Complexation of trivalent lanthanides (Eu) and actinides (Cm) with aqueous phosphates at elevated temperatures


Complexation of trivalent lanthanides (Eu) and actinides (Cm) with aqueous phosphates at elevated temperatures

Jordan, N.; Demnitz, M.; Lösch, H.; Starke, S.; Brendler, V.; Huittinen, N.

In this study, the complexation of Eu(III) and Cm(III) with aqueous phosphates was investigated using laser-induced luminescence spectroscopy. Experiments at 25 °C and different ionic strengths (0.6 to 3.1 mol∙L−1 NaClO4) established the formation of EuH2PO42+ and CmH2PO42+. From the conditional stability constants, the respective values at infinite dilution as well as the ε(Me(H2PO4)2+;ClO4−) (Me = Eu or Cm) ion interaction coefficients (using the specific ion interaction theory - SIT) were derived. Further experiments (at constant ionic strength of 1.1 mol∙L−1) showed, that upon increasing the temperature (25-80 °C), the formation of both EuH2PO42+ and CmH2PO42+ was favored. Using the van’t Hoff equation, the enthalpy ∆_R H_m^0 and entropy ∆_R S_m^0 of these reactions were derived, corroborating an endothermic and entropy driven complexation process. This work contributes to a better understanding of the coordination chemistry of both trivalent actinides and lanthanides with phosphate ions.

Keywords: complexation; europium; curium; aqueous phosphate; temperature; luminescence spectroscopy

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Publ.-Id: 27200