Characterization and blinding of carbonaceous preg-robbers in gold ores

Preg-robbing amorphous carbon and graphite were identified in two ore samples using optical microscopy to identify the mineral phases, followed by the direct analysis of gold on these phases using electron microprobe analysis. Pyrite showed a slight preg-robbing effect. The samples were also mineralogically quantified and the mica and chlorite that was present was shown to have a negligible preg-robbing effect in comparison with the carbonaceous phases. Several surfactants were found to have a blinding effect on carbon, reducing the adsorption of gold cyanide. Activated carbon was first used as a model preg-robber, and the best blinding agents were then tested on a highly preg-robbing shale ore sample. NP10 (a long-chain polyoxyethylene), sodium lauryl sulphate (SLS) and petroleum sulphonate were found to be the best potential blinding agents. There are some indications, however that these reagents also blind the gold surface to some extent, thereby decreasing the leaching efficiency. (C) 1998 Elsevier Science Ltd. All rights reserved.