%0 Journal Article %A Rouff, Ashaki A. %A Elzinga, Evert J. %A Reeder, Richard J. %A Fisher, Nicholas S. %D 2004 %T X-ray Absorption Spectroscopic Evidence for the Formation of Pb(II) Inner-Sphere Adsorption Complexes and Precipitates at the Calcite−Water Interface %U https://acs.figshare.com/articles/journal_contribution/X_ray_Absorption_Spectroscopic_Evidence_for_the_Formation_of_Pb_II_Inner_Sphere_Adsorption_Complexes_and_Precipitates_at_the_Calcite_Water_Interface/3346558 %R 10.1021/es0345625.s001 %2 https://acs.figshare.com/ndownloader/files/5185771 %K batch sorption %K oxygen neighbors %K 2.34 Å %K structure data %K 10 μ M %K 1 μ M %K 60 μ M Pb %K Pb coprecipitation %K sorption mechanism %K octahedral coordination %K metal interactions %K Pb concentrations %K Pb sequestration %K metal concentration %K Pb partitioning %K macroscopic studies %K surface sites %K cerussite phase %X Combined batch sorption and in situ X-ray absorption spectroscopy provide direct assessment of the mechanisms for Pb(II) sorption at the calcite−water interface under low-temperature conditions. At low metal concentration, 1 μM initial Pb, X-ray absorption fine structure data indicate the formation of Pb mononuclear inner-sphere complexes at the surface. A first-shell Pb−O bond length of 2.34 Å is consistent with nearest oxygen neighbors in 3- or 4-fold coordination with a distorted trigonal pyramidal or square pyramidal geometry with a stereochemically active electron lone pair. For high initial Pb concentrations, 20 and 60 μM Pb, precipitation of hydrocerussite and cerussite secondary phases dominates Pb partitioning. At 5 and 10 μM initial Pb, the sorption mechanism is dual in nature with persistence of the mononuclear adsorption complex combined with precipitation of a cerussite phase occurring prior to saturation of theoretically available surface sites. The formation of inner-sphere complexes implies strong metal interactions with the surfacethe mechanistic reason for the affinity of Pb for calcite as observed in macroscopic studies. The geometry of the adsorbed complex can influence Pb coprecipitation, as a change to octahedral coordination is required for incorporation into calcite. The results provide the basis for predictions of Pb sequestration by calcite in natural systems. %I ACS Publications