Ion Adsorption at Clay-mineral Surfaces: the Hofmeister Series For Hydrated Smectite Minerals
K+ > Na+ > Ca2+ > Cs+ > Ba2+
The results also revealed the energetically favorable position of the ions above the clay basal surfaces. Key features of the free-energy profiles are illustrated by Boltzmann population inversions and analyses of the water structures surrounding the ion and clay surface. The results show that weakly hydrated cations (K+ and Cs+) preferentially form inner-sphere surface complexes (ISSC) above the ditrigonal siloxane cavities of the clay, while the more strongly hydrated cations (Na+) are able to form ISSCs above the basal O atoms of the clay surface. The strongly hydrated cations (Na+, Ca2+, and Ba2+), however, preferentially form outer-sphere surface complexes. The results provide insight into the adsorption mechanisms of several ionic species on montmorillonite and are relevant to many phenomena thought to be affected by cation exchange, such as nuclear waste disposal, herbicide/pesticide–soil interactions, and enhanced oil recovery.
Document Type: Research Article
Publication date: August 1, 2016
This article was made available online on December 10, 2016 as a Fast Track article with title: "Ion adsorption at clay-mineral surfaces: The Hofmeister series for hydrated smectite minerals".
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