Efficient environmental recovery of Au(I) from thiosulfate solution on triphenylphosphine-oxide-modified vermiculite

Natural materials that are economical and environmentally benign are being explored as adsorbent bases for recovering Au(I) from thiosulfate solution via an efficient grafted functional group. In this work, natural vermiculite (VE) modified with triphenylphosphine oxide (TPPO) was used to adsorb Au(I) from thiosulfate solution, and it's gold recovery performance and adsorption mechanism. Fourier transform infrared spectroscopy, scanning electron microscopy–energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and nitrogen adsorption were used to characterize the adsorbents. TPPO-modified VE (VE-TPPO) showed improved gold adsorption ability at a pH of approximately 10, thiosulfate concentration of approximately 0.1 mol/L and temperature of approximately 25 °C. More than 95% of Au(I) could be recovered, and the loading capacity of Au on VE-TPPO increased with decreasing adsorption temperature, reaching an amount of 4.22 kg/t after once adsorption. TPPO was adsorbed on vermiculite through cationic-π bonds. Au(I) was adsorbed on VE-TPPO by a ligand-exchange mechanism involving charge transfer between PO groups and Au(I). Moreover, the interaction mechanism between TPPO and Au(I) was further validated by density functional theory calculations. The use of natural materials with low cost and environmental impact can make the process of leaching gold with thiosulfate safer and cleaner.