Noble metal (Ag, Au) cementation on non-stoichiometric cuprous sulphide grains

Noble metal cementation on Cu2−xS grains was studied by measuring the concentration of Ag+ (or AuCl4−) ions in the solution circulating in a special apparatus containing sample of grains. The rate of the cementation process was determined as a function of the reaction extent, which was equivalent to the deposition of approximately 50 uniform atomic layers of the noble metal on the grains surfaces. Changes in the surface microstructure and composition of the samples were determined using X-ray diffraction (XRD), scanning electron microscopy (SEM/EDS) and atomic force microscopy (AFM). Different surface products: mixed copper–silver sulphides, gold sulphides and gold crystallites were found, depending on nature of the noble metal and the solution composition. The course of cementation of gold was greatly changed using chloride instead of sulphate ions. The notable change of the process rate is ascribed to the greatly different structure of gold cementation products on Cu2−xS, as found by the analysis techniques: XRD, SEM and AFM, respectively.