simulation model for direct leaching of zinc concentrate in a continuous non-ideally mixed stirred tank reactor (CSTR) is presented. The model takes into account the surface reactions between zinc in the solids and ferric iron ions in the liquid phase, oxidation of ferrous iron back to ferric iron, gas-liquid mass transfer of oxygen, decrease of particle size as the reaction proceeds, and the effect of hydrostatic pressure on the oxygen dissolution rate. The model is pseudo-homogeneous and is approximative in the sense that it neglects the effects of particle size distributions and population balances of the concentrate particles.