Hydrothermal treatment of sphalerite and pyrite particles with CuSO4 solution

Abstract

• Hydrothermal treatment of ZnS and FeS 2 with CuSO 4 solution was studied. • Kinetics of the treatment is consistent with the shrinking core model. • Mechanism of hydrothermal conversion is elucidated. • Hydrothermal treatment of sulfide minerals is a multistage process. • Multilayer films of copper sulfides are formed on the surface of the treated minerals. The nature of the hydrothermal reaction between sphalerite (ZnS) and pyrite (FeS 2 ) particles and copper sulfate (CuSO 4 ) solution was investigated in this study. The effects of temperature (443–523 K), CuSO 4 (0.08–0.96 mol/L) and H 2 SO 4 (0.05–0.6 mol/L) concentrations, reaction time (1–120 min), stirring speed (40–100 rpm) and particle size (10–100 μm) on the conversion of sphalerite and pyrite were studied. The ZnS conversion was significant already at 443 K and the most complete conversion was observed at T > 503 K after 120 min of treatment. For FeS 2 , conversion of about 50 % was achieved only at T > 523 K. It has been experimentally shown that the FeS 2 treatment is a multistage process as the analysis of reaction kinetics suggests. The shrinking core model (SCM) was applied for describing the kinetics of the conversion process. Two stages of minerals’ transformation were conditionally identified: 1–600 s (Stage 1) and 1200–7200 s (Stage 2). Stage 1 is responsible for primary interaction between the minerals and CuSO 4 solution on the surface of the solid and the formation of a thin layer of Cu 1-x S sulfides, while in Stage 2 a denser layer of Cu 1-x S forms, which indicates a diffusion-controlled step. The reaction orders with respect to CuSO 4 and H 2 SO 4 as well as activation energies were calculated for the hydrothermal treatment of ZnS and FeS 2 with CuSO 4 solution, respectively for Stages 1 and 2. The reaction mechanisms in both stages were proposed, and some inconsistencies that were reported in previous studies were explained.