Dissolution kinetics of marmatite in sulfuric acid-ferric sulfate‑sodium chloride‑oxygen media at atmospheric pressure

Abstract

An experimental investigation was carried out to improve the zinc dissolution rate in the direct atmospheric leaching of marmatite by adding sodium chloride to the sulfuric acid-ferric sulfate‑oxygen media. The experiments were carried out by using mono-sized marmatite particles varying the concentrations of sulfuric acid from 0.1 to 1.3 M, ferric sulfate from 0 to 0.8 M, sodium chloride from 0 to 1.3 M, and temperature in the range of 60 to 95 °C. The results showed that the addition of 0.7 M of sodium chloride improved drastically the direct leaching kinetics of the zinc sulfide; therefore, this leaching media is an excellent alternative to produce zinc from marmatite concentrates at ambient pressure. The sulfuric acid concentration was also found to have a significant effect on the rate of dissolution, indicating that the non-oxidative dissolution of marmatite plays an important role in the reaction mechanism in this system. A shrinking core model with diffusion through a product layer control was found to fit the reaction rate. An apparent activation energy value of 81.8 kJ/mol was found for the temperature range of 60–95 °C. The direct atmospheric leaching of marmatite in H2SO4-Fe(SO4)1.5-NaCl-O2 is an excellent alternative method to extract zinc due to high dissolution rates obtained in the presence of chloride ions, reducing substantially the treatment times.