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Determination of complex formation constants of neptunium(V) with propionate and lactate in 0.5–2.6 m NaCl solutions at 22–60°C using a solvent extraction technique

Vasiliev, Aleksandr N.; Banik, Nidhu L.; Marsac, Rémi; Kalmykov, Stepan N.; Marquardt, Christian M.

Abstract (englisch):
Natural clay rocks like Opalinus (OPA) and Callovo-Oxfordian (COx) clay rock are considered as potential host rocks for deep geological disposal of nuclear waste. However, small organic molecules such as propionate and lactate exist in clay rock pore water and might enhance Np mobility through a complexation process. Therefore, reliable complex formation data are required in the frame of the Safety Case for a nuclear waste repository. A solvent extraction technique was applied for the determination of NpO+2 complexation with propionate and lactate. Extraction was conducted from isoamyl alcohol solution containing 10−3 M TTA and 5 · 10−4 M 1,10-phenanthroline. Experiments were performed in 0.5–2.6 m NaCl solutions at temperatures ranging from 22 to 60 °C. Formation of 1:1 Np(V) complexes for propionate and lactate was found under the studied conditions. The SIT approach was applied to calculate equilibrium constants β°(T) at zero ionic strength from the experimental data. Log β°(T) is found linearly correlated to 1/T for propionate and lactate, evidencing that heat capacity change is near 0. Molal reaction enthalpy and entropy (ΔrH∘m and ΔrS∘m) could therefore be derived from the integrated van’t Hoff equation. ... mehr



Zugehörige Institution(en) am KIT Institut für Nukleare Entsorgung (INE)
Publikationstyp Zeitschriftenaufsatz
Jahr 2019
Sprache Englisch
Identifikator ISSN: 2193-3405, 0033-8230
KITopen-ID: 1000096301
HGF-Programm 32.01.01 (POF III, LK 01)
Erschienen in Radiochimica acta
Band 107
Heft 7
Seiten 623–634
Vorab online veröffentlicht am 21.05.2019
Schlagworte Np(V); complexation; complex formation constant; lactate; propionate; solvent extraction
Nachgewiesen in Web of Science
Scopus
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