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HERO ID
4178070
Reference Type
Journal Article
Title
Modeling uranium(VI) adsorption onto montmorillonite under varying carbonate concentrations: A surface complexation model accounting for the spillover effect on surface potential
Author(s)
Tournassat, C; Tinnacher, RM; Grangeon, S; Davis, JA
Year
2018
Is Peer Reviewed?
Yes
Journal
Geochimica et Cosmochimica Acta
ISSN:
0016-7037
Volume
220
Page Numbers
291-308
Language
English
DOI
10.1016/j.gca.2017.09.049
Web of Science Id
WOS:000416502300019
URL
http://WOS:000435539901595
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Abstract
The prediction of U(VI) adsorption onto montmorillonite clay is confounded by the complexities of: (1) the montmorillonite structure in terms of adsorption sites on basal and edge surfaces, and the complex interactions between the electrical double layers at these surfaces, and (2) U(VI) solution speciation, which can include cationic, anionic and neutral species. Previous U(VI)-montmorillonite adsorption and modeling studies have typically expanded classical surface complexation modeling approaches, initially developed for simple oxides, to include both cation exchange and surface complexation reactions. However, previous models have not taken into account the unique characteristics of electrostatic surface potentials that occur at montmorillonite edge sites, where the electrostatic surface potential of basal plane cation exchange sites influences the surface potential of neighboring edge sites ('spillover' effect).
A series of U(VI) -Na-montmorillonite batch adsorption experiments was conducted as a function of pH, with variable U(VI), Ca, and dissolved carbonate concentrations. Based on the experimental data, a new type of surface complexation model (SCM) was developed for montmorillonite, that specifically accounts for the spillover effect using the edge surface speciation model by Tournassat et al. (2016a). The SCM allows for a prediction of U(VI) adsorption under varying chemical conditions with a minimum number of fitting parameters, not only for our own experimental results, but also for a number of published data sets. The model agreed well with many of these datasets without introducing a second site type or including the formation of ternary U(VI)-carbonato surface complexes. The model predictions were greatly impacted by utilizing analytical measurements of dissolved inorganic carbon (DIC) concentrations in individual sample solutions rather than assuming solution equilibration with a specific partial pressure of CO2, even when the gas phase was laboratory air. Because of strong aqueous U(VI)-carbonate solution complexes, the measurement of DIC concentrations was even important for systems set up in the 'absence' of CO2, due to low levels of CO2 contamination during the experiment. Published by Elsevier Ltd. This is an open access article under the CC BY license.
Keywords
Uranium; Adsorption; Clay; Montmorilonite; Spillover; Surface complexation modeling
Tags
IRIS
•
Uranium
Uranium Literature Search Update 7/2018
WOS
Uranium Literature Search Update 4/2020
WOS
•
Uranium Toxicological Review
Date limited literature search 2011-2021
WOS
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