Rare earth metal phosphates recovery - from solns. obtd. by dissolving calcium phosphate ores in nitric acid

摘要

A concentrate of rare earth metal phosphates is produced by dissolving a crude phosphate in HNO3, removing a substantial part of Ca2+ ions in the form of crystalline Ca(NO3)2.4H2O, and another part of Ca2+ ions by pptn. with sulphate ions, and partly neutralising the soln. with ammonia. The sulphate ions are used in an amt. determined by means of a calibration curve based on the fluoride content of the soln. The rare earth metal phosphates are pptd. by addn. of water-free ammonia and sepd. by filtration; both operations are carried out rapidly (within 15 mins) whereby the filtering props of the ppte. are improved. The process can be carried out continuously.