Study On The Adsorption Performance Of Au (Ⅰ) In Thiosulfate Gold Leaching System By Mercapto-silica Coated Magnetic Material

Thiosulfate gold leaching technology is the most promising non-cyanide gold extraction technology,which has the advantages of environmental friendliness,fast gold leaching rate and the ability to treat refractory gold ores.How to efficiently separate and recover Au（S₂O₃）₂^3-from gold leaching system is the key problem to realize industrialization of gold extraction technology of thiosulfate.It is important to develop a facile and highly efficient synthetic strategy to fabricate an adsorbent exhibiting excellent adsorption performance and separation ability to recover Au from thiosulfate solutions.A magnetic silica composite（Fe₃O₄@SiO₂-SH）was synthesized by an economical and efficient one-pot method and used to recover gold from thiosulfate solution.The synthesis conditions of Fe₃O₄@SiO₂-SH were optimized as follows:the dosage of TEOS at 3.4 m L,dosage of modifier at 1 m L,p H at 10,reaction time at 40min and temperature at 70℃,the gold adsorption effect was better.XRD,TEM,FTIR,Zeta potential,VSM,BET and LPSA were used to analyze the structure and functional properties of the adsorbent,and the acid resistance of the adsorbent was investigated.The results showed that the prepared adsorbent was a mesoporous magnetic adsorbent with strong acid resistance,high saturation magnetization（37.52emu/g）,moderate particle size（5.7μm）and core-shell structure.The effects of adsorption time,solution p H,initial gold concentration,thiosulfate concentration and temperature on the adsorption of gold by Fe₃O₄@SiO₂-SH were investigated.The results show that the recovery of gold from thiosulfate solution by Fe₃O₄@SiO₂-SH basically reaches the adsorption equilibrium state when the adsorption time is 48 h.In the range of p H（6-11）investigated,the adsorption rate of the adsorbent for gold in the solution is greater than 75%,and the adsorption rate increases gradually with the increase of p H.With the increase of initial gold concentration,the adsorption capacity of Fe₃O₄@SiO₂-SH increases gradually.Increasing the concentration and temperature of thiosulfate is not conducive to the recovery of gold,and increasing the temperature to inhibit the adsorption indicates that the adsorption process is an exothermic process.The adsorption kinetics and adsorption isothermal model were studied.It was found that the adsorption process could be well-explained by the Elovich kinetic model and Langmuir isothermal model,indicating that the process was a single layer adsorption process dominated by chemical adsorption,and the single saturated adsorption capacity was 15.11 kg/t.EDS and XPS were used to analyze the surface elements and chemical environment of the materials before and after adsorption.It was proved that Fe₃O₄@SiO₂-SH successfully adsorbed gold.The adsorption mechanism of gold may be ligand exchange,that is,the-SH on the adsorbent is deprotonated to form-S^-,and the Au（Ⅰ）in the Au（S₂O₃）₂^3-complex ion is detached and combined with-S^-to form Fe₃O₄@SiO₂-SAu.The effects of Cu²⁺,ammonia,ethylenediamine concentration and NH₃（en）/Cu molar ratio on gold adsorption by Fe₃O₄@SiO₂-SH in Cu-NH₃（en）-S₂O₃^2-system were investigated.The results show that copper ion can inhibit the recovery of gold,and the inhibition effect becomes more obvious with the increase of its concentration.The addition of ammonia and ethylenediamine can promote the recovery of gold.The adsorption effect of Fe₃O₄@SiO₂-SH on gold in simulated Cu-NH₃-S₂O₃^2-system is better than that in Cu-en-S₂O₃^2-system.Similarly,Fe₃O₄@SiO₂-SH has a better adsorption effect on gold in Cu-NH₃-S₂O₃^2-gold leaching system when recovering gold from ores.In this gold leaching system,regardless of the AIP or AIL process,the gold recovery rate of Fe₃O₄@SiO₂-SH is greater than 90%,and the adsorbent in the slurry can be simply separated by a magnet.Gold-loaded Fe₃O₄@SiO₂-SH desorption experiment found that Na OH,acid thiourea solution and Na₂S₂O₃ solution could effectively desorb gold,but Na OH and acid thiourea solution would destroy the structure of the adsorbent.Therefore,Na₂S₂O₃ solution with mild properties was used as the green eluent.After stirring in 3mol/L Na₂S₂O₃ solution（100 m L）for 12 h,95.53%gold on the adsorbent could be eluted.The eluted adsorbent can be reused for adsorption without regeneration,and Fe₃O₄@SiO₂-SH can still recover 55%of the gold in the thiosulfate solution after five adsorption-desorption cycles.