An XPS, AES, and SEM study of the interactions of gold and silver chloride species with PbS and FeS 2: Comparison to natural samples

Abstract

Reactions of solver and gold chloride-bearing solutions with pyrite (FeS 2) and galena (PbS) were probed using X-ray photoelectron (XPS) and Auger electron spectroscopies (AES) as well as using Scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDXA). The effect of metal and chloride ion concentrations as well as pH on the metal uptake by the minerals was investigated. As shown by XPS analysis, the presence of metallic gold and silver sulphide was observed on the PbS surfaces within 30 seconds, while metallic silver was observed after several hours. While gold metal was observed on FeS 2 almost immediately, silver sulphide was not observed until after a minimum of a one hour reaction time. Changes in metal and chloride ion concentrations contribute significantly to influencing the uptake of the metal (Au or Ag) by the mineral surfaces. In contrast, for the pH's investigated, there was no visible effect on the Au or Ag uptake by the mineral samples. Auger depth profiling has revealed very similar trends in metal composition (higher silver content at the surface) when comparing reacted PbS and FeS 2 substrates. This observation is in good agreement with Auger depth profile analysis of precious metal crystallites on naturally occurring FeS 2 samples.