Recovery of Au(III) by using low cost adsorbent prepared from persimmon tannin extract

Abstract

An adsorption gel was prepared by crosslinking the persimmon tannin with concentrated sulfuric acid and adsorption behavior of Au(III) from acidic chloride media on the crosslinked gel as well as crude persimmon tannin powder was evaluated. The crosslinked gel exhibited 100% adsorption of Au(III) over a whole concentration range of HCl from 0.1 to 6.0 M (M = mol dm −3) while crude persimmon tannin powder achieved 100% adsorption only in the low concentration region of HCl. The maximum adsorption capacity of the crosslinked gel for Au(III) was evaluated as high as 7.7 mol/kg whereas it was only 5.8 mol/kg for the crude tannin powder. The phenomenon of adsorption coupled reduction is considered to be responsible for the high adsorption of Au(III). The reduction of Au(III) to its elemental form was confirmed by XRD and digital micrograph of the adsorbents after the adsorption of Au(III). The reaction kinetics at different temperatures for both adsorbents was evaluated in terms of pseudo-first-order and pseudo-second-order kinetic models. As revealed by the high activation energy ( E a) value, adsorption of Au(III) on both the adsorbents was found to be a chemical phenomenon.