With the recent increase in gold production, low-grade, fine-grained gold ores difficult to cyanide and refractory gold ores containing harmful impurities such as sulfur, arsenic, copper, etc. have become the major resources for gold production.
In order to effectively extract gold from the refractory gold ore, oxidative pretreatment must be conducted prior to leaching to oxidize the sulfide bearing gold particles and convert their physical and chemical properties.
There are several pretreatment methods, each with their own advantages and disadvantages. Hydrothermal oxidation pretreatment of refractory gold ores is an effective one, which has been widely used in recent years, due to its high rate of desulfurization, little environmental pollution and high reaction rate.
Sin Hyok, a researcher at the Faculty of Chemical Engineering, has investigated the thermodynamic process of nitric acid oxidation and the factors affecting gold extraction when pyrite-and-arsenopyrite-based gold concentrates are pretreated by mechanochemical activation and nitric acid oxidation.
He has found the following.
The factors affecting gold extraction are nitric acid concentration, mechanical activation time and liquid-solid ratio. The decomposition of pyrite and arsenopyrite in nitric acid medium proceeds from above 1mol/L of nitric acid concentration at room temperature, and the mechanical activation starts decomposition from above 0.5mol/L.
After pretreatment using mechanical activation and nitric acid oxidation, the cyanidation leaching rate for gold concentrates is over 87%.
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