ORNL-1771 - Oak Ridge National Laboratory

obtained. The following reactions were postulated
to explain these waves:
and
He also reported that anhydrous hexavalent uranium
gave no reduction wave until after an aging period
during which the compounds were reduced by the
ammonium formate to a lower valence state, probably
quadrivalent.
Since it appeared that this technique could be
appiied to the determination of tetravalent uranium
in the presence of lorge quantities of trivalent
uranium, experiments were carried out to obtain
polarograms of solutions of UF,. In preliminary
experiments it was found that UF, and NaZrF,.
and NaF-KF-Li F-base fuels dissolved readily in
molten ammonium formate at 125°C to form green
solutions containing as much os 1 mg of uranium
per milliliter. Although UF, alone was found to be
much less soluble, UF, which had been fused with
NaZrF, was reodi Iy soluble. Similar relationships
were found when molten ammonium acetute was
used as a solvent.
No U(IV) reduction wwes were obtained when
polarograms of solutions of UF, were recorded
immediately after dissolution, and no reduction
waves were observed in the polarograms of a
sample of NaF-KF-Li F-base fuel that contained
both UF, and UF,. When these solutions were
aerated, a single reduction wave with a half-
wave potential of approximately -0.2 v was ob-
served. The potential and the diffusion current of
this wave corresponded closely to those recorded
immediately after the dissolution of an equivalent
quantity of K,UO,F, in molten formate. Since the
U($V) waves may have been shifted to potentials
outside the range of the solvent (0 to -0.9 v) by
the cmplexing action of the fluoride ions, addi-
tional polarograms were taker] of solutions con-
taining UCI,. Except for a small reduction wave
at about -0.2 vp no evidence? of reduction was found.
The diffusion current of this wave was increased
by aeration to values corresponding to those ob-
tained For hexavalent uranium, and therefore &e
increase was attributed to the oxidation 04 &IC/,,
It appears that in molten ommoniurn formate IPO
oxidation state of uranium other than hexavalent is
reduced at he drapping-mercury electrode.
PERIOD ENDlMG SEPTEMBER 70, 1954
Conversion of UF, and UF, to the Respective
Chlorides with BCI,
A. S. Meyer, Jr. D. L. Manning
Analytical Chemistry Division
It was reported previously3 that, on the basis of
free-energy calculations, UF, UF, ZrF4, and
NaF are quantitatively converted to the chlorides
when at equilibrium with boron trichloride. Since
the exchange reaction in organic solvents at moder-
ate temperatures was found to be too slow for
analytical application, tests were carried out with
gaseous BCI, at elevated temperatures. This tech-
nique offered on additional advantage in that the
resulting chlorides could be separated by sublima-
tion.
When a sample of NaZrF,-UF, fuel was heated
in a stream of BCI, and helium at 350°C, the bulk
of the zirconium was sublimed as ZrCI, within 90
min, and all but traces were removed after heating
for an additional hour at 450OC. It has been re-
ported* that uranium can be sublimed as UCI, by
treating UF, with BCI, at 600 to 65OoC, but in
these tests only a small fraction of the UCI, was
volatilized when the UCl,-NaCl residue, which
fused at about 45OoC, was heated to temperatures
as high as 750°C.
Analyses of the residues showed that when the
conversion was carried out ot 40OOC for 90 min the
uranium in the NaZrF,-UF, samples was quanti-
tatively converted tu UCI, and that all the uranium
remained in the residue. When the conversion was
carried out at 5oO°C, 2% of the uranium was
volatilized, while at 750Dc, 4% was volatilized.
When UF, samples were converted to UCI, by
this method, significant fractions of the uranium
were oxidized to UCI,, It is believed that this
oxidation will be eiiminated when all traces of
oxidizing contaminants are removed from the gase-
ous reactants,
Solubility of Tri- and Tetravalent Uranium
FBuorides in Fused NaAsCl ,
A, S. pjleyer, Jr. w. J. Ross
Analytical Chemistry Division
In the continuation of experiments to determine
the optrmum conditions for the conversion of UF,
_ _ ~ __~-
'A.
@an
S. Meyer, Jr., I3. I. Manning, and W. J. Ross, ,4NP
Prog. Rep- June 10, 1954, 0RNL.-1729, p 110.
'V, P, Calkin5, Drrect Conversion 01 TF6 to TCL,,
CEW-IEC C-0.350.4 (Septa 23, 1986).
151