PROCESS FOR OBTAINING FLUORINE COMPOUNDS FROM DIGESTION SOLUTIONS OF CRUDE PHOSPHATES WITH NITRIC ACID OR HYDROCHLORIC ACID

摘要

1,145,022. Calcium fluorosilicate; phosphoric acid; alkali metal fluorosilicate; HF; SiF 4 . FARBWERKE HOECHST A.G. 25 Feb., 1966 [27 Feb., 1965], No. 8434/66. Heading C1A. The fluorine values in crude phosphate rock are obtained as calcium fluorosilicate by digesting the crude phosphate with aqueous nitric or hydrochloric acid and in a concentration such that the resulting digestion solution contains, when nitric acid is used, 20-40% of water or when hydrochloric acid is used, 40-60% of water, said water percentages being calculated on the total weight of aqueous acid and crude phosphate and separating hydrated calcium fluoro-silicate (CaSiF 6 .2H 2 O) from the undissolved matter obtained from the digestion solution. Preferred ranges of water content calculated on the above basis are 28-32% for HNO 3 and 45 to 50% for HCl. The nitrated digestion solution is preferably cooled to a temperature in the range 0‹ to 10‹ C. and the undissolved CaSiF 6 and CaF 2 separated from the larger crystals of Ca(NO 3 ) 2 .4H 2 O. The separation may be achieved using a sedimentation or a solid jacket centrifuge. The insoluble fluorosilicate obtained may be treated with dil. acid, filtered and alkali metal fluorosilicate obtained by the addition of an alkali metal salt to the filtrate. The residue from the filtration may be distilled with H 2 SO 4 to give HF and SiF 4 .