Back to results
US 11,873,229 B2Granted
Process for preparing calcium fluoride from fluosilicic acid
AssigneeOcp SA
InventorsKamal Samrane, Abdelaali Kossir
Life of this patent
Estimating the term…
Abstract
A process for preparing synthetic calcium fluoride (CaF2) (min 90% CaF2 by weight) from fluosilicic acid is provided. The processes comprises the steps of (a) reacting fluosilicic acid (H2SiF6) with ammonium hydroxide or ammonia in a first reactor so as to obtain a first slurry and filtering the first slurry so as to obtain a filtrate containing a solution of ammonium fluoride (b) precipitating the solution of ammonium fluoride with calcium in a second reactor so as to produce a second slurry containing calcium fluoride and (c) evolving the major part of ammonia from the second reactor and then scrubbing and returning said ammonia to the first reactor.
Claims10
A process for preparing synthetic calcium fluoride (CaF2) from fluosilicic acid, comprising the following steps:
- (a) directly reacting fluosilicic 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;
- (b) precipitating ammonium fluoride the solution of ammonium 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 fluoride and a filtrate containing the 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 the major part 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 solutions to recover liquid ammonia;
- and recycling the recovered liquid ammonia to the first reactor,
- wherein the calcium fluoride obtained at step (b) presents a purity greater than or equal to 90% wt CaF2.
7 more elements
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.
7 more elements
A process for preparing synthetic calcium fluoride (CaF2) from fluosilicic acid, comprising the following steps:
- (a) directly reacting fluosilicic 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;
- (b) reacting ammonium fluorie from the solution of ammonium 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 fluoride 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 carobnate;
- wherein a portion of the second slurry ranging form 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 solutions 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 amorphous precipitated silica and said silica cake is further washed and dried, and
- the washing of the filter cake in step (a) produces filter cake washing that contains a solution of ammonium fluoride, said solution of ammonium fluoride being recycled to the first reactor or to the second reactor.
8 more elements
Dependencies are inferred from the claim text.