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Radiochimica Acta

International Journal for chemical aspects of nuclear science and technology

Editor-in-Chief: Qaim, Syed M.

IMPACT FACTOR 2018: 1.339

CiteScore 2018: 1.20

SCImago Journal Rank (SJR) 2018: 0.333
Source Normalized Impact per Paper (SNIP) 2018: 0.720

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Volume 98, Issue 9-11


Solubility of tetravalent actinides in alkaline CaCl2 solutions and formation of Ca4[An(OH)8]4+ complexes: A study of Np(IV) and Pu(IV) under reducing conditions and the systematic trend in the An(IV) series

D. Fellhauer / Volker Neck / Marcus Altmaier / Johannes Lützenkirchen / Thomas Fanghänel
Published Online: 2010-11-23 | DOI: https://doi.org/10.1524/ract.2010.1751


The solubility of Np(IV) and Pu(IV) hydrous oxides was studied at 22±2 °C under reducing conditions in alkaline CaCl2 solutions. Redox conditions were adjusted either with 2 mM Na2S2O4 or additions of iron powder. In 2.0 and 4.5 M CaCl2 and pHc=11–12, the neptunium and plutonium concentrations increase with a slope of +4 (log[An] vs. pHc) as expected for the formation of the complex Ca4[An(OH)8]4+ recently identified for Th(IV). At CaCl2 concentrations ≤1.0 M this effect is negligible for both Np(IV) and Pu(IV). The conditional equilibrium constants log*Ks,(4,1,8) for the reaction

An(OH)4(am) + 4 H2O + 4 Ca2+ ⇔ Ca4[An(OH)8]4+ + 4 H+

are evaluated with the SIT and Pitzer model using the parameters derived from analogous data for Th(IV) in 0.5–4.5 M CaCl2. The log*K°s,(4,1,8) values and the complex formation constants logβ°(4,1,8) follow systematic trends in the series Th(IV), Np(IV) and Pu(IV) which allows the estimation of the corresponding data for U(IV).

Keywords: Neptunium; Plutonium; Solubility; Ternary Ca-An(IV)-OH complexes; SIT

About the article

* Correspondence address: Karlsruhe Institute of Technology, Institut für Nukleare Entsorgung, PO Box 3640, 76021 Karlsruhe,

Published Online: 2010-11-23

Published in Print: 2010-11-01

Citation Information: Radiochimica Acta International journal for chemical aspects of nuclear science and technology, Volume 98, Issue 9-11, Pages 541–548, ISSN (Print) 0033-8230, DOI: https://doi.org/10.1524/ract.2010.1751.

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