Sulphidation of Au-Ag alloys in the presence of pyrite (experimental data)

Dry annealing of Au-Ag alloys (Au, Au_0.56Ag_0.44, Au_0.35Ag_0.65, Au_0.19Ag_0.81 and Ag), together with pyrite as a source of sulphur, at 450 °C was used to study the mechanisms of corrosion and transition of metal forms of noble metals to sulphide forms. In the experiment with Ag plates the silver completely sulphidates to form acanthite Ag₂S and pyrite desulphidates to form pyrrhotite Fe_1-yS. In the experiments with the Au-Ag plates there also formation of an uytenbogaardtite phase and ennobling of Au-Ag alloys take place. Gold in the absence of silver stabilizes pyrite and prevents its transition to pyrrhotite.