GB674400A - Treatment of monazite - Google Patents

Abstract

Ground monazite is attacked by, say 55-70 per cent, caustic soda solution near the boiling point, and the reaction mixture is diluted at above 55 DEG C, with water or a mother liquor from a subsequent operation to produce a solution of sodium phosphate, which is crystallized, and insoluble thorium, uranium and rare earth hydroxides which are subsequently separated. For the separation, the hydroxides are washed with dilute caustic soda solution-the wash liquor being used in the dilution operation -to reduce the P2O5 content to less than 1 per cent by weight of the hydroxides, and treated by hydrochloric, nitric or sulphuric acid to effect separation of the rare earths from the uranium and thorium. The acid treatment comprises (a) complete dissolution followed by neutralization with rare earth carbonates to pH about 4 to precipitate thorium, or (b) addition of acid to pH about 3.2 to dissolve the rare earths leaving the thorium and uranium insoluble. During the acid extraction, iron is oxidized. The rare earth chloride, say, solution may be evaporated to dryness, or the carbonates precipitated by sodium carbonate. The thorium concentrate may be dissolved in hydrochloric or nitric acid, and thorium sulphate then precipitated by sulphuric acid. The mother liquor is treated with potassium sulphate to precipitate the remainder of the thorium as thorium-potassium sulphate, and residual rare earths. The double salt is attacked by caustic soda, and the hydroxides returned to the acid treatment stage, (a) or (b) above. The mother liquor containing uranium is treated with sodium carbonate, and the uranium precipitated by caustic soda. The caustic soda mother liquor from the crystallization of the sodium phosphate may be used in the dilution operation, or may be concentrated for reuse in the attack on the monaazite.