Reduction of gold(III) chloride to gold(0) on silicate surfaces.

The mechanism of adsorption and reduction of the gold chloride complex on silicate minerals is investigated. Gold chloride, supplied as HAuCl(4) solution, is rapidly adsorbed on the silicate surfaces, the Au(III) is reduced to metallic gold, and gold particles grow on the surface. SEM images show agglomerates of gold unevenly distributed on the surface of the silicates, including in some areas forming agglomerates, especially on quartz and feldspar. Silica gel forms via dissolution of silicates in acidic conditions and also has strong adsorption/reduction potential for gold. A mechanism for the adsorption and reduction is proposed, involving ligand substitution between gold chloride and OH() groups on defect sites in silicate surfaces. Consequently, gold can be reduced by hydrogen or silicon radicals at the defect sites. Adsorption of Au(III) by silicate minerals, followed by reduction, could play an important role in the deposition of gold in natural systems, as well as causing loss of gold from leaching processes during hydrometallurgical gold recovery.