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ANP QUARTERLY PROGRESS REPORT
In these experiments, pure preparations of CrF,
or CrF, were added to the NaF-KF-LiF eutectic
in apparatus of nickel, maintained at the indicated
temperature for 5 hr, and filtered. Data obtained
by analysis of the filtrates are shown in Table
5.2.
TABLE 5.2. STABILITY OF CrF, AND CrF3 IN
MOLTEN NaF-LiF-KF
120 1.08 260
520 0.74 40
90 0.91 60
370 1.00 820
800 600 3.63 15
430 4.22 30
480 4.22 30
440 3.60
Cr2 .+
(%I
CrF, equivalent 600 0.39 1.12 40
to 5.8 wt % Cr2' 0.33 0.86 50
0.32 0.87 30
0.10 1.11 50
8 00 1.05 2.97 40
0.94 3.30 30
0.99 3.24 90
0.98 3.35 20
These data indicate that CrF, in NaF-KF-LiF
eutectic is quite stable toward reduction by
nickel. In the most favorable case, less than 10%
of the CrF, appears as Cr". The solubility of
trivalent chromium seems to be at least 10,000
ppm at 600°C and at least 40,000 ppm at 800°C;
the solid phases observed in the cooled melts
were complex fluochromates.
When CrF, is the additive, however, the situ-
ation is entirely different. Most of the dissolved
chromium is trivalent; complex fluochromates are
observed in the cooled filtrate. The amount of
material added was such as to exceed the solu-
bility of CrF, at 600°C; so at that temperature
no material balance is possible. At 800"C, how-
ever, the solubility limit was, apparently, not
exceeded, and the concentrations found corre-
sponded extremely well to those to be expected
if chromium metal were not soluble in the melt
and if the reaction
3CrF,+2CrF3 + Cr' T
had occurred. Published figures for AFO for CrF,
and CrF, show that the standard free energy for
the reaction, as written, is +14 kcal and suggest
that
a2crF3
Keq = -- - lo-, at 800°C .
',CrF2
This disproportionation must be considered to be
surprising. If Keq is to be reconciled with the
observed value, the activity coefficient of CrF
in the melt must be less than lo-,. Additional
data at various temperatures and concentration
levels to be obtained in the near future should
afford a more accurate estimation of the equi-
librium constant for this reaction.
When ferrous fluoride is added to the NaF-KF-
LiF mixture in equipment of nickel, no appreci-
able reaction is observed. The solubility of FeF,
appears to be 12 wt % at 600°C and 19 wt % at
800"C, and it appears that FeF, is dispropor-
tionated very slightly, if at all.
If ferric fluoride is added to NaF-KF-LiF in
equipment of nickel, considerable quantities of
NiF, are observed in the filtrate, and thus re-
duction of the Fe3+ by nickel metal is indicated.
However, the experiments made to date have not
afforded reasonable material balances between
NiF,, FeF,, and FeF, in the system. Additional
data will be required before this reaction can be
evaluated.
Reduction of UF, by Structural Metals
J. D. Redrnan C. F. Weaver
Materials Chemistry Divi sion
The apparatus and techniques for experimental
determination of equilibrium constants for the
react ions ? -
and
Cr" + 2UF4 = CrF, + 2UF,
Fe" + 2UF4 = CrF, + 2UF,
t
a -