Adsorption of gold and silver glycinate on graphene and graphene oxide surface: A DFT study

Abstract

The non-toxicity and efficiency of glycinate make it an attractive alternative for cyanide in the extraction of gold and silver from ores. In this study, the adsorption behavior of gold and silver complexes with cyanide and glycinate anions on graphene and graphene oxide surfaces was investigated based on the density functional theory calculations. Contrary to cyanide complexes, glycinate complexes prefer parallel orientation to graphene and graphene oxide surfaces. Based on the obtained adsorption energies, interaction of all complexes with graphene oxide surface is stronger than with graphene surface. The adsorption energies of Au(gly)2- and Ag(gly)2- on the graphene surface are −1.46 and −1.11 eV, whereas Au(CN)2- and Ag(CN)2- adsorb on this surface with energies of −0.62 and −0.51 eV. PDOS diagram analysis confirms that the hydroxyl group is responsible for strong interaction between complexes and graphene oxide surface. The adsorption energies of Au(gly)2- and Ag(gly)2- complexes on the GO2 and GO3 surfaces are −2.19 and −1.85 eV, respectively, which implies the applicability of graphene oxide surface at recovering gold and silver ions from the leaching solution. Charge density difference and Mulliken population analyses show charge transfer occurs from the adsorbed complex to the surface which is intensified by adding functional groups to the surface.