THE URANIUM DETERMINATION IN COMMERCIAL IODINATED SALT

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1 ENVIRONMENT PHYSICS THE URANIUM DETERMINATION IN COMMERCIAL IODINATED SALT C. A. SIMION, C. CIMPEANU, C. BARNA, E. DUTA Horia Hulubei National Institute of Physics and Nuclear Engineering, Romania, 407 Atomistilor Street, Com.Magurele, jud.ilfov, C.P. MG-6, cod tel. (4021) , fax (4021) , (4021) , Received March 22, 2006 This method extends a classical determination of uranium and thorium in natural waters to a new series of solid inorganic and / or organic samples. A technique based on chemical separations using cation / anion exchange columns was used. The UV-VIS absorption spectroscopy was employed for the determination of cations. The limit of detection using characteristic band absorptions of colored complexes of Arsenazo III with these cations is in the ppb range. These values are usually expected for natural samples. Finally, an improved correlation on absorption spectra of uranium, iron and thorium concentrations has been done. An iodinated sodium salt was taken into account as example. Key words: uranium determination, thorium separation, UV / VIS spectroscopy, Arsenazo III complexes. 1. INTRODUCTION In the environment, Uranium, Thorium and Iron appear in many oxidation states with different solubility in water. The actinide solutions are confined in nuclear power plants and in the radiochemical laboratories specialized in research working with radioactive materials. The nuclear explosions as well as the storage of different wastes make possible the artificial actinides dispersion in the environment. A subsequent rising of natural actinides radioactivity is possible. The manufacturing of used nuclear combustible may generate some artificial actinide solutions with hundreds of grams of Uranium (as U(VI) the most stable and soluble chemical form in aqueous media). Several grams of Pu (IV), and several hundred of milligrams of Np(V) or Am(III) [1]. In exchange, the aqueous natural environmental solutions are extremely diluted, as seen from the Table 1 [2]. The radiological impact at these concentrations may be neglected; for reaching annual ingestion limit of incorporation, an immense quantity of water or food stuff for daily uptake is necessary. Uranium in environmental samples is usually determined by liquid scintillation counting or by UV/VIS spectroscopy. Depending on sample type, Rom. Journ. Phys., Vol. 51, Nos. 7 8, P , Bucharest, 2006

2 846 C. A. Simion et al. 2 Natural Uranium present in samples Table 1 Natural Uranium content in the environmental samples Average concentration in Uranium of the samples as μgu/cm 3 or μgu/g (1 μgu/cm 3 or 1 μgu/g represents 1 ppm uranium or 1000 ppb) Radioactive concentration corresponding to average concentration in natural Uranium species in environmental samples, in Bq/cm 3 or Bq/g Ordinary ores Soils Oceanic water Sea water Sea ores salt Drinking water Human body (70 kg) different chemical pre-treatments are used for Uranium extraction in aqueous solution after chemical operations including concentration and separation as main steps. The method presented below represents the IFIN-HH procedure of determining Uranium in environmental samples. [2] This method was successfully used to determine the Uranium concentrations in soils, groundwater and surface waters coming from rivers, lakes and sea, and permits to measure up to 10 7 μgu/l (10 ppb) [3, 4, 5]. In this paper we present the results issued from applying the procedure to the salt samples arising from natural salt ores as well as from commercial iodinated salt. Briefly, the procedure of Uranium measurement is as follows: bringing the natural sample into an analytical aqueous solution after an appropiate chemical and physical pre-treatment depending on the nature of the sample; concentration of the analyte solution on the cationite resin Dowex 50W 8 ( mesh); separation of Th, U and Fe on anionite column Dowex 1 4 (Cl ); spectrophotometric determination of the complexes of Arsenazo III with Th (IV), U (IV), and Fe (II). In a classical determination, the water samples are prepared as in AC-PL technique. The quantity varies between 1 to 5 liters. All stages are in agreement with the normative of STAS METHODS As a special treatment, in the case of a solid water soluble sample (e.g. commercial iodinated salt), we taken into account the total dissolution of all

3 3 The uranium determination in commercial iodinated salt 847 uranium, thorium and iron species into the 1 L distillated water. In this order, we developed an oxidation stage by boiling the resulted saturated solution (~250 g/l) with oxygenated water. Cationic soluble species represent the final goal of the chemical and physical pre-treatment (P0). In the concentration stage, the filtered analytic solution is passed through a cationite column in order to reduce the final volume from 1 L to 250 cm 3 range. At this stage, Uranium, Thorium, together with Iron, Radium, rare earths and the another cations are concentrated on cationite and then eluted 4% oxalic acid (P1). After washing (P2) and eluting the column material (P3), an oxidation stage is needed to discard some organic and volatile species from the elute (P4). In the separation stage, the concentrated analytical solution is passed through the anionite resin. After some pre-treatment techniques, thorium is finally eluted (P5) followed in the next fractions by the iron (P6) and uranium salts soluble in acid media (P7). Every fraction (P0 through P7) is then pre-conditioned for the colorimetric determination. The U(VI) chemical form is complexed with the organic reagent Arsenazo III. The colored new compound has a specific wavelength for concentration determination on a reference curve (determined with standard solutions of uranyl nitrate). For Thorium and Iron determination, the method follows the stages for the uranium determination; the only difference consists in the reference solutions. By a priori column separation the superposition of the signals is avoided. Finally, the Uranium (μg/l) content is calculated in the above manner: C = c100, μg/l; C η V U = 4 C, μg/kg sample where: c = the quantity of natural uranium determined on the calibration curve, μg; η = global recovery yield, determined for each experiment technique, %; V = the sample volume (or sample solution obtained by the dissolution of pre-weighed solid sample into a known distillated water quantity), L. 3. RESULTS Using an iodinated commercial salt we applied the modified procedure for conditioning, separation and concentration of uranium salts in a final chemical form for a complexation with an organic specific reagent for UV/VIS subsequent determination. For an initial quantity of 250 grams of salt sample in 1 L (V) distilled water, the global recovery yield was 76% (η). The value was calculated as a ratio

4 848 C. A. Simion et al. 4 between recovered Iron (in P6) and initial Iron (in P0) as seen below. In this case, the Iron had the role of a chemical carrier for Uranium concentration and separation in all common processing steps of the method. For the experimental determination of U (P7), The (P5) and Fe (P6) an UV/VIS spectrophotometer Perkin Elmer Lambda EZ 150 was employed. Simultaneously, a several determinations were taken into account and consisting in a series of intermediary determinations of the general and particular content of the fractions in order to appreciate with a great accuracy the yield of recovery (P0, P1, P2, P3, P4). The content of cationic species (c) that determines the changes in the Arsenazo III structure as color variation with their concentration in the sample (C) is expressed as molar coefficient of extinction versus wavelength in the next figures (against a blank solution and using calibration curves). The limit of detection was in the ppb range. From the absorption spectra represented in Fig. 1 we may see that the original signal of P7 corresponds to the standard curves of Uranium on the range of nm. The other original signals for Th (P5) and Fe(P6) do not have any maximum absorption in the 562 nm area (maximum of absorption of the characteristic band in Fig. 2). In this region of the spectra, only the iron complex signal at 548 nm may be taken into account. The nature of the Iron absorption spectra may be very well followed in the P0, P1, P2, P3 and P4 spectra (U and Th having a very low concentration in the mixtures). From the signal original signal of the iron (548 nm) and the composed signal (556 nm) we calculated the global recovery yield of the process. The maximum initial value of the complex concentration is almost the same as in the final separated iron fraction. So, the iron estimations indicate a high content of 100 mg Fe/Kg of salt. In this order, the initial Uranium concentration in the salt sample (C U ) is up to 10 μgu/kg sample. 3. CONCLUSIONS The uranium content of the iodinated commercially available sodium salt sample is 10 ppb, an expected value for maritime water salt ores. The iron content is of 0.10 mg Fe/g of salt that represents a slightly greater unexpected value, due to the origin of the salt exploitation. At a daily necessary of 500 mg of sodium (~ 1.3 g commercially sodium chloride salt), in an adult body, the uranium intake will be of μgu/g, that represents 2% from admitted value. For an adult, the daily intake of 3 L water will bring 180 μgu. The ratio between the daily intake sample value and the value for drinking water consumption represents no more than 10 3 %.

5 5 The uranium determination in commercial iodinated salt 849 REFERENCES 1. R. Guillamont, Ch. Madic, Clefs CEA, 31 ( ), V. Andrei, F. Glodeanu, T. Chirica, Deseurile radioactive. Mituri si adevaruri, Ed. Modelism Bucuresti, N. Paunescu, J. Radioanal and Nucl. Chem.Letters, 104, (1986), N. Paunescu, J. Radioanal and Nucl. Chem.Letters, 163, (1992), N. Paunescu, Uranium in the environment in Surrounding areas of the Romanian NPP during the Pre-operational Period in Actinides and the Environment, edited by P. A. Sterne, A. Gonis and A. A. Borovoi, NATO ASI Series 2. Environment, 41 (1998),

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