In:
ract, Walter de Gruyter GmbH, Vol. 98, No. 9-11 ( 2010-11), p. 541-548
Abstract:
The solubility of Np(IV) and Pu(IV) hydrous oxides was studied at 22±2 °C under reducing conditions in alkaline CaCl 2 solutions. Redox conditions were adjusted either with 2 mM Na 2 S 2 O 4 or additions of iron powder. In 2.0 and 4.5 M CaCl 2 and pH c =11–12, the neptunium and plutonium concentrations increase with a slope of +4 (log[An] vs . pH c ) as expected for the formation of the complex Ca 4 [An(OH) 8 ] 4+ recently identified for Th(IV). At CaCl 2 concentrations ≤1.0 M this effect is negligible for both Np(IV) and Pu(IV). The conditional equilibrium constants log * K s,(4,1,8) for the reaction An(OH) 4 (am) + 4 H 2 O + 4 Ca 2+ ⇔ Ca 4 [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 CaCl 2 . 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).
Type of Medium:
Online Resource
ISSN:
2193-3405
,
0033-8230
DOI:
10.1524/ract.2010.1751
Language:
English
Publisher:
Walter de Gruyter GmbH
Publication Date:
2010