On the use of zinc for gold cementation from ammoniacal–thiosulphate solutions

The use of zinc as a cementation agent for gold from ammoniacal–thiosulphate solutions has been studied. The experimental variables investigated were: (i) pH (9–10.5), (ii) thiosulphate concentration (0.05–0.4 M), (iii) temperature (5–50 °C), (iv) presence of zinc in the system (both as cementation agent and in the gold solution), (v) presence of Cu(II) (0–0.05 M) in the solution, and (vi) [NH3]/[S2O32−] molar ratio in the aqueous solution. The cementation process was considered to be under diffusion control. A general mechanism for gold cementation is proposed.