| Abstract
| - The sorption and desorption of Pb on RuO2·xH2O wereexamined kinetically and thermodynamically via spectroscopicand macroscopic investigations. X-ray absorptionspectroscopy (XAS) was employed to determine thesorption mechanism with regard to identity and interactionof nearest atomic neighbors, bond distances (R), andcoordination numbers (N). The kinetics of the Pb−Ru−oxide sorption reaction are rapid with the equilibrium loadingof Pb on the surface achieving approximately 1:1 wt/wt(129 μmol m-2). XAS data indicate that Pb adsorbed asbidentate innersphere complexes with first shell Pb−Oparameters of RPb-O = 2.27 Å and NPb-O = 2.1−2.5. Pb−Ru interatomic associations suggest two distinct bidentatesurface coordinations of Pb to edges (RPb-RuI ∼3.38 Å, NPb-RuI∼1.0) and shared corners (RPb-RuII ∼4.19 Å, NPb-RuII∼0.8) on RuO2 octahedra (cassiterite-like structure), andan additional second neighbor backscattering of Pb indicatesthe formation of Pb−Pb dimers (RPb-Pb ∼3.89 Å, NPb-Pb∼0.9). Desorption studies as a function of aging time (1 hto 1 year) using a continuous stirred-flow reactor witha background electrolyte (0.01 M NaNO3, pH 6) demonstratedthat Pb was tightly bound (99.7−99.9% retained). The Pbsorption capacity and retention on RuO2·xH2O is greater thanthat of other metal oxides examined in the literature.The results of this study imply that RuO2·xH2O may serveas a high capacity remediation treatment media.
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