The Effect of Diluents on Extraction of Actinides and Lanthanides
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The Effect of Diluents on Extraction of Actinides and Lanthanides Teodora Valeria Retegan, Christian Ekberg, Anna Fermvik, and Gunnar Skarnemark Nuclear Chemistry, Chalmers University of Technology, Kemivagen no. 4, Gothenburg, 412 96, Sweden ABSTRACT A screening experiment was carried out, where the organic phase consisted of different concentration of 2,6-bis-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]triazy-3-yl)[2,2’]bipyridinyl or CyMe4-BTBP [1],which is the extracting molecule, dissolved in different diluents. The aqueous phase consisted of 0.01 M HNO3 and was spiked with trace amounts of 241Am and 152 Eu. The ionic strength was kept constant at 1.0 M using NaNO3. Three of the selected diluents used to dissolve CyMe4-BTBP were abandoned: n-hexane, TPH and TBB. Another extraction experiment screened out anisole, 1,1,2,2-tetrachloroethane and benzaldehyde. A kinetic experiment was then performed. In three different organic systems, three very different kinetic behaviors were observed. For a proper understanding of the kinetic mechanism, further investigations are needed. INTRODUCTION The need for a sustainable use of the nuclear power and long time storage of the waste leads to a series of improvements of the reprocessing of the waste. When trying to design a larger scale separation system based on solvent extraction, using novel extraction agents, a clear procedure for selection of e.g. organic diluent must be made. Typically a simple dissolution test screens out the totally unsuitable diluents. Then extraction and extraction kinetic experiments are performed to find the optimal diluent. As mentioned above, the selection of the diluents is an important factor for a scale up project and this study will present screening experiments performed in this direction. A series of diluents previously used for screening experiments were chosen [2] including long chain alcohols. Some new and more “exotic” diluents were added, for the desire of introducing less harmful substances into the systems: p-anisaldehyde, cinnamaldehyde, linalool. A dissolution test was performed, which in the first stage screened out the solvents which were not dissolving the molecule. Extraction tests were made with diluents mainly following the CHON principle [3] (containing only carbon, hydrogen, oxygen, nitrogen), which is preferred because then the molecules are completely incinerable and thus not producing secondary wastes. However, some diluents not following this principle were also included. The reason of using these diluents was that in case of a higher performance from the e.g. 1,1,2,2-tetrachloroethane, there will be a comparison base to rely on for further search of a less polluting diluent, but with similar properties and performance as the one mentioned before. A kinetic experiment was also conducted, but only the most interesting results are presented here. For a scale up of a system, the kinetics is a very important issue when selecting the appropriate contactor (pulse columns, mixer-settlers, counter current
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