Gold recovery with ion exchange used resins

In this paper one strong acidic, one strong basic and one weak basic ion-ex change resins, considered as exhausted in an industrial demineralizing plan t. are screened for gold recovery from cyanide solutions. Based on the obse rved ability for the recovery and on the ease of regeneration. the weak bas e anion exchanger Purolite A-100 is selected. This spent resin is stable un til 60 degreesC and, after regeneration. conserves its physical properties as compared with a new one. Equilibrium data for the resin are determined. proving the very high capacity of the resin for gold ( similar to 500 ma Au /g dry resin) and modeled by the Freundlich and mass action isotherm models . A kinetic experiment is conducted in a batch adsorber and modeled with an equivalent Fick's diffusivity using the linear driving force approximation , showing that the film resistance to mass transfer controls the operation. Finally, a fixed bed adsorber is saturated with gold aurocyanide and regen erated with a potassium hydroxide solution. The model used for the Simulati on of both steps incorporates axial dispersion and the same equivalence for the ionic diffusivity. During the elution process. precipitation of dihydr ated potassium aurocyanide occurs inside the resin, increasing the intrapar ticle resistance to mass transfer. The model is able to reasonably represen t the experimental elution results when a large internal resistance to mass transfer is used. A 25-fold concentration of the initial gold solution is obtained in this saturation/elution process, albeit the precipitation, show ing the feasibility of the method for the recovery of gold, increasing the useful life of the resins and decreasing pollution. The anionic Purolite A- 100 resin showed also a significant capacity for removing silver, although less than for gold, probably because silver cyanide complexes occupy, on th e average, more than one ion exchange site in the resin. (C) 2001 Elsevier Science B.V. All rights reserved.