The interaction between metal cyanides, fine particles and porous adsorbents in an agitated slurry

Abstract

Slurry reactors are used extensively throughout the chemical, biochemical and mineral processing industries. This paper describes the interaction between fine silica or alumina particles and granular porous adsorbents such as activated carbon and ion-exchange resins in a stirred-tank reactor. Gold and silver cyanides were used as adsorbates to detect changes in the mass transfer characteristics of the adsorbents, which were ashed to determine the loading of silica or alumina. A dual rate kinetic model incorporating film diffusion, intraparticle diffusion and the adsorption equilibrium was used to interpret kinetic data and to estimate the effect of slurry conditions on the diffusion parameters. It was observed that the equilibrium loading of fines in the adsorbents was independent of their concentration in the slurry. Furthermore, the presence of these particles inside an adsorbent decreases the effective diffusion of gold or silver cyanides into the adsorbent matrix. When fine suspended solids are present in the reactor, a decrease in the effective availability of the superficial surface of the presaturated adsorbent particles for mass transfer from the liquid phase was observed. This newly defined surface availability factor was dependent on the concentration, particle size and the zeta potential of the fine particles in suspension.