Spectrophotometric Determination of Uranium in Thorium TetrafIuoride lwao Okumura, Sachio Shimada, and Kunio Higashi Department of Nuclear Engineering, Kyoto University, Sakyo. Kyoto, J a m n
In the development of fluoride volatility processing of spent thorium nuclear fuels, it is essential to analyze a small amount of U in one of the typical refractory compounds, ThF4. A few special reagents can be used for dissolving ThF4. For rapid and accurate determination of U in ThF4, we propose here spectrophotometry with a specific pretreatment. The pretreatment consists of dissolving a solid sample in H~B03-HC104solution, fuming t o dryness, and stabilizing by adding base. This pretreatment may also be applicable to spectrophotometric analysis of other elements in ThF4. The final coloring procedure and measurement are based on the “direct procedure” of Kimball and Rein ( I ) with minor changes. The differences from Kimball and Rein’s coloring procedure are in the following two points; the end point of the addition of (NH4)&03, and the wave length chosen. Considering the discussion by Opalovskii and Kuznetsova ( 2 ) ,thiocyanate-acetone is much superior t o Arsenazo-I11 as a chromogenic reagent for the determination of U contained in fluorides. In fact, we failed in every attempt to find a simple method by using Arsenazo111.
EXPERIMENTAL Apparatus. A Beckman Model DU spectrophotometer and 1-cm quartz cells were used for absorbance measurements. Reagents. Stannous chloride-hydrochloric acid solution (SnClZ-HCl) was prepared by dissolving 10 g of SnC12 in 100 ml of iiV HCI. Thiocyanate-acetone was prepared by dissolving 114 g of NH4SCN in 440 ml of acetone and making up to 500 ml by acetone. Procedure. The solid sample of 500 mg of ThFI including U is put into a beaker. Added to it are 20 ml of 60% HClOl solution and 20 ml saturated solution of boric acid. After about a half hour of mild heating, white fumes are released from the solution. After an additional half hour of heating, the boiling solution becomes transparent and finally dries to a solid. The addition of more HC104 for dissolving seems to make the colored solution unstable. Though a small amount of H F makes the solution of ThFI ( 1 ) R. 6. Kirnball and J. E. Rein, U . S . At. Energy Comm Rep.. IDO14369 (1956). (2) A. A . Opalovskii and Z. M. Kuznetsova. Izv. Sib. O f d . Akad. Nauk SSSR. Ser. Khim. Nauk. 1 . 1 3 0 (1965).
easier, its addition produces a trace of undissolvable white solid. To make the solution basic. 10% ammoniuni carbonate is added a drop a t a time. With the increase or pH. a white suspension forms first. The solution becomes clear a t p H 7.5. This clear solution is diluted to 100 ml with 10% (NH4)2C03. The p H of the resulting solution is close to 8.5. Eight ml of the solution produced above is mixed with 1 ml of SnC12-HC1 solution and 13 ml d thiocyanate-acetone and its volume adjusted to 25 ml with cold distilled water. Atter shaking the solution, the absorbance is measured against a blank a t 350 nm, the wave length of maximum absorbance. For the preparation of the blank, distilled water (8 ml) is substituted for the sample. If the room temperature is higher than 15 “C, the solution to be measured should be kept in a refrigerator. The spectrophotometric measurements are to be carried out quickly before the temperature in the cells becomes higher than 15 “C. The calibration curve is obtained from solid mixtures of known content of U in THF4.
RESULTS AND DISCUSSION The absorbances of the solutions made from solid samples containing 0.57, 2.2, and 4.4 mg U in 0.5-g sample are 0.0655, 0.250, and 0.500, respectively. The apparent molar absorbance is 0.84 X 104. The applicable lower limit of U/Th ratio is as low as 5 x by using 1 cm cells. The tolerance of thiocyanate-acetone method has been examined against many impurities. We made an additional study to make sure of the high tolerance in the proposed method. We tested the impurities of Cu, Sr, Zr, Al, Fe, and Ni separately. Some of these elements are thought to be contained in a sample as impurities when Th-U nuclear fuels are fluorinated by fluorine or other fluorinating gases in a reactor made of noncorrosive materials against fluorinating gases. The cations corresponding to these elements were added as nitrates. The content of each cation was varied from 0 t o 3 atomic per cent of T h + U. At the chosen wave length (350 nm), measurable effect was not observed.
ACKNOWLEDGM.ENT The authors wish to thank W. Kuhrt and R. Kreutz of Kali Chemical Co., Ltd. for their instructive infcxmation. Received for review September 15, 1972. Accepted February 15, 1973.
ANALYTICAL CHEMISTRY, VOL. 45. NO. 11, SEPTEMBER 1973
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