Determining an effective replacement for cyanide in the leaching of low-grade gold ores using an emerging industry standard and similar substitutions in the form of thiosulfate

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Pastor, Ryan
Swindle, Andrew L.

In the mining industry, heap leaching is the most common form of extraction for many metals, especially gold, from low-grade ores in open-pit facilities. Cyanide solutions are the most commonly used solutions for the process of leaching low-grade gold ore. These solutions lead to relatively high yield of gold content within low-grade ore. Cyanide solutions pose an environmental risk. Cyanide is a reducing agent that interacts with free oxygen and is hazardous to both people and the environment. A common eco-friendly substitution comes in the form of thiosulfates. These solutions, although better for the environment, have lower yield than the common cyanide solutions. As such, higher concentrations are needed for similar yields relative to cyanide solutions. At the moment, the common thiosulfates used in the industry are sodium thiosulfate and ammonium thiosulfate. Thiosulfate usage and testing has been limited and focused on ammonium thiosulfate. How would changing the cation composition of the thiosulfate compounds affect gold dissolution? Would these varying solutions of thiosulfate lead to higher yields with lower concentrations, more similar to cyanide solutions? This study tests various thiosulfates (sodium, magnesium and calcium thiosulfates), each with varying concentrations, to identify any variations that would produce similar or even better yields than cyanide and ammonium thiosulfate.

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Thesis (M.S.)-- Wichita State University, College of Liberal Arts and Sciences, Dept. of of Geology