An EXAFS study of uranium(VI) sorption onto silica gel and ferrihydrite

Structural parameters of the near-neighbor surrounding of uranium(VI) sorbed onto silica gel and ferrihydrite surfaces have been determined by U L-III-edge extended X-ray absorption fine structure (EXAFS) analysis. The sorption on silica gel was studied at pH 4 with uranium(VI) concentrations in the range of 5 x 10(-2)-2 x 10(-5) mol/l. Sorption experiments with ferrihydrite have been performed at pH 5.8 with uranium(VI) concentrations of 10(-4) and 10-5 mol/l and at pH 7.8 with 10(-5) mol/l uranium(VI). The structural parameters for the uranium coordination shells (U-O-ax, U-O-eq, and U-Si/Fe) indicate formation of inner-sphere, mononuclear uranyl complexes at the silica gel and ferrihydrite surfaces. (C) 1998 Elsevier Science B.V. All rights reserved.