Adsorption Of Gold Thiosulfate Complex Ions By Nitrogen-doped Modified Activated Carbon After Thermal Activation

Gold as precious metals,accounts for an important role in economic and society.The extraction of gold generally uses the cyanide leaching method,but the cyanide immersion gold has a vicious,which is extremely harmful to the environment.Sulfate thiosulfate is non-toxic,economically environmentally friendly,and has become a new method of replacing cyanide immersion.However,activated carbon cannot effectively adsorbate Au（S₂O₃）₂^3-,affecting the industrial application of thiosulfate soil.In this paper,the three different graded activated carbon were nitrogen doped and thermally activated,examine the adsorption effect of modified activated carbon to Au（S₂O₃）₂^3-,optimiee modification conditions.The morphology,structure,specific surface area,pore siee distribution and surface chemical properties of modified activated carbon were characterieed by XPS,BET and SEM.The adsorption mechanism of Au（S₂O₃）₂^3-on modified activated carbon and the effect of various ions on the adsorption of gold were discussed..Modified experimental study showed that the optimal modification of activated carbon having 0.9 to 3.2mm:melamine mass was 1.88%of activated carbon,and the nitrogen doped temperature was 50℃,the heat activation temperature was 900℃,and the heat activation time was 60 min,the product obtained is AC₁-N900,the adsorption amount of 294.21μg/g for Au（S₂O₃）₂^3-.The optimal modification of activated carbon having 0.45～0.9mm:melamine mass is 3.75%of activated carbon,the nitrogen doped temperature is 50℃,the heat activation temperature is 750℃,the heat activation time is 60 min,and the AC₂-N750 is obtained,have the largest adsorption amount553.35μg/g.The optimal modification conditions of activated carbon powder（-200mesh≥96%）:melamine quality is 3.125%of activated carbon,nitrogen doped temperature is 50℃,the heat activation temperature is 450℃,the thermal activation time is 30 min,the AC₃-N450 is obtained,and the maximum adsorption amount is210.31μg/g for Au（S₂O₃）₂^3-.The adsorption amount of modified activated carbon to Au（S₂O₃）₂^3-is higher than that of untreated activated carbon,the results show that after nitrogen doping and thermal activation modification,activated carbon can improve the adsorption effect of Au（S₂O₃）₂^3-,and the adsorption effect of the AC₂-N750 to the Au（S₂O₃）₂^3-is best.Tests of modified activated carbon suction Au（S₂O₃）₂^3-showed that the p H of the solution was 7 to 8,and the adsorption temperature was 35℃more advantageous to adsorption.When the gold concentration is 20 mg/L,the adsorption time is 30h,the adsorption process is basically saturated.Study the impregnation reagent,metal ions and sulfur ions,etc.in solution,affecting the AC₂-N750 suction Au（S₂O₃）₂^3-,it is found that the adsorption amount of the AC₂-N750 decreases with the increase in Na₂S₂O₃and S₄O₆^2-concentration,and with concentration of Cu²⁺、Pb²⁺and Zn²⁺increase,the absorption amount of the AC₂-N750 is increased first and then decreases.When Cu²⁺/NH₃ is added,the adsorption increases with the increase of Cu²⁺concentration.Adsorption kinetics found that at different gold concentrations,the adsorption temperature at 25℃and 35℃,the adsorption process of Au（S₂O₃）₂^3-by AC₂-N750conforms to the particle diffusion model.When the adsorption temperature is 45℃and55℃,the AC₂-N750 adsorption process meets the pseudo-first-order kinetic model.When the adsorption temperature was 55℃,the concentration of gold was 40 mg/L,the AC₂-N750 had the largest adsorption amount of 1718.32μg/g.