SEPARATION OF NEPTUNIUM-237 USING EXTRACTION CHROMATOGRAPHY M. Reich 1 , P. Rajec 1

1. SEPARATION OF NEPTUNIUM-237 USING EXTRACTION CHROMATOGRAPHY M. Reich1, P. Rajec1 1 Department of Nuclear Chemistry, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia e-mail: reich@fns.uniba.sk Abstract The presentation will be focused on separation methods of 237Np in environmental samples and nuclear wastes. Research of separation techniques and the most promising methods from the literature will be presented as well.Except other methods there is possibility to separate components of a mixture of actinides by using extraction chromatography. One of the extraction phases (stationary phase) is fixed on a surface. The second phase (mobile phase) is flowed over its surface.Contaminants such as neptunium and plutonium are important due to their extreme toxicity. Furthermore, long-lived radionuclides such as 239Pu, 240Pu and 237Np (half-lives of 2.41x104, 6.56x103 and 2.14x106 y, respectively) also present a long term threat.The chemistry of neptunium is complicated because neptunium exists in several oxidation states (especially IV, V and VI). The main prior for application of this method is requirement to transform neptunium into appropriate oxidation state. Mostly, it is suitable to transform neptunium into the oxidation state Np(IV) used in separation processes using different redox reagents e.q. ferrous sulfamate, sodium nitrite, hydrogen peroxide and other compounds. Separation of neptunium from soil samples is possible after total dissolution of sample. There are available many dissolution methods e.q. using mixture of HNO3/HF. Also, characterization of radioactive waste is possible after its change to liquid state.Analytical procedure for determination of neptunium can be divided into four main sections: 1.) dissolution of sample, 2.) purification of neptunium from interfering radionuclides and other specific substances, 3.) isolation of neptunium for measuring and 4.) measuring and analytical quantification of neptunium. The major interfering nuclides in a - spectrometry such as 234U, 230Th, 231Pa and 239,240Pu presented in samples must be considered.The large number of analytical methods is based on using of TEVA-Spec, UTEVA-Spec, TRU-Spec, Bio Rad and other sorbents. Consecutively, the column is coupled to an ICP-MS detector or the radioactivity is measured by radiometric detector. The main radiometric methods employed for the determination of 237Np are a-spectrometry, neutron activation analysis and a liquid scintillation with rejection of β and g emitters.During preparation of this poster were studied different articles but the main attention was paid to articles which described separation methods including using of TEVA-Spec resin. Preparation of proposed sorbent 50 g of silica gel dry in the oven at 105°C hydrophobisate with adding 100 ml of 3% Lukooil-H/Acetone solution (twice) dry for 20 min. in the oven at 180°C add 100 ml of 40% Aliguat-336/Benzene solution dry to the dryness at 25°C Introduction Neptunium was the first transuranium element to be discovered when in 1940 McMillan and Abelson synthesized Np-239. This nuclide can now be detected in environmental materials as a result of the atmospheric testing of nuclear weapons and the discharge of low-level aqueous radioactive wastes into the environment.[1] Interest in Np-237 determination is quite essential due to its production mode (241Pu 241Am 237Np) and long period.[2] For the characterisation of conditioned radioactive waste, the actinides to be analysed must be separated from matrix components, if possible, element-specific. The most commercially used sorbent for separation of neptunium is TEVA resin from Eichrom technologies Inc. The active component of the TEVA resin is an aliphatic quaternary amine. It has been applied on a routine basis to the analysis of the tetravalent actinides. Tetravalent neptunium show maximum uptake in the region of 2M to 4M nitric acid. The tetravalent actinides can be loaded from 3M nitric acid. Valence adjustment may be required to assure that the actinides are tetravalent.[3] Column separation of Np-237 based on Kenna (2002) [5] Different redox reagents and relevant oxidation states of neptunium [4] Redox reagent Neptunium Ammonium and iron (II) sulfate IV Sodium sulfite IV and V Hydrogen peroxide IV Sodium nitrite IV and V Ascorbic acid IV Registered alpha-spectrum Separation procedure Afterdrying muffle-ashing and homogenisation of soil sample is weighed out portion of ashed sample large enough to provide sufficient amount of neptunium nuclide for analysis. Concentrated HNO3 and HCl is added and simmer on a hotplate for several hours. Acid extract is evaporated. Another leaching mixture can contain Aqua Regia and HF. Follows the purification step. Residuum is dissolved in 0.5M Al(NO3)3 – 3M HNO3. Ferrous iron as a solution of ferrous sulphate or ferrous ammonium sulphate is added. Fe2+ reduces Np(V) to Np(IV) in room temperature. Load solution is filtered for removing any particulate material that would interfere with flow through ion exchange sorbent. Load solution is eluted through prepared sorbent. Neptunium in final solution 0.02M HNO3 – 0.02M HF is co-precipitated with NdF3 and measured using a - spectrometry. Conclusions Implementation of proposed sorbent is easy to prepare in Lab and has the same parameters as commercial TEVA sorbent as was proved in Tc separation procedure. It’s possible to separate neptunium on TEVA resin from the other radionuclides. This trend is possible to apply at proposed sorbent, because of the same structure of the active component of the TEVA resin and Aliquat-336 (aliphatic quaternary amine). References [1] Harvey B.R., Thurston L.M., Analytical procedures for the determination of neptunium radionuclides in marine waters, sediments and biota, Ministry of agriculture fisheries and food, Directorate of fisheries research, Lowestoft, 1988 [2] Baglan N.,Bouvier-Capely C., Cossonnet C., Radiochim. Acta, 2002, 90, 267-272 [3] TEVA Resin, Eichrom technologies Inc., http://www.eichrom.com/products/tech/tevaresin.cfm, 2004 [4] Perna L., Betti M., Barero Moreno J.M., Fouco R., J. Anal. At. Spectrom., 2001, 16, 26-31 [5] Kenna T.C., J. Anal. At. Spectrom., 2002, 17, 1471-1479