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Formation of CaUO2(CO3)32- and Ca2UO2(CO3)3(aq) Complexes at Variable Temperatures (10 – 70 °C)


The ternary complexation of calcium uranyl tricarbonate species, CaUO2(CO3)32- and Ca2UO2(CO3)3(aq), which are the predominant U(VI) complexes in groundwater and seawater conditions, was investigated at variable temperatures from 10 to 70 °C. Time-resolved laser fluorescence spectroscopy (TRLFS), calcium ion-selective electrode potentiometry, and ultraviolet/visible (UV/Vis) absorption spectroscopy were complementarily employed to determine the formation constants (log Kx13, x = 1 and 2 for mono- and dicalcium complexes, respectively). log K°x13 at infinite dilution (zero ionic strength) was determined by the correction using specific ion interaction theory (SIT), and the increasing tendency of log K°x13 with temperature was observed. In addition, the molar enthalpy of complexation (∆rHm) was measured by calorimetry at 25 °C. Based on thermodynamic data obtained in this work, the approximation models were examined for the prediction of the temperature effect on the complexation, and the constant enthalpy approximation with the chemical complexation reaction modified to an isoelectric reaction showed a satisfactory prediction of log K°x13 in the temperature range of 10 – 70 °C. Finally, the results of U(VI) speciation in groundwater indicated that the dominance of calcium uranyl tricarbonate complexes would be weakened at elevated temperatures by strongly enhanced hydrolysis of U(VI).

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The article was received on 19 Mar 2019, accepted on 12 Apr 2019 and first published on 13 Apr 2019

Article type: Paper
DOI: 10.1039/C9DT01174A
Citation: Dalton Trans., 2019, Accepted Manuscript

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    Formation of CaUO2(CO3)32- and Ca2UO2(CO3)3(aq) Complexes at Variable Temperatures (10 – 70 °C)

    Y. Jo, A. Kirishima, S. Kimuro, H. Kim and J. Yun, Dalton Trans., 2019, Accepted Manuscript , DOI: 10.1039/C9DT01174A

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