Adsorption-desorption and co-migration of vanadium on colloidal kaolinite

A molecular extraction process for vanadium based on tandem selective complexation and precipitation

Recycling vanadium from alternative sources is essential due to its expanding demand, depletion in natural sources, and environmental issues with terrestrial mining. Here, we present a complexation-precipitation method to selectively recover pentavalent vanadium ions, V(V), from complex metal ion mixtures, using an acid-stable metal binding agent, the cyclic imidedioxime, naphthalimidedioxime (H2CIDIII). H2CIDIII showed high extraction capacity and fast binding towards V(V) with crystal structures showing a 1:1 M:L dimer, [V2(O)3(C12H6N3O2)2]2-, 1, and 1:2 M:L non-oxido, [V(C12H6N3O2)2] ̶ complex, 2. Complexation selectivity studies showed only 1 and 2 were anionic, allowing facile separation of the V(V) complexes by pH-controlled precipitation, removing the need for solid support. The tandem complexation-precipitation technique achieved high recovery selectivity for V(V) with a selectivity coefficient above 3 × 105 from synthetic mixed metal solutions and real oil sand tailings. Zebrafish toxicity assay confirmed the non-toxicity of 1 and 2, highlighting H2CIDIII's potential for practical and large-scale V(V) recovery.

Transport and retention of n-hexadecane in cadmium-/naphthalene-contaminated calcareous soil sampled in a karst area

Studying the transport of petroleum hydrocarbons in cadmium-/naphthalene-contaminated calcareous soils is crucial to comprehensive assessment of environmental risks and developing appropriate strategies to remediate petroleum hydrocarbons pollution in karst areas. In this study, n-hexadecane was selected as a model petroleum hydrocarbon. Batch experiments were conducted to explore the adsorption behavior of n-hexadecane on cadmium-/naphthalene-contaminated calcareous soils at various pH, and column experiments were performed to investigate the transport and retention of n-hexadecane under various flow velocity. The results showed that Freundlich model better described the adsorption behavior of n-hexadecane in all cases (R2 > 0.9). Under the condition of pH = 5, it was advantageous for soil samples to adsorb more n-hexadecane, and the maximum adsorption content followed the order of: cadmium/naphthalene-contaminated > uncontaminated soils. The transport of n-hexadecane in cadmium/naphthalene-contaminated soils at various flow velocity was well described by two kinetic sites model of Hydrus-1D with R2 > 0.9. Due to the increased electrostatic repulsion between n-hexadecane and soil particles, n-hexadecane was more easily able to breakthrough cadmium/naphthalene-contaminated soils. Compared to low flow velocity (1 mL/min), a higher concentration of n-hexadecane was determined at high flow velocity, with 67, 63, and 45% n-hexadecane in effluent from cadmium-contaminated soils, naphthalene-contaminated soils, and uncontaminated soils, respectively. These findings have important implications for the government of groundwater in calcareous soils from karst areas.

Role of tailing colloid from vanadium-titanium magnetite in the adsorption and cotransport with vanadium

The geochemical cycling of vanadium (V) in mining areas has attracted much attention. However, little knowledge was about the effects of tailing colloids on the fate and transport of vanadium in tailing reservoirs which was ignored before. This study investigated the interactions of tailing colloids from vanadium-titanium magnetite with vanadium. Colloid characterization, tailing leaching, adsorption, and column experiments of single and cotransport of tailing colloid with V were conducted. Results show that 98.08% V in the vanadium-titanium magnetite tailing was in the residual state with limited leachable V under various conditions. The adsorption of V to the tailing colloid was via electrostatic attraction and surface complexation on the heterogeneously distributed sorption sites on the colloid surface. The adsorption control step was the diffusion of V into the tailing colloid pores. The increase in pH and the decrease in ionic strength (IS) promoted the single transport of tailing colloid and V in quartz sand columns. In cotransport scenarios, V promoted the transport of tailing colloids via the surface coating effect. In contrast, the transport of V was retarded by the adsorbed tailing colloid on the quartz sand surface. The pre-adsorbed V in the column enhanced the subsequent transport of tailing colloids by electrical repulsion, while the pre-adsorbed tailing colloids facilitated the subsequent transport of V via cotransport of the released colloids with V. The high mobility of the tailing colloid and V and their cotransport in the porous media highly demonstrated the potential V pollution pathways that need to be taken into account.

Optimization of Carboniferous Egyptian Kaolin Treatment for Pharmaceutical Applications

This paper quantitatively determines the occurrences of potentially toxic elements in Carboniferous kaolin in southwestern Sinai, Egypt. This research describes, in detail, the experimental treatment optimization to be used in pharmaceutical applications. The concentrations of As, Co, Ni, Pb, and V in these kaolin deposits exceed the Permitted Concentrations of Elemental Impurities for oral use in pharmaceutical applications. Herein, six desorbing agents (acetic acid, citric acid, DTPA, EDDS, EDTA, and NTA) were utilized as extracting solutions in batch-wise extractions to select the proper reagents. Parameters such as the pH, the mixing speed and time, and the solid–solution ratio were varied to optimize the extraction conditions. The findings indicate that citric acid and EDTA were effective in the removal of the aforementioned elements. The results reveal that the optimum removal of potentially toxic elements from kaolin can be achieved using citric acid and EDTA concentrations of 0.2 M and 0.1 M, respectively, for the treatment of 5 g of kaolin, under a pH of 4 for citric acid, and a pH of 10 for EDTA. The ideal mixing speed and time are 500 rpm and 6 h, respectively. Using 1:10 S/L of citric acid and EDTA showed removal rates of 100% for all the investigated PTEs. We recommend this treatment for different kinds of kaolin showing various degrees of contamination.

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.

Experiments and simulation of co-migration of copper-resistant microorganisms and copper ions in saturated porous media

Heavy metal (HV) pollutants may migrate to the groundwater environment through leaching, causing groundwater pollution. Compared with surface water pollution, groundwater pollution is complex and hidden. Existing methods for treating HV pollution in the vadose zone have had limited application owing to various problems. In recent years, microorganisms have been used in the field of pollution control and remediation owing to their outstanding adsorption and degradation properties and low cost, but their environmental safety and behavior in porous media are still poorly understood. This study aimed to investigate the migration behavior and mechanisms of copper ions in saturated porous media under the action of copper-resistant microorganisms and to establish a corresponding numerical model to simulate the results. The key parameters of adsorption and migration were determined through batch adsorption and soil column experiments. A one-dimensional soil column was used to conduct a co-migration experiment using copper-resistant microorganisms and Cu²⁺ in water-saturated quartz sand, and a co-migration mathematical model was constructed. It was found that the existence of microorganisms had an inhibitory effect on the migration of Cu²⁺ in quartz sand, and Cu²⁺ promoted the migration of microorganisms, reduced their adsorption, and increased their concentration in the column experiment effluent. The selected solute transport mathematical model had a good fitting effect on the breakthrough curves of copper ion and copper-resistant microorganisms during their co-migration. The results can provide parameters and a theoretical basis for the risk assessment and prevention of HV pollution in the saturated zone or aquifers.

Simultaneous reduction and immobilization of Cr(VI) in seasonally frozen areas: Remediation mechanisms and the role of ageing

Among the toxic metals, hexavalent chromium [Cr(VI)] has attracted much attention due to its high mobility and toxicity, rendering considerable challenges for long-term remediation. In this study, the soil was collected from a dichromate contaminated industrial site in Liaoning Province, a seasonally frozen area in northern China, and subjected to frequent freeze-thaw cycles. Three additives, including (i) ferrous sulfate; (ii) calcium polysulfide; and (iii) combined biochar and calcium polysulfide were applied to reduce and immobilize Cr(VI) in the soils. The samples underwent 28 days of incubation followed by 16 freeze-thaw cycles. The toxicity characteristic leaching procedure (TCLP) and simulated acid rain leaching were adopted to test the remediation performances. It was observed that all three treatments can significantly reduce and immobilize Cr(VI) after short-term incubation, while biochar with abundant functional groups could adsorb and reduce Cr(VI) effectively. Notably, the concentration of Cr(VI) in TCLP leachates after incubation in combined treatment decreased by 67.87% and 37.27%, respectively, compared with the application of ferrous sulfate or calcium polysulfide alone. Freeze-thaw cycles induced the disintegration of soil particles and increased the risk of contaminant mobilization. Conversely, biochar particles has become finer and even produced nanoparticles with ageing, accompanied by the increase in oxygen-containing surface functional groups. Additionally, the specific surface area increased with the pyrolysis of biochar, which further enhanced the retention of soil colloidal particles and suppressed the migration of contaminants. Therefore, the cumulative release of Cr(VI) in the combined treatment (i.e., 10.97 ~ 32.97 mg/kg) was much lower than that of the other two treatments after freeze-thaw ageing. Overall, the combination of biochar and calcium polysulfide displayed advantages in the reduction and immobilization of Cr(VI), and offered a long-term, effective strategy for the remediation of Cr(VI) contaminated soils in cold regions.

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.