THE RADIOCHEMISTRY OF PLUTONIUM - Sciencemadness.org

Other Systems
Moore’” found that the hexavalent actinides U(VI) and Pu(VI) could
be quantitatively extracted from 1 M acetic acid solutions and 1 ~ acetic acid – 0.1
—
~ nitric acid solutions by 5~. TIOA -xylene. Of the fission products only Ru, Zr, and
Nb extracted appreciably, and these could be scrubbed with 5 ~ HC1. A preliminary
ferric (or ursnyl) hydroxide precipitation in the presence of niobium carrier improved
the decontamination from the se elements. The U and Pu were leached from the insoluble
Nb205 with 1 ~ acetic acid. The uranium could be stripped with dilute HN03 m- HC1,
NH40H or ammonium bicarbonate. The Pu(VI) could be stripped by these reagents
or reductively stripped, since Pu(lV) and Pu(III) do not extract under these conditions,
Alcohols, Ketones, Ethers, and Amides
The se compounds have in common the fact that they contain a basic oxygen
atom which can solvate a proton or metal atom. This type of extractant was once very
popular, but the newer organo phosphorous compounds and amines have received more
attention in recent years. Nevertheless, they are still important in laboratory and
process separations. Indeed, one of the large-scale processes for the processing of
irradiated U, the “redox” process, uses methylisobutylketone (MIBK or “hexone” )
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as the primary extractant for U and Pu as do several laboratory procedures. The
extractive properties of the ethers for b“, Fe, and other elements have been known for
many years.
Ifitrate systems have received by far the most attention as extraction media for
Pu. Both Pu(IV) and Pu(VI) are extractable at high nitric acid concentrations, or at
moderately high nitrate concentrations provided by a salt such as aluminum
nitrate. Pu(III) is practically inextractable at any nitrate concentration. The extracted
species depends on the aqueous phase composition. It has been shown that, for example,
the extraction of Pu(VI) from nitric acid solutions by dibutyl carbitol (DBC, the dibutyl
ether of diethylene glycol) the extracted species is the neutral plutonyl dinitrate at low
nitric acid ( < 0.8 IS) is a mixture of dinitrate and trinitrate at intermediate acidities
(0. 8- 3N), is predominately trinitrate at higher acidities (3-6 N), and finally is more
complex than trinitrate above 6N. 171 At these higher acidities the extraction must in-
volve the solvation of a proton to form the species H(DBC )2 PU(N03 )3, rather than
direct solvation of the Pu in the case of the extraction of the dinitrate species.
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Similarly, Pu(IV) extracts into hexone as PU(N03 )4 from 1.5 ~ HN03 and as H2Pu(N0 )
at 6 — M HN03, with intermediate composition of the organic phase in between.
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The species extracted into triethyleneglycol dichloride at high nitrate concentration have
been foumd to be H2Pu(N03)6 for Pu(IY) and H PU02(N03)3 for Pu(VI). 76 Dibutyl ether
behaves similarly. 413
Pu extraction by hexone has received the most attention, undoubtedly because of
its use in processing. The extraction of Pu(IV) and Pu(VI) as a function of nitric acid
concentration and the concentration of various salts has been measured by several
groups.
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