Moscow State University of Fine Chemical Technologies named after M. V. Lomonosov, Moscow, Russia:

G. V. Zimina, Senior Researcher, e-mail: gzimina@mail.ru

M. V. Tsygankova, Senior Researcher

JSC “Akron”, Veliky Novgorod, Russia:

I. I. Nikolaeva, Deputy Head of Central Chemical Laboratory
M. V. Tauk, Chief Development Officer

There are investigated the main industrial systems of rare earth elements' separation, which use organophosphorus extractants, such as tributyl phosphate (TBP), di-2-ethilgeksilphosforic acid and carboxylic acids. Rare earth elements are separated by liquid-liquid extraction with tributyl phosphate from nitric acid solutions, containing rare earth elements' nitrates. Extraction is carried out with formation of solvatation compound Ln(NO₃)₃·TBP(org). Tributyl phosphate efficiently extracts rare earth elements from weakly acidic solutions in the presence of salting-out agents (aluminum nitrate, sodium, calcium and lithium). When rare earth elements are separated for several subgroups by the process of extraction with tributyl phosphate, one should take feed solutions with HNO₃ concentration of 7–10 mole per liter for the result achievement. Finally, yttrium is concentrated in the group of heavy-weight rare earth elements (Dy–Lu). Distribution coefficients' inversion takes place for elements, included into europium – lutetium group in nitric acid solutions with HNO₃ concentration, lower than 5 mole per liter. Extraction process is typically carried out in cascade of “mixer – settler” extractors, using full counter-current with the total number of cascade stages of 50–90. In the beginning of full counter-current separation, rare earth elements are derived into following subgroups: light-weight (La, Ce, Pr, Nd), middle- weight (Sm, Eu, Gd, Tb) and heavy- weight (Dy–Lu + Y), carrying out the division of elements into each subgroup. A cascade, including cycling treatment with aqua solution, is also used for separation of (Nd–Sm) binary mixtures, which allows to obtain pure fine product and to diminish the quantity of both treatment solution and the extractant. This article describes various schemes of complete rare earth elements' separation from sulfuric acid solutions, using di-2-ethilgeksilphosforic acid as an extractant, namely both separation of elements, belonging to cerium subgroup, and realization of processing of phosphate minerals, containing rare earth elements. There is shown the advantage of oleic acid, compared with tributyl phosphate applying to complex processing of low concentration crude materials.

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