A mechanistic model has been developed to describe the equilibrium adsorption of copper cyanide species onto activated carbon.This model included the species equilibrium calculation for both aqueous and carbon phases.The activity of species was found to have a significant effect on the copper cyanide speciation and therefore solution non-ideality was taken into account in the calculation.The use of a theoretical equilibrium constant (a linear isotherm) to describe the adsorption of CuCN2-and CuCN32-onto carbon under-estimates the equilibrium loading for low loadings but over-estimates it for high loadings.