National Research Nuclear University MEPhI

A. V. Valkov, Professor

V. V. Sergievskiy, Professor of a Chair of General Chemistry, e-mail: ale1534@yandex.ru

D. Mendeleev University of Chemical Technology of Russia

S. I. Stepanov, Professor

A. M. Chekmarev, Professor, Head of a Chair “Technology of a Rare, Scattered Elements and Nanotechnologies”

The results of alkaline leaching of Krasnoufimsryi’s monazite by concentrated KOH solutions are presented. Monazite is crushed about 0.05–0.1 mm size, is mixed with 350–400 g/l KOH solution under relation monazite : KOH = 1:1.2(1.5) and is heated and agitated under 110–115 ^oС during 2–4 hours. The pulp is diluted in 2 times with water and hydroxides of Th, U, Ln are precipitated and filtrated. The filtrate is evaporated by 3–4 times, is cooled down 20–25 ^oС and K₃PO₄ crystals are separated. The residue is washed by nitric acid under pH 3.5–4.5 and than solution of Ln(NO₃)₃ is filtrated. From contained solution after deactivation the carbonate of REE is precipitated by K₂CO₃. The residual nitrate solution of KNO₃ is used for fertilizers production. From residual cake uranium is leached by K₂CO₃ solution as complex K₄[UO₂(CO₃)₃]. From solution uranium is recovered as ammonium polyuranate. From cake contained Th, crude monazite and waste rock are leached by 50% excess of nitric aced up to all Th and residual lanthanide hydroxides are passed into the solution. This solution is separated from cake by filtration and This precipitated from it by K₂CO₃. The Thorium carbonate than is converted into ThO₂. The residue is crushed; waste rock is separated and recycled in to alkaline leaching. The concentrate of REE is dissolved in nitric acid and than Ln are separated using solvent extraction with 100% TBP. At the first stage Cerium is recovered as Ce(+4) from solution using electrochemical process. The residual REE are separated by solvent extraction using cascades, contained 70—80 stages. Three products: Lanthanum and Cerium concentrates for polishing paste, Samarium, Gadolinium and Yttrium concentrate which used for recovery Samarium for Sm magnets and Gadolinium for fuel elements and Neodymium — Praseodymium concentrate for Nd—Fe—B magnets are obtained.

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6. Patent 323989 RF, MPK C 01 F 17/00. Sposob pererabotki monatsita (The way of the monazite processing). Valkov A. V., Stepanov S. I., Sergievskiy V. V., Chekmarev A. M. Published 17.05.2005.

7. Patent 2151206 RF, MPK C 01 F 17/00. Sposob pererabotki monatsitovogo kontsentrata (The way of the monazite concentrate processing). Lebedev V. N., Lokshin E. P. Published 28.06.1999.

8. Patent 2331681 RF, MPK C 01 V 59/00. Sposob razlozheniya monatsita (The way of the monazite decomposition). Nizov V. A. et al. Published 30.04.2004.