SPONTANEOUS DEPOSITION OF GOLD ON PYRITE FROM SOLUTIONS CONTAINING AU(III) AND AU(I) CHLORIDES .1. A SURFACE STUDY

The adsorption and deposition of Au on the surface of naturally occurr ing pyrite under ambient conditions has been studied by scanning elect ron microscopy (SEM), X-ray photoelectron (XPS) and Rutherford backsca ttering spectrometry (RES). Gold is reduced on the pyrite surface from either Au(I) or Au(III) solutions and tends to nucleate as small sphe res at microfractures on the mineral surface; each gold cluster is sur rounded by a reaction halo of unknown composition. The rate of Au depo sition is approximately inverse first order in Cl- and is independent of AuCl4- and pH. Pyrite is found to be the reducing agent for Au(III) ; it reacts with surface ferrous iron to produce Au(I) and ferric iron . The Au(I) in turn reacts with pyrite again to form metallic gold. Th e need for careful interpretation of the XPS binding energy data is sh own; the Au 4f(7/2) binding energy is a function of not only oxidation state but also Au particle size.