Characterization of Sulfide Mineral Surfaces

Abstract

The metal sulfides constitute the most important group of ore minerals since they are the source of the world's supplies of nonferrous metals. Sulfide minerals are, in general, electronic conductors and can sustain coupled anodic and cathodic reactions at the interface with an electrolyte. The significance of conductivity in determining the properties of sulfides has been recognized for some considerable time. Fox, commenting in 1830 on the properties of metalliferous veins in mines in Cornwall, England, that contained iron, copper, and lead sulfides, stated(I) "many of the phenomena ... bear striking analogies to common galvanic combinations and the discovery of electricity in veins seems to complete the resemblance." Corrosion-type reactions play an important role in a number of processes of practical importance in the winning of metals from their ores. Mixed-potential systems are evident in the alteration of the composition of ore bodies in the ground; in oxidation during mining, storage, and transport; in concentration of the valuable minerals by flotation methods; and in hydrometallurgical extraction of the metal values. Thus, in order to understand these processes, a knowledge of the electrochemical and surface properties of sulfide minerals is required. A number of techniques have been employed for the characterization of sulfide mineral surfaces. In this chapter, the application of these techniques to the understanding of froth flotation will be reviewed. The flotation process is used to extract the valuable components of an ore with a view to producing essentially monomineral concentrates of a grade suitable for feeding to pyrometallurgical or hydrometallurgical operations. Flotation involves crushing the ore to liberate separate grains of the various valuable minerals and gangue components, pulping the ore particles with water, and then selectively rendering hydrophobic in tum the surfaces of the minerals of interest by interaction with organic collector species. A stream of air bubbles is then passed through the pulp; the bubbles attach to and levitate the hydrophobic particles and collect them in a froth layer that flows over the weir of the flotation cell. It is now generally accepted that the interaction of thiol collectors with sulfide minerals involves anodic oxidation of the collector coupled with the reduction of oxygen. The mixed-potential nature of collector/mineral interaction has been demonstrated experimentally, in particular for the galena/xanthate systemY-5)