AI Article Synopsis
- Different cations interact with clay minerals in contrasting ways, forming either outer-sphere or inner-sphere complexes, which significantly affects their environmental behaviors.
- This study is the first to investigate how radium (Ra) adsorbs onto clay minerals using EXAFS, revealing that Ra forms inner-sphere complexes on vermiculite despite its typical hydration preference.
- The research identified key factors influencing these complex formations, emphasizing the role of ionic radius and hydration enthalpy, and connected findings to environmental implications by analyzing core samples that show Ra's fixation by clay minerals.
Article Abstract
Adsorption reactions of various cations on clay minerals have different effects on their environmental behaviors depending on the molecular-scale adsorption structure. Some cations form outer-sphere complexes via hydration, while others create inner-sphere complexes through dehydration. This preference dictates their environmental impact. However, the factors controlling these complex formations remain unclear. Furthermore, research on the adsorption preferences of radium (Ra) is lacking. Thus, this study conducted the first EXAFS study of Ra adsorbed on clay minerals and showed that Ra forms inner-sphere complexes on vermiculite, which can be surprising because Ra is a divalent cation and prefers to be hydrated. In order to investigate the factors controlling the complex formations, this study conducted systematic EXAFS measurements and DFT calculations for alkali and alkaline earth metal cations. The results showed the importance of the size-matching effect between the adsorbed cation and the cavity of the tetrahedral sheets and that the complex formation can be estimated by the combination of the ionic radius and hydration enthalpy of the adsorbed cation. Furthermore, this study also analyzed environmental core samples. Their results showed the fixation of Ra by clay minerals and the controlling factors can effectively predict cation environmental behavior.
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| http://dx.doi.org/10.1016/j.jcis.2024.01.120 | DOI Listing |
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