A mathematical model of heap leachingpreviously developed by Dixon and Hendrix (1993) wasmodified to include the specialization of all cyanide andhydroxide complexes and precipitates of copper, gold and iron.This new model was validated in column testing of anAustralian Cupriferous low-grade gold ore containingapproximately 0.35 percent copper, primarily as coppersulfides, and 0.6 percent g/t gold.It was found that, in the presence of significant coppermineralization, no dissolved gold appears in the columneffluent for a significant period of time, depending on theinfluent cyanide concentration and the height of the column.This phenomenon is explained by the precipitation of goldcyanide salt, caused by the total depletion of free cyanide fromsolution in the presence of oxidized copper minerals, whichtend to buffer the column to a pH below 4. Once dissolved,gold appears in the column effluent, its leaching kinetics are astrong function of the leaching kinetics of the secondarycopper sulfide minerals such as chalcocite. Chalcoyrite has ofcyanide losses at high cyanide concentrations.
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