Green leaching of tungsten from synthetic scheelite with sulfuric acid-hydrogen peroxide solution to prepare tungstic acid

Abstract

Synthetic scheelite are considered as an important source of tungsten. In this study, an environment-friendly medium, H2SO4-H2O2 solution, was used to decompose synthetic scheelite. In the leaching process, tungsten was completely dissolved in peroxytungstic acid and separated from the insoluble CaSO4·nH2O. The solution containing tungsten was then treated by thermal decomposition to produce tungstic acid. The effects of the leaching and thermal decomposition parameters were investigated with the optimum conditions obtained as follows: leached at temperature of 50 °C, H2SO4 concentration of 2.0 mol/L, H2O2 concentration of 2.5 mol/L and L/S of 6 mL/g for 60 min; thermal decomposed at 90 °C for 4 h. Under the optimum conditions, 98.0% of tungsten was leached from CaWO4 and 99.3% of tungsten was precipitated from lixivium. Mineralogical characterization of the residue shows that solid CaSO4·nH2O dispersedly distributes in the residue and does not wrap the unreacted CaWO4, thus CaWO4 can be leached effectively.