Effect of Mechanical Activation on the Kinetics of Ammoniacal Thiosulfate Leaching of a Refractory Oxide Gold Ore

The effect of mechanical activation on the kinetics of ammoniacal thiosulfate leaching of a refractory oxide gold ore containing 2.8 ppm Au was investigated. The gold extraction of 99.81% was achieved by 16 h leaching of a sample mechanically activated for 60 minutes. The gold extraction observed for a similar reference sample without mechanical activation was only 55%. Studies revealed that leaching progresses at two different rates depending on the leaching time (0-2 h and 2-16 h). It was observed that diffusion through an ash layer as a dominant mechanism controls the leaching of samples mechanically activated up to 45 minutes during total leaching time, while reaction control and liquid 􀀮lm diffusion are dominant mechanisms for leaching of a sample mechanically activated for 60 minutes during 0-2 h and 2-16 h, respectively. The extraction observed during the ash diffusion step depends signi􀀮cantly upon mechanical activation time. Mechanical activation of 60 minutes results in high gold extraction when combined with subsequent chemical reaction gives close to 100% gold extraction in a 16-hour leach. Mechanical activation for up to 45 minutes leads to a modest improvement in overall gold extraction compared with the reference test without mechanical activation.