Abstract
Abstract The presence of copper-bearing minerals is known to bring on many challenges during the cyanidation of gold ore, like high consumption of cyanide and low extraction of metal, which are undesirable impacts on the auriferous recovery in the subsequent process step. The high copper solubility in cyanide prevents the direct use of classical hydrometallurgical processes for the extraction of gold by cyanidation. Additionally, the application of a conventional flotation process to extract copper is further complicated when it is oxidized. As a result, an acid pre-leaching process was applied in order to clean the ore of these copper minerals that are cyanide consumers. The objective was to evaluate the amount of soluble copper in cyanide before and after acidic cleaning. From a gold ore containing copper, the study selected four samples containing 0.22%, 0.55%, 1.00% and 1.36% of copper. For direct cyanidation of the ore without pre-treatment, copper extraction by cyanide complexing ranged from 8 to 83%. In contrast, the pre-treatment carried out with sulfuric acid extracted 24% to 99% of initial copper and subsequent cyanidation extracted 0.13 to 1.54% of initial copper. The study also showed that the copper contained in the secondary minerals is more easily extracted by cyanide (83%), being followed by the copper oxy-hydroxide minerals (60%), while the copper contained in the manganese oxide is less complexed by cyanide (8% a 12%). It was possible to observe that minerals with low acid solubility also have low solubility in cyanide. Cyanide consumption decreased by about 2.5 times and gold recovery increased to above 94% after acidic pre-cleaning.
Highlights
Cyanidation is the most common method employed to recover gold and silver from their respective ores
The use of pre-conditioning of the gold ore proposed in this study was able to show the extraction potential of copper cyanide, reaching highly satisfactory values, allowing the cyanidation of gold and expressive lower complexation of copper by cyanide
The final values of cyanide-soluble copper reached a peak of 1.54% with the preliminary acid cleaning step, and the direct cyanidation values reached 99% of cyanide-soluble copper
Summary
Cyanidation is the most common method employed to recover gold and silver from their respective ores. In this process, other metals, besides gold and silver, can be dissolved in certain circumstances and interfere with the extraction efficiency of these targets. Chalcopyrite is the most abundant of the copper minerals, it is poorly soluble in cyanide. Other minerals such as azurite, malachite, cuprite and chalcocite exhibit a high solubility (Dai and Jeffrey, 2006; Habashi, 1967; Nguyen et al, 1997)
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