Exploring Non-ammoniacal Thiosulfate Gold Leaching and Limited Gold Recovery from a Refractory Gold Ore Oxidized in Alkaline Pressure Conditions

The application of pressure oxidation (POX) followed by thiosulfate gold leaching is an efficient method used to extract gold from double refractory gold ores containing both sulfide and carbonaceous matter. This process is expected to result in high gold recovery rates, as it liberates gold from sulfides and eliminates the preg-robbing behavior of carbonaceous matter. Despite these expectations, the optimization study showed a maximum gold recovery of only 59% after 24 h of leaching. The optimal conditions occurred when the thiosulfate concentration was 0.14 M, the cupric ion concentration was 0.78 mM, and the temperature was set to 50 °C. To address the problem of low gold recovery, additional investigations involving kinetics tests and characterization techniques were conducted. After optimizing the conditions, it was observed that the leaching recovery was hindered at 1 h. However, this impairment did not have a significant impact on the overall recovery at 24 h. An investigation using TEM-mapping revealed that fine gold particles were disseminated within the minerals, and high concentrations of gold were also detected in locked pyritic minerals. This finding exposed the challenge of low gold recovery from alkaline POX discharge. A thiosulfate leaching test following mineral decomposition demonstrated that the complex mineralogy and poor gold liberation of the original ores were the primary factors contributing to low gold recovery. Therefore, this study suggests that increasing the degree of gold liberation is essential to address the issue of leaching recovery from alkaline POX feed.

Graphical Abstract