Decomposition of rare earth containing ores by alkaline hydrothermal process

Xenotime, monazite and ion exchange ores were reacted with NaOH solution in the micro-autoclave under high temperature and pressure to produce a mixture of rare earth hydroxides. The decomposition reaction of phosphate ores such as xenotime and monazite required higher temperature and NaOH concentration than those for the decomposition of carbonatite ore, bastnaesite. The recovery of phosphate from the ores was limited by the solubility of Na₃PO₄ in the NaOH solution. The recovery of yittrium was decreased with the increase in the reaction temperature because the equilibrium phase changed from Y(OH)₃ to YOOH above 610K, which was determined by the experiment.