Gold process modelling. I. Batch modelling of the processes of leaching, preg-robbing and adsorption onto activated carbon

Abstract

In this paper an overall batch model is developed to describe the simultaneous processes of leaching, preg-robbing and adsorption onto activated carbon. These processes were quantified for an oxide ore and three sulphide ores, which consisted of a flotation feed, a pyrite concentrate and a copper concentrate. The effect of the kinetics of preg-robbing on gold extraction with or without activated carbon was also closely examined for these ores. A variable order empirical Mintek-type model described the leaching, while the film diffusion equation with a Freundlich isotherm was used to describe both the preg-robbing at the ore surface and adsorption of aurocyanide onto activated carbon. The model developed fitted the observed experimental data well, and was used to decouple preg-robbing from leaching for the refractory ores and simulate the simultaneous leaching, adsorption and preg-robbing processes. Overall the most important factor governing the extraction of gold was found to be the relative rates of leaching, adsorption and preg-robbing. The Telfer oxide ore model parameters were calibrated from leaching and simultaneous leaching and adsorption data, as this ore was not preg-robbing. For the weakly preg-robbing flotation feed it was necessary to decouple the preg-robbing from the leaching data and use the updated parameters to calibrate the adsorption parameters when simultaneous leaching, adsorption and preg-robbing experiments were performed. The same technique was used for the pyrite concentrate, and it was shown that the enhanced extraction of gold in the presence of activated carbon was not solely due to overcoming preg-robbing for this ore. Preg-robbing could not be decoupled from leaching for the copper concentrate as this ore was very strongly preg-robbing, with preg-robbing occurring at a faster rate than the adsorption of gold onto activated carbon.