The influence of pH, dissolved oxygen and organics on the adsorption of metal cyanides on activated carbon
The carbon-in-pulp (CIP) process has become the preferred route for the recovery of gold from cyanided pulps. This paper describes the effect of organic fouling on activated carbon, as well as the influence of pH and dissolved oxygen on the equilibrium adsorption capacity of the carbon. Gold and silver cyanide were used as adsorbates in order to quantify the inhibition of mass transfer to activated carbon caused by these effects. Adsorption tests were carried out when prior contact between the carbon and the foulant was followed by gold or silver adsorption, as well as the simultaneous adsorption of gold or silver and the foulant species. These tests were performed in a batch stirred tank reactor and a packed column. UV-spectrophotometry showed that the organics were all adsorbed fairly irreversibly. The Freundlich-type multicomponent isotherm was applied successfully to describe the equilibrium adsorption capacity of gold or silver in the presence of a single organic foulant. At low organic loadings on the carbon, the reduction in the rate of adsorption of metal cyanides appeared to be a kinetic influence, and could be caused by pore blocking. By fitting a dual resistance model to the profiles for the adsorption of gold or silver cyanide in the presence of low organic concentrations, the decrease in the intraparticle diffusivity was quantified. This model was also applied to the simultaneous adsorption of gold or silver and humic acid. However, at higher organic loadings on the carbon, a profound effect on the equilibrium loadings of gold and silver cyanide was observed, which indicated a mechanism of poisoning. The influence of pH and dissolved oxygen could also be related to an equilibrium effect. © 1991.