D. Mendeleev University of Chemical Technology of Russia, Moscow, Russia:

E. S. Kondrateva, Researcher
V. A. Kolesnikov, Professor, Rector
A. F. Gubin, Researcher, e-mail: gubin53@mail.ru
S. S. Pozdeev, Post-Graduate Student of a Chair of Electrochemical Production Technology

REM separation and obtaining of individual high-purity metals is difficult. Several flow sheets of REM separation include the methods of fractional precipitation of metal hydroxides, liquid extraction and re-extraction, sorption methods, electrolysis from melts etc. In most cases, processing of REMcontaining concentrates is started from the Ce ion separation, because its content is larger, than other element content. The process of electrochemical oxidation of Ce (III) – Ce (IV) ions in nitric acid solutions was considered for the purpose of further separation from accompanying REM. There is shown the installation diagram and procedure of the process in membrane electrolyser with platinized niobium anode. The optimal technological parameters were defined, which showed the possibility of electrochemical oxidation with anode current density of 2 A/dm², electrolyte temperature of 20 °C, free NHO₃ concentration of 10–15 g/l and a number of electrolyte exchanges in electrolyser chambers of 250 h^–1. After dissolution of industrial raw materials, consisting of REM carbonates, there were obtained the nitric acid solutions, where Ce (III) ion oxidation is quantitative with current output of 65%. There was made an assessment of consumption of electric power, required for 1 kg of cerium oxidation. There was offered the scheme of the process, making possible to keep anolyte and catholyte pH values permanent. 90% of Ce (IV) ions may be isolated from the bulk concentrate using sedimentation in metal hydroxide form.
This work was carried out with the financial support of Ministry of Science and Education of Russian Federation within the Agreement about the subsidization No. 14.574.21.0110 of October 20, 2014 (unique identifier of the Agreement is RFMEFI57414X0110).

1. Postolateva A., Tverdov A., Zhura A. Redkozemelnye mestorozhdeniya — osobennosti, slozhnosti i perspektivy (Rare earth deposits – peculiarities, difficulties and prospects). Zoloto i tekhnologii = Gold and Technologies. 2013. No. 1 (19). pp. 32–36.
2. Abreu R. D., Morais C. A. Purification of rare earth elements from monazite sulphuric acid leach liquor and the production of high-purity ceric oxide. Minerals Engineering. 2010. Vol. 23, iss. 6. pp. 536–540.
3. Morais C. A., Benedetto J. S., Ciminelli V. S. T. Recovery of Cerium by Oxidation/Hydrolysis with KMnO₄–Na₂CO₃. Hydrometallurgy 2003: proceedings of the 5^th International symposium honoring professor Ian M. Ritchie. Vancouver : TMS, 2003. pp. 1773–1782.
4. Mikhaylichenko A. I., Mikhlin E. B., Patrikeev Yu. B. Redkozemelnye metally (Rare-earth metals). Moscow : Metallurgiya, 1987. 231 p.
5. Um N., Hirato T. Precipitation of Cerium Sulfate Converted from Cerium Oxide in Sulfuric Acid Solutions and the Conversion Kinetics. Materials Transactions. 2012. Vol. 53, No. 11. pp. 1986–1991.
6. Sedneva T. A., Tikhomirova I. A. Okislenie tseriya v membrannom elektrolizere (Cerium oxidation in membrane electrolyzer). I. V. Tanaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials. Apatity, 2002. 11 p.
7. Randle T. H., Kuhn A. T. The Lead Dioxide Anode. II. The Kinetics and Participation of the Lead Dioxide Electrode in Electrochemical Oxidation Reactions in Sulfuric Acid. Australian Journal of Chemistry. 1989. Vol. 42, No. 9. pp. 1527–1545.
8. Vasudevan S., Sozhan G., Mohan S., Pushpavanam S. An electrochemical process for the separation of cerium from rare earths. Hydrometallurgy. 2006. Vol. 76. pp. 115–121.
9. Randle T. H., Kuhn A. T. The Lead Dioxide Anode. I. A Kinetic Study of the Electrolytic Oxidation of Cerium (III) and Manganese (II) in Sulfuric Acid at the Lead Dioxide Electrode. Australian Journal of Chemistry. 1989. Vol. 42, No. 2. pp. 229–242.
10. Palanisami N., Chung S. J., Moon I. S. Cerium (IV)-mediated electrochemical oxidation process for removal of polychlorinated dibenzo-pdioxins and dibenzofurans. Journal of Industrial and Engineering Chemistry. 2015. Vol. 28. pp. 28–31.
11. Ludek J., Yuezhou W., Kumagai M. Electro-Oxidation of Concentrated Ce (III) at Carbon Felt Anode in Nitric Acid Media. Journal of Rare Earths. 2006. Vol. 24, No. 3. pp. 257–263.
12. Xiong F., Zhou D., Xie Z., Chen Y. A study of the Ce³⁺/Ce⁴⁺ redox couple in sulfamic acid for redox battery application. Applied Energy. 2012. Vol. 99. pp. 291–296.
13. Pozdeev S. S., Kondrateva E. S., Gubin A. F., Kolesnikov V. A. Elektrookislenie ionov tseriya (III) v elektrolizere membrannogo tipa (Electric oxidation of cerium (III) ions in membrane electrolyzer). Uspekhi v khimii i khimicheskoy tekhnologii = Adnvances in Chemistry and Chemical Technology. 2014. Vol. XXVIII, No. 5. pp. 98–100.
14. Pozdeev S. S., Kondrateva E. S., Gubin A. F. Elektrokhimicheskoe poluchenie ionov tseriya (IV) dlya primeneniya v protsesse ochistki stochnykh vod ot organicheskikh primesey (Electrochemical obtaining of cerium (IV) ions for application during waste water purification from organic impurities). Galvanotekhnika i obrabotka poverkhnosti = Electroplating and surface processing. 2014. No. 4. pp. 37–39.