Susceptibility to cyanidation of pyrrhotite-associated gold in pyrite calcines from (non)oxidizing roasting environments

Abstract

The susceptibility to leaching of pyrrhotite-associated gold in roasted pyrite calcines was studied, with emphasis on the effects of the roasting environment and galvanic contacts under cyanidation conditions. The first part scrutinized the thermal treatment of pyrite under different oxidizing and non-oxidizing atmospheres, and demonstrated that air roasting promoted the coexistence of multiple pyrrhotites, while He, CO2, and steam environments resulted in single hexagonal pyrrhotites with increasing iron deficiency and decreasing porosity. The second part employed a bilayer leach cell to control the electrochemical contacts between gold powder and raw/roasted pyrite during cyanidation, and found that the topology of pyrrhotite and iron oxides was influenced by the type of roasting treatment, which could impact the kinetics of gold dissolution, particularly in cases involving refractory gold or ore preg-robbing recalcitrance. Therefore, when it comes to extracting encapsulated gold associated with refractory pyrite that requires heat treatment, air roasting was the most effective for leaching gold from calcine, outperforming both inert and mild oxidative environments. In addition, the presence of CO2 (and/or moisture) in the roasting atmosphere to mimic the combustion of carbonaceous material could moderately enhance gold recovery regardless of whether or not there was galvanic contact with the roasted pyrite.