While roasting has been widely applied to reduce the negative effect of carbonaceous matters on gold extraction from fine-grained carbonaceous gold ores

the phase and structure changes of minerals during roasting and their influences on the leaching rate of gold have not been fully understood. This limits the extraction of carbonaceous gold deposits. The current work examines the oxidation process of a fine-grained carbonaceous gold ore during roasting using a range of techniques including X-ray diffraction (XRD)

scanning electron microscopy (SEM)

Energy Dispersive Spectrometer (EDS) analysis and pore structure analysis together with gold leaching tests. The results show that during the process of oxidative roasting

the carbonaceous matters (organic carbon and graphitic carbon) and pyrite were completely decomposed at 600℃ with the carbonaceous components burned and pyrite oxidized into hematite. At 650℃

while dolomite was decomposed into calcia

magnesia

calcium sulfate etc.

the calcine structure became loose and porous

leading to a high gold leaching rate from the roasted product. Above 750℃

the porous calcite structure started to collapse along with the agglomeration

leading to the secondary encapsulation of gold particles

which contributed to the sharp drop in the gold leaching rate of the roasted product. This study suggests optimum phase and structure changes of minerals during roasting to achieve maximum gold extraction from fine-grained carbonaceous gold deposits.