Thiourea-thiocyanate leaching system for gold

The leaching of gold in thiourea-thiocyanate solutions has been studied by the rotating-disk technique using ferric sulfate as oxidant. The effects of initial concentrations of ferric, thiourea (Tu) and thiocyanate as well as temperature and pH values on gold leaching rates were studied. An initial gold leaching rate in the order of 10-9 mol cm-2 s-1 was obtained at 25℃, which was higher than rates obtained when either ferric-thiocyanate or ferric-thiourea solutions were used separately. The synergistic effect was attributed to the formation of a mixed ligand complex Au(Tu)2SCN. Determinations of apparent activation energy indicate that the process was controlled by a combination of chemical reaction and diffusion in the mixed lixiviant system. Open circuit potentials show that thiocyanate stability is increased in the mixture.