The sorption and desorption of Pb on Ru0_2(centre dot)xH_20 were examined kinetically and thermodynamically via spectroscopic and macroscopic investigations.X-ray absorption spectroscopy (XAS)was employed to determine the sorption mechanism with regard to identity and interaction of nearest atomic neighbors,bond distances (R),and coordination numbers (N).The kinetics of the Pb-Ru-oxide sorption reaction are rapid with the equilibrium loading of Pb on the surface achieving approximately 1:1 wt/wt (129 mumol m~(-2)).XAS data indicate that Pb adsorbed as bidentate innersphere complexes with first shell Pb-0 parameters of R_(Pb-O)=2.27 A and N_(Pb-O)=2.1-2.5.Pb-Ru interatomic associations suggest two distinct bidentate surface coordinations of Pb to edges (R_(Pb-Rul)approx3.38 A,N_(Pb-Rul)-1.0)and shared corners (R_(Pb-Rull)approx4.19 A,N_(Pb-Rull)approx0.8)on Ru02 octahedra (cassiterite-like structure),and an additional second neighbor backscattering of Pb indicates the formation of Pb-Pb dimers R _(Pb-Rull)approx3.89 A,N_(Pb-Pb)approx0.9).Desorption studies as a function of aging time (1 h to 1 year)using a continuous stirred-flow reactor with a background electrolyte (0.01 M NaN0_3,pH 6)demonstrated that Pb was tightly bound (99.7-99.9 retained).The Pb sorption capacity and retention on Ru0_2(centre dot)xH_20 is greater than that of other metal oxides examined in the literature.The results of this study imply that Ru0_2(centre dot)xH_20 may serve as a high capacity remediation treatment media.
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