Influence of adipic acid on the speciation of Eu(III): review of thermodynamic data in NaCl and NaClO$_4$ media, and a new determination of Eu-adipate complexation constant in 0.5 mol.kg$_w$$^{-1}$ NaClO$_4$ medium by time-resolved luminescence spectroscopy

Elodie Fromentin (1, 2) , Pascal E. Reiller (3, 4)

1 SECR - Service d'Etudes du Comportement des Radionucléides
2 LRMO - Laboratoire de Radiolyse et de la Matière Organique
3 SEARS - Service d'études analytiques et de réactivité des surfaces
4 LANIE - Laboratoire de développement Analytique Nucléaire Isotopique et Elémentaire

The complexation of Eu(III) by adipic acid — AdipH$_2$, hexane-1,6-dioic acid —, one of the major hydro-soluble degradation products (HDPs) from radio-oxidized polyesterurethane, is investigated by time-resolved luminescence spectroscopy (TRLS) in NaClO$_4$ ionic medium (0.5 mol.kg$_w^{-1}$). The solubility and deprotonation constants of adipic acid, as well as specific interaction theory (SIT) coefficients of aqueous AdipH$_2$(aq) and adipate ions (AdipH$^–$ and Adip$^{2–}$) were estimated using available literature data in NaCl and NaClO$_4$ ionic media. A 1:1 (EuAdip$^+$) complex is evidenced in TRLS with log$_{10}$β(0.5 m) = 2.09 ± 0.16. Using reaction constant at another NaClO$_4$ ionic strength from literature, the logarithm of reaction constant log$_{10}$β° = 3.88 ± 0.40 at 0 ionic strength and specific ion parameter $\varepsilon$(EuAdip$^+$,ClO$_4^-$) = (0.10 ± 0.40) kg$_w$.mol$^{-1}$ is estimated. This implies that adipic acid can control the Eu(III) speciation from mildly acidic to mildly basic conditions, but not in highly basic solutions characteristic of cementitious interstitial waters.

Keywords: Europium; hydro-soluble degradation products; 6-dioic acid; hexane-1; adipic acid

Domains: Coordination chemistry; Analytical chemistry

Elodie Fromentin, Pascal E. Reiller. Influence of adipic acid on the speciation of Eu(III): review of thermodynamic data in NaCl and NaClO$_4$ media, and a new determination of Eu-adipate complexation constant in 0.5 mol.kg$_w$$^{-1}$ NaClO$_4$ medium by time-resolved luminescence spectroscopy. Inorganica Chimica Acta, 2018, 482, pp.588-596. ⟨10.1016/j.ica.2018.06.035⟩. ⟨cea-01845618v2⟩