AN XPS, AES, AND SEM STUDY OF THE INTERACTIONS OF GOLD AND SILVER-CHLORIDE SPECIES WITH PBS AND FES2 - COMPARISON TO NATURAL SAMPLES

Reactions of silver and gold chloride-bearing solutions with pyrite (F eS2) 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 upta ke by the minerals was investigated. As shown by XPS analysis, the pre sence of metallic gold and silver sulphide was observed on the PbS sur faces within 30 seconds, while metallic silver was observed after seve ral hours. While gold metal was observed on FeS2 almost immediately, s ilver sulphide was not observed until after a minimum of a one hour re action time. Changes in metal and chloride ion concentrations contribu te significantly to influencing the uptake of the metal (Au or Ag) by the mineral surfaces. In contrast, for the pH's investigated, there wa s no visible effect on the Au or Ag uptake by the mineral samples. Aug er depth profiling has revealed very similar trends in metal compositi on (higher silver content at the surface) when comparing reacted PbS a nd FeS2 substrates. This observation is in good agreement with Auger d epth profile analysis of precious metal crystallites on naturally occu rring FeS2 samples. Copyright (C) 1997 Elsevier Science Ltd.