1-step acidic gold bioleaching by the use of iron and sulfur oxidizing and thiocyanate (SCN) generating microorganisms

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The conventional gold extraction process from low grade sulphide gold ores is to heap leach the ore at low pH to oxidize sulphides with the help of bacteria, and then wash the solids and finally leach the heap with cyanide containing solution to leach gold into cyanide. The process has environmental and cost disadvantages as the cyanide application in the heap operation has environmental consequences, and also the heap pH is acidic after sulphide oxidation and will require neutralization with lime to increase the pH to the required level for gold cyanide leaching, i.e. pH 9.5 to 10.5. The lime cost and environmental issues of cyanide use are the main challenges with this standard process. Here it is proposed to do both the sulfide oxidation and gold leaching in acidic pH in one step. In this proposed process, sulfide minerals are oxidized with the usual bacteria, but in addition, thiocyanate producing bacteria are used in the heap to produce thiocyanate as the lixiviant for gold leaching in acidic pH. The process will reduce the lime consumption of the plant (the whole process will be carried out at acidic pH) and will eliminate cyanide use. Thiocyanate is 200x less toxic than cyanide thus making it much more attractive for gold recovery. Through this project a PhD student will be trained.