Persimmon tannin-based new sorption material for resource recycling and recovery of precious metals

A low cost and environmentally “green” adsorption material was developed by anchoring tetraethylenepentamine (TEPA) groups on persimmon tannin and its potentiality for adsorptive preconcentration and recovery of precious metal ions from acidic chloride media was evaluated. This adsorbent exhibited outstanding selectivity for the sorption of Au(III) from wide concentration range of HCl medium. The species of Pt(IV) and Pd(II) were also selectively adsorbed over base metal ions in HCl medium. Sorption of metallic species followed typical Langmuir isotherm and the adsorption capacity for Au (III) was 5.93 mol kg−1, which is exceptionally higher than that of Pd(II) (1.76 mol kg−1) and Pt(IV) (1.48 mol kg−1). The chloroanionic species of Au(III), Pd(II) and Pt(IV) were adsorbed on the positive centers of the adsorbent by anion exchange coupled electrostatic interaction. Adsorption of Au(III) was accompanied by subsequent reduction to elemental gold. The loaded metals were quantitatively desorbed with acidic thiourea solution and the regenerated adsorbent exhibited undiminished sorption efficiency for at least four cycles. The adsorbent also exhibited superior performance over commercial anion exchange resin both in terms of adsorption selectivity and efficiency.