Abstract
In this research, cyanide and chloride–hypochlorite leaching of gold from a pyritic concentrate (particle size: −75+53 µm, gold content: 27.15 g/t) were compared. It was shown that only 13.6 % of gold was extracted after 24 h leaching by cyanide, as compared to 37.2 % after 8 h by chloride–hypochlorite. Effect of ultra–fine milling of the concentrate on the leaching was investigated using a high–energy planetary ball mill at different milling times. It was found that the leaching rate of gold by both leachants could be substantially enhanced after the milling of the particles to sub–micron dimensions. This was attributed to the increase of specific surface area and the accumulation of energy in the pyrite particles. After 480 min milling (air atmosphere, 300 rpm, sample/ball:1/20), 96.1 % of gold was extracted by 24 h cyanide leaching, while 100 % extraction could be achieved after only 45 min milling and 30 min chloride–hypochlorite leaching. This was attributed to the oxidation of pyrite by the hypochlorite oxidant and the complete liberation of gold encapsulated in the pyrite particles.
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