Comparative performance of porous adsorbents in presence of gold cyanide, organic foulants and solid fines

Abstract

Activated carbon and ion exchange resins are being extensively used in the mining industry to extract metal cyanides from leached liquors. The application of ion exchange membranes and fibres as possible alternatives to carbon and resin has recently received special attention. The adsorption profile of gold cyanide in the presence of organic and inorganic substances was studied, and compared for the different adsorbents. The membrane and fibre showed much faster rates for Au uptake than the C or resin, and can be attributed to their large external surface areas. Results obtained showed that the kinetic parameters in a film/surface diffusion model are affected by inorganic substances and low organic solution concentrations for all the adsorbents. At higher organic concentrations both kinetic and equilibrium influences were observed. This was ascribed to permanent pore blocking of the adsorbents by organic compounds. Furthermore, tests involving the intrusion of inert silica particles into the adsorbents indicated that the adsorption profile is affected only for activated C and ion exchange resins. These results were confirmed by ashing tests performed on the adsorbents. However, the diffusion of gold cyanide to all adsorbents was inhibited owing to the physical blinding of the superficial surface by the fine particles in suspension. This result was obtained by exposing a presaturated adsorbent to suspended solids and dissolved gold cyanide. Furthermore, the effect of blinding was accounted for in the model with the introduction of an availability factor. The availability factor was determined by comparing results for a clear Au solution and pretreated adsorbents in suspended solids.