Preg-robbing usually refers to the adsorption of a gold cyanide complex, i.e. Au(CN)₂⁻, on the components of a gold ore including carbonaceous materials and other minerals during the gold leaching process (1-3). The adsorption of gold ions on carbonaceous materials is one of the most common phenomenon responsible for gold losses from the cyanide leaching process (1, 4). Depending on the carbon content of the ores, gold losses may reach 90 % of leachable gold due to preg-robbing during cyanidation (5). Chemical blinding agents have previously been investigated to passivate the surface of carbonaceous preg-robbers in the ores, thus reducing the extent of preg-robbing and allowing an increase in gold recovery (1, 3, 6, 7). However, the mechanism by which such agents suppress the ion-adsorption capability of the carbonaceous materials as well as their interactions with other components of the ore, including pyrite, and more importantly, gold, are yet to be fundamentally investigated. The latter process could severely affect final gold recovery if the surface of the gold becomes passivated.

This study investigates the effect of various blinding agents on the main components of a gold-containing concentrate: carbon, gold and pyrite. A novel electrochemical approach is employed, i.e. double-layer capacitance measurements combined with electro-oxidation/reduction peaks obtained from cyclic voltammetry tests. Our group is the first to employ the electric double-layer theory to study the preg-robbing capacity of carbonaceous ores with total carbonaceous matter (TCM) contents as low as 0.3 % by weight.

Figure 1 shows a comparison between the blinding activity, and durability, of various surfactants and chemical reagents, at different concentrations, on the surface of activated carbon particles over a 24-hour contact period. The capacitance is an indication of how well the chemical reagents have been adsorbed on the activated carbon particles with the lowest capacitance values showing the best surface adsorption. The study reveals that kerosene, Lecithin and Polymax 30 are among the best blinding agents for the activated carbon surfaces in terms of adsorption and durability.

Further cyclic voltammetry studies on gold surfaces in alkaline cyanide solutions (with the added blinding agents) have shown that kerosene is the least detrimental to the gold cyanide leaching process, i.e. the electrochemical oxidation reaction for the formation of AuCN complex.

Figure 1. A comparative study for the effect of various chemical reagents, i.e. Aristonate H and L, Lecithin, Sodium dodecyl sulfate (SDS), kerosene and Polymax 30, on the ion adsorption capability of the activated carbon particles over 24 hours.

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