Effects of the textural and surface properties of activated carbon on the adsorption of gold di-cyanide

The influence of the surface, condition of activated carbon on the adsorption of aurodicyanide was investigated to gain a better understanding on the influence of the pore volume distribution and heat treatment on the adsorption capacity of the carbon. Three activated carbons were heat-treated at 850°C in nitrogen gas. Adsorption of gold di-cyanide on heat-treated carbon increased compared to the untreated carbon. However, no drastic change in the pore volume was observed after heat treatment of the activated carbon. Therefore, the combined effects of textural and surface properties of the activated carbon are relevant for the equilibrium adsorption of gold di-cyanide. second part of the paper one of the major assumptions in adsorption modelling onto activated carbon based on aqueous surface chemistry principles is investigated, that of accounting for electrostatic interactions. The surface of activated carbon contains acidic and basic surface groups, which influence the adsorption of gold di-cyanide from the aqueous solution. The surface charge density that arises from ionisation of these surface groups in response to the solution pH and ionic strength was evaluated by potentiometric titration. The surface potential based on the Gouy-Chapman relationship for a flat surface does not reflect a realistic picture of the potential distribution inside the microporous carbon as the size of the micropore is too small to allow such a potential distribution to develop. This currently forms the basis available adsorption models. It is proposed that the overlapping of the potential fields inside the micropores could be handled by using the Donnan potential.