Fundamental Studies On The Leaching And Separation Of V³⁺ From Iron Vanadate Spinel Minerals

Vanadium is widely used in metallurgical,aerospace,chemical industry,and energy fields,thereby it is also nominated as "Aginomoto of modern industry".In recent years,the demand for vanadium has continuously increased due to the extensive application of vanadium products.However,to meeting this increasing demand,the sustainable development of vanadium production is a big challenge.Currently,the iron vanadate spinel(Fe3-xVxO4)minerals is the major feedstock for vanadium production,and vanadium in which is extracted mainly by oxidation roasting followed by wet leaching,such as sodium roasting-water leaching process?calcification roasting-acid leaching process,etc.Firstly,the structure of Fe3-xVxO4 is destroyed by oxidation roasting,and V3+is oxidized to V4+or V5+and form soluble vanadate.Then,the V-bearing leaching solution is obtained by wet leaching.However,these processes face the dilemma of seriouis environmental problems,such as high energy consumption,harmful gas emissions and poisonous residual,etc.In addition,a large amount of ammonia nitrogen wastewater is also produced in the subsequent vanadium precipitation process.To solve the above-mentioned problems from the source,a favorable choice is to directly leach and separate the V3+ ions from the Fe3-xVxO4 minerals.Therefore,the Fe3-xVxO4 concentrate beneficiated from stone coal was taken as the object,and the following studies was carried out:(1)Firstly,the E-pH diagram of V-Fe-H2O system at different temperature was constructed to study the feasibility of leaching V3+from the Fe3-xVxO4 minerals.Then,the leaching process of Fe3-xVxO4 concentrate by sulfuric acid solution was studied.The results indicated that V3+ in the Fe3-xVxO4 minerals was ultimately leached as V02+ions with leaching rate of 92.5%,and the impurity Fe was leached together with leaching rate of 98.5%.Then,after the iron impurity in the pregnant solution was removed efficiently by the precipitation method with Fe2O3 as nucleating agent,V2O5 with purity of 92%can be obtained by ammonium salt precipitation process.(2)To achieve the dircet leaching of V3+in the Fe3-xVxO4 minerals,the oxalic acid with complex ability was selected as the leaching agent in the follow experiments.Fistly,the dissolution behavior of Fe3-xVxO4 compounds with different Fe/V in oxalic acid aqueous solution was investigated,the results show that the leaching rate of V3+increased dramatically with the incrase of Fe/V ratio in the Fe3-xVxO4 compounds.In addition,the kinetics results of oxalic acid hydrothermal leaching the Fe3-xVxO4 concentrate show that the controlling step for the leaching process was interfacial chemical reaction.Therefore,it implies that reducing the concentration of Fe3+ in the leaching solution will intensify the dissolving of the Fe3+from the lattice of Fe3-xVxO4,and ultimately improve the V3+leaching rate.(3)Based on the above results,a novel method to extract vanadium by oxalic acid synergized with Fe powder under hydrothermal conditions was proposed,by which the direct leaching of V3+in the Fe3xVxO4 concentrate was achieved.With the synergy of Fe powder,the leaching rates of V3+ in the Fe3-xVxO4 concentrate were enhanced significantly,and simultaneously Fe3+ ions present as impurity in the pregnant leachate were eliminated effectively by forming FeC2O4·2H2O precipitate.Under the optimal leaching conditions,the leaching rate of vanadium can reach 95%,reducing Fe3+ ions contents to less than 100 mg/L.Untimately,the V-bearing oxalic acid leachate containing[V(C2O4)3]3-complex ions and FeC2O4·2H2O by-product with 98%purity were obtained.(4)To achieve the clean and effective precipitation of V3+ from the V-bearing oxalic acid leachate,the hydrothermal precipitation mechanism of V3+ from the V-bearing oxalic acid leachate was studied in detail.The results show that part of[V(C2O4)3]-complex ions could be oxidized to form VOC2O4 with the increase of temperature due to the existence of oxygen in the hydrothermal system.With the further increase of temperature,vanadium was precipitated as a mixture due to hydrothermal decomposition of[V(C2O4)3]3-complex ions and VOC2O4,and a higher than 99%of vanadium precipitation extent was obtained.(5)To further prepare vanadium oxide products from the V-bearing oxalic acid leachate,the dissolving and the precipitating behavior of V3+ions in V2O3-H2C2O4-H2O system were first studied at various H2C2O4 concentractions,and temperatures.According to the hydrothermal features of this system,two routes of preparing V2O3 were designed.In addition,the method of VO2 hydrothermal synthesis in the V2O5-H2C2O4-H2O system was introduced into the vanadium precipitation process to prepare VO2 product.Finally,V2O3 product with 91%purity and VO2 product with 97%purity were prepared,respectively.