Reduction and accumulation of Au(III) by grape waste: A kinetic approach

Recovery of Au(III) in hydrochloric acid using grape waste was studied. The adsorption gel prepared from grape waste was found to highly selectively adsorb Au(III) showing negligible affinity for other precious metals and some base metal ions tested so far. The adsorption isotherm study exhibited the maximum loading capacity of the gel as high as 9.6 mol or 1.9 kg gold per kg dry weight of gel. XRD analysis and the digital micrograph of the gel taken after adsorption revealed the formation of gold particles during adsorption process which is associated with the high selectivity and high capacity of the gel for Au(III). Kinetic and electrochemical study was conducted at various temperatures to confirm an endothermic adsorption process following pseudo-first order kinetics.