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

11.1 Neptunium nitrogen compounds and complexes 191and Moskvin [71MOS] lack experimental details and have possible experimentalshortcomings, cf. Appendix A.The same types of problems are found for the studies of Stromat, Peekema andScott [58STR/PEE], Sykes and Taylor [62SYK/TAY] and Kusumakumari et al.[79KUS/GAN] (cf. Appendix A). Except for the value obtained using high ionicstrength (I = 9 M) solutions by Barbanel and Muravieva [72BAR/MUR], the datafrom the other studies have been used to estimate a value for the formation constantfor NpNO 3+3 .All inner sphere complexes beyond the first are extremely weak at even moderatenitrate concentrations, and calculations have shown (Appendix A) that effects of highercomplexes can often be accounted for by considering activity coefficient changes insequential substitution for large amounts of the medium ions (e.g., perchlorate) bynitrate ions, and assuming only the formation of the first complex up to 2 M nitrate[98SPA/PUI]. Such assumptions do not greatly influence the selection of a value for thefirst complexation constant as shown in Figure 11.1. The value of the constant reportedby Danesi et al. [71DAN/CHI] was obtained in an electrolyte mixture consisting of3MNaClO 4 +1MHClO 4 , and the filled symbol in Figure 11.1 represents the valuerecalculated in 4 M HClO 4 in order to plot it together with the other values.Table 11.4: Experimental equilibrium data for the Np(IV) nitrate system.Method Ionic t log 10 β q (I) (a) log 10 β q (I) (c) Referencemedium ( ◦ C)Np 4+ + NO − 3Å NpNO 3+3pot 1.0 M HNO 3 25 0.38 [58STR/PEE]kin 2.0 M HNO 3 25 0.11 [62SYK/TAY]dis, TTA 0.5 M HClO 4 20 0.45 (0.48±0.10) [66SHI/NAZ](0.62±0.20) (b)dis, TTA 1 M HClO 4 20 0.34 (0.34±0.10)(0.23±0.20) (b)dis, TTA 1.5 M HClO 4 20 0.36 (0.28±0.10)(0.41±0.20) (b)dis, TTA 2 M HClO 4 20 0.30 (0.20±0.10)(0.11±0.20) (b)sp, kin 2 M HClO 4 25 0.34 (0.42±0.15) [66RYK/YAK](0.34±0.20) (b)dis, TOA 8 M HClO 4 20 −1.52 [70LAH/KNO]dis, TBP 2 M HClO 4 25 0.83 [71MOS]dis, TBP 4 M HClO 4 25 0.72dis, TTA 4 M (Na,H)ClO 4 25 −(0.15 ± 0.12) −(0.12±0.10) [71DAN/CHI]−(0.15±0.12) (b)sp 9 M HClO 4 25 0.9 (1.2 ± 0.1) [72BAR/MUR]dis, DNNS 2 M HClO 4 25 0.20 (d) [72PAT]sp 7 M HClO 4 25 0.9 (d) [73ESC]dis, HTTA 6 M (Na,H)ClO 4 25 0.53 [79KUS/GAN](Continued on next page)