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

598 A. Discussion of selected references[63MOS/GÉL]A NpO 2 HCO 3 (aq) formation constant is reported from “unpublished” work:log 10 K =−2.2atI= 0.15 M and −2.4 at 0 M with indication about neither the ionicstrength correction procedure, nor the experimental procedure, nor the interpretation(of the experimental results), nor the definition of the equilibrium constant. HighCO 2 (g) partial pressures would be more likely to stabilise a NpO 2 HCO 3 (aq) species;but no evidence of any Np(V) bicarbonate complex has been found in other studiesusing such conditions [84VIT, 86GRE/ROB, 90RIG, 98VIT/CAP]. It is concludedthe value in this publication [63MOS/GÉL] is in error. In a later paper, one of theauthors [71MOS2] proposed different (incorrect) Np(V) carbonate complexes forother chemical conditions (cf. discussion of [71MOS2]).[63MUS]This is a polarographic study of the change in the half-wave potential of the Np 4+ /Np 3+reduction potential in the presence of bisulphate ion. All SO 4 wasassumedtobeHSO − 4. Experiments were performed at 3 M ionic strength and 1.1 M acid strength.The data are provided in sufficient detail to enable recalculation of the associationquotients and errors. In the recalculation, using a quadratic model, a correction wasmade for the presence of SO 2−4 .[64GAI/SYK]This is a cation exchange study of Np(V) nitrate complexes in 2 M H (ClO 4 ,NO 3 )mixtures at 25 ◦ C. The ligand concentration was varied from 0.2-1.8 M. It is assumedthat no adsorption of the complex by the resin occurred and only the first complexformed. The authors obtained β 1 = (0.56 ± 0.06) as the average of 0.54 and 0.58 fromtwo separate runs, both with 0.01 standard deviation. The disproportionation of Np(V)was accounted for by estimating log 10 K disprop. =−6.08 at 2 M acid, (it was concludedthat less than 1.5 % of Np(V) disproportionated). The spectra in methanol showed nonew bands and the same peak height was observed; only a solvation change could beobserved.The reaction with the resin, denoted R-H can be written:R-H + NpO + 2Å R-NpO 2 + H +assuming that no other ions are exchanged. The thermodynamic constant of the exchangereaction is:whereK ◦ cix =[R-NpO 2 ] r·[H + ] aq·f cpx,r·f H + ,aq[NpO + 2 ] aq·[R − H] r·f NpO+2 ,aq·f R-H,r= C f[R-NpO 2 ] r·f H + ,aq[NpO + 2 ] aq·f NpO+2 ,aqC f = [H+ ] aq·f cpx,r[R-H] r·f R-H,r