A mechanistic model of the equilibrium adsorption of copper cyanide species onto activated carbon

A mechanistic model has been developed to describe the equilibrium adsorption of copper cyanide species onto activated carbon. This model was based on the calculation of equilibrium between the various copper cyanide complexes in both the aqueous and carbon phases. Solution non-ideality was also incorporated, as changes in ionic strength have a significant effect on the copper cyanide speciation. The use of a theoretical equilibrium constant (i.e. a linear isotherm) was found to poorly describe the adsorption of Cu(CN)2− and Cu(CN)32−, but better results were obtained by using a Freundlich isotherm for both species. Despite this, there were significant deviations under conditions of higher free cyanide, and hence the model was updated to include a desorption reaction, which is a function of the free cyanide concentration, to account for the irreversibility. This new model was found to predict the copper loading over a wide range of copper and cyanide concentrations.