| As a characteristic vanadium resource in China,vanadium-bearing shale has a huge reserve of vanadium and great potential for development.Extracting vanadium from vanadium-bearing shale is an important way.Due to the complexity of vanadium shale,the extraction of vanadium requires a complex process contains leaching-purification enrichment-precipitation(calcination).The vanadium precipitation is an indispensable part,and its purification function determines the quality of the product.At present,the most widely used vanadium precipitation process in the industry is ammonium salt vanadium precipitation,but it will produce high concentration ammonia nitrogen wastewater and waste gas,which seriously hinders the green sustainable development of the vanadium industry.This study developed an environmentally friendly vanadium precipitation process by hydrothermal method with oxalic acid,which not only solves the ammonia nitrogen problem produced by the traditional ammonium salt vanadium precipitation process,but also can produce vanadium products directly used as battery electrode materials.The optimum conditions of vanadium precipitation for the preparation of Na V2O5 and VO2(B)by hydrothermal method with oxalic acid were studied by means of conditional experiments.The characteristics and electrochemical propertities of the product obtained under optimal conditions were studied by tests.The reaction mechanism of vanadium precipitation was investigated by analyzing the chemical reactions in the process.The effect of impurity ions in stripped vanadium solution on vanadium precipitation also be researched.Finally,a new type of green vanadium precipitation process from stripped vanadium solution of vanadium-bearing shale was developed.The main research contents and results are as follows:(1)By controlling experiment factors such as the p H value,temperature,time and molar ratio of oxalic acid to vanadium in the process of vanadium precipitation by hydrothermal with oxalic acid,the pure phase of Na V2O5 microrods and VO2(B)nanorod with high vanadium precipitation rate and purity were successfully prepared.(2)The effects of the main impurities like Al,Fe,Si and P in stripped vanadium solution on the vanadium precipitation of VO2(B)by hydrothermal method oxalic acid were studied.The three impurities like Al,Fe and Si in the stripped vanadium solution have little effect on the vanadium precipitation rate,but have a great influence on the content of V and impurities in the product.The presence of these three impurity ions in the solution will also affect VO2(B).The growth of these crystal faces causes the microstructure of the product to evolve from a rod shape to a granular shape,a block shape or a sheet shape.The vanadium precipitation is greatly affected by the concentration of P in the solution.When the P concentration is higher than 0.2 g·L-1,the product of vanadium precipitation changes from VO2(B)to Na0.45VOPO4·1.58H2O.(3)Different impurities have different effects on vanadium precipitation in the process of preparing Na V2O5 by hydrothermal method with oxalic acid.They reduced not only the vanadium precipitation rate,but also the purity of the product.The micro-morphology of Na V2O5 is also affected by the impurity ions in the stripped vanadium solution.When the impurity concentration was too high,it also combined with vanadium in the solution to form vanadates.In particular,an increase in the concentration of P caused the product to gradually convert from Na V2O5 to VO2(H2O)0.5 and then to Na3.053((V5O9)(PO4)2(OH)0.1(H2O)8.(4)In the vanadium precipitation process by hydrothermal method with oxalic acid,in order to obtain Na V2O5 or VO2(B)products with high vanadium precipitation rate and purity,it is necessary to control the concentration of Al,Fe and Si in the stripped vanadium solution to not exceed 0.5 g·L-1 and make the concentration of P lower than0.2 g·L-1.(5)By analyzing the chemical reactions of vanadium in the vanadium precipitation by hydrothermal process with oxalic acid from stripped vanadium solution,the formation mechanism of Na V2O5 is condensation(oxidation and oxidation)-embedded-reduction and self-assembly,and the formation process of VO2(B)is VO2+?VO2(C2O4)-?VOC2O4?VO2.The particle size and SEM image analysis of the products obtained from different reaction times showed that the formation of Na V2O5layered microrods conforms to the typical dissolution and recrystallization theory.(6)The Na V2O5 and VO2(B)products obtained under the optimal vanadium precipitation process conditions were directly used as battery electrode materials and showed good electrochemical performance.(7)A new process route of vanadium precipitation of Na V2O5 and VO2(B)by hydrothermal method with oxalic acid from stripped vanadium solution is proposed.Firstly,the ammonia nitrogen pollution caused by the traditional ammonium salt vanadium is sourcely avoided from this process.Simultaneously,the products of Na V2O5 and VO2(B)can be directly used as battery electrode materials,shortening the preparation process.The new process not only has good environmental benefits but also significant economic benefits. |
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