Visible-NIR absorption spectroscopy study of the formation of ternary plutonyl(VI) carbonate complexes

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We present the first experimental evidence for the ternary complexation of calcium and magnesium ions with plutonyl(VI)tricarbonate species in carbonate-containing aqueous solutions using visible-NIR spectrophotometric titration. Prior to studying the ternary plutonyl(VI) carbonate complexation, visible-NIR absorption spectral information of PuO2(CO3)(2)(2-) and PuO2(CO3)(3)(4-) was successfully obtained. PuO2(CO3)(2)(2-) has a prominent peak at 853 nm and its molar absorptivity was determined to be epsilon(853, PuO2)(CO3)(2)(2-) = 49.0 +/- 4.2 M-1.cm(-1). The spectrophotometric titration results by adding calcium or magnesium to the plutonyl(VI) carbonate system consisting of PuO2(CO3)(2)(2-) and PuO2(CO3)(3)(4-) indicate the formation of CaPuO2(CO3)(3)(2-) and MgPuO2(CO3)(3)(2-) complexes and provide the formation constants at 0.1 M H/NaClO4 for MPuO2(CO3)(3)(2-) from PuO2(CO3)(3)(4-), log K = 4.33 +/- 0.50 and 2.58 +/- 0.18 for M = Ca2+ and Mg2+, respectively. In addition, the formation constants of CaPuO2(CO3)(3)(2-) and MgPuO2(CO3)(3)(2-) from PuO2(CO3)(3)(4-) at infinite dilution (log K degrees) were proposed to be 6.05 +/- 0.50 and 4.29 +/- 0.18, respectively, based on the correction of ionic strength using the Davies equation. The absorption spectrum of the ternary plutonyl(VI) complexes of CaPuO2(CO3)(3)(2-) is similar to that of PuO2(CO3)(3)(4-) with the exception of a characteristic absorption peak at 808 nm (epsilon(808, CaPuO2(CO3)32-) = 42.9 +/- 1.6 M-1.cm(-1)). According to the calculated aqueous plutonyl(VI) speciation including the ternary plutonyl(VI) complexes, CaPuO2(CO3)(3)(2-) is considered the dominant Pu(VI) species under environmental conditions, and plutonyl(VI) may be more mobile than expected in previous assessments.
Publisher
ROYAL SOC CHEMISTRY
Issue Date
2020-07
Language
English
Article Type
Article
Citation

DALTON TRANSACTIONS, v.49, no.33, pp.11605 - 11612

ISSN
1477-9226
DOI
10.1039/d0dt01982h
URI
http://hdl.handle.net/10203/276112
Appears in Collection
NE-Journal Papers(저널논문)
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