Direct reduction and distillation of zinc sulfide with metallic iron

A direct reduction and distillation of zinc sulfide with metallic iron, which is a new zinc distillation process, has been proposed to realize both the unnecessary oxidizing roasting and sintering steps and the fixation of sulfur as pyrrhotite, that is, not sulfuric acid. The reaction experiments of zinc sulfide reduction with metallic iron under vacuum and kinetic analysis have been carried out. A shrinking unreacted-core model has been applied to analyze the reaction data based on the observation of the cross section of partially reacted sample. In the shrinking unreacted-core model, the following steps are taken into account. The first step is the chemical reaction step at the reaction interface, and the permeation step of zinc vapor through the pores of the product layer. The rate parameters such as the chemical reaction rate constant k_c at the reaction interface and the specific permeability k_p of zinc vapor through the pores of the product layer were determined by numerical solution by means of Runge-Kutta-Gill's method so that the calculated reduction curve could represent the experimental results. The rate parameters are given by the following equations: k_c= exp {-138.4×10³/(RT)+10.533} A_p=exp {-304.9×10³/(RT)+7.337} where R is the gas constant. The zinc sulfide could be reduced and distilled with metallic iron, the reaction proceeded faster as the temperature increased. The overall reaction rate is mainly controlled by the permeation step at the lower temperature, while at the higher temperature the chemical reaction step determines the overall reaction rate.