Study On Selective Dissolution Of Tungsten From Acid Decomposition Residues Based On The Self-coordination Property Of Tungsten

In order to solve the problem that tungstic acid is difficult to dissolve efficiently from sulfuric acid decomposition residues.This paper draws on the polycondensation theory of silicate melt,a method of dissolving tungstic acid based on the self-coordination property of tungsten is proposed.This paper investigates the dissolution mechanism of tungstic acid in tungstate solution,the leaching kinetics of decomposition residues,the optimization experiments of leaching conditions,the circulation and treatment of leaching solution,etc.The contents and conclusions are as follows:（1）The dissolution behavior of tungstic acid in tungstate solution was studied.Based on the self-coordination characteristics of tungsten,tungstic acid is dissolved by tungstate solution.After the reaction,the solid tungstic acid entered the solution in the form of isopolytungstate.The solubility of tungsten increased with the increase of temperature,p H and concentration of tungsten.The solubility of pure tungstic acid in isopolytungstate solution could reach 0.37 g/g,and the concentration of WO₃ was 549.8 g/L.（2）The kinetics of leaching of tungsten from scheelite sulfuric acid decomposition residue in isopolytungstate system was studied.The experimental data of dynamics under different conditions were fitted by Avrami equation with good linear correlation.The apparent activation energy of the reaction was 14.301 k J/mol,indicating that the reaction belonged to mixed control.The established kinetic equation was as follows:-ln（1-x）=7.5055C^0.1627 D^-0.4248W^-0.7576exp（-14301/8.314T）t^0.89（3）A new process of leaching tungsten from scheelite acid decomposition residue with isopolytungstate system/sodium tungstate system was developed,the feasibility of recycling leaching solution was investigated.Under the temperature of 80℃,initial concentration of 100g/L,liquid-solid ratio of 6:1,scheelite sulfuric acid decomposition residue was leached with isopolytungstate solution at p H 6.5.The leaching efficiency of tungsten was 98.94%（the leaching efficiency of tungstic acid was 100%）.The main chemical reaction equation in this process was:Na₆W₇O₂₄（aq）+5WO₃·H₂O（s）=Na₆H₂W₁₂O₄₀（aq）+4H₂O（l）.In the experiment,0.6-0.8 mol of tungstic acid could be dissolved by 1 mol of polymerized tungsten.Under the best conditions,sodium tungstate was used to leach hydrochloric acid decomposition residue,and the leaching efficiency of tungsten was 98.34%（the leaching efficiency of tungstic acid was 100%）.The main chemical reaction equation in this process was5Na₂WO₄（aq）+7WO₃·H₂O（s）=Na₁₀H₂W₁₂O₄₂（aq）+6H₂O（l）.And,the complete dissolution of tungstic acid could be achieved by adjusting the acidity and concentration of the leaching solution to leach acid decomposition residues of scheelite of different grades.The titration results showed that the alkali consumption of the leaching solution was very small.（4）A method of precipitating white tungstic acid from isopolytungstate solution was proposed and the effect of washing conditions on sodium removal from white tungstic acid was investigated.The isopolytungstate solution（p H=6）was pumped into 2.5 mol/L HNO₃solution at 40℃,the precipitation efficiency of white tungstic acid was about 97.43%.The white tungstic acid was easy to wash and remove impurities.After three times washing,it could achieve deep sodium removal combined with hydrogen peroxide solution,and most impurities reached the standard of 0-grade tungstic acid.Compared with the traditional treatment process,the leaching of acid decomposition residues by the tungstate system is not only environmentally friendly,the leaching solution can be recycled and alkali consumption is greatly reduced,but also economically feasible,which is expected to become a new clean and efficient tungsten leaching agent in the future.There are 66 figures,26 tables and 113 references in this paper...