The fate of selected impurities in the recrystallization of zirconium oxychloride and in its conversion to zirconium tet
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Kenneth J. Ewing and Ishwar D. Aggarwal Naval Research Laboratory, Code 6573, Washington, DC 20375-5000
(Received 10 April 1989; accepted 26 September 1989) The fate of Fe, Co, Y, and Ce impurities is determined in the process of recrystallization of zirconium oxychloride and in its subsequent fluorination with aqueous hydrofluoric acid to ZrF4 • H 2 O. Techniques of gamma ray spectrometry were used to follow radioisotopes introduced at critical steps in the process. All impurities remained in the recrystallization liquor. The liquor and its associated impurities, which is retained on the crystals, can be displaced by acid washing. In fluorination, Fe and Co are rejected while Y and Ce are retained and cannot be removed by washing.
I. INTRODUCTION
Cations which absorb light near 2.5 /xm in low-loss ZBLAN-type fluoride glasses are impurities which must be minimized. Among cations which must be thoroughly removed during the synthesis of zirconium tetrafluoride for use in glass are Fe, Co, and Nd.1 To understand better the purification mechanisms at work in a process for making zirconium and hafnium tetrafluorides,2 we undertook a radiochemical study of two steps of the synthesis, focusing on the fates of introduced radiotracer cations detectable by gamma ray spectrometry. The isotopes 59Fe and 60Co are readily available, but a suitable Nd isotope is not conveniently available. We take advantage of the similarity in the aqueous chemistry of 88Y and 139Ce to predict the fate of Nd. It was expected that such a study would be immune to difficulties arising in attempts to analyze all reactants and products of the synthetic steps by graphite furnace atomic absorption spectroscopy. We found that even carefully executed determinations gave erratic and high iron recoveries at the level of low tens of ppb. II. EXPERIMENTAL
The two synthetic steps of oxychloride recrystallization and fluorination were performed in the presence of radiotracer impurities introduced as a spike solution. Liquid and solid fractions from the synthesis were analyzed by gamma ray spectrometry to determine the destination of the impurities. Gamma rays were detected with a closed end coaxial type lithium drifted germanium Ge(Li) semiconductor detector with a relative efficiency of 20% and a FWHM resolution at 1333 keV of 2.0 keV. The detector was manufactured by Princeton Gamma-Tech, Princeton, NJ. The detector's output pulses were ulti392
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mately collected with a NIM-based multichannel analyzer (MCA). These spectral data were ultimately reduced to the count rates of the isotopes of interest with an IBM PC computer clone. The MCA hardware and software are available from Nuclear Data, Inc., Schaumburg, IL. All of the analyzed samples were contained in 6.7 cm diameter plastic jars with a nominal sample depth of 1.4 cm (volume 50 cm3). The sample jar was placed on the aluminum end-cap of the detector. All samples were analyzed for 3600 s; the maximum deadtime for any sample was less than 1.6%. The spectrum was collected in
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