Lead sorption on ruthenium oxide: a macroscopic and spectroscopic study

The sorption and desorption of Pb on RuO2.xH2O 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 micromol m(-2)). XAS data indicate that Pb adsorbed as bidentate innersphere complexes with first shell Pb-O parameters of RPb-O = 2.27 A and NPb-O = 2.1-2.5. Pb-Ru interatomic associations suggest two distinct bidentate surface coordinations of Pb to edges (RPb-RuI approximately 3.38 A, NPb-RuI approximately 1.0) and shared corners (RPb-RuII approximately 4.19 A, NPb-RuII approximately 0.8) on RuO2 octahedra (cassiterite-like structure), and an additional second neighbor backscattering of Pb indicates the formation of Pb-Pb dimers (RPb-Pb degrees 3.89 A, NPb-Pb approximately 0.9). 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 NaNO3, pH 6) demonstrated that Pb was tightly bound (99.7-99.9% retained). The Pb sorption capacity and retention on RuO2.xH2O is greater than that of other metal oxides examined in the literature. The results of this study imply that RuO2.xH2O may serve as a high capacity remediation treatment media.