title: X-ray Analyses of Lead Adsorption on the (001), (110), and (012) Hematite Surfaces.
abstract: Predicting the environmental fate of lead relies on a detailed understanding of its coordination to mineral surfaces, which in turn reflects the innate reactivity of the mineral surface. In this research, we investigated fundamental dependencies in lead adsorption to hematite by coupling extended X-ray absorption fine structure (EXAFS) spectroscopy on hematite particles (10 and 50 nm) with resonant anomalous X-ray reflectivity (RAXR) to single crystals expressing the (001), (012), or (110) crystallographic face. The EXAFS showed that lead adsorbed in a bidentate inner-sphere manner in both edge and corner sharing arrangements on the FeO6octahedra for both particle sizes. The RAXR measurements confirmed these inner-sphere adsorption modes for all three hematite surfaces and additionally revealed outer-sphere adsorption modes not seen in the EXAFS. Lead uptake was larger and pH dependence was greater for the (012) and (110) surfaces, than the (001) surface, due to their expressing singly- and triply coordinated oxygen atoms the (001) surface lacks. In coupling these two techniques we provide a more detailed and nuanced picture of the coordination of lead to hematite while also providing fundamental insight into the reactivity of hematite.
authors: Department of Civil, Environmental and Geodetic Engineering, The Ohio State University , Columbus, Ohio 43210, United States.
authors: Matthew R
authors: MR
authors: Noerpel
authors: Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
authors: Sang Soo
authors: SS
authors: Lee
authors: Department of Civil, Environmental and Geodetic Engineering, The Ohio State University , Columbus, Ohio 43210, United States.
authors: John J
authors: JJ
authors: Lenhart
mesh_terms: D000327:Adsorption; D005290:Ferric Compounds / Q000737:chemistry*; D007854:Lead / Q000737:chemistry*; D008903:Minerals; D010316:Particle Size; D056928:X-Ray Absorption Spectroscopy; D014965:X-Rays
chemical_list: D005290:Ferric Compounds; D008903:Minerals; C000499:ferric oxide; D007854:Lead