Dissolution kinetics of smithsonite ore in ammonium chloride solution

The results of a dissolution kinetics study of smithsonite ore in ammonium chloride are presented. Effect of stirring speed, ore particle size, reaction temperature, and the concentration of ammonium chloride on zinc dissolution rate are determined. The results obtained show that leaching of about 91.2% of zinc is achieved using 84-110 μm ore particle size at a reaction temperature of 90 °C for 240 min reaction time with 5 mol/L ammonium chloride. The solid/liquid ratio was maintained constant at 1:10 g/mL. Leaching kinetics indicates that chemical reaction at the new particle surface and the diffusion through the inert particle pores together are the rate control steps. A corresponding mixed control model is found suitable to explain the relationship between the reaction time and the fraction of zinc leached. The apparent activation energy of this process is determined to be 21.3 kJ/mol.