Selective Adsorption of Au^III from Aqueous Solution Using 2,5-Dimercapto-1,3,4-thiadiazole Modified Persimmon Tannin

A one-pot synthesized persimmon tannin (PT)-based novel biosorbent modified with 2,5-dimercapto-1,3,4-thiadiazole (DMTD) was prepared for the selective adsorption of Au^III from aqueous mixtures. The synthesized biosorbent was designated as DMTD-PT and characterized using elemental analysis, zeta potential, Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The batch adsorption experiments in a model electronic waste leachate revealed that both DMTD-PT and PT had poor affinity for coexisting base metal ions, however, DMTD-PT and PT adsorbed 97.7 and 32.7%, respectively, of Au^III with an initial Au^III concentration of 78.0 mg L^-1 in the mixtures with a dosage of 2.5 g L^-1 each at pH 3.0 at ambient temperature. The adsorption results indicate the superior selectivity of DMTD-PT for Au^III compared to that of PT. The continuous column experiments further proved that DMTD-PT can be used to separate Au^III from aqueous mixtures. The maximum adsorption capacity of DMTD-PT for Au^III was determined to be 0.42 mmol g^-1. A kinetic study in combination with XPS and FTIR analyses of fresh and spent DMTD-PT further revealed that the potential biosorption mechanism can be attributed to the collaboration of electrostatic interactions and coordination.

Keywords:
persimmon tannin; 2,5-dimercapto-1,3,4-thiadiazole; modification; selective adsorption; Au^III