VNIIKhT JSC, Moscow, Russia:

Yu. M. Trubakov, Head of the Department of Comprehensive Processing of Rare Metal Materials
V. D. Kosynkin, Principal Researcher at the Laboratory of Rare, Rare Earth and Radioactive Elements, Doctor of Technical Sciences, Professor

National University of Science and Technology MISiS, Moscow, Russia:
O. N. Krivolapova, Associate Professor at the Department of Non-Ferrous Metals and Gold, Candidate of Technical Sciences, e-mail: onk@misis.ru

This paper describes three process flows designed for monazite concentrate: two of them are based on pressure alkaline leaching (full cycle and short cycle) and were developed by VNIIKhT JSC under the contracts with Rosatom; and one is based on sulphuric acid leaching and was developed by Frontier from South Africa. The pressure alkaline leaching process involves prior separation of thorium concentrate, which also contains uranium. The choice of the process is dictated by the concentration of rare earth metals (REM), thorium and uranium in the monazite concentrate. If the concentration of thorium in the monazite concentrate does not exceed 0.2%, the sulphuric acid process, in which the radioactive thorium and uranium are not extracted and the product includes REM concentrate, would be well applicable. If the concentration of thorium is quite high, one should apply the full-cycle pressure alkaline leaching process as it allows to concentrate radioactive metals due to prior separation of uranium and thorium. A major advantage of using the full-cycle pressure leaching process versus the sulphuric acid process is in a minimized amount of radioactive and hazardous waste that is to be buried. The proposed process uses a combination of sorption and extraction techniques which help lessen the amount of radioactive waste due to prior separation of thorium and uranium. The presence of heavy REMs, such as neodymium, praseodymium, terbium, and dysprosium, adds to the feasibility of processing monazite concentrates with high concentrations of thorium and uranium. The recovered REMs (i. e. neodymium, praseodymium, terbium, and dysprosium) can be used to produce hard materials and assemblies with them designed for innovative products, including those for medical use (e. g. CT scanners).

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