An investigation of the electrochemical nature of the ferric chloride leaching of sphalerite

Abstract

Although considerable research has been reported on the hydrometallurgical behavior of zinc sulfide in chloride media, the electrochemical nature of the dissolution reaction involving a ferric/ferrous couple and the accelerating effects of the chloride ion and of cupric chloride have not been fully elucidated. It is shown that the decrease in dissolution 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 relatively little effect on the cathodic half cell. It is also shown that Ag + has no effect on the dissolution of ZnS in a ferric chloride electrolyte. In addition the data suggests that cupric ion may accelerate the dissolution of sphalerite through a mechanism other than simply providing an additional oxidizing reagent to complement ferric ion. This investigation has demonstrated the utility of a relatively simple, dual cell technique for the study of electrochemical leaching reactions by separating the two half reactions. Although this technique would not replace standard leaching experiments, it does provide a useful complementary approach, and in some cases can provide data that would be particularly difficult or impossible to obtain through typical, standard leaching experiments.