Chloride–hypochlorite leaching of gold from a mechanically activated refractory sulfide concentrate

In this research, effect of mechanical activation on the chloride–hypochlorite leaching of gold from a refractory pyritic concentrate containing ca. 27 g/t gold was investigated for the first time. Results showed that after 30 min leaching, 100% of gold was extracted from a 45 min-milled sample while only 37.2% of gold was obtained from the un-milled sample after 480 min leaching (at 25 °C and 600 rpm). This improvement occurred due to the increase in specific surface and accumulated strain in the crystal structure of particles by mechanical activation. It was concluded from the experiments that sensitivity of leaching rate to the temperature decreased after mechanical activation. Results of kinetic study showed that there were two stages in the leaching rate of gold from un-milled sample. The rate of the first stage was controlled by chemical reaction and the second stage was mixed controlled (chemical reaction and diffusion through the Fe(OH)3 layer formed on the pyrite particles). In the case of milled sample, there was one stage in which chemical reaction and liquid film diffusion controlled the rate of leaching.