Preparation And Adsorptive Characteristics Of Persimmon Tannin-based Adsorbent For Recovery Of Au(Ⅲ)and Pd(Ⅱ)

To improve the adsorption efficiency of persimmon tannin adsorbent,Pentaethylenehexamine（PEHA）was grafted on the surface of persimmon powder formaldehyde resin（PPFR）to synthesize new biosorbent named PH-PPFR.PH-PPFR were characterized by FTIR,SEM,EDS,XRD and XPS,the adsorption performance of PH-PPFR were evaluated through batch and dynamic adsorption test.The main results are as following.1.The protocal of PEHA modification on PPFR were optimized,which composed of1 g PPFR,0.5%glutaraldehyde,2%PEHA and 0.03%acetic acid in 100 mL water,stired for 24 h on 298 K.2.According to the experimental data,PH-PPFR shows higher adsorption capacity to Au（Ⅲ）and Pd（Ⅱ）than PPFR,with a tolerance of strong acid condition as high as 3.0mol·L^-1HCl solution.The pseudo-second-order model was appropriate for fitting the kinetic experimental data of PH-PPFR,which indicated that chemisorption is the main rate-limiting step for the adsorption process.The adsorption isotherms followed the Langmuir model,the maximum adsorption capacity of Au（Ⅲ）and Pd（Ⅱ）accounted for2893.1 mg g^-11 and 263.1 mg g^-11 at 318 K respectively.There are high adsorption selectivity based on column adsorption-desorption test with little or even no adsorption of coexisting metal ions including Pb（Ⅱ）,Cu（Ⅱ）,Fe（Ⅱ）,Ni（Ⅱ）and Zn（Ⅱ）.About 97%adsorbed Au（Ⅲ）on PH-PPFR could be desorbed by 1 mol L^-11 thiourea in 0.5 mol L^-1HCl and 94.3%adsorbed Pd（Ⅱ）by 0.5 mol L^-11 thiourea in 0.5 mol L^-11 HCl.3.A large number of amine groups showed in FTIR spectra and N elements showed in EDS on PH-PPFR revealed that PPFR was successfully modified with PEHA.Appearence of Cl^-on surface of PH-PPFR was relevant to ion exchange reaction between metal ions and amino groups.The XRD pattern presented that Au（Ⅲ）was reduced to Au（0）,suggesting that there was an oxidation-reduction reaction between phenolic hydroxyl groups and Au（Ⅲ）.XPS analysis revealed the chelation reaction occurrence.Considering the characterization and batch adsorption experimental data,the adsorption process was initially affected by ion exchange reaction and electrostatic effect,then followed by chelation reaction and redox reaction,which explained the main mechanism of Au（Ⅲ）and Pd（Ⅱ）adsorption on PH-PPFR.In conclusion,PH-PPFR shows high adsorption capacity and selectivity to Au（Ⅲ）and Pd（Ⅱ）,which is a promise way in efficient enrichment and separation of precious metals in waste printed circuit board lixivium.