Features of the Interaction of Scheelite with HCl Solutions at 400 and 500°C, 100 MPa, and Various f(O2) (According to Experimental and Calculated Data)

Abstract

Experimental studies were carried out on the solubility of scheelite in HCl solutions in the concentration range from 0.01 to 0.316 mol/kg H2O at 400 and 500°C, a pressure of 100 MPa and the fugacity of oxygen (hydrogen) specified by the buffers Cu2O–CuO, Fe3O4–Fe2O3, Ni–NiO, and Co–CoO. It was found that scheelite in HCl solutions at the specified parameters dissolves incongruently. In solutions containing from 0.01 to 0.0316 m HCl, minor amounts of WO3 and/or WO3 – x tungsten oxides are found in the run products, along with scheelite. In solutions containing from 0.1 to 0.316 m HCl, the formation of calcium tungsten bronzes CaxWO3 is observed, the average composition of which corresponds to the formula Ca0.07WO3. Based on the analysis of the experimental data obtained, the free energies of the formation of tungsten oxides WO3, WO2.9, scheelite, and calcium tungsten bronze were calculated. Using mutually agreed thermodynamic data, the solubility of Sch in solutions of HCl and (Na, K)Cl with the participation of aluminosilicates is calculated. It is shown that the scheelite has a wide area of congruent solubility in saline systems.