Microtomography based identification of gold adsorption mechanisms, the measurement of activated carbon activity, and the effect of frothers on gold adsorption

Microtomography gives a visualisation of the adsorption of gold di-cyanide onto activated carbon. The computed tomography (CT) images show that the loading of gold in macro pores is negligible, and indicate that surface diffusion is the dominant mechanism for the penetration of the gold cyanide complex into the internal carbon structure. The images also show that at loadings typically obtained in a carbon in pulp (CIP) plant, the gold is predominantly adsorbed on the external surface of the carbon, with film diffusion being the rate limiting mechanism. At high gold loadings, the external surface sites become saturated and further adsorption requires the transport of the adsorbed gold into the interior of the carbon. The use of conditions which result in film diffusion are recommended for activity testing of carbon, as they are more representative of plant conditions. A method based on solvent extraction and gas chromatography has been developed for analyzing the concentration of the flotation frother IF50 in cyanide leach solutions. This frother adsorbs very strongly onto activated carbon, severely hindering both the equilibrium adsorption of gold and, more importantly, the rate of gold adsorption.