N-aminoguanidine modified persimmon tannin: a new sustainable material for selective adsorption, preconcentration and recovery of precious metals from acidic chloride solution.

A new adsorption gel has been developed by immobilizing N-aminoguanidine (AG), a chelating ligand, on persimmon tannin extract through consecutive reactions. Adsorption behavior of the gel was investigated for the adsorptive separation and recovery of precious metal ions from varying concentration of HCl medium. The adsorption isotherms of precious metal ions on the gel were described by the typical monolayer type of Langmuir model and the maximum adsorption capacities were evaluated as 8.90 mol kg(-1) for Au(III), 2.01 mol kg(-1) for Pd(II) and 1.01 mol kg(-1) for Pt(IV). Real time applicability of the gel was examined for the recovery of precious metals from actual leach liquor of e-waste leached with chlorine containing hydrochloric acid. The gel was found to be highly efficient and selective for the uptake of targeted metal ions in the presence of excess base metal ions and also exhibited superior selectivity over commercially available anion exchange resins.