Journal Article
Radiochimica Acta, vol. 102, iss. 10, pp. 861-874, 2014
Authors
Andrew R. Felmy, Dean A. Moore, Edgar Buck, Steven D. Conradson, Ravi Kukkadapu, Lucas Sweet, David Abrecht, Eugene S. Ilton
Abstract
Abstract
The solubility of different forms of precipitated 242PuO2(am) were examined in solutions containing aqueous Fe(II) over
a range of pH values. The first series of 242PuO2(am) suspensions were prepared from a 242Pu(IV) stock that
had been treated with thenoyltrifluoroacetone (TTA) to remove the 241Am originating from the decay of
241Pu. These 242PuO2(am) suspensions showed much higher solubilities at the same pH value and Fe(II)
concentration than previous studies using 239PuO2(am). X-ray absorption fine structure (XAFS) spectroscopy of the
precipitates showed a substantially reduced Pu–Pu backscatter over that previously observed in 239PuO2(am) precipitates,
indicating that the 242PuO2(am) precipitates purified using TTA lacked the long range order previously found
in239PuO2(am) precipitates. The Pu(IV) stock solution was subsequently repurified using an ion exchange resin and an
additional series of 242PuO2(am) precipitates prepared. These suspensions showed higher redox potentials and total
aqueous Pu concentrations than the TTA purified stock solution. The higher redox potential and aqueous Pu concentrations were in
general agreement with previous studies on 242PuO2(am) precipitates, presumably due to the removal of possible organic
compounds originally present in the TTA purified stock. 242PuO2(am) suspensions prepared with both stock solutions
showed almost identical solubilities in Fe(II) containing solutions even though the initial aqueous Pu concentrations before the
addition of Fe(II) were orders of magnitude different. By examining the solubility of 242PuO2(am) prepared from both
stocks in this way we have essentially approached equilibrium from both the undersaturated and oversaturated conditions. The final
aqueous Pu concentrations are predictable using a chemical equilibrium model which includes the formation of a nanometer sized Fe(III)
reaction product, identified in the 242PuO2(am) suspension both by use of 57Fe Mössbauer spectroscopy and
transmission electron microscopy (TEM) analysis.