Thermodynamic Analysis of Zinc Sulfide Dissolution Stoichiometry in Sulfuric Acid Solution with Oxygen Participation

Abstract

In this work, a thermodynamic study of zinc sulfide high temperature oxidative leaching was carried out. At the metals sulfides dissolution under oxidants action in acidic solutions several simultaneously proceeding reactions are possible. With the aim finding the proportion of potential reactions, a thermodynamic calculation was carried out using stoichiometric equations with equal oxidant consumption. Moreover, stoichiometric coefficients were chosen in such a way that reagents could exchange 1 mole of electric charge. Such an approach allows one to ensure a comparison of different oxidants’ usage effectiveness for sulfide leaching. Thermodynamic analysis results are in accordance with experimental data, which confirm that reactions with the formation of sulfur and sulfate-ions are uppermost at zinc sulfide dissolution in sulfuric acid solutions under oxygen action. Oxygen consumption and initial sulfuric acid concentration influence on proportion of this reactions and zinc equilibrium concentration in solution were investigated. Thermodynamic analysis showed that at insufficient acid concentration, which limits the maximum degree of zinc sulfide oxidation reaction advancements with sulfur formation, oxygen is consumed on oxidation reaction with the formation of sulfate-ions, which spend oxygen less effectively, due to four times smaller zinc dissolution. Thermodynamic calculations carried out allowed us to find out optimal proportions of oxygen consumption and initial sulfuric acid concentration, which provide achievement of a maximal zinc equilibrium concentration in solution at a higher effectiveness of oxidant consumption without labor-intensive experiments. At optimal acid consumption, a zinc equilibrium concentration is directly proportional to initial acid concentration. Directly proportional dependence of zinc cations’ formation on acid consumption was also detected at acid concentration optimal values.