National Research Nuclear University MEPhI (NRNU MEPhI), Chair for General Chemistry, Moscow, Russia:

A.V. Valkov, Professor, Doctor of Technical Sciences, e-mail: ale11534@yandex.ru
E. A. Ananyeva, Associate Professor, Candidate of Chemical Sciences
V. V. Sergievsky, Professor, Doctor of Chemical Sciences

The generally accepted method for extracting the required element from a mixture of rare earth elements (REE) is to use two cascades, with elements with a higher ordinal number being separated in one cascade, and those with a lower ordinal number in the second cascade (or vice versa). The features of the extraction and separation of rare-earth and associated elements in ores (actinium, yttrium) by extraction with mixtures of cation-exchange and anion-exchange extractants are considered. For the indicated extractants, the dependences of the REE distribution coefficients on the atomic number are opposite. Therefore, a change in the composition of mixtures of these extractants makes it possible to regulate their extraction ability and selectivity of the extraction of elements in a wide range. It is shown that the selection of the composition of the mixtures makes it possible to create conditions under which the required element is extracted worse than the others, and it can be isolated in a single-stage extraction process. In this case, the greater the separation coefficients of neighboring REEs during extraction with each of the extractants, the higher the separation selectivity. For the successful isolation of the required element from a mixture of lanthanides within the framework of one extraction cascade, the separation coefficients between neighboring elements during extraction with individual extractants must be at least 3.0. For some elements (yttrium, actinium), there is a shift in the position of an element in the REE series in terms of distribution co efficients, which consists in the fact that during extraction with one extractant, the distribution coefficient of this element is closer to lanthanum, and with the other extractant, closer to lutetium. It is shown that in this case it becomes possible to separate such an element (for example, yttrium) within one cascade, and the separation coefficients between neighboring elements can be much lower. The separation selectivity increases with the shift of the selected element in the series of lanthanides (according to the distribution coefficients): the greater the shift of the isolated element, the higher the separation factor of the isolated element from the rest of the REEs. Using one extraction cascade instead of two significantly reduces production costs.

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