Adsorption And Separation Of Palladium By Three Novel Heterocyclic Polymers

In this dissertation,three novel heterocyclic polymer adsorbents,PS-MBO,PS-MBI and PS-MMBT were prepared through grafted 2-mercaptobenzoxazole,2-mercaptobenzimidazole,and 4-methyl-2-mercaptobenzothiazole on the matrix of chloropolymer,respectively.They were used for selective recovery of Pd(?)from mixed solutions containing Pd(?),Pt(IV),Rh(?I),Cu²⁺,Ni²⁺,Fe³⁺and Zn²⁺in chlorinated medium.Key adsorption and separation parameters such as the optimal adsorption pH value,maximal adsorption capacity,and mixed ion separation conditions of Pd(?)were studied.The adsorption separation mechanism was also discussed in detail.The result of research shows that PS-MBO?PS-MBI and PS-MMBT have excellent adsorption effects on Pd(?)in 0.1mol/L hydrochloric acid solution.The maximum adsorption capacities were 171.2mg/g,143 mg/g and 142 mg/g,respectively.The adsorption processes all conform to the"Langmuir"model and are spontaneous endothermic reactions.The kinetic study shows that the adsorption process conforms to the quasi-second-order kinetic model and the intra-particle diffusion model.Under the optimum conditions,all the three adsorbents can separate Pd(?)from the mixed solutions containing Pd(?),Pt(IV),Rh(?I),Cu²⁺,Ni²⁺,Fe³⁺and Zn²⁺.The separation coefficient of Pd/M(M:Pt,Rh,Cu,Ni,Fe,Zn)is higher than 1.0×10³.PS-MBO has good reuse performance.After three adsorption-elution cycles,the recovery rate of PS-MBO adsorption Pd(?)was higher than 93.0%.FT-IR,XPS characterization and density functional theory(DFT)calculation show that PS-MBO,PS-MBI and PS-MMBT adsorb Pd(?)as the coordination mechanism.Pd(?)was separated from the mixed solution of metal ions by forming coordination bonds with the S or N atoms on oxazole,imidazole or thiazole rings,respectively.In order to analyze and reveal the selective adsorption mechanism of anion metal chlorides adsorbed by PS-MBO resin,one structural unit of PS-MBO resin was chosen as model molecule(denoted as L).Chlorophilic property of metal ion,coordination strength of model molecule L with anion metal chloride and the average charge density of anion metal chlorides have been investigated by using density functional theory(DFT)in gas phase.The average coordination bonding energy(ACE)of[PdCl₄]^2-,[RhCl₄]^-,[RhCl₅]^2-,[RhCl₆]^3-and[PtCl₆]^2-has been calculated at B3LYP/6-311++G**/SDD//B3LYP/6-31G**/SDD level.The calculation results showed that ACE of[PdCl₄]^2-is the smallest,indicating that Pd(?)ion has the weakest chlorophilic property.Furthermore,due to that Pd(?)coordinate with both of the N and S atom of L.Meanwhile,Pt(?)and Rh(?I)coordinate with only the N atom of L,theoretically,the coordination interaction of Pd(?)with L should be stronger than Pt(?)and Rh(?I).Hence,[PdCl₄]^2-is adsorbed by PS-MBO through coordination mechanism.The average charge density of[PdCl₄]^2-,[RhCl₄]^-,[RhCl₅]^2-,[RhCl₆]^3-and[PtCl₆]^2-is calculated with the charge of anion divided by its volume.The order of average charge density of those metal chloride anions is[RhCl₄]^-<[PtCl₆]^2-<[RhCl₅]^2-<[PdCl₄]^2-.Based on“the experiential principle of the smallest charge density”,Rh(?I)and Pt(IV)are more easily adsorbed by anion-exchange mechanism than Pd(?).