An electrochemical study of the effect of potential on the selective dissolution of base metal sulphides in sulphuric acid

Abstract

Diagnostic leaching is an analytical tool which was developed at Anglo American Research Laboratories to examine the deportment of gold in an ore, or any type of plant product or intermediary. In this study we make use of the same principle to study the effect of potential and pH on the dissolution of base metal sulphides in a sulphate medium (sulphuric acid) at high temperatures (80°C). This technique was developed to preferentially liberate a particular base metal from a complex ore. In this way, existing base metal sulphide extraction processes, especially where other unwanted base metal sulphides are present, can be optimised so as to yield substantial savings in operating costs. An oxidizing sulphuric acid leach at high temperatures will destroy pyrrhotite, uraninite, labile base metal sulphides (chalcopyrite, sphalerite, orpiment, marcasite), and to a lesser degree pyrite and arsenopyrite. From the results of this testwork it is possible to find an optimum between reagent consumption (MnO 2 and H 2SO 4), temperature, leaching time, potential (Eh), costs and to a lesser degree pH, for the optimal extraction of the selective base metal, and/or gold. This can be achieved without the dissolution of less desirable base metal sulphides associated with the preferred mineral.