Institute of Chemistry and Chemical Technology, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk, Russia:

S. N. Kalyakin, Senior Researcher, Candidate of Chemical Sciences
V. I. Kuzmin, Chief Researcher, Doctor of Chemical Sciences
M. A. Mulagaleyeva, Junior Researcher, e-mail: maral7508@mail.ru

The use of binary extractants (BE) in schemes of countercurrent extraction cascades designed for the separation of rare earth metals (REMs) has been studied. It has been shown that the main difference between the use of BE and cation-exchange extracts (CE) is the possibility of using deionized water in the re-extraction cascades, rather than solutions of mineral acids. When optimizing the REM separation scheme, a mathematical model was used to dynamically calculate the distribution of separated metals over the stages of counterflow extraction cascades. The modeling of cascades was carried out on the basis of the physicochemical description previously obtained by the authors of the processes of extraction of REM nitrates with various BE compositions prepared on the basis of industrial cation- and anion-exchange extractants. Calculation of the balance of lanthanides during successive separation by stages of cascades was performed for the initial mixture of REM nitrates with the ratio of elements corresponding to the composition of the ore of the Chuktukonskoe rare metal deposit. A scheme of cascades is proposed for isolating in pure form the five REMs of light and light/medium groups (Pr, Nd, Sm, Eu, Gd) most demanded by the industry, concentrate of La, Ce, and concentrate of REM of medium/heavy and heavy groups. The scheme includes 10 countercurrent extraction cascades with a total number of extraction stages of 390. The scheme uses BE based on di-(2-ethylhexyl)phosphoric acid, synthetic fatty acids, tri-n-octylamine, and an industrial diluent. For the proposed scheme, mineral acid is used only at the stage of obtaining REM nitrates from the initial oxides; 1.8 kg (65%) of nitric acid is consumed per 1 kg of REM oxides. For the precipitation of REM carbonates from re-extracts, the consumption of sodium carbonate is approximately 1 kg per 1 kg of the initial REM oxides. The use of BE in comparison with CE makes it possible to significantly reduce the consumption of mineral acids and bases during the separation and production of individual REMs.

The work was carried out within the framework of the state task of the Institute of Chemistry and Chemical Technology of the Siberian Branch of the Russian Academy of Sciences (project 0287-2021-0014) using the equipment of the Kranoyarsk Regional Center for Collective Use of the Federal Research Center of the KSC of the Siberian Branch of the Russian Academy of Sciences.

1. Xie F., Zhang T. A., Dreisinger D., Doyle F. A critical review on solvent extraction of rare earths from aqueous solutions. Minerals Engineering. 2014. Vol. 56. pp. 10–28.
2. Liao C., Wu S., Cheng F., Wang S., Liu Y., Zhang B., Yan C. Clean separation technologies of rare earth resources in China. Rare Earths. 2013. Vol. 31, No. 4. pp. 331–336.
3. Belova V. V. Trends in the development of extraction processes for the extraction and separation of rare earth metals. Khimicheskaya tekhnologiya. 2016. Vol. 17, No. 5. pp. 228–240.
4. Kalyakin S. N., Kuzmin V. I., Mulagaleeva M. A. Binary extraction of neodymium nitrate using 2-ethylhexylphosphonic acid 2-ethylhexyl mono ester and tri-n-octylamine. Journal of Molecular Liquids. 2019. Vol. 273. pp. 45–49.

5. Belova V. V. Trends in the use of ionic liquids and binary extractants in the extraction and separation of lanthanides and actinides. Radiokhimiya. 2021. Vol. 63, No. 1. pp. 3–12.
6. Belova V. V., Tsareva Yu. V. Extraction of lanthanide chlorides in waterorganic two-phase systems with salts of tertiary and secondary amines. Khimicheskaya tekhnologiya. 2019. Vol. 20, No. 10. pp. 469–474.
7. Liu Y., Lee M., Senanayake G. Potential connections between the interaction and extraction performance of mixed extractant systems: a short review. Journal of Molecular Liquids. 2018. Vol. 268. pp. 667–676.
8. Belova V. V., Tsareva Yu. V. Interphase distribution of lanthanide nitrates in aqueous organic two-phase systems with amine and organic acid salts. Theoretical Foundations of Chemical Engineering. 2020. Vol. 54, No. 4. pp. 769–774.
9. Belova V. V., Petyaeva M. M., Tsareva J. V., Kostanyan A. E. Solvent extraction of lanthanides (III) from chloride and nitrate media with di(2-ethylhexyl) phosphoric acid and ionic liquids in three-component biphasic solvent systems. Hydrometallurgy. 2021. Vol. 199. Article 105526.
10. Kholkin А. I., Kuzmin V. I., Pashkov G. L. Binary extraction and prospects for its application. Izvestiya Sibirskogo otdeleniya AN SSSR. Seriya khimicheskikh nauk. 1990. No. 5. pp. 3–17.
11. Serdyuk S. S., Lomayev V. G., Kuzmin V. I., Flett D. S., Gudkova N. V. et al. The Chuktukon niobium-rare earth metals deposit: Geology and investigation into the processing options of the ores. Minerals Engineering. 2017. Vol. 113. pp. 8–14.
12. Singh D. K., Singh H., Mathur J. N. Extraction of rare earths and yttrium with high molecular weight carboxylic acids. Hydrometallurgy. 2006. Vol. 81. pp. 174–181.
13. Basualto C., Valenzuela F., Molina L., Munoz J. P. et al. Study of the solvent extraction of the lighter lanthanide metal ions by means of organophosphorus extractants. Journal. Chil. Chem. Soc. 2013. Vol. 58. pp. 1785–1789.
14. Kholkin А. I., Kuzmin V. I. Binary extraction. Zhurnal neorganicheskoy khimii. 1982. Vol. 27, No. 2. pp. 2070–2074.
15. Sahoo A., Swain J., Bhatta B. C. Extraction of La (III) from nitric acid using tri-octyl amine in kerosene. Journal of Applied Chemistry. 2017. Vol. 10, No. 10. pp. 52–58.
16. Korobeinikov A. I., Kalyakin S. N. Optimization of the technology of extraction-based separation of rare earth and transplutonium elements using a new numerical method for calculating chemical equilibria. Chemistry for Sustainable Development. 2021. Vol. 29, No 3. pp. 325–332.
17. Zimina G. V., Nikolaeva I. I., Tauk М. V., Tsygankova М. V. Extraction schemes of rare earth metal`s separation. Tsvetnye Metally. 2015. No. 4. pp. 23–27.
18. Setyadji M., Purwani M. V. Solvent Selection for Extraction of Neodymium Concentrates of Monazite Sand Processed Product. Journal of Physics: Conference Series. 2018. Vol. 962. Article 012062.