The Role of Oxalate on Thiourea Leaching of Gold in the Presence of Jarosite Ke Li, Qian Li*, Yongbin Yang, Bin Xu*, Tao Jiang, Rui Xu

The biooxidation pretreatment of refractory gold ores and concentrates has been the predominant process used for the past two decades due to its environmental friendliness and low operating costs. It is widely acknowledged that the sulfur-containing intermediates and products, such as jarosite, could be formed during bio-leaching. The effect of jarosite on thiourea leaching of gold, the role of oxalate and the possible mechanisms were studied in this work. The results showed that jarosite could accelerate the thiourea consumption and hinder the gold dissolution. The dominant cause for the detrimental effect was that the mixed pulp potential increased owing to the release of iron from jarosite in acidic solution, and resulting in the decomposition of thiourea and the passivation of gold surface. The passivation film on gold surface consisted of S2- , S22- , S0 and SO42- . The addition of oxalate could effectively reduce the harmful effect of thiourea consumption and its impact on gold dissolution. The acting mechanism of oxalate during the leaching was established through the analysis of mixed pulp potential, zeta potential and XPS. It is proposed that oxalate could not only weaken the interaction between Fe(III) and thiourea via complexing with Fe(III), but also prevented passivation species from coating on gold surface through electrostatic repulsion.