Metallic elements at oxidation levels IV and VI are more easily extracted by TBP than levels I, II, III or V. So, uranium and plutonium existing at valences VI and IV respectively are significantly extracted while other actinides (americium, curium at valence III, neptunium at valence V) and most of the fission products (FPs) are poorly extracted.

As a result, the following organic complexes are preferentially solubilized in the organic phase:

UO2 (NO3)2.2TBP and Pu2 (NO3)4.2TBP

which enables the uranium and plutonium to be separated from the fission products.

TBP also has the ability, however, to complex some metallic cations that are ionically bound to nitrate anions:

M”+(aqueous phase) + mNO3- (aqueous) + n TBP ^ M(NO3)m. nTBP (organic phase)

Scrubbing the TBP solvent with nitric acid (fission product scrubbing) can improve the separation of uranium and plutonium by re-extracting into the aqueous phase those fission products that were dragged along by the solvent, particularly the zirconium and ruthenium. A second scrubbing removes the technetium, which is troublesome for uranium/plutonium partition.