National University of Science and Technology MISIS, Moscow, Russia

Е. V. Bogatyreva, Professor of the Department of Non-ferrous Metals and Gold, Doctor of Technical Sciences, e-mail: Нelen_Вogatureva@mail.ru
F. Мelnik, Postgraduate Student of the Department of Non-ferrous Metals and Gold

Based on thermodynamic studies, the compositions of solutions of the (NH₄)₂CO₃ – NH₄HCO₃ – H₂O system precipitator at t = 20 ^oC have been calculated, the dependences of their composition on pH have been determined, and a technological solution for the organization of the process of neodymium carbonate precipitation from nitric acid solutions (supply of a nitric acid solution of neodymium into a solution of carbon ammonium salts to obtain easily filterable pulps) has been substantiated. Comprehensive studies using mathematical experimental planning have confirmed the effectiveness of the solution. Neodymium carbonate pulps with a specific filtration rate of more than 1 m³/(m²·h) are suitable for filtration on high-performance continuous drum filters. Mathematical modeling of the precipitation process has been performed and the regression equation of the specific pulp filtration rate has been calculated as a function of the process temperature (32.5±7.5 ^oC), the proportion of ammonium bicarbonate in a mixture of carbon ammonium salts used to prepare a 20 % solution of the precipitator (0.5± 0.5, in fractions of 1) and the duration of the deposition process (30±10 min). The conditions for achieving an acceptable result for production (a specific pulp filtration rate of more than 1.6 m³/(m²·h)) have been determined: a temperature of 40 oC, a minimum content of ammonium bicarbonate in a mixture of carbon ammonium salts of no more than 25% used to prepare a 20% solution of the precipitator and the duration of 20–40 minutes. The effect of ammonium bicarbonate content on the morphology of neodymium carbonate precipitation has been established. A method for obtaining easily filtered neodymium carbonate precipitates from nitric acid solutions with concentrations of 40–263 g/l Nd₂O₃ and 4–30 g/l HNO₃ by precipitation with 20 % solutions of carbon ammonium salts has been developed. This method provides a reduction of wastewater volume by 1.5–2.0 times and an increase of neodymium carbonate productivity by 2–5 times due to the use of Nd₂O₃ concentrated solutions.

1. On approval of the goals and main directions of sustainable (including green) development of the Russian Federation, Decree of the Government of the Russian Federation No. 1912-р of July 14, 2021. Available at: https://www.garant.ru/products/ipo/prime/doc/401409630/#0 (accessed: 20.12.2025).
2. State report on the state and use of mineral resources of the Russian Federation in 2023. Moscow : FBSI VIMS, 2024. 716 p.
3. Qi D. Method hydrometallurgy of rare earths separation and extraction. Chapter 7. Chemical Separation. 2018. pp. 671–741.
4. Mikhailichenko А. I., Мikhlin Е. B., Patrikeev Yu. B. Rare earth metals. Мoscow : Metallurgiia, 1987. 232 p.
5. Komissarova L. N., Shatsky V. М., Pushkina G. Ya. et al. Compounds of rare earth elements. Carbonates, oxalates, nitrates, titanates. Moscow : Nauka, 1984. 235 p.
6. Kaczmarek A. M., Van Heckeb K., Van R. Deun Nano- and micro-sized rare-earth carbonates and their use as precursors and sacrificial templates for the synthesis of new innovative materials. Chem. Soc. Rev. 2015. Vol. 4. pp. 2032–2059.
7. Polyakov Е. G., Nechaev А. V., Smirnov А. V. Metallurgy of rare earth metals : study guide for universities. 2nd Ed. Moscow : Izd-vo Yurait, 2021. 501 p.
8. Liu S., Ma R. Preparation of crystalline precipitation of mixed rare earth carbonates. Chin. J. Nonferrous Met. (in Chinese). 1998. Vol. 8, Iss. 2. pp. 331–334.
9. Cui Zh., Guo J., Wang D., Cao J., Wang. Zh. Stability of amorphous neodymium carbonate and morphology control of neodymium carbonate in non-hydrothermal synthesis. Journal of Crystal Growth. 2022. Vol. 579. 126460.
10. Vallina B., Rodriguez-Blanco J. D., Brown A. P., Blanco J. A., Benning L. G. The role of amorphous precursors in the crystallization of La and Nd carbonates. Nanoscale. 2015. Vol. 7. pp. 12166–12179.
11. Shtutsa M. G., Kardapolov A.V., Filippov V. B., Sysina N. A. Studying the process of precipitation of REE carbonates. Izvestiya Tomskogo politekhnicheskogo universiteta. 2003. Vol. 306, No. 5. pp. 71–74.
12. V. O. Gerya, B. A. Bydanov, A.V. Aldushkin et al. Method of obtaining carbonates of rare earth elements. Patent RF, No. 2693176. Registered: 01.07.2019. Applied: 28.12.2018.
13. Nechaev A.V., Polyakov E. G. On the concept of development of the Russian raw materials base of the REM. Mineralnye resursy Rossii. Ekonomika i upravlenie. 2025. No. 2. pp. 48–57.
14. Lidin R. A., Molochko V. A., Andreeva L. L. Inorganic chemistry in reactions: a reference book. Moscow : Drofa, 2007. 640 p.
15. Lidin R. A., Andreeva L. L., Molochko V. A. Constants of inorganic substances: a reference book. Moscow : Drofa, 2008. 685 p.
16. Belan F. I. Water treatment: (calculations, examples, tasks). Moscow : Energia, 1980. 256 p.
17. Tretyakov Yu. D., Martynenko L. I., Grigoriev A. N., Tsivadze A. Y. Inorganic chemistry. Chemistry of the elements. Iss. 2. Moscow : Khimiia, 2001. 583 p.
18. E. V. Bogatyreva, F. Melnik, A. G. Ermilov, A. A. Semenov et al. Method of obtaining carbonates of rare earth elements. Patent RF, No. 2729573. Applied: 30.12.2019. Published: 07.08.2020.