Evaluating the catalytic effect of pyrite on thiourea leaching of gold in the absence and presence of citrate

Abstract

With the depletion of high-quality ore, the extraction of gold from refractory gold ores/concentrates is a promising endeavor. Pyrite is an important gold-bearing sulfide mineral. It is of great significance to study its influence on gold leaching to realize the maximum utilization of refractory sulfide gold ores/concentrates. In this paper, the effect of pyrite on thiourea leaching of gold was investigated through leaching experiment, surface characterization and density functional theory (DFT) calculation. Results showed that the presence of pyrite sharply decreased both gold dissolution and thiourea stability, and its adverse effect of pyrite is likely that pyrite catalyzes the oxidation of thiourea by Fe3+, resulting in the high thiourea consumption, which deteriorates the gold dissolution. The catalytic mechanism is believed to be that thiourea firstly adsorbs on the pyrite surface, and then electrons transfer from thiourea to the oxidant of Fe3+ through the conduction band of pyrite. Citrate was used as an additive to improve the thiourea stability and gold dissolution, and its mechanism was proposed as follows: citrate weakens the interaction between Fe3+ and thiourea by complexing with Fe3+, and competes with thiourea to adsorb on the surface of pyrite, reducing the adsorption of thiourea. Furthermore, the formation of Fe-citrate complexes, as terminal electron acceptor, has a lower oxidation capacity than Fe3+, thus relieving the catalytic effect of pyrite on thiourea oxidation by Fe3+.