Title: Adsorption of metal ions at kaolinite surfaces: Ion-specific effects, and impacts of charge source and hydroxide formation
Abstract: Adsorption of metal ions at clay surfaces plays a critical role in a variety of geochemical, environmental and engineered processes, and p-DFT calculations with dispersion corrections were employed with aim to comprehensively understand the adsorption of metal ions at hydrated kaolinite surfaces, considering both (001¯) and (001) surfaces and different metal ions (Mn+ = Li+, Na+, K+, Mg2+, Ca2+, Al3+, Fe3+). Ion-specific effects resulting from adsorption also became the focus of this study. For adsorption of alkali ions, inner-sphere complexes dominated for (001¯) surface while owing to hydroxide formation, outer-sphere complexes dominated for (001) surface. Both charge sources and surface structures can significantly alter adsorption structures and their relative stabilities, and surface structures can further perturb ion-specific sequences. Hydroxide formation at (001¯) surface was favored for metal ions (Mn+) of higher oxidation states: Non-existent for M+, geometrically stable but disfavored for M2+ while dominant for M3+. Al3+ adsorption was likely to form AlOH2+, Al(OH)2+ and Al(OH)3 and released more H+ than base cations, which further caused soil acidification. Hydroxide formation affected significantly the extents of ion-specific effects and may further alter their sequences. Results were also helpful to rationalize and guide experimental studies.
Publication Year: 2020
Publication Date: 2020-06-04
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 18
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