Separation And Determination Of Precious Metal In The Solution By2,2’-Diaminodiethylamine Modified Adsorbents

As we know that the d orbital of precious metal is not full, which makes it easyto chelate with the material containing lone pair electrons. Therefore, in this paper, wehave synthetized two adsorbents by chemical modification of multi walled carbonnanotubes (MWCNTs) and silicon gel (SG) with2,2’ Diaminodiethylamine(abbreviated as MWCNTs DETA and SG DETA). FT IR, XRD and elementalanalysis were used to characterize the productions. Flame atomic absorptionspectrometer as a means of detection equipment was employed to investigate the threemetal ions of gold, platinum and palladium in solution. The effect of solution pH,contact time, initial concentration of Au(III), Pt(IV) and Pd(II), desorption reagents,adsorption isotherms and kinetics were also discussed, respectively. The results are asfollows:(1) MWCNTs was firstly oxidized with mixed acid, and carboxyl functionalgroups emerged on the surface. Then MWCNTs DETA was obtained viacondensation of oxidized MWCNTs with DETA. N,N’ Dicyclohexylcarbodiimide(DCC) was used as a dehydration agent. We used MWCNTs DETA as an adsorbantto the sorption of Au(III) and Pd(II) in solution. The optimum adsorption pH of Au(III)and Pd(II) onto MWCNTs DETA were2.06.0and4.06.0, respectively. The highestelution ratios were determined as94.48%for Au(III) and89.06%for Pd(II) when1.0mol/L thiourea1.0mol/L hydrochloric acid solution was used as the eluent. Underthe optimum conditions, the adsorption capacities were about50.4541mg/g and25.6805mg/g for Au(III) and Pd(II). There were no influences on the determinationof Au(III) and Pd(II) when there were250,50,250,125,250,200,200,100times of Ca(II), Zn(II), Cu(II), Mg(II), KCl, NaCl, Al(III), Fe(III) in solution. In theinvestigation of adsorption isotherms, Langmuir isotherm model agreed well withthe equilibrium experimental data of Au(III) while Freundlich isotherm modelagreed with those of Pd(II). The adsorption dynamics of the two metal ions bothobeyed the pseudo second order model.(2) Chloropropyltrichlorosilane was used as a coupling reagent to alkylate thesurface of SG. Then DETA was bonded onto the alkylated SG. The production wasused to research on the sorption of Pt(IV) and Pd(II). The adsorption of Pt(IV) andPd(II) onto SG DETA was both best at pH2.0. The optimum desorption reagentswere2.0mol/L thiourea1.0mol/L hydrochloric acid solution for Pt(IV) and1.5mol/L thiourea1.0mol/L hydrochloric acid solution for Pd(II) with the bestdesorption ratios about98.15%and98.87%, respectively. The recoveries of Pt(IV)and Pd(II) were as high as265.2520mg/g and124.0695mg/g. The influences of K(I),Na(I), Ca(II), Mg(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Pb(II), Cd(II) were alsoinvestigated. The selective coefficients were all very large except a slight influence ofFe(III) and Cd(II). Regarding to the adsorption isotherms, both of the two metal ionsobeyed Langmuir model better. The adsorption kinetic data were fitted with thepseudo second order model and the intraparticle diffusion model.The results indicated that MWCNTs DETA and SG DETA which we havesynthesized both had a high affinity with the precious metal ions compared with theother metal ions. In addition, the maximum adsorptions of Pt(IV) and Pd(II) ontoSG DETA were large. So this experiment has a certain research significance for theseparation and determination of precious metal, and can be used to separation andenrichment of Au(III)、Pt(IV) and Pd(II) in solution.