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UBC Theses and Dissertations

Atmospheric alkaline pre-oxidation of refractory sulphide gold ores Rego, Alan Joseph


Four iron-sulphide-containing gold ores from the White Mountain mine in the Jilin Province, China were studied to examine the benefits of using oxidative treatment prior to conventional cyanidation to leach gold. This pre-treatment consisted of bubbling air into an ore/water mixture for eight hours while adding enough caustic sodium hydroxide to maintain a pH of 11 throughout the test. Three physical parameters were studied: total consumption of sodium hydroxide, rate of slurry aeration, and temperature of the slurry. Cyanide consumption was studied to determine whether increased oxidation of the ore would result in excessive degradation of sodium cyanide or otherwise impact the level of gold extraction. X-Ray Diffraction analysis was conducted on untreated samples as well as the final residues from the end of select tests to investigate by-products that precipitated after oxidation. Finally, an indicative economic analysis was conducted for each ore sample by comparing the increased dosage of caustic reagent applied during pre-treatment with the corresponding increased gold extraction. Results of this study show that aerated pre-oxidation of three of the four ores tested increased gold extraction compared to conventional cyanidation. Higher caustic dosages may have led to increased oxidation and were symptomatic of elevated release of sulphuric acid due to sulphide oxidation. Gold extraction was seen to rise in most cases after an increased rate of aeration during pre-treatment. Finally, the iron-sulphide ores tested responded extremely favourably to raised temperatures, showing both increased iron and sulphur oxidation, as well as higher gold extractions. Major losses of cyanide, likely due to production of cyanate and thiocyanate, were observed. Residual cyanide levels in the leach remained positive and did not affect gold extractions. Iron oxides such as hematite, and magnetite, and iron oxy-hydroxides such as goethite and ferrihydrite were observed in oxidized ore residues, indicating a high level of iron and sulphur oxidation.

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