns in groundwater purification units around the world to remove arsenate contaminations. Groundwater can contain also other toxic (e.g., antimonite and vanadate) and non-toxic oxo-anions (phosphate and silicic acid) that are known to affect FBA lifetimes. Therefore, understanding the breakthrough of toxic compounds intended for removal by FBA is essential to their design, and is important to predict accurately breakthrough curves (BTCs) for FBAs in waterworks to plan future operating costs. Rapid small-scale column tests (RSCCT) and pilot-scale FBA were used to simulate vanadate BTCs for complex groundwater chemistries. The BTCs were simulated successfully using a homogeneous surface diffusion model (HSDM) combining equilibrium chemical adsorption and kinetic mass transfer. Adsorption parameters for various groundwater compositions were predicted using the CD-MUSIC surface complexation model, which was set up for the first time for akaganéite-based granular ferric hydroxide with a competitive multi-solute system. The results indicated that V(V) is less prone to competitive adsorption effects, and use of the homogeneous surface diffusion model to predict the BTCs requires then the kinetic mass transfer Biot number to be used as the only fitting parameter. On the other hand, a concentration overshoot could be observed for the two weaker absorbed oxo-anions arsenate and phosphate because of displacement by the vanadate. Results of pilot scale test column BTCs of vanadate for three waterworks with different groundwater compositions could be favorably extrapolated with a unique Freundlich constant k_F of 3.2 derived on basis of the multi-solute CD-MUSIC model, and a unique Biot number of 37 fixed for all three different test sites.

Microbial vanadate reduction coupled to co-metabolic phenanthrene biodegradation in groundwater

Vanadate [V(V)] and phenanthrene (PHE) commonly coexist in groundwater aquifer, posing potential threats to ecological environment and public health. However, little is known about the complicated biogeochemical processes involving microbial V(V) reduction coupled with co-metabolic PHE biodegradation. Herein we demonstrated that synchronous removal of V(V) and PHE could be realized under anaerobic condition. Complete V(V) removal and PHE degradation efficiency of 82.0 ± 0.8% were achieved in 7-d operation in batch experiment. 250-d continuous column experiment implied that hydrochemical condition affected V(V) and PHE removals. V(V) was reduced to insoluble vanadium (IV) and PHE was degraded into small molecule organics (e.g. salicylic acid). Geobacter and Acetobacterium used methanol and intermediates from PHE degradation as electron donors for V(V) reduction. PHE was decomposed by Mycobacterium and Clostridium with methanol as co-metabolic substrate and V(V) as electron acceptor. Genes encoding proteins for V(V) reduction (omcA, omcB and mtrC) and PHE degradation (phnAc) were upregulated. Cytochrome c and nicotinamide adenine dinucleotide promoted electron transfer for V(V) and PHE detoxification. Extracellular polymeric substances could bind V(V) and improve the bioavailability of PHE. Our findings provide a robust strategy for remediation of V(V) and PHE co-contaminated groundwater.

Spatiotemporal vanadium distribution in soils with microbial community dynamics at vanadium smelting site

Whereas the adverse effects of vanadium released from smelting activities on soil microbial ecology have been widely recognized, little is known about spatiotemporal vanadium distribution and microbial community dynamics in typical contaminated sites. This study describes vanadium contents associated with health risk and microbial responses in both topsoil and subsoil during four consecutive seasons around an ongoing-production smelter in Panzhihua, China. Higher levels of vanadium concentration exceeding soil background value in China (82 mg/kg) were found close to the smelter. Vanadium concentrations decreased generally with the increase in distance to the smelter and depth below surface, as soil vanadium pollution is induced mainly by atmospheric deposition of vanadium bearing dust during smelting. Residual fraction was the predominated vanadium form in soils, with pronounced increase in bioavailable vanadium during rainfall period due to frequent drought-rewetting process. Topsoil close to the smelter exhibited significant contamination, inducing high probability of adverse health effects. Spatiotemporal vanadium distribution creates filtering effects on soil microorganisms, promoting metal tolerant genera in topsoil (e.g. Microvirga) and subsoil (e.g. Bacillus, Geobacter), which is the key in maintaining the community structure by promoting cooperative relation with other taxa. Our results reveal spatiotemporal vanadium distribution in soils at site scale with potential health risk and microbial responses, which is helpful in identifying severe contamination and implementing bioremediation.

Electrochemical Selective Recovery of Heavy Metal Vanadium Oxyanion from Continuously Flowing Aqueous Streams

An electrochemical flow cell with redox-active electrodes was used for selective removal and recovery of vanadium(V) oxyanions from aqueous streams. The cell relies on intrinsic affinity of the redox-active polymer poly(vinyl)ferrocene (PVFc) and demonstrates selectivity of >10 towards vanadium compared to a background electrolyte in 40-fold abundance. We demonstrate highly selective vanadium removal in the presence of various competing anions (i.e., fluoride, bromide, nitrate, and sulfate). Surface elemental analysis reveals significant correlation between PVFc moieties and vanadium-rich regions after adsorption, corroborating the central role of PVFc modulation on vanadium separation. We further propose a vanadium speciation mechanism in which high and low pH environments during adsorption and desorption steps favor formation of, respectively, H2 VO3 - / HVO4 2- and H2 VO3 - / H3 VO4 / VO2 + . Results have implications for the development and optimization of flow devices, as per our observations, excessively low pH environments during desorption can lead to subsequent re-adsorption of cationic vanadium(V).

Lead immobilization by phosphate in the presence of iron oxides: Adsorption versus precipitation

As a commonly used corrosion inhibitor, phosphate (PO₄) has a complicated effect on the fate and transport of lead (Pb) in drinking water systems. While the formation of pyromorphite has been recognized to be the major driving force of the Pb immobilization mechanism, the role of adsorption on iron oxides is still not clear. This study aims to clarify the contributions of adsorption and precipitation to Pb removal in a system containing both iron oxides and PO₄. A combination of batch experiments, X-ray absorption spectroscopy, infrared spectroscopy, and electron spectroscopy was employed to distinguish the adsorbed and precipitated Pb species. The results indicated that the adsorption of Pb on iron oxides still occurred even when the solution was supersaturated to pyromorphite (i.e., 5 mg/L P with 0.1-30 mg/L Pb in 0.01 M NaCl solution at neutral pH). In the tap water containing 0.92 mg/L P and 1 mg/L Pb, adsorption on iron oxides contributed more (62-67%) than precipitation (33-38%) in terms of Pb removal. Surprisingly, the pre-formed pyromorphite is transformed to adsorbed species after mixing with iron oxides in water for 24 h. The illustration of this transformation is important to understand the immobilization mechanisms and transport behaviors of Pb in drinking water systems after the utilization of PO₄.