Study On Preparation Of Modified Phenolic Resin And Its Selective Adsorption To Au(?)

Gold has attracted much attention because of its extremely high economic value and wide application in high technology.With the gradual consumption of gold resources,the recovery of gold resources has become a research focus at home and abroad.A variety of methods for recovering gold have been developed.Among these methods,the chelating resin adsorption and separation method has become a more popular precious metal recovery method due to its simple operation,low equipment requirements and environmental friendliness.This paper designs and synthesizes a new modified adsorption material based on phenolic resin,then it was used to recover Au(?).Its optimal synthesis process and adsorption mechanism was discussed,and a new method recovering gold from waste liquid was proposed.Using resorcinol and formaldehyde as raw materials and urea as modifier,modified phenolic resin RFU was prepared by St(?)ber method,and its preparation process was optimized.The RFU synthesized under the optimized conditions was used to adsorb Au(?).The experiment showed that the adsorption capacity of Au(?)on the resin was increased from 700 mg/g to 1400 mg/g under the same conditions after the resin was modified,and RFU has a higher adsorption rate for Au(?)in the range of 2-6.The adsorption kinetics conforms to the pseudo-second-order kinetic model,the isothermal adsorption process conforms to the Langmuir adsorption model,and the adsorption process is a spontaneous endothermic process.The adsorption regeneration experiment of RFU shows that the adsorbed Au(?)can be eluted by the eluent prepared by hydrochloric acid and thiourea,the elution rate is more than 90%,and the eluted RFU can be used to adsorb Au(?)again.After four times of repeated use,its adsorption capacity decreases.Combining the fluorescence micrographs,FT-IR,XRD and XPS characterization analysis of RFU before and after adsorption,it is concluded that the adsorption of Au(?)by RFU is mainly achieved by the strong relationship between the N and O atoms in the urea molecule and Au(?).Au(?)is adsorbed on RFU by electrostatic and coordination effect,and part of Au(?)is reduced by carbonyl and phenolic hydroxyl to Au(I)and Au(0)and exists inside RFU resin.The structure of thiourea is similar to that of urea,but the difference between the two is that the S atom in the thiourea molecule occupies the position of the O atom in the urea molecule.From this,the difference in affinity between S and O atoms for Au(?)can be studied.The phenolic resin-based adsorbent prepared with thiourea as the modifier was named RFT,and its preparation process was optimized.The research results show that,due to the high similarity of the structure of RFT and RFU,the adsorption conditions,adsorption behavior and characterization results are similar to the research results of RFU.The difference is that the adsorption performance of RFT resin for Au(?)is slightly better than that of RFU resin.Characterization shows that the affinity of S atoms to Au(?)is stronger than that of O atoms.In view of the better adsorption performance of Au(?)by RFT resin,the paper uses the periodic structure of RFT as a model to study the effect of S and O atoms on Au(?)by using density functional theory.Calculations show that when O atoms and S atoms are present at the same time,Au(?)is more inclined to bond with S atoms;in the unmodified resin,the binding energy of Au(?)to the phenolic hydroxyl group on the matrix is-726.66 kcal/mol,and the binding energy between Au(?)and C=S in RFT resin is-889.18 kcal/mol,comparing the binding energy shows that the interaction between C=S and Au(?)is higher than that of phenolic hydroxyl;its HOMO and LUMO orbitals are mainly distributed around S atoms,which are consistent with their theoretical active sites;the changes in the orbital layout of the RFT resin before and after Au(?)adsorption show that when adsorption occurs,the S atoms at the adsorption site are 3p The charge on the orbital transfers to Au(?).Since the valence orbitals of the RFT molecules are connected to each other,the valence electrons of the remaining atoms move to the S atom at the adsorption site through the valence orbital,and part of the Au(?)accepts the S atom The provided electrons are restored.The modified resin(RFT-Au)after adsorption of Au(?)was applied to the reduction of 4-nitrophenol.The gold loading was 7 mg/g.The results showed that with the participation of Na BH4 and RFT-Au,more than 90% of 4-nitrophenol is reduced to 4-aminophenol within 90 min;while at the absence of RFT-Au,4-nitrophenol hardly changes within 90 min.In addition,the effects of the gold loading in RFT-Au and the calcination temperature of RFT-Au on the reduction performance of 4-nitrophenol are studied.The results show that the increase in gold loading and the increase in calcination temperature will accelerate 4-nitrophenol.The reduction of phenol provides a new method for the treatment of waste liquid containing 4-nitrophenol.