Radiochemical Technology for Production of Preparations of Technetium - 99m on Extraction Centrifugal Semi-Countercurrent Generator

Abstract

radionuclides, used in medicine as well as in the other fields of science and technology. Mostly, these are elements with different valence state for which selective, well studied and available extraction systems can be found, so that the separation coefficients in those systems are higher than 100. In our opinion, the extraction semi-countercurrent separation method is most suitable for the practical solution of such problems. The essence of this method is that one of the phases (for example, aqueous) is kept in one or several stages not communicating in this phase, while the organic phase (extractant), passes successively through all stages, extracting the extractable components of the mixture of elements in decreasing order of values of the distribution coefficients. The process can also, if necessary, be carried out in inversed form, when the organic phase is stationary and the selective extraction process is carried out by an aqueous solution.The classical semi-countercurrent process and its calculations are well known [1,2]. The semi-counter current extraction process of separation of elements in a dynamic mode was first described in 1951 [3].The main feature of semi-countercurrent separation method is the fact that, if the initial mixture of the components is in the aqueous phase, than the less extractable component can be obtained with any purity level, but the yield continuously decreases. At the same time, the more extracted component has a maximum of the concentration rate equal to the value of the separation coefficient at the beginning of the extraction process.In semi-counter current extractors of the mixer-settler types with gravitational phase separation were used [1][2][3]. The main disadvantages of such devices are high retention volume of the mobile phase, low efficiency and productivity, as well as the possibility of entrainment of the emulsion.Semi-countercurrent processes are used in the separation of similar components in Craig apparatuses, but they are of little use for radiochemical purposes for many reasons: low stratification rate, complex and cumbersome construction, long time needed to achieve equilibrium when the process of mixing is simple wiggle.One of the first papers describing the use of centrifugal semi-countercurrent extractors for the separation of multi-component mixtures requiring a large number of stages was published in 1974 by GV Korpusov et al., [4]. The centrifugal extractor considered is not intended to be used for obtaining individual radionuclide's, since in this case the requirements for the purity of the product are much more stringent at a high recovery rate [4].Considering the need to implement the process of isolation of short-lived isotopes in a short period of time, semi-counter flow extractors with forced phase separation in a centrifugal field were developed. The use of such apparatuses makes it possible to shorten the time of the process and increase the purity of the products, since in this case intensive mixing is acceptable (equilibrium in the extracti...