Study On Surface Modification Of Activated Carbon By Chemical Vapor Deposition And Its Adsorption Of Gold Thiosulfate Complex Ions

The thiosulfate method has been widely concerned for its advantages such as low cost,low toxicity,high reactivity,and low corrosion.However,in the Cu²⁺-NH₃-Na₂S₂O₃ leaching system,the activated carbon adsorption method is difficult to effectively recover the gold in the leaching solution compared with the technology of carbon-in-pulp,which limits this non-toxic gold extraction technology.Therefore,research on modified activated carbon to enhance the affinity of gold thiosulfate complex is of great significance to promote the development of gold thiosulfate gold leaching.In this paper,chemical vapor deposition of thiourea was used to modify activated carbon?SCN-AC?to increase its affinity for gold thiosulfate complex,and to increase its adsorption capacity of gold.The modification process of activated carbon was optimized,and the influence of adsorption performance on gold recovery rate was studied.The surface properties of the modified carbon were characterized by SEM-EDS,XPS,N₂ adsorption-desorption,and FT-IR,and the adsorption mechanism of gold on the modified carbon was also analyzed.The effects of base metal ions on the gold recovery rate and the desorption-recycling process of gold-loading carbon were explored.Experimental research shows that the recovery rate is up to 92%when the thiourea modifier is 1 g,the activated carbon is vapor-deposited at 150°C for 5 hours.The recovery rate was higher than 85%on the p H 6-11,and decreased with the increase of gold concentration,temperature and sodium thiosulfate concentration.The adsorption capacity was 11.85 kg/t-AC at 25°C when the gold concentration of 150mg/L.The adsorption of gold thiosulfate complex ions by SCN-AC follows Freundlich isothermal model and pseudo-second-order kinetic model,indicating that the adsorption reaction is multi-molecular chemical adsorption.The values of?G^?,?H^?and?S^?are all less than 0,indicating that the adsorption reaction is spontaneous,exothermic,and the interface disorder is reduced.FT-IR showed that the thermal decomposition product of thiourea on the surface of activated carbon was ammonia thiocyanate.SEM-EDS and N₂adsorption-desorption show that during the modification process,the pore structure of the SCN-AC surface was blocked by the modifier,and sulfur-containing functional groups played a key role in the adsorption of gold.XPS and FT-IR studies show that the valence state of gold does not change before and after adsorption.A?₈⁸ or?⁸₁₄conjugate system may be formed between the C and N atoms of the N?C–S^-group on the SCN-AC surface and the benzene ring on the carbon surface,and the electrostatic interaction between the C=O group on the carbon surface.The effect of interfering ions on the recovery rate of gold shows that the recovery rate decreased with the increase of concentration of Cu SO₄,Na₂SO₃,and and increased with the increase of concentration of NH₃,en,Na₂SO₄,Cu-NH₃ molar ratio,and Cu-en molar ratio.The desorption-cycle investigation of gold-loading carbon showed that the desorption rate was about 85%in 0.3 mol/L Na₂S₂O₃ at 55°C for 12 hours.The desorbed activated carbon could be directly modified by chemical vapor deposition.After 5 cycles of modification-adsorption-re-modification,the recovery rate was still higher than 85%,indicating that chemical vapor deposition of thiourea modified activated carbon has a good application prospect for gold recovery.The experimental basis and theoretical guidance of this paper provide a reference for the application of activated carbon adsorption Au[S₂O₃]₂^3-.