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Issue 33, 2020

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

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Abstract

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)22− and PuO2(CO3)34− was successfully obtained. PuO2(CO3)22− has a prominent peak at 853 nm and its molar absorptivity was determined to be ε853, PuO2(CO3)22− = 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)22− and PuO2(CO3)34− indicate the formation of CaPuO2(CO3)32− and MgPuO2(CO3)32− complexes and provide the formation constants at 0.1 M H/NaClO4 for MPuO2(CO3)32− from PuO2(CO3)34−, 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)32− and MgPuO2(CO3)32− from PuO2(CO3)34− at infinite dilution (log K°) 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)32− is similar to that of PuO2(CO3)34− with the exception of a characteristic absorption peak at 808 nm (ε808, 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)32− is considered the dominant Pu(VI) species under environmental conditions, and plutonyl(VI) may be more mobile than expected in previous assessments.

Graphical abstract: Visible-NIR absorption spectroscopy study of the formation of ternary plutonyl(vi) carbonate complexes

Supplementary files

Article information


Submitted
03 Jun 2020
Accepted
23 Jul 2020
First published
27 Jul 2020

This article is Open Access

Dalton Trans., 2020,49, 11605-11612
Article type
Paper

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

Y. Jo, H. Cho and J. Yun, Dalton Trans., 2020, 49, 11605 DOI: 10.1039/D0DT01982H

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