Raman spectroelectrochemical investigations of the leaching of gold in chloride and thiosulphate media.

Real-time surface-enhanced Raman spectroscopy, used to identify the surface species formed during leaching, showed that chloride ion is adsorbed prior to gold dissolution but that its coverage is significantly diminished when leaching begins. A gold chloride band is again observed whem dissolution is rapid, together with bands characteristic of AuCl4(-) ions in solution. With thiosulphate. a thin gold sulphide layer is formed slowly in the potential region where leaching occurs. At higher potentials, thiosulphate is oxidised to sulphur and sulphate; the rate of oxidation is independent of pH, indicating that the rate-determining step is the first electron transfer from adsorbed thiosulphate ions.
Real-time surface-enhanced Raman spectroscopy, used to identify the surface species formed during leaching, showed that chloride ion is adsorbed prior to gold dissolution but that its coverage is significantly diminished when leaching begins. A gold chloride band is again observed whem dissolution is rapid, together with bands characteristic of AuCl4(-) ions in solution. With thiosulphate. a thin gold sulphide layer is formed slowly in the potential region where leaching occurs. At higher potentials, thiosulphate is oxidised to sulphur and sulphate; the rate of oxidation is independent of pH, indicating that the rate-determining step is the first electron transfer from adsorbed thiosulphate ions.