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UBC Theses and Dissertations

Thiocyanate leaching of gold Yeboah, Sarpomah Roselyn


This study focused on evaluating sodium thiocyanate as an alternative reagent to the conventional cyanidation process for leaching of gold ores. Goldcorp’s Coffee project in Yukon-Canada supplied three mineral samples namely, Supremo Oxide 68151, Supremo oxide 68151, Supremo Composite 72142 for this study. As a baseline for comparison with thiocyanate extraction results, cyanidation tests performed on all the three samples showed that the samples are amenable to the conventional cyanidation leaching, yielding gold extractions as high as 97% for Supremo composite 72142. A series of leaching tests were performed on the 72142 B sample with SCN⁻ solutions to determine the feasible regions of gold dissolution and to maximize gold dissolution. The leaching tests were conducted in the acidic regime (pH 1.5 -2) for these samples. Notable results with SCN⁻, ferric sulphate and potassium iodide variation showed gold extractions of 91 % in solutions containing 0.15 M thiocyanate; 92% with 0.15 M SCN⁻ and 0.10 M Fe(III); 94 % with 0.10 M SCN⁻ and 0.05 M KI; 94 % with 0.10 M SCN⁻, 0.05 M Fe(III) and 0.02 M KI and 95 % with 0.15 M SCN⁻ and 10 g/L H₂O₂. The kinetic leach data were well fitted by the CIP/CIL leach model developed by Nicol et al, giving estimates of the leach rate parameter of 72.1 hr⁻¹ and leach tails grade after infinite leach time of 0.17 g/t, confirming fast leaching of the 72142 B sample. The tests ended with gold adsorption from thiocyanate solution onto carbon. The average gold loading onto carbon was 2100 g/t and 48 g/t for carbon concentrations of 0.25 g/L and 20 g/L, respectively. Results obtained were excellent with greater than 98 % gold adsorbed in less than 0.5 hr when carbon concentration was above 5 g/L. The results show that the gold ore from the Goldcorp’s Coffee project in Yukon-Canada is amenable to extraction with acidified thiocyanate based lixiviant and subsequent adsorption of the gold-thiocyanate complex onto activated carbon, giving gold extraction results that are comparable to cyanide-based gold extraction. The thiocyanate system is, therefore, a competitive and alternative leaching reagent to conventional cyanidation.

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