Gold cementation from thiocyanate solutions by iron powder

Gold cementation with iron powder from thiocyanate solutions was conducted without de-aeration. The effects of various parameters such as pH, thiocyanate concentration, gold concentration, iron/gold mass ratio, temperature, stirring speed and presence of iron(III) in the solution were examined. These parameters were varied according to the ranges typically found in the literature. The effect of gas atmosphere on cementation of gold was also examined by flowing nitrogen gas through the solution during the runs and the recovery of gold was enhanced. The presence of iron(III) results in the low efficiency of gold precipitation as well as the low grade of the cements. It was established that the rate of the reaction was first-order with respect to the gold concentration. The activation energy was found to be 9.3 kJ/mol and the cementation process was considered to be diffusion-controlled. A general mechanism for gold cementation is proposed.