Selective adsorption of gold ion in wastewater with competing cations by novel thiourea-reduced graphene oxide

Abstract

In this study, selective adsorption experiments of Au were carried out using graphene oxide (GO) and thiourea-reduced GO (TU-rGO). Adsorption experiments using Au, Cu, Pb, and Zn were performed with GO and TU-rGO in order to selectively adsorb Au from simulated waste electric and electronic equipment leachate or printed circuit board wastewater. Optimal adsorption conditions were determined, adsorption isotherm models were fitted, and desorption and regeneration experiments were performed. Additionally, GO and TU-rGO were characterized to better understand the material and propose the adsorption and desorption mechanisms for TU-rGO. It was found that TU-rGO could selectively adsorb Au, achieving a high efficiency of 95‒99% at initial Au concentrations of 0.1‒10 mg L−1 with little to no adsorption of Cu, Pb, and Zn. Moreover, the desorption efficiency of Au by ammonium thiosulfate reached 94% with the adsorption efficiency of TU-rGO decreasing from 99 to 78% after five adsorption and desorption cycles. Isotherm adsorption experiments indicated that the Langmuir model better fitted the adsorption of Au than the Freundlich model. This implied that the adsorption process was mainly controlled by monolayer coverage, with a high Au adsorption capacity of approximately 833 mg g−1 for TU-rGO.