The effect of calcium on aqueous uranium(VI) speciation and adsorption to ferrihydrite and quartz

Geochimica et Cosmochimica Acta
By: , and 



Recent studies of uranium(VI) geochemistry have focused on the potentially important role of the aqueous species, CaUO2(CO3)32− and Ca2UO2(CO3)30(aq), on inhibition of microbial reduction and uranium(VI) aqueous speciation in contaminated groundwater. However, to our knowledge, there have been no direct studies of the effects of these species on U(VI) adsorption by mineral phases. The sorption of U(VI) on quartz and ferrihydrite was investigated in NaNO3 solutions equilibrated with either ambient air (430 ppm CO2) or 2% CO2 in the presence of 0, 1.8, or 8.9 mM Ca2+. Under conditions where the Ca2UO2(CO3)30(aq) species predominates U(VI) aqueous speciation, the presence of Ca in solution lowered U(VI) adsorption on quartz from 77% in the absence of Ca to 42% and 10% at Ca concentrations of 1.8 and 8.9 mM, respectively. U(VI) adsorption to ferrihydrite decreased from 83% in the absence of Ca to 57% in the presence of 1.8 mM Ca. Surface complexation model predictions that included the formation constant for aqueous Ca2UO2(CO3)30(aq) accurately simulated the effect of Ca2+ on U(VI) sorption onto quartz and ferrihydrite within the thermodynamic uncertainty of the stability constant value. This study confirms that Ca2+ can have a significant impact on the aqueous speciation of U(VI), and consequently, on the sorption and mobility of U(VI) in aquifers.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title The effect of calcium on aqueous uranium(VI) speciation and adsorption to ferrihydrite and quartz
Series title Geochimica et Cosmochimica Acta
DOI 10.1016/j.gca.2005.11.027
Volume 70
Issue 6
Year Published 2006
Language English
Publisher Elsevier
Contributing office(s) Toxic Substances Hydrology Program
Description 9 p.
First page 1379
Last page 1387
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