Steady-state modeling of zinc-ferrite hot-acid leaching

Mathematical modeling of leaching processes involving porous solid particles can be of crucial importance for the design, performance analysis, and further improvement of several hydrometallurgical plants. In this work, a mathematical model is developed for the description and analysis of the steady-state response of the hot-acid leaching (HAL) process, whereby zinc-ferrite porous particles are leached inside a cascade of continuous stirring-tank reactors by relatively concentrated sulfuric acid solutions at temperatures close to 373 K. The model incorporates the intrinsic reaction kinetics and the particle dissolution pattern, as the last can be described by the grain model for surface-reaction control. In particular, the mathematical basis of the model is a population-balance equation for dissolving ferrite grains, which is coupled together with appropriate mass-balance equations for all dissolved species. By solving numerically this system of equations, the distribution of zinc-ferrite grain size, concentrations of dissolved species, and conversion values are estimated for each reactor. The model shows that it can predict very successfully the performance of an industrial HAL circuit, and for this reason, it has been used for exploring operation alternatives for that particular circuit.