HYDROMETALLURGY PROCESS ON RADIOACTIVE AND RARE EARTH ELEMENTS EXTRACTION FROM MONAZITE IN INDONESIA

摘要

Monazite, one of the minerals in the tailings from tin mining activities, contains valuable and strategic elements, such as Rare Earth Elements (REEs), uranium, and thorium. BATAN has developed extraction methods for those elements. The process stages consist of milling, alkaline leaching, selective dissolution, and multistage precipitation. As required for the alkaline leaching stage, milling is aimed to obtain monazite in the fine particle size of-325 mesh. The alkaline leaching uses sodium hydroxide to dissolve phosphate, and convert monazite from phosphate compounds into hydroxides. Leaching residue is reacted with hydrochloric acid at a certain pH condition and temperature to dissolve REEs selectively. The solution obtained from the selective dissolution stage is reacted with ammonium hydroxide to precipitate REEs and U/Th based on the difference of the precipitation pH.The products obtained are sodium tri-phosphate, REEs hydroxides, and uranium-thorium hydroxides concentrate. The process technology has already been brought to pilot scale with 50 kg monazite per batch of capacity in 2016. In 2017, the pilot plant was operated on as many as 14 batches with products averaging 15 kg of REEs hydroxide per batch, with uranium and thorium contents 8 ppm and 484 ppm, respectively. In 2018, the pilot plant operated on as many as 9 batches with product quality better than 2017, namely a thorium content in REEs hydroxide of 16.5 ppm and no uranium content. Besides REEs hydroxide, the pilot plant also produces uranium-thorium hydroxides concentrate which is ready for a purification process using solvent extraction.