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 Na 2 CO 3 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 °C and CaO and Na 2 CO 3 concentrations of 16 and 32 g/L, respectively. At lower concentrations of OH − or CO 3 2− , pyrite oxidation and quartz corrosion were both limited. Interestingly, at higher concentrations of OH − and CO 3 2− , pyrite was ultimately converted to Fe 2 O 3 and SO 4 2− under aerobic conditions ; meanwhile, partial dissolution products of quartz reacted with the intermediates of pyrite oxidation, generating a new phase of Fe 2 SiO 4 . In addition, the soluble intermediate ferric carbonate complexes, formed by the induction of sufficient CO 3 2− , 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 °C, but limited at 90 °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 Na 2 CO 3 , 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.