Selective recovery of vanadium and scandium by ion exchange with D201 and solvent extraction using P507 from hydrochloric acid leaching solution of red mud

A green extraction process for the selective recovery of Sc(iii) based on hydrophobic betaine derivative ionic liquids

The efficient extraction recovery of scandium (Sc(iii)) is crucial for its application in high-end technology. Two novel hydrophobic carboxylic acid ionic liquids (ILs), namely, [lauryl betaine][bis(trifluoromethanesulphonyl)imide] ([Laur][Tf2N]) and [cocamidopropyl betaine][bis(trifluoromethanesulphonyl)imide] ([Coca][Tf2N]), were synthesized using two inexpensive amphoteric surfactants as cation sources. [Laur][Tf2N] (257 °C) and [Coca][Tf2N] (251 °C) exhibited good thermal stability and strong hydrophobicity. The viscosity of [Coca][Tf2N] (4.29 × 103 mP s) was higher than that of [Laur][Tf2N] (2.55 × 103 mPa s) at 25 °C. The optimal extraction conditions were an extraction equilibrium time of 40 min, an initial Sc(iii) concentration of 0.001 mol L-1, a sodium nitrate concentration of 0.5 mol L-1, and a pH of 3. The extraction efficiency of [Laur][Tf2N] and [Coca][Tf2N] could even exceed 98.7% and 96.0%, respectively. The cation exchange extraction mechanism was studied by slope analysis, IR spectroscopy and 13C NMR spectroscopy. Sc(iii) extracted using [Laur][Tf2N] and [Coca][Tf2N] could be completely stripped with 0.1 mol L-1 and 0.2 mol L-1 HNO3 once, respectively. The structure of the ILs was not broken after stripping, and the extraction efficiency of the ILs remained almost unchanged after five cycles. In addition, the extraction differences at different pH levels made it possible to separate Sc(iii) from other rare earths using ionic liquids [Laur][Tf2N] and [Coca][Tf2N].

Recovery of valuable metals from red mud: A comprehensive review

As a bulk solid waste with high alkalinity, red mud (RM) not only occupies a large amount of land and requires high maintenance costs, but also unavoidably generates serious hazards to the surrounding ecological environment. The comprehensive treatment of RM has become an enormous challenge for the green, low-carbon and high-quality development of the global alumina industry. To minimize the RM destruction to the ecology and the waste of secondary resources, the sustainable utilization of RM was widely investigated in the past decades, especially for the recovery of valuable metals. This paper systematically summarized the research status of recycling valuable metals (Al, Fe, Na, Ti, Sc, Ga, V and RE) from RM in recent years. The recycling technology mainly includes physical beneficiation, hydrometallurgy, pyrometallurgy and electrodialysis. The technical principles and characteristics as well as the current problems of various recovery processes from RM were comprehensively introduced, and the future development directions of sustainable utilization were also prospected. The advantages and disadvantages based on the different aspects of recovery efficiency, energy consumption and environmental impact were also discussed. The proposal of new technologies for the harmless, high-value and full utilization of RM is beneficial to the future research on the comprehensive utilization of bulk industrial solid wastes.

Defining the optimal conditions using FFNNs and NARX neural networks for modelling the extraction of Sc from aqueous solution by Cryptand-2.2.1 and Cryptand-2.1.1

The main aim of this study is to figure out how well cryptand-2.2.1 (C 2.2.1) and cryptand-2.1.1 (C 2.1.1) macrocyclic compounds (MCs) work as novel extractants for scandium (Sc) by using an artificial neural network (ANN) models in MATLAB software. Moreover, C2.2.1 and C2.1.1 have never been evaluated to recover Sc. The independent variables impacting the extraction process (concentration of MC, concentration of Sc, pH, and time), and a nonlinear autoregressive network with exogenous input (NARX) and feed-forward neural network (FFNN) models were used to estimate their optimum values. The greatest obstacle in the selective recovery process of the REEs is the similarity in their physicochemical properties, specifically their ionic radius. The recovery of Sc from the aqueous solution was experimentally evaluated, then the non-linear relationship between those parameters was predictively modeled using (NARX) and (FFNN). To confirm the extraction and stripping efficiency, an atomic absorption spectrophotometer (AAS) was employed. The results of the extraction investigations show that, for the best conditions of 0.008 mol/L MC concentration, 10 min of contact time, pH 2 of the aqueous solution, and 75 mg/L Sc initial concentration, respectively, the C 2.1.1 and C 2.2.1 extractants may reach 99 % of Sc extraction efficiency. Sc was recovered from a multi-element solution of scandium (Sc), yttrium (Y), and lanthanum (La) under these circumstances. Whereas, at a concentration of 0.3 mol/L of hydrochloric acid, the extraction of Sc was 99 %, as opposed to Y 10 % and La 7 %. The Levenberg-Marquardt training algorithm had the best training performance with an mean-squared-error, MSE, of 5.232x10-6 and 6.1387x10-5 for C 2.2.1 and C 2.1.1 respectively. The optimized FFNN architecture of 4-10-1 was constructed for modeling recovery of Sc. The extraction process was well modeled by the FFNN with an R2 of 0.999 for the two MC, indicating that the observed Sc recovery efficiency consistent with the predicted one.

Sustainable Selective Recovery of Sulfuric Acid and Vanadium from Acidic Wastewater with Two-Step Solvent Extraction

A two-stage extraction process was proposed to recover sulfuric acid and vanadium from simulated acid solution and titanium dioxide waste acid (TDWA). Some extractants were compared and studied, in which the enthalpy changes (ΔH) of the extraction process and the extracted complex were analyzed by using thermodynamics. The microscopic characteristics of the loaded organic phase were compared and investigated by infrared spectroscopy (FT-IR), where the extraction mechanism was described. The extraction efficiency of sulfuric acid was more than 99% by three-stage countercurrent extraction with 60% triisooctylamine (TEHA) and 35% N-pentanol, in which ΔH was -61.31 kJ/mol and the extracted complex of H2SO4·TEHA·2-N-pentanol was obtained. The extraction efficiency of vanadium was above 98% by using 20% bis-2-ethylhexyl phosphate (P507) and 80% sulfonated kerosene, where ΔH was 14.69 kJ/mol and the extracted complex of VO·2A (vanadium as VO2+ and P507 as HA) was obtained. The stripping efficiencies of sulfuric acid and vanadium were more than 90% and 98%, respectively. The extraction effect of used organic phase after regeneration was equivalent to that of the new organic phase with cycle numbers of less than 10. The real waste acid of TDWA was operated to extract and separate sulfuric acid and vanadium with the same parameters, in which the characteristics of high extraction efficiency and good selectivity were obtained. The technique may provide a new thinking for the separation and recovery of valuable components from TDWA.

Surface Modification of Biomass with Di-(2-Ethylhexyl)phosphoric Acid and Its Use for Vanadium Adsorption

The method of carbonizing biomass using di-(2-Ethylhexyl) phosphoric acid and tributyl phosphate impregnation (SICB) was studied in this research. SICB combines the benefits of an extractant and an ion exchange resin. The adsorption and desorption properties of vanadium were investigated, and the adsorption mechanism was analyzed. The results showed that the carrier was first prepared at a temperature of 1073.15 K using sawdust as a biomass substitute and then cooled to room temperature. The best adsorption performance was obtained by impregnating the carriers with di-(2-Ethylhexyl) phosphoric acid and tributyl phosphate for 60 min. The vanadium adsorption rate of 98.12% was achieved using the biomass at an initial V(IV) solution concentration of 1.1 g/L, a pH value of 1.6, and a solid-to-liquid ratio of 1:20 g·mL for 24 h. Using 25 wt.% sulfuric acid solution as desorbent, the desorption rate of vanadium was as high as 98.36%. The analysis showed that the adsorption of vanadium by SICB was chemisorption, and the adsorption process was more consistent with the proposed second-order kinetic equation. Therefore, SICB has high selectivity and high saturation capacity because of the mesopores and micropores produced by carbonization.

Dissolution behavior of representative elements from red mud (RM) by leaching with titanium white waste acid (TWWA)

Titanium white waste acid (TWWA) was used to dissolve the representative elements from red mud (RM) to achieve the goal of "treating waste with waste." The leaching parameters on the leaching efficiency of Na, Sc, and Al were investigated, in which the analysis of XRD and SEM-EDS on RM and leaching residue was performed. The leaching kinetics of Na, Sc, and Al was studied with unreacted shrinking core model (USCM). The results show that the dealkalization efficiency was close to 100%, and the leaching efficiency of Sc and Al was 82% and 75%, respectively. Cancrinite was dissolved from RM, and then the elements such as Na, Al, and Ca reacted with H₂SO₄ of TWWA. Na existed in the leaching liquor in the form of ions. Ca reacted with sulfuric acid to form anhydrite, which existed in the leaching residue. The particles of RM became smaller and dispersed with each other by acid leaching. The leaching apparent activation energy of Na, Sc, and Al was 4.947 kJ/mol, 6.361 kJ/mol, and 31.666 kJ/mol, respectively. The leaching kinetic equation of Na, Sc, and Al was 1 - (1 - a)^2/3 = 0.084·exp[- 595.05/T]·t by external diffusion, 1 - 2a/3 - (1 - a)^2/3 = 0.021·exp[- 765.16/T]·t by internal diffusion, and ln(1 - a)/3 + (1 - a)^-2/3 - 1 = 67.12·exp[- 3808.8/T]·t by joint action, respectively.

A selective hydrometallurgical method for scandium recovery from a real red mud leachate: A comparative study

The aim of this study was to recover Sc as the main product and Fe as a by-product from Hungarian bauxite residue/red mud (RM) waste material by solvent extraction (SX). Moreover, a new technique was developed for the selective separation of Sc and Fe from real RM leachates. The presence of high Fe content (∼38%) in RM makes it difficult to recover Sc because of the similarity of their physicochemical properties. Pyrometallurgical and hydrometallurgical methods were applied to remove the Fe prior to SX. Two protocols based on organophosphorus compounds (OPCs) were proposed, and the main extractants were evaluated: bis(2-ethylhexyl) phosphoric acid (D2EHPA/P204) and tributyl phosphate (TBP). The results showed that SX using diethyl ether and tri-n-octylamine (N₂₃₅) was efficient in extracting Fe(III) from the HCl leachate as HFeC1₄. Over 97% of Sc was extracted by D2EHPA extractant under the following conditions; 0.05 mol/L of D2EHPA concentration, A/O phase ratio of 3:1, pH 0-1, 10 min of shaking time, and a temperature of 25 °C. Sc(OH)₃ as a precipitate was efficiently obtained by stripping from the D2EHPA organic phase by 2.5 mol/L of NaOH with a stripping efficiency of 95%. In the TBP system, 99% of Sc was extracted under the following conditions: 12.5% vol of TBP, an A/O phase ratio of 3:1, 10 min of shaking time, and a temperature of 25 °C. The Sc contained in the TBP organic phase could be efficiently stripped by 1 mol/L of HCl with a stripping efficiency of 92.85%.

Clean dealkalization technology from aluminum industry hazardous tailings-red mud by displacement with Mg-based agent

Red mud is a kind of strong alkaline hazardous slag discharged from aluminum metallurgy industry. In this study, the water immersion with high temperature and high pressure was developed for the selective dealkalization from red mud by adding Mg-based additives. The removal efficiency of alkali could reach 92% by using 12% MgCl₂ with 9 mL/g at 250 °C for 60 min. The MgCl₂ was the most effective leaching reagent to promote the decomposion of cancrinite lattice. The new minerals bearing Mg, i.e., chlorite (Mg₅Al₂Si₃O₁₀(OH)₈) and pyrope (Mg₃Al₂Si₃O₁₂) could be formed, which was in favor of transforming the structural alkali into the free alkali by the analysis and validation of XRD and SEM-EDS. The dealkalization process was mainly controlled by chemical reactions according to the analysis of unreacted shrinking core model (USCM) of leaching kinetics. The leaching kinetics equation of 1 - (1 - x)^1/3 = 32.2 × exp[4582.6 / T] × t was built and the apparent activation energy of 38.1 kJ/mol was obtained. This method may provide a new and cleaner way for the efficient dealkalization of red mud and a basis for the utilization of leaching residue as the soil amendment.

Will Vanadium-Based Electrode Materials Become the Future Choice for Metal-Ion Batteries?

Metal-ion batteries have emerged as promising candidates for energy storage system due to their unlimited resources and competitive price/performance ratio. Vanadium-based compounds have diverse oxidation states rendering various open-frameworks for ions storage. To date, some vanadium-based polyanionic compounds have shown great potential as high-performance electrode materials. However, there has been a growing concern regarding the cost and environmental risk of vanadium. In this Review, all links in the industry chain of vanadium-based electrodes were comprehensively summarized, starting with an analysis of the resources, applications, and price fluctuation of vanadium. The manufacturing processes of the vanadium extraction and recovery technologies were discussed. Moreover, the commercial potentials of some typical electrode materials were critically appraised. Finally, the environmental impact and sustainability of the industry chain were evaluated. This critical Review will provide a clear vision of the prospects and challenges of developing vanadium-based electrode materials.

Scandium Recovery Methods from Mining, Metallurgical Extractive Industries, and Industrial Wastes

The recovery of scandium (Sc) from wastes and various resources using solvent extraction (SX) was discussed in detail. Moreover, the metallurgical extractive procedures for Sc recovery were presented. Acidic and neutral organophosphorus (OPCs) extractants are the most extensively used in industrial activities, considering that they provide the highest extraction efficiency of any of the valuable components. Due to the chemical and physical similarities of the rare earth metals, the separation and purification processes of Sc are difficult tasks. Sc has also been extracted from acidic solutions using carboxylic acids, amines, and acidic β-diketone, among other solvents and chemicals. For improving the extraction efficiencies, the development of mixed extractants or synergistic systems for the SX of Sc has been carried out in recent years. Different operational parameters play an important role in the extraction process, such as the type of the aqueous phase and its acidity, the aqueous (A) to organic (O) and solid (S) to liquid (L) phase ratios, as well as the type of the diluents. Sc recovery is now implemented in industrial production using a combination of hydrometallurgical and pyrometallurgical techniques, such as ore pre-treatment, leaching, SX, precipitation, and calcination. The hydrometallurgical methods (acid leaching and SX) were effective for Sc recovery. Furthermore, the OPCs bis(2-ethylhexyl) phosphoric acid (D2EHPA/P204) and tributyl phosphate (TBP) showed interesting potential taking into consideration some co-extracted metals such as Fe(III) and Ti(IV).

Efficient Separation and Recovery of Vanadium(V) from Hydrochloric Acid Solution Using N1923 as an Extractant

Hydrochloric acid leaching has been widely used in the recovery process of vanadium due to its efficient selectivity. It was necessary to further separate vanadium from hydrochloric acid leaching solution. Four extractants of P204, P507, Cyanex272, and N1923 were compared for extraction of vanadium from a simulated hydrochloric acid solution, and it is concluded that N1923 was an effective extractant suitable for the extraction and separation of V (V) in the medium. The single-stage extraction efficiency of vanadium reached more than 90% with a pH value of 2.0, extraction time of 5 min, and X _N1923 of 0.2 at 30 °C. The functional group characteristics of the extraction complex were analyzed by means of an extraction slope method, FT-IR, and ¹H NMR to judge the extraction mechanism of vanadium with N1923 as an extractant. The extraction of V (V) by using N1923 was in the coordination form of a molar ratio of 2:1, and the extraction process was an endothermic reaction. The N-H vibrational absorption peak in the -NH₂ group still appeared in the loaded N1923, in which the chemical shift of ¹H in the primary amine and secondary carbon still existed. This technology was a more efficient process for extraction of vanadium from hydrochloric acid solution.

Novel Technology for Vanadium and Chromium Extraction with KMnO4 in an Alkaline Medium

This paper focused on the oxidation-alkaline extraction process of vanadium-chromium-reducing residue. The affected parameters including reaction temperature, KMnO₄ dosage, reaction time, NaOH dosage, and liquid-to-solid ratio on the extraction process were investigated. The E-pH diagram and the thermodynamic analysis indicated that KMnO₄ was suitable for the oxidation of low-valence vanadium and chromium. Vanadium (97.24%) and chromium (56.20%) were extracted under the following optimal reaction conditions: reaction temperature of 90 °C, reaction time of 90 min, dosage of KMnO₄ at m(KMnO₄)/m(residue) = 0.40, dosage of NaOH at m(NaOH)/m(residue) = 0.30, and liquid-to-solid ratio at 5:1 mL/g. The extraction process of vanadium was controlled by the reactant through the solid product layer and the extraction kinetics behavior fitted well with the shrink core model with an E _a of 15.37 kJ/mol. At the same time, the surface chemical reaction was the controlling step for chromium extraction, which was difficult with an E _a of 39.78 kJ/mol.

Thermodynamic and Kinetic Studies on Adsorption of Vanadium with Glutamic Acid

Many hydrometallurgy methods, including chemical precipitation, ion exchange, solvent extraction, and adsorption, have been used to recover vanadium from vanadium solution, but the final step of these methods involved precipitation with ammonium salts, high concentrations of which are harmful to the environment. The key point is to find a new compound to replace ammonium salts without reducing the vanadium precipitation efficiency. The adsorption process of vanadium with glutamic acid is investigated. The effects of experimental factors, including dosage of glutamic acid, reaction temperature, concentration of H2SO4, and reaction time, on the adsorption process are investigated. The results show that nearly 91.66% vanadium is adsorbed under the following reaction conditions: reaction temperature of 90 °C, H2SO4 concentration of 20 g/L, glutamic acid dosage at n(glu)/n(V) = 3.0:1, and reaction time of 60 min. The response surface methodology is applied to optimize the reaction conditions. The analysis results indicate that the reaction temperature has the greatest effect on the adsorption efficiency of vanadium and the influence of experimental factors follows the order: reaction temperature > dosage of glutamic acid to vanadium > reaction time > concentration of H2SO4. The pseudo-second-order model is selected to describe well the adsorption kinetic behavior, and the thermodynamic analysis results indicate that the adsorption process of vanadium is unspontaneous and exothermic. The results will be useful for further applications of glutamic acid, and they provide a bright future for vanadium recovery.

Extraction of Valuable Elements from Red Mud with a Focus on Using Liquid Media—A Review

Bauxite residue, known as red mud, is a by-product of alumina production using the Bayer process. Currently, its total global storage amounts to over 4.6 billion tons, including about 600 million tons in Russia. The total global storage of red mud occupies large areas, leading to environmental damage and increasing environmental risks. Moreover, it contains a significant amount of sodium, which is easily soluble in subsoil water; therefore, a sustainable approach for comprehensive recycling of red mud is necessary. The bauxite residue contains valuable elements, such as aluminum, titanium, and scandium, which can be recovered using liquid media. In recent years, many methods of recovery of these elements from this waste have been proposed. This paper provides a critical review of hydrometallurgical, solvometallurgical, and complex methods for the recovery of valuable components from red mud, namely, aluminum, titanium, sodium, and rare and rare-earth elements. These methods include leaching using alkaline or acid solutions, ionic liquids, and biological organisms, in addition to red mud leaching solutions by extraction and sorption methods. Advantages and disadvantages of these processes in terms of their environmental impact are discussed.

Adsorption behavior of Fe (III) in aqueous solution on melamine

This paper focused on the adsorption behavior of Fe (III) in aqueous solution on melamine. The effects of experimental conditions including dosage of melamine, reaction time and reaction temperature were investigated. The results showed that nearly 99% Fe (III) was adsorbed under the optimal conditions: melamine dosage (mole ratio) at n(C₃H₆N₆)/n(Fe) = 3.5:1, reaction time of 60 min and reaction temperature of 90 °C. The optimal processing factors were obtained from response surface methodology and the effects of processing parameters on the removal efficiency of Fe (III) followed the order: mole ratio (n(C₃N₆H₆):n(Fe)) > reaction temperature > reaction time. The adsorption kinetics behavior was fitted well with the pseudo-second-order model. The thermodynamic study showed that the adsorption process was unspontaneous and endothermic. The value of free energy change and standard enthalpy change disclosed that the mechanism of adsorption onto melamine was physisorption. The results will be useful for further applications of system design in the treatment of practical waste effluents.

Solvent Extraction of Sc(III) by D2EHPA/TBP from the Leaching Solution of Vanadium Slag

The solvent extraction of scandium by the mixture of di-(2-ethylhexyl) phosphate (D2EHPA) and tri-n-butyl phosphate (TBP) has been investigated in the acidic leaching solution of vanadium slag. Thermodynamic analysis of the species distribution diagrams on the Sc-S-H2O system showed that scandium mainly exists as Sc3+ and Sc(SO4)+, and sulfur mainly exists as HSO4− in the actual leaching solution of vanadium slag (pH = −0.75). The extraction process was studied to optimize various parameters such as the extractant concentration, dosage of TBP, phase ratio, and stirring speed. The results indicated that 83.64% of scandium and less than 2% of co-extracted elements were extracted under optimal conditions. Then, over 95% of the co-extracted elements and less than 1.1% of scandium were scrubbed from the loaded organic phase by 4.0 mol/L of HCl. Finally, 87.20% of scandium was stripped with 2 mol/L of NaOH and 1 mol/L of NaCl at a stripping O/A of 1:1.

Oxidative Leaching Kinetics of Vanadium from the Vanadium-Chromium-Reducing Residue with K2Cr2O7

Oxidative-alkaline leaching of vanadium from vanadium-chromium-reducing residues with K2Cr2O7 was investigated in this paper. The effects of processing parameters including dosage of NaOH, dosage of K2Cr2O7, reaction time, and reaction temperature on the leaching efficiency of vanadium were studied. The results simulated by response surface methodology indicated that vanadium leaching was affected significantly by the dosage of K2Cr2O7 and NaOH, and the processing parameters that affected the leaching efficiency of vanadium followed the order m(NaOH)/m(residue) > m(K2Cr2O7)/sssssm(residue) > reaction temperature > reaction time. The leaching efficiency of vanadium was up to 99.92% under optimal conditions: reaction temperature of 90 °C, reaction time of 60 min, liquid-to-solid ratio of 5:1 mL g-1, m(K2Cr2O7)/m(residue) = 0.10, and m(NaOH)/m(residue) = 0.30. The kinetics analysis indicated that diffusion through the product layer was the controlling step and the apparent activation energy for vanadium leaching was calculated to be 58.275 kJ·mol-1.

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.

A Novel Technology for Recovery and Separation of Vanadium and Chromium from Vanadium-Chromium Reducing Residue

This paper was to develop an efficient process for efficient recovery and separation of vanadium and chromium. The vanadium-chromium reducing residue was conducted by oxidation acidic leaching with MnO2, followed by selective adsorption of vanadium and precipitation of chromium, respectively. The results showed that 97.93% vanadium was leached out and then adsorbed by melamine at pH 1.8 at 90 °C for 60 min. Almost all chromium was leached out and efficiently recovered as Cr2O3. The leaching process was mainly controlled by surface chemical reaction, and its kinetic behaviors fitted well with the shrink core model. The apparent activation energy for vanadium and chromium leaching out wascalculated as 19.93 kJ·mol−1 and 21.26 kJ·mol−1, respectively.

Reductive Smelting of Neutralized Red Mud for Iron Recovery and Produced Pig Iron for Heat-Resistant Castings

The chemical and mineral composition of the red mud from the Ural Aluminum Plant were studied by XRF, XRD, and Mössbauer spectroscopy. Experiments on reductive smelting of red mud were carried out in a range of temperatures (1650–1750 °C) to recover iron from the aluminum production waste with maximum efficiency. It was found that it is possible to obtain pig iron with a high content of titanium, phosphorus, and vanadium, and low sulfur content. The efficiency of iron recovery at 1750 °C was found to be around 98%. Thermodynamic calculations were carried out to assist in finding the optimal conditions for the process (e.g., carbon content, furnace temperature, slag liquidus temperature). It was also found that the pig iron phase obtained at 1650 to 1700 °C is not separated from the slag phase into ingot compared with the sample obtained at 1750 °C. Pig iron obtained at 1750 °C can be used to produce molds for the steel-casting equipment.

Selective Parameters and Bioleaching Kinetics for Leaching Vanadium from Red Mud Using Aspergillus niger and Penicillium tricolor

In the present study, using Aspergillus niger and Penicillium tricolor, the influence of the selected parameters, including sucrose concentration, inoculation size of spores, pulp density, and pre-culture time, on the bioleaching efficiency (biomass, organic acids production, and vanadium extraction, respectively) of red mud were studied. The bioleaching kinetics under optimal conditions were also explored. Sucrose concentration showed a positive linear effect on bioleaching efficiency below 143.44 and 141.82 g/L using A. niger and P. tricolor, respectively. However, a higher concentration was unfavorable for vanadium extraction. The inoculation size of spores showed an insignificant effect on both biomass and vanadium extraction if it exceeded the lowest coded levels (0.5 × 107/mL). Red mud pulp density showed a negative effect on the bioleaching efficiency of A. niger but a positive effect on organic acids production and vanadium extraction of P. tricolor. A pre-culture was indispensable for A. niger but not for P. tricolor due to the fact of its isolation from the red mud examined in this study. The kinetics analysis showed that the leaching rate of vanadium followed a two-domain behavior: initially, a rapid leaching period of approximately 10–15 days and, subsequently, a slow leaching period. Considering the change of the particles’ appearance as well as in the elemental composition of the bioleached red mud, it is speculated that the rate of leaching agents through the silicon minerals was the rate-limiting step of dissolution kinetics under the fungal bioleaching process.

A Review on Comprehensive Utilization of Red Mud and Prospect Analysis

Red mud (RM) is a by-product of extracting of alumina from bauxite. Red mud contains high quantities of alkali-generating minerals and metal ions, which can cause significant environmental damage. Many valuable components such as rare-earth elements, Al, and Fe, in RM are difficult to be utilized owing to their particle size and alkalinity. Thus, developing an economical and efficient technology to consume a large amount of RM can efficiently solve RM disposal issues. This paper systematically reviews the comprehensive utilization methods for reducing RM environmental pollution and divides the comprehensive utilization of RM into three aspects: the effective extraction of valuable components, resource transformation, and environmental application. Based on resource, economic, and environmental benefits, the development of new technologies and new processes with market competitiveness, environmental protection, and ecological balance should be the prerequisite for the low-energy, low-pollution, low-cost, and high-efficiency comprehensive utilization of RM. The direction of future research to solve RM disposal issues is also suggested.

Adsorption characteristics of vanadium on different resin-active carbon composite electrodes in capacitive deionization

Three kinds of anion exchange resins (AERs) (D201, D301, D314) and one kind of cation exchange resin (D860) were used with activated carbon (AC) to fabricated the ion exchange resin-AC (IER/AC) composite electrodes in capacitive deionization (CDI) for selective adsorption of V(V). The characteristics of four kinds of composite electrodes, such as wettability, pore distribution and electrochemical properties, indicates IER/AC composite has great potential as electrode materials for the electro-adsorption in CDI. The pH of solution has apparent influence on the adsorption capacity of the composite electrodes for V(V) because of the various V(V) species in the solution with different pH. The reduction rate of V(V) on IER/AC electrodes mainly relates to the amount of VO₂⁺ in solution. The adsorption capacity of AER/AC electrodes for V(V) is slightly affected by the applied voltage may be due to that the adsorption of V(V) is mainly dependent on ion exchange with AERs and only a minority of V(V) is adsorbed by electrostatic adsorption. The adsorbed V(V) on D860/AC electrode decreases with the rising applied voltage because the pH increases with the increase of voltage. The separation of V(V) from V(V), Al and P indicates that the selective adsorption capability of IER/AC composite electrode is related to the migration rate of V(V), Al, P at different voltages and the selectivity of resins. This study may provide reference for recovering and separating metal ions from aqueous solution with CDI.

Recovery of V(V) from complex vanadium solution using capacitive deionization (CDI) with resin/carbon composite electrode

The resin-activated carbon composite (RAC) electrodes were fabricated and applied in capacitive deionization for recovery of V(V) from complex vanadium solution. The adsorption capacity of the RAC electrode for V(V) is extremely low and the reduction of V(V) is significant in low pH solution, but the adsorbed V(V) on the electrode increases obviously and the reduction of V(V) gradually diminishes with the rise of pH. However, as the pH is increased to 10, the adsorbed V(V) on the RAC electrode declines. The higher applied potential is beneficial to the adsorption of V(V) and 1.0 V is appropriate for the adsorption. The impurities ions (Al, P and Si) are mainly adsorbed in the electric double layers on the RAC electrode and V(V) is dominantly adsorbed by the resins in the electrode. The adsorbed impurity ions can be easily removed by diluted H₂SO₄ and V(V) can be effectively eluted by 10% NaOH solution. The vanadium-bearing eluent can be recycled to recover and enrich vanadium from the complex solution. The performance of the RAC electrode keeps stable during the cyclic operation. This study may provide a promising and novel method for the recovery and separation of metals from aqueous solution.

Mechanism of Novel K2SO4/KCl Composite Roasting Additive for Strengthening Vanadium Extraction from Vanadium–Titanium Magnetite Concentrate

In this paper, a novel K2SO4/KCl composite roasting additive was used to extract vanadium from vanadium–titanium magnetite concentrate. Further, the mechanism of K2SO4/KCl for extracting vanadium was studied. The results indicate that the vanadium leaching efficiency reached 82.04%, an increase of 7.43% compared to that of single K2SO4 and 10.05% compared to single KCl under the following conditions: a total dosage of K2SO4/KCl of 7 wt % with a mass ratio of 6/4, a roasting temperature of 950 °C, a roasting time of 1 h, a leaching temperature of 95 °C, a sulfuric acid concentration of 10% (v/v: volume percentage), and a leaching time of 1.5 h with a liquid-to-solid ratio of 3 mL/g. Moreover, crystal chemistry analyses indicated that the essence of the vanadium extraction with roasting was the conversion of cubic crystal systemic vanadium-bearing magnetite (FeO(Fe,V)2O3) to trigonal crystal systemic hematite (α-Fe2O3), and as most Fe(V)–O bonds were broken with the reconstructed conversion, the dissociation of V(III) occurred. Furthermore, the main decomposition products of K2SO4/KCl were K2O, SO2, and Cl2. X-ray diffraction (XRD) and related SEM-EDS analyses indicated that there were mainly three aspects in the mechanism of K2SO4/KCl for extracting vanadium. Firstly, activated K2O could combine with vanadium to generate soluble KVO3 rather insoluble Ca(VO3)2; secondly, SO2 could react with CaO to form CaSO4 to prevent the generation of acid-consuming Ca(VO3)2, which was beneficial to the dissolution of vanadium-bearing sphene (Ca(Ti,V)SiO4O); thirdly, Cl2 could destroy the structure of hematite (Fe2O3) to reduce its wrapping extent to KVO3.