Modification of activated carbon by chemical vapour deposition through thermal decomposition of thiourea for enhanced adsorption of gold thiosulfate complex

Modified activated carbon (SCN-AC) was prepared by chemical vapour deposition through the thermal decomposition of thiourea. Compared with the AC-modified by impregnation, the benefits of SCN-AC were a simpler modification process and a shorter modification time. The Au(I) ion adsorption performance of SCN-AC in thiosulfate solution was systematically studied. The adsorbent was well characterised by scanning electron microscopy-energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The effects of contact time, pH, temperature, and gold concentration were investigated, and the gold adsorption performances in Cu2+-NH3-Na2S2O3 and Cu2+-en-Na2S2O3 systems were also evaluated. More than 85% of Au(I) could be recovered over a wide pH range, and the adsorption capacity increased with decreasing adsorption temperature, reaching a maximum of 11.86 kg/t-AC. The adsorption followed pseudo-second order kinetics and was well explained by the Freundlich model. Analysis of the thermodynamic parameters indicated that the adsorption of Au(I) on SCN-AC was exothermic and spontaneous. The adsorption of Au (I) on SCN-AC was attributed to the strong affinity between the soft acid and soft base, the formation of a pi-pi conjugated system, and the electrostatic interaction between the adsorbent and adsorbate. Additionally, SCN-AC showed good adsorption properties in the Cu2+-NH3-Na2S2O3 system and the Cu2+-en-Na2S2O3 system. This strategy could be used as a green and environmentally friendly method for gold recovery.