Efficient leaching of scheelite in sulfuric acid and hydrogen peroxide solution

Abstract

The leaching of scheelite using H2O2 in a H2SO4 solution was assessed. In this sulfuric acid‑hydrogen peroxide leaching system, the conversion of CaWO4 to CaSO4·nH2O and H2WO4 together with the complexation of H2O2 with tungstic acid was utilized to efficiently and cleanly treat scheelite. The results showed that leaching of scheelite in this system was feasible, and the most suitable reaction conditions for the leaching of scheelite were defined, including the effects of sulfuric acid and hydrogen peroxide concentrations, reaction temperature and time, and the liquid-solid ratio (L/S ratio). Increasing the concentration of sulfuric acid to as high as 3 mol L−1 could significantly increase the leaching efficiency of scheelite. Increased concentration of H2O2 was also beneficial to the reaction. The decomposition of both H2O2 and peroxytungstic acid at temperatures above 45 °C decreased the leaching efficiency. The most suitable experimental reaction conditions were as follows: c(H2SO4) =3 mol L−1, c(H2O2) = 1.5 mol L−1, L/S = 10, 45 °C, and a reaction time of 90 min. Under these conditions, the leaching efficiency could reach as high as 99.7%. As such, it was apparent that the treatment of scheelite in this sulfuric acid‑hydrogen peroxide system could achieve a high leaching efficiency at a low temperature and normal pressure.