LEACHING OF GOLD IN THIOCYANATE SOLUTIONS .3. RATES AND MECHANISM OF GOLD DISSOLUTION

The leaching of gold in ferric thiocyanate solutions has been studied by the rotating-disk technique. Leaching was carried out at pH 1.5 and the main variables that were studied were the initial concentrations of Fe(III) and thiocyanate and temperature (from 25 to 85-degrees-C). The correlation between the rates of dissolution of gold and of autore duction of the Fe(III)-thiocyanate complexes is interpreted in terms o f the participation of the intermediate thiocyanate species, particula rly (SCN)2 and (SCN)3-, in the leaching mechanism. Determinations of a pparent activation energies indicate that the process of gold dissolut ion is chemically controlled. Initial gold dissolution rates of the or der of 10(-9) and 10(-8) mol cm-2 s-1 were obtained at 25 and 85-degre es-C, respectively. The overall conclusions are that thiocyanate is an effective lixiviant for gold in acidic conditions, yielding dissoluti on rates that are comparable to those obtained with thiourea while off ering the advantage of much greater stability against oxidative decomp osition.