Gold recovery with ion exchange used resins

Abstract

In this paper one strong acidic, one strong basic and one weak basic ion-exchange resins, considered as exhausted in an industrial demineralizing plant. are screened for gold recovery from cyanide solutions. Based on the observed ability for the recovery and on the ease of regeneration. the weak base anion exchanger Purolite A-100 is selected. This spent resin is stable until 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 regenerated with a potassium hydroxide solution. The model used for the Simulation of both steps incorporates axial dispersion and the same equivalence for the ionic diffusivity. During the elution process. precipitation of dihydrated potassium aurocyanide occurs inside the resin, increasing the intraparticle resistance to mass transfer. The model is able to reasonably represent 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, showing 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 the average, more than one ion exchange site in the resin.