Thermodynamic analysis of zinc sulfide dissolution stoichiometry in sulfuric acid solution with oxygen

A thermodynamic study of zinc sulfide high temperature oxidation leaching was conducted. Several processes can run simultaneously while metal sulfides are dissolved by oxidants in acidic solutions. Thermodynamic calculations were made using stoichiometric equations with equal oxidant consumption in order to identify the proportion of potential reactions. Moreover, stoichiometric coefficients were chosen in such a way as to reagents could exchange 1 mole of electric charge. This approach ensures a comparison of different oxidants in terms of their effectiveness in sulfides leaching. Thermodynamic analysis results obtained agree with experimental data confirming that oxidizing reactions with the formation of sulfur and sulfate ions prevail in zinc sulfide dissolution in sulfuric acid solutions under the oxygen effect. The effect of oxygen consumption and initial sulfuric acid concentration on the proportion of these reactions and equilibrium concentration of zinc cations in the solution was studied. Thermodynamic analysis showed that if the acid concentration is insufficient and limits the maximum progress of zinc sulfide oxidation with sulfur formation, oxygen is also consumed for the oxidation reaction with the formation of sulfate ions spending oxygen less effective due to 4 times less zinc cations passing to the solution. Thermodynamic calculations made it possible to find out the optimal proportions of oxygen consumption and initial sulfuric acid concentration to achieve the maximum zinc equilibrium concentration in the solution with more effective oxidant consumption without any labor-intensive experiments. The equilibrium concentration of zinc cations in the solution is in direct proportion to the initial acid concentration, and zinc cation formation is in direct proportion to oxygen consumption at the optimal acid concentration.