Interfacial properties of mercaptopropyl-functionalised silica gel and its adsorption performance in the recovery of gold(I) thiosulfate complex

Abstract

Abstract Silica gel (SG) was modified using 3-mercaptopropyl trimethoxysilane (MPTMS) and used as an adsorbent for the recovery of gold(I) from a thiosulfate solution, based on the hard and soft acids and bases theory. The interfacial properties of the mercaptopropyl-functionalised silica gel (MP–SG) and its performance for the adsorption of gold(I) from a thiosulfate solution were examined. An optimized modification procedure was determined to produce a MP–SG mercapto group content of 1.1 mmol·g−1. Characterisation of the prepared samples revealed the immobilisation of the MPTMS on the SG surface through chemical adsorption, and that the modification process was accompanied by the release of methanol. The ratio of methanol to the mercapto groups was determined to be 2.06, indicating the formation of 1, 2, or 3 bonds between the SG and MPTMS. The effects of the solution pH, adsorption temperature, thiosulfate concentration and gold concentration on the adsorption of gold(I) onto MP–SG, were also evaluated. The adsorption of gold onto the MP–SG surface was determined to involve ion-interchange between the mercapto groups and Au(S2O3)23−. Numerical investigation of the gold adsorption mechanism, revealed that the charge of gold(I) decreased through charge transfer from the ligand to gold(I). The Au–MP–SG could be eluted using mixture of 1% thiourea and 2 mol·L−1 HCl. The findings of this study demonstrate the potential of SG for practical application to gold recovery from a thiosulfate solution.