Model for the ferric chloride leaching of galena

A shrinking core model for the FeCl₃ leaching of galena (PbS), which accounts for the microstructure previously observed during this process, is presented. The microstructure is characterized by two distinct product layers—PbCl₂ in direct contact with the PbS core and S^o above the PbCl₂ layer. Rate equations for the evolution of the three solid phases and the PbS leaching conversion are derived for the case of flat plate geometry appropriate for the reaction of massive galena fragments. In the case of rate control by diffusion of the lead chloride reaction products through the S^o layer, the system is shown to exhibit parabolic behavior as long as the S^o layer is built up primarily at the PbCl₂-S^o interface. For the mechanism considered in this study, negative deviation from parabolic behavior is observed to increase as the amount of S^o forming at the external S^o-solution interface rises. When the system is controlled by surface reaction kinetics, the model predicts linear rates under all circumstances.