Vanadium Precipitation Research Articles

An innovative process for clean ammonium-free vanadium precipitation and one-step preparation of vanadium dioxide based on hydrothermal enhancement of organic alcohols

As a transition metal oxide, VO2 has excellent optical and electrical properties and is widely used in many fields. The production of VO2 by the reduction of NH4VO3 and V2O5 will inevitably produce ammonia–nitrogen wastewater and NH3 emission during the production of NH4VO3 and V2O5, which will cause serious environmental pollution and will increase economic costs. The large-scale and low-cost synthesis of VO2 still faces great challenges. In this paper, VO2(B) was successfully prepared by a one-step hydrothermal method using NaVO3 as the vanadium source and CH3CH2OH as the reducing agent, and the optimal conditions for vanadium precipitation are as follows: vanadium concentration = 30 g/L, CH3CH2OH dosage = 20 % (percentage of solution volume), initial pH = 1, reaction temperature = 220 °C, reaction time = 12 h. The vanadium precipitation efficiency under the optimal conditions could reach 98.93 %, and the purity of VO2(B) could reach 98.59 %. The precipitation products were characterized by XRD, TG, FTIR, XPS, and SEM-EDS. The mechanism of VO2(B) preparation by ethanol reduction was proposed. This process is characterized by green, clean, and high efficiency. At the same time, the vanadium precipitation effect and vanadium precipitation products of various alcohols were studied to provide technical and theoretical support for the preparation of VO2(B).

Thermodynamic simulation of stepwise precipitation of NH4VO3 and NaHCO3 from carbonating Na3VO4 solution

Thermodynamic simulation was conducted to design a new process of stepwise precipitating NH4VO3 and NaHCO3 from regulating the CO2 carbonation of Na3VO4 solution. Firstly, a new V(V) speciation model for the aqueous solution containing vanadate and carbonate is established by using the Bromley−Zemaitis activity coefficient model. Subsequently, thermodynamic equilibrium calculations are conducted to clarify the behavior of vanadium, carbon, sodium, and impurity species in atmospheric or high-pressure carbonation. To ensure the purity and recovery of vanadium products, Na3VO4 solution is initially carbonated to the pH of 9.3−9.4, followed by precipitating NH4VO3 by adding (NH4)2CO3. After vanadium precipitation, the solution is deeply carbonated to the final pH of 7.3−7.5 to precipitate NaHCO3, and the remaining solution is recycled to dissolve Na3VO4 crystals. Finally, verification experiments demonstrate that 99.1% of vanadium and 91.4% of sodium in the solution are recovered in the form of NH4VO3 and NaHCO3, respectively.

The effect of impurity in vanadium-rich solution on vanadium precipitation of VO2(B) by hydrothermal method

The effect of iron, aluminum, silicon and phosphorus in the vanadium-rich solution on the vanadium precipitation of VO2(B) by hydrothermal method were studied. Through the analysis of vanadium conversation efficiency, the content of V and impurity elements in precipitates and their existing form, product crystal structure and micromorphology, it is concluded that the effect following the order of P > Fe > Si > Al. As the impurity concentration increased, V content of the precipitates decreased to varying degrees, while impurity content increased. The exist of Al, Si, Fe and P could alter the diffraction peaks intensity of some crystal faces and the micromorphology of VO2(B). The high concentrations of Fe and P transformed the VO2(B) to Fe2.5V7.1O16 and Na0.45VOPO4·1.58 H2O, respectively. V and P are easily combined by covalent bonds, affecting the precipitation of VO2(B). Silicon is adsorbed on the surface of the precipitate as silica gel, thereby reducing the purity of the precipitate. The influence of impurity elements in vanadium-rich solution on the precipitation of VO2(B) by hydrothermal method is studied, which will provide a theoretical basis for the application of the new process of vanadium precipitation by hydrothermal method.

Rapid precipitation of vanadium from solution using melamine as precipitant with high efficiency

AbstractBACKGROUNDSelective catalytic reduction (SCR) can effectively remove NOx from flue gas in a coal‐fired power plant. As the core of SCR technology, the catalyst has a limited lifespan. The process of reducing acid leaching and roasting water leaching can efficiently extract vanadium and tungsten from spent SCR catalyst. For vanadium recovery in solution, the traditional vanadium precipitation process by NH4Cl has the disadvantages of consuming high precipitant dosage and producing large amounts of waste water.RESULTSThis study focused on the vanadium precipitation process using a solution containing vanadium obtained from adopting some steps to handle the spent SCR catalyst. First, melamine was screened out as the vanadium precipitant. Then, the vanadium precipitation conditions were optimized as follows: solution pH value of 1.0, n(C3H6N6)/n(V) = 0.8, 110 °C and 30 min. Under the best precipitation conditions, the vanadium precipitation efficiency of melamine can reach 99.32%. Finally, the mechanisms of vanadium precipitation by NH4Cl and melamine were discussed, respectively.CONCLUSIONThe results showed that the vanadium precipitation process by NH4Cl followed the chemical reactions between NH4+ and vanadium ions, while the vanadium precipitation process by melamine followed the redox and complexation reactions which essentially belonged to the types of chemical adsorption. The vanadium precipitation product was roasted at 550 °C for 2 h to obtain the vanadium product. The main component of the vanadium product was V2O5, with a purity of 93.27 wt%. The total recovery efficiency of vanadium from spent SCR catalyst was 78.24%. © 2024 Society of Chemical Industry (SCI).

A clean metallurgical process for vanadium precipitation from vanadium-rich solutions

Ammonium salt vanadium precipitation process has excellent performance in industrial production, but its shortcomings such as high cost and environmental impact are not conducive to sustainable development. In this paper, ethylenediamine was selected as the precipitant, and vanadate was precipitated from acidic simulated vanadium-rich solutions by the ammonium salt precipitation process. The high purity V2O5 product was obtained after calcination. Under optimal conditions, the precipitation rate of vanadium reached 94.8 %, and the purity of vanadium was as high as 99.1 %. The vanadium precipitation product was hexamethyl ammonium, and the vanadium product was V2O5. It can be derived by the differential method that the reaction order was n = 2.4, the reaction rate equation was CV-1.4=kt+a, and the apparent activation energy was 27.8097 kJ/mol, which can be classified as the diffusion-controlled reaction. This innovative process enables a savings of 5050 yuan per ton of V2O5. On this basis, a complete V2O5 production process with zero waste discharge was designed.

Comprehensive recovery of valuable elements from vanadium precipitation liquor using selective impurity removal-reduction precipitation process

The vanadium precipitation liquor produced by the vanadium slag extraction process contains various valuable elements, which are not utilized at high value. In this paper, chromium is recovered through aluminum salt impurity removal - chemical reduction precipitation method. Moreover, the ammonia nitrogen and sodium sulfur in the vanadium precipitation liquor are recovered by stripping and crystallization, thereby achieving comprehensive resource recovery and utilization. The aluminum salt slag removal reduction chemical precipitation method is used to separate Cr from Si, Ca and V impurities. As a result, the obtained Cr2O3 product has a purity of 98.20%, the chromium recovery efficiency is 97.58%, and the silicon removal efficiency reaches 99.66%. The ammonia nitrogen was recovered by stripping, which would be reused to the vanadium precipitation process, with an ammonia nitrogen stripping efficiency of 98%. The purity of NH4Cl is 99.13% and meets the 99-level national standard. The Na2SO4 was recovered by evaporation concentration - crystallization method, which would be reused to the vanadium slag roasting process, with a Na2SO4 recovery efficiency of 88.38%. And the purity of Na2SO4 is 98.85%, which meets the industrial standard for Class II Na2SO4 products. The final solution after comprehensive recovery of valuable elements would be reused to the leaching process, thereby achieving water circulation. This process realizes the high-value utilization of chromium, ammonia, nitrogen, sodium and sulfur, and has no wastewater discharge and is an environment-friendly route.

OPTIMIZING VANADIUM CONVERTER SLAG UTILIZATION: TARGETED ENRICHMENT AND STABILIZATION OF VANADIUM THROUGH NON-EQUILIBRIUM SOLIDIFICATION

The objective of this research was to optimize the comprehensive utilization of vanadium converter slag through targeted enrichment and stabilization of heavy metal vanadium. Employing the non-equilibrium solidification theory and FactSage software, we investigated the potential of modifying vanadium converter slag. When the original slag failed to generate vanadium-rich spinel with usable V elements, introducing modifying agents Fe and Al proved effective. Fe facilitated the enrichment of Cr within spinel, while Al significantly promoted the V enrichment. Expanding on this, we systematically examined the influence of Fe2O3, Al2O3 and MgO contents on spinel phase precipitation during vanadium slag solidification. The addition of Al resulted in the precipitation of corundum, hematite, spinel, olivine and diopside phases. With an increase in the Fe2O3 content, the precipitation of FeV2O4 and MgV2O4 initially increased, peaking at 9.67 % before subsequently decreasing. Maintaining the Fe2O3 content within a range of 25–30 % proved optimal for enhancing vanadium precipitation and enrichment. In contrast, variations in the Al2O3 content had minor impacts on SP-V phase precipitation, with slight effects on FeV2O4 reaching 10.34 %. Furthermore, the incorporation of MgO facilitated the precipitation of MgV2O4 while concurrently suppressing the FeV2O4 precipitation. By judiciously controlling the MgO content at approximately 20 %, vanadium enrichment in the form of FeV2O4 and MgV2O4 spinel phases reached a remarkable 94.46 %.

Preparation of V2O3 by a short process of ammonium salt reduction and its electrocatalytic properties investigation

Ammonium salt vanadium precipitation is the main method of vanadium metallurgy at home and abroad, but the traditional ammonium precipitation of vanadium can only obtain high valence of V2O5, and the NH3 produced in the calcination process cannot be fully utilized. And the preparation of low-valence vanadium oxide V2O3 is long and costly. Self-reduction of thermal decomposition of nitrogen-containing precipitation products to produce V2O3 is a novel and short process method that can achieve full utilization of ammonia. NaVO3 was used as the vanadium source, choline chloride (C5H14ClNO (ChCl)) was used as the vanadium precipitation reagent, and the vanadium concentration was 30 g/L, n(ChCl)/n(V) = 1.5, the initial pH was 1.5, the temperature was 85°C, the time was 2 h, and the vanadium precipitation efficiency could reach 97.05%. V2O3 with purity of 97.98% can be obtained by calcination at 550°C for 3 h in an argon atmosphere. XRD, FTIR, XPS, SEM-EDS were used to characterize the product, which further proved that the final product was V2O3. The electrocatalytic hydrogen evolution reaction (HER) of V2O3 in acidic media showed high stability after 1000 cyclic voltammetry (CV) cycles, with a low Tafel slope of 88.5 mVdec−1. The electrochemical double layer capacitance (EDLC) was measured by CV at different scan rates, and the EDLC of V2O3 was 1.104 mFcm−2. This study provides a short-flow preparation method for V2O3 and can provide predictions for the application of V2O3 in HER and supercapacitors.

Recovery of Vanadium from Carbonated Solution by Extraction with Transformed Aliquat 336 and Stripping-Precipitation

ABSTRACT The leaching solution from the direct reduction-sodium smelting process of ultra-poor vanadium-bearing titanomagnetite contained sodium, vanadium, and impurities. It was carbonated to ensure sodium recovery, and the recovery of vanadium proved challenging. This study proposed and optimized a novel process of extracting vanadium from this alkaline carbonated solution using the transformed organic phase of 20 vol% (0.44 mol/L) Aliquat 336, 8 vol% 2-octanol, and 72 vol% sulfonated kerosene. To achieve superior vanadium extraction, Aliquat 336 in the organic phase was transformed into carbonate type by successively washing with NaHCO3 and NaOH solutions. The single-stage extraction efficiency of vanadium exceeded 85% at a pH of 8.0‒9.0 and an organic-to-aqueous phase ratio of 1:1. The thermodynamics of the vanadium extraction process was examined, confirming that the extraction process is an exothermic reaction (ΔH 0 = −9.56 kJ/mol). Furthermore, using a solution of 4 mol/L NH4Cl and 1 mol/L NH4OH with a pH of 8.8 as the effective stripping reagent to realize one-step stripping and precipitation of vanadium, the single-stage stripping efficiency of vanadium was 99.8%, and the precipitation efficiency was about 95%. Through this stripping-precipitation process, solid ammonium metavanadate with a purity of 98.14% was obtained in one step. The mechanisms of transformation, extraction, and stripping were studied via infrared spectra of the organic phases.

A Review of Capacity Decay Studies of All-vanadium Redox Flow Batteries: Mechanism and State Estimation.

As a promising large-scale energy storage technology, all-vanadium redox flow battery has garnered considerable attention. However, the issue of capacity decay significantly hinders its further development, and thus the problem remains to be systematically sorted out and further explored. This review provides comprehensive insights into the multiple factors contributing to capacity decay, encompassing vanadium cross-over, self-discharge reactions, water molecules migration, gas evolution reactions, and vanadium precipitation. Subsequently, it analyzes the impact of various battery parameters on capacity. Based on this foundation, the article expounds upon the significance of battery internal state estimation technology. Additionally, the review also summarizes domestic and international mathematical models utilized for simulating capacity decay, serving as a valuable reference for future research endeavors. Finally, through the comparison of traditional experimental methods and mathematical modeling methods, this article offers effective guidance for the future development direction of battery state monitoring. This review generally overview the problems related to the capacity attenuation of all-vanadium flow batteries, which is of great significance for understanding the mechanism behind capacity decay and state monitoring technology of all-vanadium redox flow battery.

A novel ammonium-free vanadium precipitation process for the integrated actions of ascorbic acid reduction and enhanced hydrolysis under hydrothermal influence

Vanadium-titanium magnetite is an important source of vanadium, and V2O5 is the main vanadium product. At present, the production of V2O5 is mainly obtained by sodium salt roasting and ammonium salt precipitation, while ammonia nitrogen wastewater and NH3 discharge will cause serious environmental pollution. Calcium and iron salts are mainly intermediate products, and vanadium oxides cannot be obtained directly. Therefore, a clean and sustainable method is proposed to produce V2O5 by ascorbic acid hydrothermal reduction in one step. When the vanadium concentration is 25.48 g/L, under the optimal vanadium precipitation conditions: the ascorbic acid addition ratio is n(ASA): n(V) = 0.1:1, the reaction temperature is 210 °C, the solution pH is 1.25, and the reaction time is 10 h, the precipitation efficiency and V2O5 purity can be 99.60% and 99.12%, respectively. The kinetics and apparent activation energy of the reaction were investigated, and the apparent activation energy was calculated to be 68.80 kJ/mol. The product obtained was characterized by XRD, SEM-EDS, XPS and FTIR, proving that the final product is V2O5. The reaction mechanism of ascorbic acid and vanadium in solution is single electron transfer and recombination, and the formation process of V2O5 is: VO3- → VO2+ → VO2 or V2O3 → V2O5, and ascorbic acid is oxidized to dehydroascorbic acid. In conclusion, the production of V2O5 by hydrothermal reduction of ascorbic acid is environmentally friendly, clean, simple, and efficient.

Cleaner and cost-efficient hydrometallurgical process for extraction of vanadium from Bayer vanadium sludge based on BaSO4, NaOH, ammonium, and water circulation

Bayer vanadium sludge(BVS) is a hazardous waste due to its high contents of V, P, As, and F. Full or partial utilization of this sludge could not only minimize the potential environmental risk but also promote resource recycling. In this work, a cleaner and cost-efficient process was proposed to selectively extract vanadium from BVS by employing BaSO4 as precipitant. Under the optimal conditions, a maximum vanadium precipitation efficiency of 97.86% is achieved, whereas only 1.15% arsenate and 0.12% fluoride are co-precipitated. Afterwards, the generation of 2Na3AsO4·NaF·19 H2O and NaSO4·NaF has enhanced the simultaneous removal of As and F during evaporation crystallization, and achieving the recycling of NaOH. A new strategy was adopted to in-situ convert Ba3(VO4)2 into Ba(VO3)2·H2O which can be directly leached in (NH4)2SO4 solution. Furthermore, 99.78% vanadium is precipitated as (NH4)2V6O16 from the leachate and the V2O5 product with a purity of 99.85% is prepared after calcination. The leaching residues and the spent liquor containing large amounts of NH4+ after (NH4)2V6O16 precipitation can be circulated to the next batch of vanadium precipitation and leaching, respectively. Herein, the process realizes the internal circulation of BaSO4, NaOH, ammonium, and water, saving production costs and avoiding environmental pollution.

Effects of key impurities (Al, Fe, P, Si and Na) on the precipitation process of vanadium in the novel ultrasound-assisted precipitation system

The effects of Al, Fe, P, Si and Na on the precipitation characteristics of vanadium in the ultrasound precipitation (UP) system were firstly investigated to establish the applicable vanadium-rich solution system and reveal the relevant mechanisms. The experimental results indicate that NaAl8V10O38•30H2O generated at 3.0 g/L Al hinders the reaction between vanadium and NH4+ and hence decreases the precipitation efficiency and purity of the vanadium products. Iron barely affects vanadium precipitation efficiency. Nevertheless, it might integrate into the precipitates by superficial adsorption or formation of an iron-bearing phase at 0.2 g/L and 0.4 g/L, respectively, leading to a significant decrease of the purity of products. Sodium has a negative effect on the purity of products when the concentration exceeds 15 g/L, ascribing to the formation of NaV3O8 and Na2V6O16•3H2O. Phosphorous can unevenly adsorb on the crystals' surface when the concentration exceeds 0.02 g/L, and it would induce the generation of sodium vanadate salts, which further hinders the growth process of the crystals and deteriorates the crystallinity and structure of the precipitates. Silicon has no adverse effects on the precipitation of vanadium at the studied concentration ranges. Herein, the concentration upper limit of Al, Fe, P and Na is confirmed as 0.3 g/L, 0.05 g/L, 0.02 g/L and 15 g/L, respectively. The precipitation rate constant at corresponding upper limit of Al, Fe, P and Na is 0.092 min−1, 0.118 min−1, 0.209 min−1 and 0.433 min−1, respectively, implying that the magnitude of the negative influence of impurities on vanadium precipitation kinetics decreases in the order Al > Fe > P > Na. The present work may provide theoretical and technical support for the industrial application of the UP technology.

Cleaner and cost-efficient extraction of vanadium from Bayer vanadium sludge based on BaCO3, NaOH, and ammonium circulation

Bayer vanadium sludge, as a by-product generated from the Bayer process, is a potential secondary resource for vanadium recovery. To alleviate the problems of reagent consumption and effluent treatment presented in vanadium extraction processes, a novel and sustainable process featuring phosphate removal by CaCO3, vanadium precipitation by BaCO3, and NH4HCO3 leaching is carried out to separate and recover vanadium from Bayer vanadium sludge efficiently based on thermodynamic analysis. A maximum phosphate removal efficiency of 99.88% is achieved with a Ca/P molar ratio of 5 at 90 °C for 3 h, whereas the loss of vanadium is only 0.25%. Moreover, 98.57% of vanadium along with only 1.15% arsenate and 0.12% fluoride are co-precipitated from phosphate-free liquors containing 60 g/L NaOH with a Ba/V molar ratio of 1.6 at 90 °C for 4 h. After vanadium precipitation, the remaining large amounts of NaOH in supernatant can be recycled after the removal of arsenate and fluoride by evaporation crystallization. The NH4HCO3 leaching results illustrate that the vanadium leaching efficiency reaches 95.99% under 100 g/L NH4HCO3 at 70 °C for 30 min with a liquid-to-solid ratio of 20. The NH4VO3 in the leaching liquor can be readily crystallized by cooling, and then V2O5 product with a purity of 99.81% is prepared after calcination. The leaching residues and the spent liquor after crystallization can be circulated as vanadium precipitant and leaching medium, respectively. Herein, three circulation routes realize the closed-circuit circulation of BaCO3, NaOH, and ammonium, saving production costs and avoiding effluent pollution.

Reactive crystallization of ammonium polyvanadate from vanadium-bearing solution assisted by efficient ultrasound irradiation: Crystallization characteristics and growth process

Ultrasound crystallization (UC) technique was previously proposed to solve the issues caused by the acidic ammonium salts crystallization of vanadium. In this work, the influence of various parameters on vanadium crystallization characteristics were detailedly investigated. Results showed that high vanadium precipitation ratio (99.67%) and V2O5 purity (99.50%) of the final products can be obtained under the conditions of ultrasonic power of 600 W, initial pH value of 2.0, reaction temperature of 95 °C, ammonium salt addition coefficient of 0.5, reaction duration of 5 min and vanadium concentration of 20 g/L. Moreover, the NH4+ content in the supernatant liquid was notably reduced to 1.08 g/L. Crystallization kinetic analysis manifests that the crystallization rate constant augments with the increasing temperature, and the activation energy and pre-exponential factor is 71.87 kJ/mol and 7.44 × 109, respectively. Ultrasound enhances the collision frequency between NH4+ and vanadium ions, further improving the crystallization rate of the (NH4)2V6O16 crystals. Meanwhile, ultrasound induces a secondary nucleation, which would promote the intercalation among small flakes and further improves the nucleation and growth of the (NH4)2V6O16 crystals. Scanning electron microscopy analysis demonstrates that the flaky crystals are firstly formed, then a part of flakes gradually intercalate with each other, and finally most of the lamellar crystals complete the intercalation process. Meanwhile, selected area electron diffraction verifies the single crystalline characteristic of the micron-flakes, which grows along the (010) crystal plane. This work will lay theoretical and technical basis for UC technique appliance and promote the progress of the vanadium extraction industry.

Implication of hydrolysis on vanadium precipitation with acidic ammonium salt from high concentration of alkaline vanadium solution

Implication of hydrolysis on vanadium precipitation with acidic ammonium salt from high concentration of alkaline vanadium solution

Short-Process Preparation of High-Purity V2O5 from Shale Acid Leaching Solution via Chlorination

The conventional V2O5 preparation processes include ion exchange, chemical precipitation, solvent extraction, and other processes. Given the long process and complex operation nature of traditional V2O5 production methods, we herein developed a short-process, low-temperature, and convenient operation method of isolating vanadium (in the form of V2O5) from shale acid leaching solution. The acid leaching solution was oxidized with NaClO3 and pH-adjusted with NaOH to form a vanadium-containing precipitate, which was mixed with AlCl3 (V:AlCl3 = 1:5, mol/mol) and roasted for 120 min at 170 °C to afford vanadium oxytrichloride (VOCl3) with a purity of 99.59%. In addition, the vanadium-containing precipitate was mixed with AlCl3 and NaCl (V:AlCl3:NaCl = 3:12:8, mol/mol/mol) and roasted for 120 min at 170 °C to afford VOCl3 with a purity of 99.94%. VOCl3 (purity of 99.94%) was dissolved in ultrapure water, and the solution (32 gvanadium/L) was treated with NH3·H2O (NH3:V = 1.34, mol/mol) at 50 °C for 120 min. The obtained precipitate (vanadium precipitation rate = 99.28%) was roasted at 550 °C for 3 h to afford high-purity vanadium pentoxide (V2O5) with a purity of 99.86%. Compared with the traditional hydrometallurgical method of V2O5 preparation, our method avoided solvent extraction and other undesired processes and the overall process flow is greatly shortened, thus having high practical value.

Study on Precipitation Kinetics of Calcium Pyro-Vanadate and Thermodynamics of Vanadium Water System

Selective catalytic reduction (SCR) is a technology widely used in large coal-fired units to remove nitrogen oxides from flue gas, but it also generates a large number of waste catalysts every year. At present, the recovery of V from discarded SCR catalysts has good application prospects and environmental significance. In this paper, the kinetics and thermodynamics of vanadium precipitation process are described with the vanadium-containing liquid of waste denitration catalyst recovered by alkali leaching as raw material and CaCl2 as precipitant in order to further explore the mechanism of vanadium precipitation. The kinetics study showed that the crystallization process of calcium pyrovanadate can be well-described by Avrami kinetic model when the precipitation time is 95–130 min, and the vanadium precipitation temperature is 60–80 °C. After that, the Arrhenius equation was used to analyze the fitted kinetic data, and the apparent activation energy Ea of vanadium precipitation reaction was calculated to be 98.196 kJ/mol, and the pre exponential factor A = 8.59 × 1039 min−1. Thermodynamic study showed that when the pH of the vanadium water system is low, the +5 valence vanadium in the solution mainly exists in the form of VO2+ cation. When the pH is between 0–1, the solubility of vanadium reaches the minimum and then increases the solution pH again, and various polymerized anions are formed in the vanadium water system. When the temperature is 25 °C, the activity of vanadium in vanadium-containing solution is 10−1, the pH of solution is 8–12, and the existence form of +5 valence vanadium in solution is mainly HV2O73−. By analyzing the existing forms of V with different activities in a vanadium water system at 25 °C, it can be seen that with the decrease of V activity in liquid, the dominant region of polymerized vanadium-containing species in the potential pH diagram will disappear, indicating that vanadium mainly exists in the form of mononuclear ions in low-concentration vanadium-containing solutions, which is not conducive to precipitation. Therefore, in the process of precipitation of vanadium in solution, the concentration of V should be increased as much as possible.

Selective Leaching of Vanadium from Calcification-Roasted Pellets of Vanadium–Titanium–Iron Concentrate by a Cyclic Two-Stage Sulfuric Acid Process

Here, a process for leaching vanadium from calcified roasting pellets (CPVC) of vanadium–titanium-iron concentrate by a two-stage sulfuric acid cycle was proposed. The first stage of leaching was mainly for the removal of silicon from the pellet and leaching solution. After the second stage, the total leaching rates of vanadium and iron were 75.52% and 0.71%, respectively. The concentration of vanadium in the leaching solution reached 6.80 g/L, which can subsequently direct a vanadium precipitation process without extraction and enrichment. After the second roasting, the crushing strength of the pellets reached 2250 N, which met the requirement for blast furnace iron making. The Eh-pH diagrams of the V-Fe-H2O system at different temperatures were plotted. Thermodynamically, it was difficult to selectively leach vanadium and iron by changing the conventional acid leaching conditions. In addition, the pellets before and after leaching were analyzed. The grade of iron in the pellets increased slightly after leaching, and the main phases in the pellets remained as Fe2O3 and Fe9TiO15. The S in the sulfuric acid solution entered the leached pellets during the acid leaching reaction and was removed by the second roasting of the leached pellets.

Short flow and eco-friendly process for V2O3 preparation via hydrogen-catalyzed solution-phase method

V2O3 is mainly used to prepare ferro-vanadium. The introduction of solution-phase hydrogen reduction (SpHR) can reduce energy consumption, shorten the process and decrease ammonia pollution. In order to improve the hydrogen activity, PdCl2, Ni powder, and anthraquinone were selected as catalysts. Under the optimum condition, the precipitation ratio of product catalyzed by Ni powder was similar to that catalyzed by PdCl2, which were 99.80 % and 99.74 %, respectively. The purity of products met the requirements of GB 40301–2021, and the particle size of product catalyzed by Ni powder was more uniform. The products of SpHR with anthraquinone and auto-catalysis were Na(V2O5) and VO2(H2O)0.5, respectively. The activation energy of reaction catalyzed by PdCl2 and Ni powder were 38.0679 kJ/mol and 140.0909 kJ/mol, respectively. In the process of hydrogen-catalyzed, H2 molecule adsorbs on the surface of Ni or Pd, and form two Me-H bonds with strong reducibility, and its s orbital is hybridized with the d orbital of Pd and Ni. PdCl2 and Ni powder reduced the hydrogen dissociation energy from 434 kJ/mol to 30.3960 kJ/mol and 63.8332 kJ/mol, respectively. The phase transformation of vanadium precipitation by SpHR with the intervention of Ni catalyst is: HV10O285- or V(V) amorphous precipitation → filamentous Na2V6O16·3H2O → irregular flake Na(V2O5) → flaky VO2(H2O)0.5 → cross-like VO2(H2O)0.5 → rhombohedral V2O3.