Construction Of Humic Acid Functionalized Resin And Study Of Its Adsorption Behavior And Mechanism For Au(Ⅲ)

As an important strategic reserve resource,gold is used in many scientific fields.Recovering gold from secondary resources has gradually become the focus of research.In this paper,a series of humic acid functionalized resins have been designed and synthesized based on the unique structure,adsorption and redox characteristics of humic acid.The adsorption behavior and mechanism of these resins to gold ions were studied.In addition,some process routes for recovering gold from gold-containing leaching solution were proposed.In order to solve the problem of partial dissolution and high swelling degree of humic acid(HA)in acidic gold ion solution,phenolic resin(RF)was used as the matrix.Humic acid functionalized resins HAR,HA/RF and HA-RF were designed and synthesized by introducing HA into the inner,outer surface and side chain of RF molecular framework by modified stober method,cross-linking method and grafting method,respectively.Analyzing and screening the performance of these resins,the results showed that HA and RF respectively provide abundant active functional groups and three-dimensional network skeleton matrix for these resins,which solves the problem that humic acid is easy to dissolve and has a high degree of swelling as an adsorbent.Among them,the HAR prepared by the improved stober method has more excellent comprehensive performance as the adsorbent for gold ion.The process conditions of HAR were optimized,and the adsorption behavior and mechanism of Au(Ⅲ)on HAR were investigated.The results showed that when the molar ratio of resorcinol to formaldehyde was 1:2,the mass ratio of humic acid to formaldehyde was 1:3,the concentration of ammonia was 0.050 mol·L-1,the reaction solvent was water,the hydrothermal time was 12 h,and the hydrothermal temperature was 80℃,HAR had the largest adsorption capacity for gold ions,up to 920 mg·g-1(removal rate 92%).On this basis,the adsorption behavior and mechanism of gold ions on HAR were studied systematically.When the pH value of the solution was 3,it was favorable for Au(Ⅲ)adsorption.When the initial concentration of gold ions was 100 mg·L-1,it took 250 min to reach adsorption equilibrium.The adsorption of gold ions on HAR belonged to multi-molecular-layer chemical adsorption,and the adsorption was a spontaneous endothermic process.Combining the fluorescence micrographs,FTER,XRD,XPS characterization of HAR before and after adsorption and the density functional theory calculations,the adsorption-reduction-deposition mechanism was proposed.Firstly,Au(Ⅲ)is adsorbed on HAR through electrostatic interaction and coordination effects,then reduced to elemental gold by orthophenolic hydroxyl group in humic acid,and finally deposited on the adsorbent mainly in the form of gold particles.In order to investigate the influence of different kinds of humic acid on the adsorption performance of humic acid functional resin,FAR and BAR were prepared by using fulvic acid(FA)and brown humic acid(BA)as raw materials,respectively.FA and BA have different molecular weights and functional groups.The influences of humic acid type,acid group content and acid group type on the adsorption capacity of the resin were investigated.The findings showed that the structure of FAR was microsphere with a particle size about 526 nm,and more regular than that of BAR and HAR.The adsorption capacity of FAR for gold ions can reach 1520 mg·g-1,which is higher than the value of BAR and HAR.When the initial Au(Ⅲ)concentration was 100 mg·L-1,it took 150 minutes to reach adsorption equilibrium.Fulvic acid contains more phenolic hydroxyl and carboxyl groups,which leads to the excellent adsorption performance of FAR for gold ions.Therefore,more Au(Ⅲ)could be adsorbed and reduced to gold element and gold chloride,which was in line with the adsorptionreduction-deposition mechanism proposed above.The adsorption process was a spontaneous endothermic process and belonged to monolayer chemical adsorption.The results of the regeneration experiment showed that the removal rate was still as high as 91%after 5 absorption-desorption experiments by using a mixture of hydrochloric acid,thiourea and hydrogen peroxide as the eluent.After adsorption,gold can be directly recovered from FAR by incineration at 600℃.In order to solve the problem that HAR has a slow adsorption rate for gold ions,sulfonic acid groups were introduced to accelerate the adsorption efficiency.Using sulfuric acid and sodium sulfite as sulfonating agents,two kinds of sulfonic acid modified humic acid functional resins SHAR and NSHAR were obtained.After sulfonic acid group modification,SHAR and NSHAR not only maintained high adsorption capacity for gold ions,but also improved the adsorption efficiency.Further,comparing SHAR(1440 mg·g-1,50 min)and NSHAR(1048 mg·g-1,10 min),the adsorption capacity of SHAR was higher,but the adsorption rate was slightly slower.This is because SHAR has a higher degree of sulfonation than NSHAR,which can form strong covalent bonds with gold species.NSHAR has a smaller particle size and larger specific surface area than SHAR,which can provide more adsorption sites for gold ions in the outer surface.The removal rates of gold ions by SHAR and NSHAR are 98%and 97%after 5 absorption-desorption experiments,which indicated they had good reuse performance.After comprehensive analysis,it is found that the adsorption performance of SHAR is better than that of HAR,FAR and NSHAR.XRD,XPS,TEM,SEM and SEM-EDS analysis results showed that the Au-S covalent bond with strong affinity was formed between gold ions and sulfonic groups in the modified resins.The gold ions can be quickly uptaked by the interaction force and reduced by phenolic hydroxyl groups,thereby improving the adsorption efficiency.The humic acid functional resin SHAR with better adsorption performance was prepared in high volume for selectively uptaking gold ions from actual leachate.The results of high-volume preparation experiments showed that the yield and adsorption properties of the resin were consistent with the above,implied that SHAR had the potential as a commercial adsorbent.The results of selective adsorption experiments showed that SHAR had excellent selectivity for gold ions in the leaching solution of circuit board and ore,and could reduce it’s concentration to about 0.001 mg·L-1.By appropriately increasing the adsorption temperature,adjusting the pH or pre-eluting the used resin with dilute nitric acid,the enrichment purity of gold on the SHAR can be improved.