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A clean method featuring non-salt roasting followed by (NH)CO leaching to recover vanadium from vanadium slag was proposed. The carcinogenic Cr compounds and exhaust gases were avoided, and the water generated from vanadate precipitation may be recycled and reused in this new leaching process. The leaching residues may be easily used by a blast furnace. Moreover, (NH)CO solution was used as a leaching medium to avoid expensive and complicated ammonium controlling operations as a result of the stability of (NH)CO at a high temperature. The transformation mechanisms of vanadium- and chromium-bearing phases were systematically investigated by x-ray diffraction analysis and scanning electron microscopy with energy-disperse x-ray spectrometry, respectively. In addition, the effects of oxygen concentration, roasting temperature, and holding time on vanadium recovery were investigated. Finally, the effects of leaching variables on the vanadium leaching rate were also examined. [ABSTRACT FROM AUTHOR]

A cleaner method has been developed for the extraction of vanadium from vanadium slag. Compared to the traditional alkaline salts roasting followed by the water leaching process, in the nonsalt roasting process because no additives are added, the chromium spinel in the raw vanadium slag will not be converted to carcinogenic chromate salts and exhaust gas will not be produced. The ammonium metavanadate is precipitated from the water leach solution. The wastewater from the vanadate precipitation process can be recycled into the leaching process. The leaching residue can be comprehensively utilized in conjunction with an iron-making process using blast furnace. The nonsalt roasting mechanism was systematically investigated in a laboratory study. The XRD and morphology analysis of roasted vanadium slag showed that the oxidation of vanadium spinel occurred in the following steps: (1) the destruction of vanadium spinel and the formation of solid solution of Fe2O3·V2O3; (2) the oxidation of solid solution of Fe2O3·V2O3to Fe2O3·V2O4and a portion of the V(IV) in the Fe2O3·V2O4was reacted with basic oxide such as MgO to generate the low-valence vanadate Mg2VO4; (3) the formation by further oxidation of highest-valence vanadates Mn2V2O7and Mg2V2O7. The effects of particle size, oxygen concentration, gas flow rate, and temperature on vanadium recovery were investigated. Simultaneously, the effects of leaching variables, including ammonium carbonate concentration and temperature, were examined. The thermodynamics of the system are also reported. [ABSTRACT FROM PUBLISHER]

A novel method that introduces an electrochemical field to enhance the decomposition of vanadium slag in concentrated NaOH solution was proposed. Under the optimal conditions (alkali concentration of 40 wt.%, reaction temperature of 120 °C, alkali-to-ore mass ratio of 4:1, stirring speed of 1000 rpm, and slot current density of 750 A/m 2 ), the extraction percentages of vanadium and chromium could reach approximately 95% and 90%, respectively, after 6 h of reaction time. Compared with the current liquid oxidation methods, the reaction temperature in this new approach is reduced by 60–280 °C and the medium concentration is decreased by more than 30%, demonstrating substantial advantages and prospects in terms of actual operation and industrial application. [ABSTRACT FROM AUTHOR]

Abstract: The redox behavior of vanadate ions in alkaline solutions has been studied with NaOH concentration ranging from 0.1M to 1M. The cyclic voltammetry results reveal that vanadate ions are irreversibly reduced to V(OH)2 via a three-electron transfer reaction, and the first electron transfer reaction is the rate-determining step. The oxidation processes involve the stepwise oxidation of V(OH)2 to V(OH)3, and V(OH)3 to vanadate ions. The reduction kinetics is discussed and the diffusion coefficient of vanadate ion is calculated to be 1.40×10−9 m2/s. Chemical and XPS analysis results suggest that due to the instability of the direct reduction product V(OH)2, the obtained deposits after reducing electrolysis are mixed-valence (+3/+4) vanadium compounds with an empirical compound formula of VO1.87·1.38H2O. X-ray diffraction and TGA/DSC analysis results further confirm that the collected reducing electrolysis products are amorphous hydrated vanadium compounds. [Copyright &y& Elsevier]

In this study, the hexamethylenetetramine complexation precipitation separation system of Mo and V is constructed, and the complexation precipitation reactions of hexamethylenetetramine with molybdenum and vanadium are through the function of the protonated hexamethylenetetramine, and the metals in the precipitates exist in the form of polyoxometalate ions. [Display omitted] • The hexamethylenetetramine complexation precipitation separation system of Mo and V is constructed. • The complexation precipitation mechanisms of hexamethylenetetramine with Mo(V), Mo(VI) and V(V) are determined. • The macroscopic kinetics of the complexation precipitation reactions of hexamethylenetetramine with Mo(V), Mo(VI) and V(V) are measured. Molybdenum (Mo) and vanadium (V) are both important strategic metals. Due to their similar physicochemical properties, it is always a challenge to realize their deep separation from a solution. However, based on the valence difference of Mo and V, this task can be achieved by the selective complexation precipitation of hexamethylenetetramine (HMT). In this study, through precipitation behavior studies in the single metal species solutions and the mixed species solutions of Mo and V in different chemical valence states, the complexation precipitation separation system of V and Mo was constructed. As a result, in the single metal species solution, the precipitation depths of Mo(V), Mo(VI) and V(V)) reached 96.83% 98.77% and 99% under the best conditions, respectively, while V(IV) remained in the solution. The results of the mixed-species complexation precipitation experiments revealed the most efficient selective separation scheme by HMT. Furthermore, combined with the characterization of the complexation precipitates of HMT with the single species of Mo(V), Mo(VI) and V(V), the mechanisms of the complexation reactions were elucidated. In particular, due to the different ion species of Mo caused by the different valence states, the complexation precipitation mechanisms of Mo(V) were different from those of Mo(VI). Finally, the differences in the mechanisms of Mo(V), Mo(VI) and V(V) complexation were also presented in their kinetics, and the reaction constants and activation energies were calculated by first-order kinetics. This study may provide further insight into the selective complexation separation of Mo and V. [ABSTRACT FROM AUTHOR]

VOx hierarchical structures are solvothermally synthesized from NH4VO3 in a 1:7 mixture of water and ethylene glycol (autoclave, 180 °C, 24 h). [ABSTRACT FROM AUTHOR]

Vanadium-titano magnetite (VTM) is a typical resource in China. The typical method used to recover valuable elements from VTM concentrates is by the blast furnace smelting method. However, titanium is nearly all wasted in the form of blast furnace slag. A new pathway towards obtaining TiO 2 -enriched material for titanium extraction was designed in this study. The main means is the combination of partial carbon reduction and mild acid leaching. After reduction and leaching, most of the iron and other elements are transferred into solution, leaving a TiO 2 -enriched residue. Iron and vanadium are reclaimed from the leaching liquid later. In this study, the reduction and leaching parameters were optimized, which included reducing at 1000 °C for 3 h with a carbon addition of 6% by mass of VTM and leaching at 80 °C for 3–4 h by using a 0.2 mol/L H 2 SO 4 solution with a liquid-to-solid ratio of 100:1. The dehydrated residue was mainly rutile containing 72.2 wt% TiO 2 , which is a satisfactory material for Ti extraction. In addition, upon determining the phase composition and the mass loss after reduction with different dosages of carbon, the reduction route for iron in the magnetite phase and the main gas byproduct during reduction were analyzed. This study provides a new idea for extracting titanium from VTM concentrates. Unlabelled Image • A pyro-hydro pathway to get TiO 2 -enriched material from VTM concentrates is designed. • Partial reduction is critical to assist separating Fe and V from Ti by mild acid leaching. • Parameters for both partial carbon reduction and mild acid leaching were optimized. • The enriched material contains 72.2 wt% TiO 2 , a satisfactory feedstock for Ti extraction. [ABSTRACT FROM AUTHOR]

An environmental friendly electrochemical detoxification and recovery process is developed for the spent SCR catalysts disposal under alkaline condition. It is revealed that the spent V 2 O 5 -WO 3 /TiO 2 catalyst is severely aggregated and poisoned by arsenic compounds. In this study, the efficient removal of arsenic is achieved by the electrochemical advanced oxidation processes (EAOPs) at surface-modified carbon felt cathode, where the HO 2 − and highly oxidative OH are in-situ generated from two-electron ORR and electro-Fenton-like reaction, respectively. The mechanism of electrochemical arsenic extraction is systematically illustrated by employing the ESR measurements, and vanadium species induced electro-Fenton-like reaction is proposed. After electro-oxidative dissolution, the crystal structure and original composition of the catalyst support (TiO 2 and WO 3 ) are well maintained for recycle or subsequently re-fabrication process. After dipping active component on the detoxified catalyst, the regenerated catalyst shows a comparable SCR catalytic activity with the fresh sample. The present electrochemical strategy provides a promising approach for the spent catalysts utilization and further understanding for the in-situ generated reactive oxygen species in alkaline media. [ABSTRACT FROM AUTHOR]

[Display omitted] • Efficient removal of V(V) and Cr(VI) of γ-AlOOH-Cr-V to 0.0656% and 0.0018%, respectively. • A method for improving the peptization index of γ-AlOOH to 98.1%. • Synergistic effect between the improvement of peptization performance and the removal of V(V) and Cr(VI). • Green process of utilizing aluminum waste in chromate industry. Cr(VI)-containing aluminum residues are inevitable industrial hazardous waste in the chromate industry. To reduce and utilize these residues, a combined desorption and peptization technology for disposing of Cr(VI)-V(V)-containing boehmite hazardous waste (γ-AlOOH-Cr-V) with NaOH solutions was proposed, which realized the removal of V(V) and Cr(VI) effectively and the improvement of peptization index (PI) of obtained pseudo-boehmite (PB) synergistically. The results showed that PB with high PI (98.1%) and low content of V(V) (0.0656%) and Cr(VI) (0.0018%) could be achieved by desorbing the γ-AlOOH-Cr-V, while the surface area and pore volume would be decreased during desorption with the increase of NaOH concentration. Besides the leaching toxicity of Cr(VI) of obtained PB of 0.09 mg/L was extremely lower than that of the standard of hazardous waste. It was noted that the evolution of structural hydroxyl groups governed the improvement of peptization performance. DFT results showed that proper interlayer water content was beneficial to the adsorption of hydroxyl ions on the structural hydroxyl groups of PB. This work not only reduced the emission of Cr(VI)-V(V)containing hazardous waste, but also paved the way for the high-valued utilization of co-associated aluminum and vanadium resources in chromite. [ABSTRACT FROM AUTHOR]

A new metallurgical process via aeration for the decomposition of vanadium slag in concentrated NaOH solution was proposed. The improvement of oxygen mass transfer coefficient when using aeration at different NaOH concentration was studied and the effects of critical reaction parameters on vanadium extraction were systematically investigated. The optimal condition was determined to be: alkali concentration of 60%, reaction temperature of 130 °C, alkali-to-ore mass ratio of 6:1, stirring speed of 500 rpm. The yield of vanadium could reach to 97.41% after reacting for 6 h under this reaction condition. The reaction temperature in this new method is 50–270 °C lower than the current liquid oxidation methods reported in the literatures, and the medium alkaline concentration declined from 85% to 60%, exhibiting significant advantages in energy consumption as well as reactor design. Kinetics study indicated that the extraction of vanadium was governed by internal diffusion, and the apparent activation energy was calculated to be 17.57 kJ/mol. [ABSTRACT FROM AUTHOR]

Chitosan-modified boehmite (AF-γ-AlOOH) was synthesized, characterized and used as adsorbent for removing vanadium and chromium from vanadium industrial wastewaters. Batch V(V) adsorption data showed that AF-γ-AlOOH possessed a V(V) adsorption capacity of 217 mg/g. The adsorption behavior followed the Langmuir isotherm model and pseudo second-order kinetics. The adsorption process was spontaneous and endothermic. Continuous fixed-bed column adsorption measurements showed that V(V) and Cr(VI) could be simultaneously decreased to less than the national emission standards (0.5 mg/L). The adsorbed AF-γ-AlOOH could be recycled by separating V(V) and Cr(VI). The XPS results indicated that the V(V) and Cr(VI) first interacted with functional groups such as –OH and –NH 2 of AF-γ-AlOOH, and then was partially reduced to V(IV) and Cr(III), respectively. A whole process was proposed to realize separation and recovery of V(V) and Cr(VI) from the vanadium industrial wastewaters. • Amino-functionalized γ-AlOOH with abundant –NH 2 and –OH groups was synthesized. • The maximum adsorption capacity of V(V) was 217 mg/g at 303 K. • The V(V) and Cr(VI) from vanadium industrial wastewaters were simultaneously removed. • The separated V(V) and Cr(VI) were reused as V 2 O 5 and Cr(OH) 3 , respectively. [ABSTRACT FROM AUTHOR]

The leach liquor of sodium-roasted vanadium slag in vanadium industry is an alkaline solution containing vanadium, sodium, chromium, and other impurities, and preparing high-purity vanadyl sulfate electrolyte (used in vanadium redox flow battery) directly from this solution is challenging but cost-effective. A novel process consisting of selective reduction–precipitation of chromium and solvent extraction of vanadium was proposed and optimized in this study. Approximately 90% of Cr(V I) in the solution was reduced to Cr(III) and precipitated after adding sodium sulfite at a pH of 5.77 and 25 °C, while V(V) remained in this process and needed a further reduction to V(IV) prior to extraction. More than 99.9% of V(IV) remained in the solution was extracted by two-stage extraction using the "P507 + TBP + kerosene" extractant system at a pH of 2.00 and an organic-to-aqueous phase ratio of 1.5:1. Sodium entrained in the organic phase was washed off through three-stage scrubbing. A high-purity vanadyl sulfate solution of 2.1 mol L−1 was prepared by two-stage stripping using 5.5 mol L−1 sulfuric acid. According to the slope analysis and infrared spectra, the extraction of V(IV) by P507 follow the cation exchange mechanism. This study provides a feasible way to remove chromium and recover vanadium in the form of vanadyl sulfate from the industrial leach liquor of sodium-roasted vanadium slag. • VOSO 4 solution was produced from leaching solution of sodium-roasted vanadium slag. • Chromium(VI) was removed by selective reduction–precipitation. • Vanadium was extracted by the "P507 + TBP + kerosene" extractant system. • Parameters of precipitation, extraction, scrubbing, and stripping were optimized. • Cation exchange mechanism was involved in the extraction of vanadium. [ABSTRACT FROM AUTHOR]

The effective separation of K3VO4 and K2CO3 from KOH–K2CO3–K3VO4–H2O system plays an important role in a new vanadium production process developed by the Institute of Process Engineering, Chinese Academy of Sciences. In order to design an effective separation strategy, the dissolution behavior of K3VO4 and K2CO3 in KOH–K2CO3–K3VO4–H2O system at (313.15 and 353.15) K was investigated, and the solubility isotherms were plotted. In addition, the solubility of K3VO4 in KOH solutions was compared with that in K2CO3 saturated KOH solutions, and the solubility of K2CO3 in KOH solutions was also compared with that in K3VO4 saturated KOH solutions. From the solubility data analysis, a method of first separation K2CO3 via cooling crystallization followed by separation K3VO4 via cooling crystallization in the concentrated alkaline solution was proposed. [ABSTRACT FROM AUTHOR]