I. V. Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials (Kola Science Center RAS), Apatity, Russia:

N. V. Mudruk, Junior Researcher, e-mail: kirnat@chemy.kolasc.net.ru
Yu. V. Korovina, Engineer
I. R. Elizarova, Senior Researcher
A. I. Nikolaev, Deputy Director, Head of Laboratory of Chemistry and Technology of Raw Materials of Refractory Rare Metals

We investigated the composition of solution, obtained during nitric-acid decomposition of perovskite concentrate. The solution was evaporated for increasing of its salt mass concentration. The solution stability is saved and 50–60% (vol.) of nitric acid are removed during the solution evaporation in gas-vapor phase from the system. Several ways of calcium nitrate sedimentation from evaporated solutions (including neutralization and freezing) were investigated. The obtained results show the partial sedimentation of calcium nitrate and rare-earth metal hydroxides during the solution neutralization up to pH = 8–10. Valuable components are lost together with rare-earth metals during the freezing of calcium nitrate from product. This loss is explained by a large mass of the formed salt, welldissoluble in water. We can not recommend these methods for purification of nitric acid solutions from calcium nitrate, because valuable components (rare-earth metals) are lost. At the same time, our work includes the investigations for purification of the solution with large salt mass from iron and thorium by calcium nitrate with iron-thorium cake sedimentation by lime milk. The sedimentation was carried out to the fixed pH = 4.7–5.0, which allowed the optimization of the composition of nitric-acid solution for the further extraction of rare-earth metals from it by liquid extraction. At the same time, there are no significant losses, and the investigated solutions are deactivated as a result of iron-thorium cake sedimentation. The obtained results allowed the choice of the condition of iron-thorium cake sedimentation from solutions from the perovskite processing (CaO concentration in lime milk, method of addition of lime milk, pH sedimentation), when iron and thorium are completely transferred in sediment, and co-sedimentation of rare earth metals is minimal.

1. Nikolaev A. I., Gerasimova L. G., Petrov V. B., Mayorov V. G. Perovskite concentrate — as a source for titanium and rare-metal products. Kompleksnoe ispolzovanie mineralnogo syrya. 2015. No. 2. pp. 26–34.
2. Nikolaev A. I., Kalinnikov V. T. By-product manufacturing of rare-earth metals during the processing of perovskite concentrate of the Afrikanda deposit. Tsvetnye Metally. 2013. No. 3. pp. 58–63.
3. Kalashnikov A. O., Konopleva N. G., Pakhomovsky Ya. A., Ivanyuk G. Yu. Rare Earth Deposits of the Murmansk Region, Russia — A Review. Economic Geology. 2016. Vol. 111. pp. 1529–1559.
4. Crane S. R., Davidson C. F., Narbuck D. D. Titanium metal production from perovskite using a sulfate-fluoride system. Light Metals. Warrendale (PA) : TMS, 1989. pp. 991–998.
5. Shirts M. B., Martin D. A., Petersen A. E. Recovery of titanium from perovskite by acid sulfation. Patent US 4562049. Filed: 20.09.1984. Published: 31.12.1985.
6. Krysenko G. F., Epov D. G., Medkov M. A., Sitnik P. V. Development of perovskite concentrate by ammonium hydrofluoride. Khimicheskaya tekhnologiya. 2015. Vol. 16, No. 4. pp. 219–223.
7. Bogatyreva E. V., Kuchina I. Yu., Ermilov A. G. Method of opening of perovskite concentrates. Patent RF, No. 2525025. Applied: 20.06.2013. Published: 10.08.2014. Bulletin No. 22.
8. Kalinkin A. M. The Kinetics of Sorption of CO₂ by Perovskite CaTiO₃ and the Degree of Perovskite Decomposition with Nitric Acid after Its Mechanical Activation. Zhurnal fizicheskoy khimii. 2008. Vol. 82, No. 3. pp. 401–404.
9. Linkevich E. G., Sokolov S. V. Perovskite behavior during hydrometallurgical production stage. Technological mineralogy of natural and technogenic deposits : collection of proceedings of the IX Russian seminar on technological mineralogy. Magnitogorsk, 22–24 April 2014. Petrozavodsk : KarNTs RAN, 2015. 171 p.
10. Gerasimova L. G., Nikolaev A. I, Petrov V. B., Bychenya Yu. G. Nitric acid decomposition of perovskite with fluor-bearing agent. Tsvetnye Metally. 2017. No. 5. pp. 50–53.
11. Sanitary Rules and Regulations SanPiN 2.6.1.2800–10. Hygienic requirements on limitating the inhabitants radiation by the sources of ionizing irradiation. Introduced: 24.12.2010.
12. Sanitary Rules SP 2.6.1.2612–10. Basic sanitary rules of the provision of radiation safety (OSPORB 99/2010). Moscow : Federalnyy tsentr gigieny i epidemiologii Rospotrebnadzora, 2010. 83 p.
13. Sanitary Rules SP 2.6.1.798–99. Treatment of mineral raw materials and materials with increased content of natural radionuclides. Moscow : Minzdrav Rossii, 2000. 16 p.
14. Pozin M. E. Technology of mineral salts (fertilizers, pesticides, industrial salts, oxides and acids). Part 1. Forth edition. Leningrad : Khimiya, 1974. 768 p.
15. Binnemans K., Jones P. T., Blanpain B. et al. Recycling of rare earths: a critical review. Journal of Cleaner Production. 2013. Vol. 51.
16. Lebedev V. N., Masloboev V. A., Sergeeva S. D., Rudenko A. V. Processing of solutions of nitric acid leaching of loparite. Apatity : Izdatelstvo KNTs RAN, 1997. 104 p.