The Fosterville Goldmine in Victoria Australia employs the BIOX~? Process to liberate gold from its sulfidic flotation concentrate through bacterial oxidation. Gold occurrence is primarily as submicron particles in pyrite and arsenopyrite and has been described as being in 'solid solution' and therefore not amenable to direct cyanidation. Once liberated by the oxidation process, the gold is then available for cyanide leaching.During the oxidation process it has been found that a portion of the liberated gold becomes suspended in the liquid phase in what appears to be a colloidal state. This liquid becomes a waste stream during washing of the oxidised solids and the suspended gold is therefore lost. A method was previously developed using an addition of quebracho tannin to significantly reduce this loss by formation of an iron-tannin precipitate which captures the gold which then reports to the cyanide leach circuit with the oxidised concentrate solids onto which it is adsorbed. This paper discusses the development and plant trial of a second processing step to further enhance gold recovery by use of flotation tailings essentially as a source of extra surface area to capture residual tannin-iron precipitate and its associated gold not recovered in the first step.
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