Removal and utilization of calcite existed in scheelite by preparation of calcium sulfate whiskers

Abstract

In order to eliminate the effect of calcite associated with scheelite on the scheelite flotation, hydrochloric acid was used to dissolve the calcite, and the soaking solution was used to prepare CaSO4 whiskers by hydrothermal reaction with sulfuric acid at ambient pressure. First, the condition experiments of preparing CaSO4 whiskers by using CaCl2 and H2SO4 were carried out to optimize reaction parameters of the crystallization process. The optimal conditions were: at 102 °C reaction temperature, 0.5 mol/L reactant concentration and 60 min reaction time. Then based on the condition experiments and considering keeping acid concentration stable for achieving HCl recycling, Calcium sulfate whiskers with the average diameter of 1.41 μm and the average aspect ratio of 109 were prepared by the soaking solution after evaporating to half of its volume and 1.0 mol/L H2SO4 at 102 °C for 60 min. After ion exchange processing, the filtrate could be used as HCl in the process of HCl dissolution. Keywords: Calcium sulfate whiskers, Scheelite, Calcite, HCl, Hydrothermal reaction