chemical thermodynamics of neptunium and plutonium - U.S. ...

Chapter 10Neptunium group 16compounds and complexes10.1 Neptunium sulphur compounds and complexes10.1.1 Neptunium sulphites10.1.1.1 Aqueous neptunium sulphites10.1.1.1.a Np(V) sulphitesThere are four reports of SO 2−3complexes of NpO + 2[65MOS/MEF, 72BLO/BUK2,78MOS/POZ, 79MOS/POZ]. Corresponding equilibrium constants are reported inTable 10.1. Moskvin et al.[65MOS/MEF] gave no original data that can be evaluated,and the work presented in [78MOS/POZ] and[79MOS/POZ] represents duplicate reportsof the same data. All four reports conclude that two dioxoneptunium(V) sulphitecomplexes are formed:NpO + 2 + SO2− 3Å NpO 2 SO − 3NpO + 2 + 2SO2− 3Å NpO 2 (SO 3 ) 3−2Blokhin et al. [72BLO/BUK2] suggest, on the basis of solubility experiments at highSO 2−3concentrations, that higher coordinated complexes may form. Although there isreasonable agreement between the reported results, there is insufficient data to permitthe reported values to be extrapolated to the infinite dilution standard state.10.1.1.2 Solid neptunium sulphitesBlokhin et al. [72BLO/BUK2] precipitated stable solids of the forms of:NaNpO 2 SO 3·H 2 O(s), NaNpO 2 SO 3·2H 2 O(s), NH 4 NpO 2 SO 3 (s) and KNpO 2 SO 3 (s).The composition of these solids was verified by chemical analysis. The Na-dihydratesalt dehydrates when heated to the monohydrate state. Thermogravimetric data aregiven in this reference. There are no thermodynamic data available for these solids.177