Web Release Date: May 4,
In Situ Spectroscopic Evidence for Neptunium(V)-Carbonate Inner-Sphere and Outer-Sphere Ternary Surface Complexes on Hematite Surfaces
and
Department of Entomology, Soils and Plant Sciences, 270 Poole Agricultural Center, Clemson University, Clemson, South Carolina 29634-0315, Department of Environmental Science & Engineering, Colorado School of Mines, Coolbaugh Hall, Golden, Colorado 80401-1887, and Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, 1500 Illinois Street, Golden, Colorado 80401
Received for review October 14, 2006
Revised manuscript received March 7, 2007
Accepted March 28, 2007
Abstract:
Np(V) surface speciation on hematite surfaces at pH 7-9 under pCO2 = 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.
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