Enthalpy of Uranium Adsorption onto Hematite

The influence of temperature on the adsorption of metal ions at the solid–water interface is often overlooked, despite the important role that adsorption plays in metal-ion fate and transport in the natural environment where temperatures vary widely. Herein, we examine the temperature-dependent adso...

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Bibliographic Details
Published in:Environmental science & technology 2020-12, Vol.54 (23), p.15004-15012
Main Authors: Estes, Shanna L, Powell, Brian A
Format: Article
Language:English
Subjects:
Adsorption
Contaminants
Contaminants in Aquatic and Terrestrial Environments
Engineering
Enthalpy
Environmental Sciences & Ecology
Ferric Compounds
Hematite
Hydrogen-Ion Concentration
Ion adsorption
Iron oxides
Metal ions
Radioactive contaminants
Radioactive contamination
Radioactive pollution
Surface chemistry
Temperature
Temperature dependence
Thermodynamics
Uranium
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Summary:The influence of temperature on the adsorption of metal ions at the solid–water interface is often overlooked, despite the important role that adsorption plays in metal-ion fate and transport in the natural environment where temperatures vary widely. Herein, we examine the temperature-dependent adsorption of uranium, a widespread radioactive contaminant, onto the ubiquitous iron oxide, hematite. The multitemperature batch adsorption data and surface complexation models indicate that the adsorption of uranium, as the hexavalent uranyl (UO2 2+) ion, increases significantly with increasing temperature, with an adsorption enthalpy (ΔH ads) of +71 kJ mol–1. We suggest that this endothermic, entropically driven adsorption behavior is linked to reorganization of the uranyl-ion hydration and interfacial water structures upon UVI adsorption at the hematite surface. Overall, this work provides fundamental insight into the thermodynamics driving metal-ion adsorption reactions and provides the specific enthalpy value necessary for improved predictive geochemical modeling of UVI adsorption in the environment.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.0c04429