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

704 A. Discussion of selected referencesestimate. In the present review, Maya’s value for the formation constant is also acceptedas a limiting value.Maximum values for the formation constants of (NpO 2 ) 3 (OH) − 7and(NpO 2 ) 3 CO 3 (OH) + 3(i.e., (NpO 2 ) 3 O(OH) 2 HCO + 3) are also proposed. Calculationsshow these could well have formed as minor species during Maya’s titrations[84MAY]. The calculated values are similar to those selected for the uranium analogues[92GRE/FUG], but there is no firm evidence that these species actually exist.The species (UO 2 ) 3 (OH) 2−8was not selected in the uranium review [92GRE/FUG],but was proposed to explain the results of a recent study [95PAL/NGU]. Theformation of the analogous neptunium species, (NpO 2 ) 3 (OH) 2−8, as a minor speciesis also not inconsistent with the data from Maya’s titrations, and the maximum valuecompatible with Maya’s data has been calculated in the present review. The recentlyproposed [95PAL/NGU] species (UO 2 ) 3 (OH) 4−10also was not selected in the uraniumreview [92GRE/FUG]; however, if a maximum value of the formation constant for(NpO 2 ) 3 (OH) 4−10is estimated based on the value proposed for the uranium species[95PAL/NGU], calculations indicate that this species would not have been detectableduring Maya’s titrations [84MAY]. A more detailed re-interpretation is given in[98VIT/CAP].Table A.14: Table of values and limiting values of formation constants based on reassessmentof Maya’s potentiometric titration data in 1 M NaClO 4 aqueous solution[84MAY].Present review Selected [84MAY] Calculated but Uranium analoguerejected [84MAY] [92GRE/FUG]log 10 β 3,6,0 ′ (42.82 ± 1.06) (42.06 ± 0.80) (40.41 ± 0.41)log 10 β 2,1,3 ′ (41.75 ± 1.46) (41.76 ± 0.94) (39.88 ± 0.60)log 10 β1,2,0′