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The cyanide heap leaching behavior of cupriferous gold ores Tahvili, Mohammad Sasan


To develop a fundamental understanding of cyanide heap leaching of low-grade gold ores, with significant copper mineralization, two sets of column leach tests were operated under two different leaching solutions. In one set, four 1.5 m tall column tests were leached with sodium cyanide solution. In the second set, another four columns were leached with solutions of cyanocuprate complexes in the absence of free cyanide. Each set was run for a period of up to 200 days. The behavior of individual species, were investigated for the purpose of developing reliable rate parameters for the mathematical model. Significant amount of weak acid soluble copper minerals was discharged from the ore, simply by pre-rinsing with water. The cyanide leaching is shown to occur in different stages with remarkable characteristics as follows: (a) Significant decrease in the pH at the beginning of the cyanide column leach tests; (b) Reductive dissolution of the remaining WAS copper salts and dissolution of copper sulfide minerals, from the first day of the experiment; (c) Dissolution of gold from the first stage while no free cyanide is present in the solution; (d) The occurrence of two distinct peaks in copper concentration, first as the result of leaching of labile copper sulfides and second as the result of redissolution of copper cyanide precipitates; (e) Free cyanide breakthrough in the effluent, which is accompanied by the appearance of dissolved iron. The second set of column leach tests showed that the leaching of gold with a solution of cyanocuprate complex and in the absence of free cyanide is accessible with rate parameters comparable to leaching with cyanide. It is also concluded that some of the copper minerals can be leached in the absence of free cyanide. Iron does not show any dissolution in cyanocuprate leaching systems.

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