Gold Extraction from a Refractory Ore Using Calcium Hypochlorite at Moderate Pressure and Temperature before Cyanidation

Conventional leaching, the standard method for gold extraction, involves using a cyanide solution to dissolve gold from the ore. However, this process is often ineffective for refractory ores due to the presence of sulfide minerals. This study aims to improve the efficiency of gold extraction from refractory ores by introducing an oxidative pretreatment step using a calcium hypochlorite. This compound plays a crucial role in the process as it facilitates the oxidation of the sulfide minerals, mainly pyrite and quartz. The study also investigates how this approach affects oxidation at different temperatures and pressures inside a titanium reactor at 600 rpm. After the pretreatment, the mineral is in contact with a solution of sodium cyanide (1000 ppm) inside a stirred reactor (300 rpm) under atmospheric conditions. Some results obtained were more than 60% extraction of gold, but there were conditions under which gold extraction was less than 40%. The effect of the concentration of calcium hypochlorite 10 and 30 wt % was more significant compared with the temperature (25, 60, and 80 °C) and oxygen pressure (80 and 120 psi). This effect is due to a protective layer confirmed in the characterization using scanning electron microscopy (SEM-EDS) of the solid material previously leached.