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ANP PROJECT PROGRESS REPORT
DETERMINATION OF BARIUM, LANTHANUM,
AND RUBIDIUM IN FLUORIDE FUELS
A. S. Meyer, Jr. B. L. McDowell
Methods were developed for the determination of
barium, lanthanum, and rubidium in NaF-ZrF,-UF,
as part of a program for determining the effect of
typical fission products on the physical properties
of molten mixtures of fluoride salts. For the barium
determination the fluoride salt mixture is dissolved
in fuming sulfuric acid, and the barium remains
in the insoluble residue, as the sulfate. After
dilution of the sulfuric acid solution with water,
the barium sulfate, which is contaminated with
uranium and zirconium, is separated by filtration
and purified by dissolving it in a hot ammoniacal
solution of ethylenediaminetetraacetic acid. It is
then reprecipitated by acidification of the solution
with hydrochloric acid. The reprecipitated barium
sulfate is filtered off. The filter paper is charred,
and the barium sulfate is then ignited to constant
weight at 600OC.
Lanthanum is separated from the filtrate from
the barium determination by precipitation, as the
oxalate, from a neutral solution of ammonium oxa-
late. Coprecipitated zirconium and uranium are
separated from the original oxalate precipitate by
dissolving the precipitate in concentrated nitric
acid and carrying out a second oxalate precipita-
tion from a neutral solution of ammonium oxalate.
The purified oxalate precipitate is converted to
the nitrate by digestion with concentrated nitric
acid and evaporation to dryness. The residue is
taken up in a small amount of water or very dilute
nitric acid. Lanthanum is finally precipitated by
the addition of solid oxalic acid to the hot, slightly
acid solution. The lanthanum oxalate is ignited
at 9OOOC and weighed as La203.
Ammonium salts in the filtrate from the lanthanum
determination are destroyed by digesting the solu-
tion with aqua regia. The alkali metals are sepa-
rated and converted to the hydroxides by passing
the solution through an anion exchange column
in the hydroxide form. After all traces of ammonia
are removed by evaporating the alkaline solution
to dryness, the rubidium is precipitated and weighed
as the sparingly soluble tetraphenylboron salt.
Potassium, which is present as a trace Contaminant
126
2.6. ANALYTICAL CHEMISTRY
J. C. White
in the base fuel, is also precipitated as the tetra-
phenylboron salt. The potassium in the tetra-
phenylboron precipitate is determined by flame
photometry, and the weight of the precipitate is
corrected accordingly.
Good precision has been obtained in analyses
of replicate samples of fluoride mixtures which
contained 1 to 3% of each of the above-mentioned
elements. These methods are also being tested
for the determination of cerium and the proximate
determination of the cerium group of the rare-earth
elements in fluoride fuels.
DETERMINATION OF NIOBIUM IN FUSED
MIXTURES OF FLUORIDE SALTS BY
THETHIOCYANATEMETHOD
A. S. Meyer, Jr. 8. L. McDoweII
R. F. Apple
A method for the spectrophotometric determina-
tion of niobium as the thiocyanate complex, re-
ported by Ward and Marranzino," was applied to
the determination of niobium in NaF-ZrF,-UF,.
The method is based upon the reaction of niobium(V)
with thiocyanate in a mixed solution of 4 M hydro-
chloric acid and 0.5 M tartaric acid to produce a
complex which exhibits an absorption maximum
at 387 mp in an ethyl ether-acetone medium. The
addition of acetone to the extract of ethyl ether
containing the complex inhibits the polymerization
of the thiocyanate ion and stabilizes the solution
for at least 20 hr.
Tartaric acid eliminates the interference of ura-
nium, which also forms a complex with thiocyanate.
The interference of the red color of the iron(ll1)-
thiocyanate complex is eliminated by shaking the
ether extract with a solution of stannous chloride
for 30 sec to reduce the iron(ll1) to iron(l1).
The concentration of the reagents in the aqueous
phase must be held within rigid limits if repro-
ducible absorbance values are to be obtained.
In order to maintain fixed concentrations, the
fluoride sample is dissolved by fusing it with
potassium pyrosulfate and dissolving the melt in
1 M tartaric acid. A 1- to 10-ml aliquot of the
resulting solution is combined with a sufficient
IF. N. Ward and A. P. Marranzino, Atlal. Chem 27,
1325 (1955).