Stoichiometric and Kinetic Effects on the Pressure Leaching of Zinc Concentrates

n this study we have sought to highlight the critical linkage between individual reaction kinetic parameters (usually determined in small bench scale experiments) and large continuous reactor performance by focusing on the industrially significant zinc pressure leach process. To this end a comprehensive mathematical model previously developed for the description of this process was employed. In this paper we have examined in particular how small variations in key kinetic parameters impact on the autoclave&apos;s performance, i.e. attainment of autogenous steady-state temperature, zinc conversion and solution chemistry. The reaction parameters studied were: (i) stoichiometry of the marmatite leaching reaction; (ii) the activation energy of the same reaction, E,; (iii) the rate constant of the ferrous to ferric oxidation reaction, k,; and (iv) the apparent equilibrium constant for ferric precipitation, K,. This parameter sensitivity analysis was done under no oxygen mass transfer control limitations. Model predictions were found to be more sensitive to the kinetic parameters under certain conditions than others. The most dramatic finding was the one related to the small amount of sulfate produced during marmatite leaching. In connection to this it was found that the small percentage (< 5 %) of sulfate produced enhances the autothermal operational stability of the autoclave. The need for accurate kinetic parameter determination under conditions similar to those encountered in industrial zinc pressure leaching was demonstrated.