title: In situ spectroscopic evidence for neptunium(V)-carbonate inner-sphere and outer-sphere ternary surface complexes on hematite surfaces.
abstract: Np(V) surface speciation on hematite surfaces at pH 7-9 under pC2 = 10(-3.45) atm was investigated using X-ray absorption spectroscopy (XAS). In situ XAS analyses suggest that bis-carbonato inner-sphere and tris-carbonato outer-sphere ternary surface species coexist at the hematite-water interface at pH 7-8.8, and the fraction of outer-sphere species gradually increases from 27 to 54% with increasing pH from 7 to 8.8. The results suggest that the heretofore unknown Np(V)-carbonato ternary surface species may be important in predicting the fate and transport of Np(V) in the subsurface environment down gradient of high-level nuclear waste respositories.
authors.affiliation: Department of Entomology, Soils and Plant Sciences, 270 Poole Agricultural Center, Clemson University, Clemson, South Carolina 29634-0315, USA. yarai@clemson.edu
authors.forename: Yuji
authors.initials: Y
authors.lastname: Arai
authors.forename: P B
authors.initials: PB
authors.lastname: Moran
authors.forename: B D
authors.initials: BD
authors.lastname: Honeyman
authors.forename: J A
authors.initials: JA
authors.lastname: Davis
mesh_terms: D002254:Carbonates / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D009405:Neptunium / Q000737:chemistry*; D013057:Spectrum Analysis; D013499:Surface Properties
chemical_list: D002254:Carbonates; D005290:Ferric Compounds; C000499:ferric oxide; D009405:Neptunium