Adsorption and Separation of Metal Ions by Using Acryloylacetone Polymer

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Polyacryloylacetone (PAA) was prepared by polymerizing acryloylacetone in a sealed tube, and examined as an adsorbent of metal ions. Its dissociation constant and overall binding constants for complexing with metal ions were determined from experimental data on pH titration.The order of stability of metal complexes was as follows :Cu(II) > Ni(II) > Co(II) > Cd(II)Sm(III) > Nd(III) > Pr(III) > Ce(III) > La(III)The adsorption behaviors of metal ions on PAA conformed to the Langmuir rather than the Freundlich isotherm. The maximum adsorptions of metal ions by PAA were very low, but Hg(II) and Cu(II) were adsorbed selectively. The maximum adsorptions of rare earth metal ions were about one order lower than those of divalent metal ions. The adsorption was strongly dependent on the pH of the solution, and metal ions adsorbed on PAA could be eluted with HCl solution in a concentration above 10 mM.The adsorption rate was analyzed using a two-resistance model which involves a mass transfer in liquid phase boundary layer, and two intraparticle solid diffusions with different diffusion coefficients ; De_0 in beta% PAA and De_1 in all others. The model equations were solved numerically, and De_0 and De_1 were determined by fitting the calculated uptake curves to the experimental ones. De_0=5 X 10^<-8>cm^2/s nad De_1=2 - 2.5 X 10^<-9>cm^2/s were independent of the initial concentrations and of the metal species employed. The separation and concentration of metal ions using a PAA column were examined. The separations of Cu(II) from Co(II), Cd(II) and Ni(II) were achieved successfully by stepwise decrease in pH of the eluent. Good resolutions for chromatographic separation of rare earth metal ions were also achieved by the same technique.