AN INVESTIGATION OF THE ELECTROCHEMICAL NATURE OF THE FERRIC-CHLORIDELEACHING OF SPHALERITE

Although considerable research has been reported on the hydrometallurg ical behavior of zinc sulfide in chloride media, the electrochemical n ature of the dissolution reaction involving a ferric/ferrous couple an d the accelerating effects of the chloride ion and of cupric chloride have not been fully elucidated. It is shown that the decrease in disso lution rate of sphalerite in the presence of ferrous ions is due to a decreased cathodic half cell potential and therefore a less favorable mixed potential. The addition of chloride ion to the anodic half cell significantly increases the cell current, indicating that chloride ion plays a direct role in the anodic dissolution of ZnS and has relative ly little effect on the cathodic half cell. It is also shown that Aghas no effect on the dissolution of ZnS in a ferric chloride electroly te. In addition the data suggests that cupric ion may accelerate the d issolution of sphalerite through a mechanism other than simply providi ng an additional oxidizing reagent to complement ferric ion. This inve stigation has demonstrated the utility of a relatively simple, dual ce ll technique for the study of electrochemical leaching reactions by se parating the two half reactions. Although this technique would not rep lace standard leaching experiments, it does provide a useful complemen tary approach, and in some cases can provide data that would be partic ularly difficult or impossible to obtain through typical, standard lea ching experiments.