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

作者：Zhang PC^*; Brady PV; Arthur SE; Zhou WQ; Sawyer D; Hesterberg DA

来源：Colloids and Surfaces A: Physicochemical and Engineering Aspects , 2001, 190(3): 239-249.

DOI：10.1016/S0927-7757(01)00592-1

• barium
• sorption
• EXAFS
• montmorillonite
• radium

Migration of radioactive radium, (226)Ra, in soil is an environmental concern, especially in areas adjacent to uranium processing facilities. Barium(II), as Ba(2+), 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 NaNO(3) concentration. As demonstrated by EXAFS, a small fraction of Ba also adsorbed on the montmorillonite edge, forming an in,ner-sphere surface complex through sharing of oxygen atom(s) from deprotonated -OH group of the Al octahedral layer. The EXAFS measured distances between Ba and O at the first shell, and Ba and Al 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.

• 出版日期2001-10-15