Efficient dissolution of tungstic acid by isopolytungstate solution based on the polymerization theory of tungsten

The rare metal tungsten is a very important strategic metal. The traditional tungsten ore alkaline process has many problems, including the generation of alkali residue, ammonia‐nitrogen wastewater, and industrial wastewater during ion exchange. The feasibility of decomposing scheelite with sulfuric acid has been confirmed due to the economic and environmental pressures faced by scheelite decomposition; however, extracting tungsten from the decomposition residue is a difficult process. This study was based on the polycondensation theory of tungsten, in which tungstic acid (H2WO4) rapidly dissolves in isopolytungstate solution during the acid adjustment process of sodium tungstate solution. Taking advantage of the different polymerization morphologies, a new idea in which tungstic acid selectively enters the solution after the polycondensation reaction between tungstic acid and isopolytungstate is proposed. In this work, the dissolution of tungstic acid in isopolytungstate solution under different experimental conditions were studied. The results indicated that isopolytungstate solution can undergo polycondensation reaction with tungstic acid, and the dissolution of W reached 0.37 g/g under suitable dissolution conditions. Additionally, the residue formed in sulfuric acid decomposition had a satisfactory leaching effect of tungsten in the isopolytungstate solution with a WO3 leaching efficiency of about 98.8%. Tungsten in the hydrochloric acid decomposition residue could also be extracted efficiently in the form of an isopolytungstate solution with a WO3 leaching yield >99%. This work proposes a cleaner and more efficient idea for the selective dissolution of tungsten from the acid decomposition residue of scheelite.