Effect of common associated sulfide minerals on thiosulfate leaching of gold and the role of humic acid additive

Compared with the thiosulfate leaching in the presence of inert quartz, the conclusion was obtained that all studied sulfide minerals including chalcopyrite, galena, sphalerite, pyrite and arsenopyrite could accelerate the thiosulfate consumption and hinder the gold dissolution in varying degree. The dominant cause for these two detrimental effect of sulfide minerals were inferred separately via the analyses of frontier orbital energy and XPS to be the catalysis of these minerals on thiosulfate decomposition and the passivation of gold surface. The passivation layer on gold surface mainly consisted of copper and sulfur species. It was also concluded by leaching tests that HA (sodium humic acid) additive could effectively reduce these harmful effect of sulfide minerals. The acting mechanism of HA during thiosulfate leaching was studied in detail mainly through the analyses of mixed pulp potential, zeta potential and XPS, and was proposed as follows: humic acid radical ions not only weakened the interaction between Cu(II) and thiosulfate via complexing with Cu(II) at axial coordinate sites and relieved the catalytic effect of minerals on thiosulfate decomposition by making the affinity of mineral surfaces for S2O32- disappear, but also prevented passivation species from coating gold surface through electrostatic repulsion.