Synthesis Of Chitosan Thiourea Imprinted Resin And Its Mechanism For Selective Adsorption Of Gold

Gold plays an extremely important role in the country's economic and social development and security strategy.However,the naturalally rich and easy-to-mine gold ore is declining.Improving the recovery efficiency of gold in low-grade gold and tailings is important for the efficient use of the importance of gold resources.After gold leaching,gold(Au)coexisted in the leaching solution in the form of complex AuCl4-and other associated elements.The most critical link in the gold production process is the efficient extraction and recovery of gold from the leaching solution,which has a direct impact on improving the efficiency of the entire production process.The ion-imprinted polymer has excellent binding performance with the target ion,and has strong memory recognition ability,it can selectively adsorb the target ion,which is a good potential solid collector.In this paper,thiourea-imprinted resin was synthesized and its mechanism for selective adsorption of gold was studied.The main conclusions are as follows:(1)The effects of the volume of glutaraldehyde,the concentration of Au(?),the amount of thiourea and the crosslinking time on the adsorption capacity of synthetic resin were investigated through single-factor experiments.The optimal conditions for the synthesis of imprinted resin were determined:the amount of chitosan was 1 g,the concentration of acetic acid was 2%,the volume of glutaraldehyde was 12 mL,the concentration of Au(?)was 3.5 mmol·L-1 and the amount of thiourea was 2 g,the crosslinking time was 5 h.Scanning electron microscopy(SEM)results showed that the imprinted resin had a network-like porous structure and formed a hole structure that could specifically recognize the target ion.Infrared analysis(FTIR)shows that both imprinted and non-imprinted resins contain thiourea characteristic groups.X-ray diffractometer(XRD)results show that during the resin synthesis process,the characteristic peaks of thiourea are connected to the resin,so it shows a good adsorption effect.(2)pH is an important factor affecting adsorption performance.The results of resin adsorption Au(?)show that the adsorption capacity reaches the highest value at pH=2.The study of adsorption kinetics shows that the time to reach equilibrium is 4 h,the adsorption conforms to the quasi-second-order kinetic equation and the adsorption kinetics is mainly chemical adsorption.The maximum adsorption capacity of the imprinted resin for Au(?)was 4.737 mmol·g-1 and the maximum adsorption capacity of the non-imprinted resin was 1.897 mmol·g-1.The imprinted resin was about 2.5 times that of the non-imprinted resin.The adsorption thermodynamics research shows that ?H°is a positive value of 167.5 KJ·mol-1,?G° is a negative value at 20-60?,and the change of the adsorption entropy ?S° is a positive value of 0.704 KJ·K-1·mol-1.The adsorption of Au(?)by imprinted resin is an endothermic reaction,the adsorption process is an irreversible spontaneous reaction,and the adsorption is an entropy increasing process.(3)Adsorption regeneration is beneficial to reduce production costs.The 4%thiourea and 0.5 mol·L-1 sulfuric acid were used as eluents.The resin loaded with Au(?)was shaken for 2 h,and the elution rate reached 99%.After elution with the eluent,the chitosan thiourea-imprinted resin(IM-TUCS)can bereused for 4 cycles,and the gold recovery rate is about 92%,which shows that the resin has a good reuse effect and high economic value.(4)The selectivity of the imprinted resin for Au(?)ions is much greater than that of the non-imprinted resin.The selective adsorption capacity of the imprinted resin for five metals in the mixed metal ion system is:Au3+>Cu2+>Fe3+>Zn2+>Mn2+.It has a high selective recognition ability for Au3+.In situ adsorption studies on tailing liquid imprinted resins after extraction showed that imprinted resins have good selectivity for gold ions and the selective adsorption rate of Au(?)reached 85%.(5)The possible adsorption mechanism between Au(?)and IM-TUCS was further discussed by XPS spectrum,infrared and X-ray diffraction analysis.The protonation of the amino group on the resin under low pH conditions promotes the adsorption of Au(?),making the resin better adsorption performance of Au(?);The N,S,and O elements in the C=N,C=S,-OH,and C-O-C groups contained in IM-TUCS coordinate with the Au(?)ion;the cross-linked formation of the imprinted resin provides a hole that can hold Au(?),and the imprinted resin supports Au(?).Adsorption has specific recognition capabilities.FTIR and XPS analysis further confirmed that Au(?)may be chemically adsorbed on the surface of IM-TUCS.