THE RADIOCHEMISTRY OF PLUTONIUM - Sciencemadness.org

Precipitation
Precipitation of macro quantities of Pu is necessary in many analytical
and radiochemical procedures. The precipitation reactions which have been found
useful in practice will be reviewed in this section. The use of various precipitates as
purification steps for Pu is illustrated by Table IV- 15, which gives decontamination
factors for Pu from Fe, Co, Zr, Mo, Ru, and Ce. 431 As usual, Zr and Ru give the
most trouble.
TABLE IY - 15. Decontamination Factors for Plutonium by Precipitation Methods. 431
Plutonium Plutonium (IH) Plutonium (IV) Plutonium (Hf)
Element peroxide oxalate oxalate fluoride
Fe 50 33 10 1.4
co 30 47 > 95 8.6
Zr 1 3.5 >44 1.1
Mo >140 > 13 > 15 1.1
Ru >14 > 38 33 36
Ce 6, 1 1 1.1
Hydroxide. Both Pu(IIZ) and Pu(IY ) may be precipitated from mineral acid
solution by sodium, potassium or ammonium hydroxide as hydrated hydroxides or
hydrous oxides. Care must be taken in redissolving Pu(I17) hydroxide in acid to pre-
vent formation of Pu(IY) polymer, by maintaining a high acid concentration during the
dissolution. Once formed, the polymer dissolves very slowly in acid solutions. This
subject is treated more fully in the section on polymeric Pu(IV).
Fluoride. PuF3 and PuF4 may be precipitated from acid solution by
addition of excess HF. Prevot et al. 325 found that PuF3 forms a more tractable,
crystalline precipitate than does PuF4. The compound is stable to oxidation if the
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precipitate is kept slurried in the supernatant solution. The freshly precipitated
compounds dissolve readily in reagents which complex fluoride ion, such as H3B03,
but if heated to 500” dissolve only with difficulty. Metathesis to the hydroxide with
sodium or potassium hydroxide is another method of solution. Jones214 found that
PuF3 was suitable for use as a gravimetric standard for Pu, at least for a period of
several months. This method has not been widely used, however. It is interesthg to
note that PU02 prepared by ignition of this PuF3 at 500”C in oxygen was readily soluble
in nitric acid, in contrast to the findings of other workers. This volubility is attrib-
uted to the extremely fine particle size of PU02 prepared in this work.
Peroxides. Pu(IV) peroxide is formed when hydrogen peroxide is added to
acid solutions of PU(III)J Pu(IV), Pu(V), and Pu(VI), because H202 can act as both an
oxidant and a reductant. Pu(IV) peroxide always incorporates some of the anion pres-
ent into the crystalline precipitate. It has been suggested7 that the presence of the
anion is due to a more or less random placement between sheets of Pu and peroxide
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