Extraction of Rare Earth Elements by Alkaline Hydrothermal Process

Abstract

An application of the alkaline hydrothermal process to the extraction of rare earth elements from complex ores was studied. A typical rare earth ore, bastnaesite, was reacted with NaOH solution under a high temperature and pressure to produce a mixture of rare earth hydroxides. The recovery of rare earth elements was measured as a function of temperature (373-723K) and NaOH concentration (1-5 mol/l). The results obtained were as follows;
1. The optimum conditions for this process were 523-573K and 4-5 mol/l NaOH.
2. Fluorine and silica in the are where extracted into the alkaline solution.
3. The recovery of rare earth was decreased when the temperature exceeded 573K, which was assumed to be caused by the formation of cerium and praseodymium oxides.