Fluidized Roasting of Carbonaceous Gold Ore in O2/CO2 Atmosphere: Effects of Temperature on Gold Leaching and Mineralogical Transformations

Carbonaceous gold ores are difficult to process due to the preg-robbing effect of carbonaceous matter and the encapsulation of gold within gangue minerals. In this study, fluidized bed oxidation roasting in a controlled O2/CO2 atmosphere (O2:CO2 ratio of 1:4 and a total flow rate of 2 L/min) was proposed as a pretreatment to enhance gold leaching from a refractory carbonaceous gold ore. The effects of roasting temperature on phase transformation, carbon removal, sulfur fixation, microstructure, porosity, gold dissociation, and leaching efficiency were systematically investigated through XRD, SEM, BET, and chemical phase analysis. The results demonstrated that roasting at 650 °C achieved efficient carbon removal (94.04%) and sulfur fixation (73.60% as anhydrite), while simultaneously inducing the thermal decomposition of carbonates and silicates, which generated a highly porous structure with an enlarged average pore diameter of 27.1 nm. These synergistic transformations liberated gold from its encapsulating matrix, increasing the proportion of exposed gold from 28.85% to 84.10% and yielding a maximum gold leaching efficiency of 80.26%. However, excessive temperature (700 °C) led to sintering and pore collapse, reducing the leaching efficiency to 73.87%. This study demonstrates that fluidized bed roasting in a controlled O2/CO2 atmosphere is a promising pretreatment strategy for refractory carbonaceous gold ores, though further optimization of roasting parameters is needed to improve gold recovery.