Adsorption of barium(II) on montmorillonite: An EXAFS study

2019-06-28 05:44:17

II inner surface BA montmorillonite

责任者: Zhang, P.-C.;Brady, P.V.;Arthur, S.E.;Zhou, W.-Q.;Sawyer, D.;Hesterberg, D.A. 单位: Geochemistry Department, MS 0750, Sandia National Laboratories, Albuquerque, NM 87185, United States 来源出处: Colloids and Surfaces A: Physicochemical and Engineering Aspects,2001,190(3):239-249 摘要: Migration of radioactive radium, 226Ra, in soil is an environmental concern, especially in areas adjacent to uranium processing facilities. Barium(II), as Ba2+, was used as a Ra analog and reacted with a Na-montmorillonite to obtain mechanistic insights into the interaction of Ra with soil matrices. The majority of sorbed Ba is associated with the permanently charged surface sites on the montmorillonite basal surface. This is indicated by the facts that (1) sorption of Ba(II) on montmorillonite is not highly sensitive to solution pH, although an increase of sorption was observed at higher pH values; and (2) displacement of sorbed Ba increased with increased NaNO3 concentration. As demonstrated by EXAFS, a small fraction of Ba also adsorbed on the montmorillonite edge, forming an inner-sphere surface complex through sharing of oxygen atom(s) from deprotonated -OH group of the A1 octahedral layer. The EXAFS measured distances between Ba and O at the first shell, and Ba and A1 of the second shell are 2.7-2.8 and 3.7-3.9 A, respectively, consistent with the results from geometry of a inner-sphere complex at the edge site. Results from bulk experiments and spectroscopic analysis suggest a co-existence of outer- and inner-sphere surface complexes for Ba sorbed to the montmorillonite surface. © 2001 Elsevier Science B.V. All rights reserved. 关键词: Barium;Radium;Soils;Positive ions;Spectroscopic analysis;Adsorption;Basal surface