ORNL-1771 - Oak Ridge National Laboratory

ond fluoride ion is being made to ascertain hose
applicable to the analysis of NaF-KF(RbF)-LiF-
base reactor fuels.
Lithium. An indirect volumetric method for the
determination of lithium in the presence of the
large concentrations of sodium and potassium and/or
rubidium which are found in NaF-KF(RbF)-LiF-base
fuels was developed. The method was designed
specifically to provide a rapid, and yet precise,
means of determining lithiuni. The alkali metals
are first separated from uranium and then converted
to chlorides. Lithium is extracted as the soluble
chloride salt by heating at about 135OC with
2-ethylhexano18 until the slightly soluble salts
of sodium and potassium become "free-flowing"
and no longer cling to the walls of the vessel.
These salts are removed by filtration, and then the
filtrate is diluted with ethanol. The chloride in the
filtrate is titrated by the Volhard meth~d,~ and the
I ithium concentration is caiculated. The coefficient
of variation is 0.5% for 1 to 50 mg of lithium. A
topical report of this work is being written.
Potassium and Rubidium. Since the concentration
of either potassium or rubidium in NaF-KF(RbF)-
LiF-base fuels is of the order of 30 wt %, the de-
termination of potassium or rubidium by means of
the flame photometer has been neither sufficiently
accurate nor precise. The conventional method for
this determination is the perchlorate separation
of potassium or rubidium perchlorate from the sodium
and lithium salts in ethyl acetate. The method is
entirely satisfactory but requires considerable
operator time. Therefore the opplication of possible
substitute procedures which are specific for potas-
sium and/or rubidium was investigated. A pro-
cedure' ' involving the precipitation of potassium
bitartrate in ethanol-water and titration of the
solution of the salt with standard base was tested.
The method is extremely simple ond rapid, and the
bitartrate salt is readily filterable. Rubidium
behaves similarly to potassium, but cesium does
not precipitote as the bitartrate salt under these
conditions. Further work is necessary to determine
the effect of acid and salt concentrations on the
8E. R. Caley md H. D. Axilrod, 2nd. Eng. Chem. Anal.
Ed. 14, 242 (1942).
91. M. Kolthoff and E. B. Sandell, Textbook of Qumti-
tatzve Inorganic Andysrs, p 477, MacMillan, New York,
1947.
"lbid., pp 414-15.
''A. F. levinsh and Yo. K. Ozoi, j. And. Cbem. USSfE
8, 57 (1953).
PERIOD ENDING SEPTEMBER IO, 1954
solubility of potassium bitartrate before o decision
can bereached as to the applicabilityof this method
to NaF-KF-LiF-base fuels.
A second method under consideration is the use of
sodium tetraphenyl boron12 as a reagent for the
direct determination of potassium, rubidium, and
cesium. The potassium salt is precipitated in
aqueous acidic solution, filtered, dried at 1 10°C,
and weighed as potassium tetraphenylborate. The
method has the advantageof being simple and rapid,
and it has a favorable weiyht factor for potassium.
The main interference in the use of tetraphenylboron
is the ammonium ion. The reagent is expensive,
but it is readily available at the present time.
Preliminory work on the solubilities of potassium,
rubidium, and cesium tetraphenylborates in non-
aqueous solvents has shown some interesting dif-
ferences in solubilities. The possibility of ex-
ploiting differential solubility as a means of
separating the salts is being explored. Acetyl-
acetone, diethylketone, and methyl i sopropylketone
are three possible solvents for this separation.
The order of solubility in organic solvents has been
estoblished as: KTPB > RbTPB 1 CsTPB (TPB =
tetrapheny I boron).
Fluoride Ion, The determinatian of fluoride ion
in fluoride fuels was previously conducted by the
pyrohydrolysis l3 procedure which was particularly
successful for NaZrF,-base fuels. Alkali metal
fluorides, however, are resistant to pyrohydrolysis,
and thus considerable time, of the order of 3 to 4 hr,
is required to pyrohydrolyre completely 100 mg of
NaF-KF-LiF-base material.
Two alternative methods have been studied,
therefore, for application to the determination of
fluoride ion in NaF-KF-LiF-base materiols. A pro-
cedure, which was formulated by ChiIton,14 was
tested. In this procedure the fluoride ion is titrated
with a standard solution of aluminum (potassium
alum), and the resulting change in acidity is re-
corded. Considerable difficulties have been en-
countered, the foremost of which is the extremely
small change in pH at the equivalence point. The
method in its present form does not appear to be
applicable to this work.
The feasibility of a spectrophotometric titration
of fluoride ion based on the decolorization of a
_ _ ~..__.._ ......_._i_.
"W. Ceilmann and W. Gcbuukr, %. mal. C,%ern. 139,
161 (1953).
I3J. C. Wurf, W. D. Cline, and R. D. Tevebaugh, hal.
CfJeVL. 26, 342 (1954).
I4J. A. Chilton, personal communication.
153