Study On The Properties Of Modified Activated Carbon And Modified Chitosan For Adsorption Of Au(?) In Thiosulfate Solution

The technology of leaching gold by thiosulfate from minerals has many advantages,such as non-toxic leaching reagent,environmentally friendly,low reagent price,fast leaching rate,high leaching rate,and effective leaching of complex gold mines.Therefore,thiosulfate leaching gold technology has attracted more and more attention.However,compared with the cyanide leaching technology,the Au(?)is difficult to be effectively recovered from thiosulfate solutions,which hinders the industrial application of the thiosulfate gold leaching technology.Therefore,research on a technology that can effectively recovery gold from thiosulfate solutions is of great significance to the industrial application of thiosulfate leaching gold technology.In this study,modified activated carbon(AC-SH)and modified chitosan(CTS-SCN)were synthesized for the adsorption of gold in thiosulfate solution.The synthesis conditions of AC-SH and CTS-SCN were studied.Results show that mass ratio of2-mercaptobenzoxazole(MBO)to activated carbon(AC)was 1:10,the AC-SH synthesized under 160?for 3 h can achieve a higher adsorption recovery percentage;when the mass ratio of ammonium thiocyanate(SCN)to chitosan(CTS)is 3:10,the CTS-SCN synthesized under 120°C for 8 h can achieve an higher adsorption recovery percentage.The factors affecting the adsorption performance of AC-SH and CTS-SCN(such as adsorption time,adsorption temperature,initial p H of the solution,thiosulfate concentration,and initial Au(?)concentration of the solution)were also investigate.The experimental results showed that AC-SH and CTS-SCN basically reached adsorption equilibrium after 24 h and 10 min,respectively.The adsorption percentage of AC-SH increased with the increase of temperature,indicating that AC-SH adsorption Au(?)in thiosulfate solution is an endothermic process,the recovery percentage of CTS-SCN decreases with the increase of temperature,that is,CTS-SCN adsorption of Au(?)is an exothermic process.A better adsorption percentage can be achieved of AC-SH and CTS-SCN,when the p H of the solution is 9and 6,respectively.The recovery percentage of Au(?)by AC-SH and CTS-SCN decreases with the increase of the concentration of thiosulfate,that is,high concentration of thiosulfate is not conducive to AC-SH,CTS-SCN adsorb gold.As the initial gold concentration increases,the gold loadings of AC-SH and CTS-SCN both increased.FT-IR,SEM-EDS,BET and XPS were used to characterize AC-SH and CTS-SCN before and after modification.The results showed that MBO was attached to the surface of activated carbon by physical adsorption,and NH₄SCN reacted with the amino group on the surface of chitosan to form—N—C(=S)—NH₂group.SEM-EDS analysis showed that the element peak of gold appeared after the adsorption of AC-SH and CTS-SCN,which indicated that both AC-SH and CTS-SCN could adsorb gold from thiosulfate solution.BET results show that AC-SH and CTS-SCN belong to mesoporous materials.XPS spectrum analysis showed that AC-SH adsorbed gold through its S—S functional group combined with gold complex.The valence state of Au(?)does not change after adsorption.CTS-SCN adsorbs[Au(S₂O₃)₂]^3-complex ions,and then the amino group on CTS-SCN reduces Au(?)to Au(0).Langmuir isothermal model can well describe the adsorption process of Au(?)in thiosulfate solution by AC-SH and CTS-SCN,which indicates that the adsorption is a homogeneous monollayer adsorption process,and the recovery rate of gold depends on the number of adsorption sites and the material properties of AC-SH.The pseudo-second-order kinetic model can well describe the adsorption process of Au(?)in thiosulfate solution by AC-SH,which indicates that the adsorption process of AC-SH is a chemisorption process.The thermodynamic calculations on the experimental data obtained at different temperatures and the result of calculating shows?G^?<0??H^?=33.46 k J/mol and?S^?=120 J/(mol·K),which means that the reaction can be spontaneous,and it is a process of heat absorption and entropy increased.The influence of impurities(such as Cu²⁺,NH₃,en,Cu²⁺-NH₃,Cu²⁺-en,etc.)on the adsorption of Au(?) by AC-SH was studied.It is found that Cu²⁺has an inhibitory effect on the gold adsorption performance of AC-SH,while NH₃and en have a promoting effect on the gold adsorption rate of AC-SH,and can inhibit the negative effect of Cu²⁺.The desorption methods of gold-loaded AC-SH and CTS-SCN were discussed respectively,and it was found that higher concentrations of sodium thiosulfate and sodium sulfite solutions can desorb most of the gold on gold-loaded AC-SH and CTS-SCN.The study of AC-SH adsorption-desorption-adsorption cycle(AC-SH was not subjected to any regeneration treatment after desorption)showed that AC-SH still has 67%gold recovery rate after five adsorption-desorption cycles.The above research results provide experimental and theoretical references for the development and application of thiosulfate gold extraction technology.