Mechanism of synergistic pretreatment with eco-friendly CaO and Na2CO3 to enhance gold leaching efficiency from fine-disseminated gold ores

Efficient pretreatment of fine -disseminated gold ore is a challenge in effective gold extraction due to the invisible occurrence of the most encapsulated gold. In this study, we investigated the mechanism of co -pretreatment with eco-friendly CaO and Na2CO3 to improve gold extraction from fine -disseminated gold ore using element content and valence measurement, phase composition analysis, micromorphology and structure characterization, and thermodynamic calculation. The results indicated that more than 75% of gold was encapsulated in pyrite, quartz and calcite. The gold leaching rate evidently increased with the reagent content and slurry temperature of the pretreatment, reaching a maximum of 86.55% at 60 degrees C and CaO and Na2CO3 concentrations of 16 and 32 g/L, respectively. At lower concentrations of OH or CO32 , pyrite oxidation and quartz corrosion were both limited. Interestingly, at higher concentrations of OH and CO32 , pyrite was ultimately converted to Fe2O3 and SO42 under aerobic conditions; meanwhile, partial dissolution products of quartz reacted with the intermediates of pyrite oxidation, generating a new phase of Fe2SiO4. In addition, the soluble intermediate ferric carbonate complexes, formed by the induction of sufficient CO32 , inhibited the accumulation of the passivation layer on the pyrite surface, resulting in constant oxidation of pyrite. Furthermore, the oxidation of pyrite was the maximum at 60 degrees C, but limited at 90 degrees C due to the hindrance of oxidation product coating. As a result, the phase transition of gold -bearing pyrite and quartz could be enhanced by the synergistic pretreatment of CaO and Na2CO3, resulting in an approximately 30% increase in both exposed gold content and gold leaching rate. This research proposes a promising green pretreatment with cost benefits for fine -disseminated gold ore and provides significant insights into phase transition regulation to improve gold leaching.