Evaluation of the Cyanidation Leaching of Gold in a Waste Rock Ore

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Samples of the waste rock obtained from Marofengin South Africa ground 60, 70 and 80% passing 75µm were leached with cyanide in bottle roll tests. The results obtained showed that the percentage gold dissolution depends more on the ore size consists than on the cyanide concentration with the highest average dissolution rates of 88.75, 94.34 and 95.90% found at 600, 500 and 500 ppm, for 60, 70 and 80% passing sizes, respectively. It was also noted that the lowest average percents cyanide consumption of 62.91, 61.73 and 58.56 at 60, 70 and 80% passing 75 µm were obtained at the 500 ppm cyanide concentrations. It was further observed that a clear pattern of increasing residual lime content was only observed at the 70% grind size, with the least lime content of 150.37 ppm at 500 ppm cyanide concentration being higher than the least lime contents for the 60 and 80% grind sizes. The results obtained thus suggest the 70% grind passing 75 µm ore with the gold dissolution percentage very close to the conventional 80% passing size at the lowest cyanide consumption of 500 ppm, much lower daily power consumption of about 925 kWh and high residual lime content that indicated the minimization of cyanide loss as hydrogen cyanide,a good choice for the leaching of the waste rock.