Complexation of UO2(CO3)34- with Mg2+ at varying temperatures and its effect on U(VI) speciation in groundwater and seawater
- Authors
- Jo, Yongheum; Kim, Hee-Kyung; Yun, Jong-Il
- Issue Date
- Oct-2019
- Publisher
- ROYAL SOC CHEMISTRY
- Citation
- DALTON TRANSACTIONS, v.48, no.39, pp.14769 - 14776
- Indexed
- SCIE
SCOPUS
- Journal Title
- DALTON TRANSACTIONS
- Volume
- 48
- Number
- 39
- Start Page
- 14769
- End Page
- 14776
- URI
- https://scholarworks.bwise.kr/hanyang/handle/2021.sw.hanyang/189463
- DOI
- 10.1039/c9dt03313k
- ISSN
- 1477-9226
- Abstract
- The ternary alkaline earth metal uranyl tricarbonate complexes, MnUO2(CO3)(3)(2n-4) (M = Mg and Ca), have been considered to be the major U(vi) species contributing to uranium mobility in natural water. Although MgUO2(CO3)(3)(2-) can account for a substantial portion of U(vi) in a Mg2+-rich aqueous system and most processes regarding uranium are subjected to variable temperatures, chemical thermodynamic data for the prediction of the formation of MgUO2(CO3)(3)(2-) at variable temperatures are still unknown. To fill the knowledge gap in the current chemical thermodynamic database, ultraviolet/visible (UV/Vis) absorption spectroscopy was employed to determine the formation constants (log K ') of MgUO2(CO3)(3)(2-) at varying temperatures of 10-85 degrees C in 0.5 mol kg(-1) NaCl. The formation constants at infinite dilution, log K degrees, were obtained with specific ion interaction theory (SIT), and an increasing tendency of log K degrees with temperature was observed. Using calorimetric titration, the endothermic molar enthalpy of reaction (Delta H-r(m)) of Mg2+ complexation with UO2(CO3)(3)(4-) was determined at 25 degrees C. According to the chemical thermodynamic data obtained in this work, approximation models for the prediction of the temperature-dependent formation constant at a given temperature were examined and the constant enthalpy approximation with modification to the isoelectric reaction showed a satisfactory agreement with our experimental results. Finally, the effects of temperature on U(vi) speciation in Mg2+-rich groundwater and U(vi) extraction from seawater by amidoxime derivatives were examined. For the first time, this work provides important chemical thermodynamic data of MgUO2(CO3)(3)(2n-4) to assess the impact of temperature on U(vi) behaviour in groundwater and seawater.
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