title: Incorporation of Pb at the calcite (104)-water interface.
abstract: Lead (Pb) is a common environmental pollutant, and its transport in surface waters and groundwater is controlled in part by sorption and precipitation reactions at mineral surfaces. Using in situ specular and resonant anomalous X-ray reflectivity measurements, we investigated the interaction of the calcite (104) surface with a dilute Pb- and EDTA-bearing solution that is slightly undersaturated with respect to calcite. The X-ray results reveal Pb coherently substituting for Ca in the near-surface layers of strained calcite with Pb/(Pb + Ca) atom fractions as high as 0.28 in the outermost layer. The larger ionic radius of Pb(2+) relative to Ca(2+) is accommodated in calcite by vertical displacements of Pb relative to the Ca site. In situ atomic force microscopy images obtained during the reaction suggest that Pb incorporation below the surface occurs after initial dissolution followed by regrowth of a strained epitaxial Pb-rich calcite solid-solution at the calcite (104)-water interface. This process could produce a widespread host phase for Pb in groundwater aquifers and soil pore fluids.
authors.affiliation: Department of Earth and Environmental Sciences, University of Illinois at Chicago , Chicago, Illinois 60607, United States.
authors.forename: Erika
authors.initials: E
authors.lastname: Callagon
authors.forename: Paul
authors.initials: P
authors.lastname: Fenter
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Nagy
authors.forename: Neil C
authors.initials: NC
authors.lastname: Sturchio
mesh_terms: D002119:Calcium Carbonate / Q000737:chemistry*; D004492:Edetic Acid / Q000737:chemistry; D007854:Lead / Q000737:chemistry*; D012996:Solutions; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D012996:Solutions; D014874:Water Pollutants, Chemical; D014867:Water; D007854:Lead; D004492:Edetic Acid; D002119:Calcium Carbonate