Preg-robbing of Gold by Carbonaceous Materials Encountered in Gold Processing

Abstract

Processing of gold from refractory ores containing carbonaceous materials (CM) poses challenges due to the ability of the CM to preg-rob dissolved gold. Depending on the type and maturity of CM encountered, preg-robbing of aurocyanide ion can lead to reduction in gold recovery ranging from a few percentages to more than 50%. Knowledge on the type of CM present, and its capacity for gold adsorption is important in predicting pre-treatment methods that can deactivate the CM and reduce its ability to preg-rob. This paper, as part of an on-going work, presents results on the degree of adsorption by the various carbonaceous materials encountered in gold processing, and estimates the amount of aurocyanide complex preg-robbed by them. To do this, various weights of carbonaceous materials (wood chips, charcoal, barren carbon and fresh activated carbon) were contacted with gold solution for a given period of time. The percentages of gold adsorbed on the various carbons were determined, and the results showed an increasing trend of preg-robbing in favour of wood chips < charcoal < barren carbon < activated carbon. Of all the CMs, wood chips have not undergone any carbonisation and/or activation, and thus exhibited the lowest affinity. The adsorption capacities in grams of gold per tonne of carbon over a 24-hr period were 30-65 for wood chips, 320-370 for charcoal, 410-420 for barren carbon and 580-650 for activated carbon. The trend shows direct correlation with the activities and the degrees of graphitisation and maturity of the various carbonaceous materials. It is thus important to characterise carbonaceous gold ores to know the maturity of the CM present, which will inform on the pre-treatment processes required. Keywords: Preg-Robbing, Wood Chips, Charcoal, Activated Carbon