COMPARISON AND MODELING OF THE ADSORPTION-KINETICS OF GOLD CYANIDE ONTO ACTIVATED CARBON AND RESIN IN A SILICA SLURRY

The gold adsorption performance of two strong base anion exchange resins and a coconut-based activated carbon are compared. Isotherm experiments were performed which showed that the equilibrium loading of gold on resins is significantly higher than on carbon. It is also shown that the presence of silica slurries does not change the isotherm substantially. Batch kinetic experiments were performed at various rates of agitation and concentrations of solids. It is shown that the kinetics of gold adsorption onto the microporous resin Duolite A-161 is determined by film mass transfer until equilibrium loading is achieved. The presence of solids is shown to have little effect on the measured film-transfer coefficient. The kinetic results for the resin Minix are successfully modelled using the Homogeneous Solid Diffusion Model (HSDM), which incorporates film mass transfer and intraparticle diffusion. The presence of high concentrations of solids is shown to have a small inhibiting effect on the adsorption kinetics. The kinetic results for the activated carbon G210 show that the kinetics are successfully modelled by the HSDM for clear solutions and low solids concentrations. At high solids concentrations, a dramatic reduction in the adsorption rate is observed. This is ascribed to blocking of the carbon macropores by fine solid material. A modified HSDM is formulated in order to take into account this effect. This model allows for the outer shell of the carbon to be partially blinded by solid fines. This model is in good agreement with the experimental results. The results, therefore, indicate that strong base anion exchange resins are favoured over carbon in concentrated silica slurries from an equilibrium and kinetic point of view.