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US 11,851,341 B2Granted
High purity synthetic fluorite, process for preparing the same and apparatus therefor
AssigneeFluorsid S.P.A.
InventorsLuca Pala, Michele Lavanga
Life of this patent
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Abstract
The present invention relates to a high purity synthetic fluorite (CaF2). The present invention further relates to a process and an apparatus for preparing said high purity synthetic fluorite (CaF2), classified as acid grade, starting from fluorosilicic acid H2SiF6 (FSA) and calcium carbonate (CaCO3). Finally, the present invention relates to the use of said high purity synthetic fluorite (CaF2) in the industrial production of hydrofluoric acid.
Claims16
A process for preparing a synthetic fluorite CaF2 comprising the following steps:
- (a) preparing a solution of NH4F by basic hydrolysis at a pH value of from 8.5 to 9.5, by:
- (i) reacting an aqueous solution of H2SiF6 having a concentration of from 15 to 30% by weight with an aqueous solution of NH3 having a concentration of from 10 to 25% by weight to form a reaction solution, wherein the pH of a mixture of the aqueous solution of H2SiF6 and the aqueous solution of NH3 reaction solution remains stable at about 9 during the addition of the aqueous solution of NH3 and the aqueous solution of H2SiF6;
- and
- (ii) stirring the reaction solution such that the pH of the reaction solution is maintained between a pH of from 8.5 to 9.5, to obtain the solution of NH4F;
- (b) filtering precipitated SiO2 from said solution of NH4F so as to yield an aqueous solution of NH4F;
- (c) treating the aqueous solution of NH4F with calcium hydroxide in an excess amount of from 0.01 to 0.5%, relative to the stoichiometric amount, so as to yield a dispersion which is maintained under stirring for a time of from 10 to 60 minutes at a temperature of from 40 to 90° C.;
- (d) filtering the dispersion resulting from step (c) so as to obtain the synthetic fluorite CaF2;
- (e) subjecting the result of step (d) to a drying and granulation step so as to yield an acid grade synthetic fluorite CaF2 in the form of granules with an average particle size greater than 1 mm for at least 50% of the same.
5 more elements
A process for preparing a synthetic fluorite CaF2 comprising the following steps:
- (a) preparing a solution of NH4F by basic hydrolysis at a pH value of from 8.5 to 9.5, by:
- (i) reacting an aqueous solution of H2SiF6 having a concentration of from 15 to 30% by weight with an aqueous solution of NH3 having a concentration of from 10 to 25% by weight to form a reaction solution, wherein the pH of a mixture of the aqueous solution of H2SiF6 and the aqueous solution of NH3 remains stable at about 9 during addition of the aqueous solution of NH3 and the aqueous solution of H2SiF6;
- and
- (ii) stirring the reaction solution such that the pH of the reaction solution is maintained between a pH of from 8.5 to 9.5, to obtain the solution of NH4F;
- (b) filtering precipitated SiO2 from said solution of NH4F so as to yield an aqueous solution of NH4F;
- (c) treating the aqueous solution of NH4F with calcium carbonate in an excess amount of from 0.01 to 0.5%, relative to the stoichiometric amount, so as to yield a dispersion which is maintained under stirring for a time of from 10 to 60 minutes at a temperature of from 60 to 90° C.;
- (d) filtering or vacuum filtering the dispersion resulting from step (c) so as to obtain the synthetic fluorite CaF2;
- (e) subjecting the result of step (d) to a drying and granulation step so as to yield an acid grade synthetic fluorite CaF2 in the form of granules with an average particle size greater than 1 mm for at least 50% of the same.
5 more elements
A process for preparing a synthetic fluorite CaF2 comprising the following steps:
- (a) preparing a solution of NH4F by basic hydrolysis at a pH value of from 8.5 to 9.5, by:
- (i) reacting an aqueous solution of H2SiF6 having a concentration of from 15 to 30% by weight with an aqueous solution of NH3 having a concentration of from 10 to 25% by weight to form a reaction solution, wherein the pH of a mixture of the aqueous solution of H2SiF6 and the aqueous solution of NH3 remains stable at about 9 during addition of the aqueous solution of NH3 and the aqueous solution of H2SiF6;
- and
- (ii) stirring the reaction solution such that the pH of the reaction solution is maintained between a pH of from 8.5 to 9.5, to obtain the solution of NH4F;
- (b) filtering precipitated SiO2 from said solution of NH4F so as to yield an aqueous solution of NH4F;
- (c) distilling under reduced pressure the aqueous solution of NH4F obtained from step (b) so as to transform the NH4F into NH4HF2 according to the following reaction:
- 2NH4F(aq)→NH4HF2(aq)+NH3(gas);
- (d) treating the aqueous solution of NH4HF2 resulting from step (c) with (A) calcium carbonate so as to yield a dispersion containing the synthetic fluorite CaF2, according to the following reaction:
- NH4HF2(aq)+CaCO3(solid)→CaF2(solid)+CO2(gas)+NH3(gas);
- or with
- (B) calcium hydroxide so as to yield a dispersion containing the synthetic fluorite CaF2, according to the following reaction:
- NH4HF2(aq)+Ca(OH)2(solid)→CaF2(solid)+2H2O(aq)+NH3(gas);
- (e) filtering or vacuum filtering the dispersion resulting from step (d) so as to obtain the synthetic fluorite CaF2;
- (f) subjecting the result of step (e) to a drying and granulation step so as to yield an acid grade synthetic fluorite CaF2 in the form of granules with an average particle size greater than 1 mm for at least 50% of the same.
11 more elements
Dependencies are inferred from the claim text.