Patent ID: 11873229
Assignee: OCP SA
Field: Materials, metallurgy (Chemistry)
Classification: CPC C  B | IPC B  C

Claim 8:
9. A process for preparing synthetic calcium fluoride (CaF2) from fluosilicic acid, comprising the following steps:
(a) reacting fluosilic acid (H2SiF6) with ammonium hydroxide or ammonia in a first reactor so as to obtain a first slurry; filtering said first slurry so as to obtain a filtrate containing a solution of ammonium fluoride;
reacting ammonium fluoride from the solution of ammoonium fluoride obtained as a filtrate in step (a) with calcium carbonate (CaCO3) as a dry form or as a suspension at a concentration ranging from 10 to 80% by weight in a second reactor so as to produce a second slurry containing a precipitate of calcium fluoride and ammonium carbonate; producing a first ammonium carbonate solution by filtering said second slurry so as to obtain a filter cake containing calcium and a filtrate containing the first solution of ammonium carbonate; producing a second ammonium carbonate solution by washing and drying said filter cake so as to obtain calcium fluoride and a filter cake washing containing the second solution of ammonium carbonate; wherein a portion of the second slurry ranging from 10 to 70% is recycled to the second reactor so as to enhance calcium fluoride crystallization in the second reactor;
(c) evolving at least half of ammonia from the second reactor in step (b) because of partial decomposition of ammonium carbonate under the second reactor conditions and then scrubbing and returning said ammonia to the first reactor; gathering and treating by distillation and condensation the first and second ammonium carbonate solution to recover liquid ammonia; and recycling the recovered liquid ammonia to the first reactor,, wherein in step (a) the first slurry contains amorphous precipitated silica, the filtration of the first slurry producing a filter cake containing said amorphour precipitated silica and said silica cake is further washed and dried to produce high grade acvtive silica.