Method for the preparation of mixed rare earth metal carbonates from monazite

A process for the preparation of mixed rare earth metal carbonate from monazite, said process comprising:

• (a) submitting particles of monazite to a leaching step with an aqueous solution of alkaline hydroxide, thus obtaining a mixture of:
• a liquid fraction A comprising trisodium phosphate and
• a solid B comprising mixed hydroxide salts of the metals comprised in monazite;
• (b) separating the solid B from the solution A, preferably by filtration;
• (c) a leaching step of the solid B comprising:
• (c-1) a first leaching step of the solid B with a hydrochloric acid aqueous solution, feeding said hydrochloric acid aqueous solution so as the resulting mixture has a pH between 1 and 2.5;
• (c-2) a second leaching step following the first leaching step (c-1) where the pH is adjusted to a value of between 3.2 and 4 by adding an alkaline hydroxide;
• thus obtaining a mixture of:
• a solid fraction C comprising hydroxide salts of thorium and uranium, and
• a liquid fraction D comprising rare earth metal chloride salts;
• and
• (d) separating the solid C from the liquid fraction D, preferably by filtration.