Preparation Of Modified Polyacrylonitrile Fiber And Its Adsorption Performance For Au (Ⅰ) In [Au(S₂O₃)₂^3-

The thiosulfate gold extraction technology has the advantages of fast gold extraction speed,non-toxic and high leaching efficiency,which make it become a green non-toxic and non-cyanide gold extraction technology that most likely to replace cyanide.However,the gold in thiosulfate leaching solution is difficult to be recovered effectively,which becomes the main bottleneck of industrialization of the technology.In this paper,the feasibility of modifying polyacrylonitrile fiber by chemical grafting and recovering Au（Ⅰ）from thiosulfate solution was investigated.The results showed that the Au（Ⅰ）in thiosulfate solution is adsorbed effectively by the amino phosphonic acid modified polyacrylonitrile fiber（PAN-NP）.The synthesis conditions of PAN-NP were optimized and the results showed that the PAN-NP fibers synthesized at 80℃,4 h,10 m L formaldehyde and 5 g phosphite had good adsorption properties for Au（Ⅰ）in thiosulfate solution.The effects of adsorption equilibrium time,the initial p H of adsorption solution,the thiosulfate concentration,the initial Au（Ⅰ）concentration and the adsorption temperature on the adsorption performance of Au（Ⅰ）were investigated,showing that the adsorption equilibrium of Au（Ⅰ）by PAN-NP in thiosulfate solution within 20 minutes,and the adsorption process of Au（Ⅰ）is affected by the initial p H of solution slightly.With the increase of the concentration of thiosulfate and the initial Au（Ⅰ）,the adsorption rate of Au（Ⅰ）by PAN-NP is decreased.The fifth-order adsorption capacity of Au（Ⅰ）by PAN-NP can reach 14.68 kg/t.The adsorption rate of Au（Ⅰ）decreased with the increase of adsorption temperature,showing that the adsorption is an exothermic reaction.The Langmuir isothermal adsorption model shows that the Au（Ⅰ）adsorbed by PAN-NP is a single molecular chemisorption.FT-IR,SEM-EDS,TGA and XPS were used to characterize the polyacrylonitrile fibers before and after synthesis and adsorption.The absorption peaks of-NH₂ and P=O were produced by the FT-IR characterization results,indicating that amino phosphonic acid was successfully grafted onto the surface of PAN fibers.The results of SEM-EDS showed that the surface structure of the fibers did not damaged by the graft process.There were peaks of Au and S elements appeared in PAN-NP-Au,indicating that PAN-NP was used for the adsorption of Au（Ⅰ）in thiosulfate solution successfully and the adsorption occurred between PAN-NP and Au（S₂O₃）₂^3-,XPS analysis showed that the valence state of Au（Ⅰ）did not change before and after adsorption.The adsorption mechanism of Au（Ⅰ）by PAN-NP are the interaction of anion exchange between H₂PO₃^-and Au（S₂O₃）₂^3-,the complexation between P=O and Au（Ⅰ）and the electrostatic attraction between RNH₃⁺and Au（S₂O₃）₂^3-.TGA shows that the material has good thermal stability in the temperature range of 30℃to 800℃.The effects of leaching components（Cu（Ⅱ）,NH₃,en）in Cu（Ⅱ）-NH₃-S₂O₃^2-and Cu（Ⅱ）-en-S₂O₃^2-systems on PAN-NP adsorption Au（Ⅰ）were investigated.The results showed that the adsorption of Au（Ⅰ）by PAN-NP can be inhibited by Cu（Ⅱ）.Due to there are complexation between NH₃ and Cu（Ⅱ）and between en and Cu（Ⅱ）.The competitive adsorption between Cu（Ⅱ）and Au（Ⅰ）can be reduced,so NH₃ and en can promote the adsorption performance of Au（Ⅰ）.The elution method of PAN-NP-Au is discussed and the results showed that the gold on the PAN-NP-Au is eluted effectively by the solution of sodium sulfite.The elution rate of gold by the sodium sulfite can reach 91.2%when the ratio of solid to liquid is 1:500（g:m L）,the concentration of sodium sulfite is 1 mol/L and the desorption time is 24 h.The eluted adsorbent still has good stability after five cycles,and the material has good repeatability.In a word,amino phosphonic acid modified polyacrylonitrile fiber has the advantages of good stability and easy separation from pulp,so it was good application potential in gold recovery stage of gold extraction process of thiosulfate.