Process for producing fluorine compounds and amorphous silica
AssigneeOccidental Research Corporation
InventorsSubhas K. Sikdar, James H. Moore
Life of this patent
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Abstract
Hydrofluoric acid and/or other fluorine compounds are recovered by reacting fluosilicic acid with a sodium-containing compound to form an alkaline aqueous slurry comprising precipitated amorphous silica and dissolved sodium fluoride. The precipitated amorphous silica is separated from the alkaline aqueous slurry leaving an aqueous solution of sodium fluoride. The sodium fluoride solution can be used as such or reacted with other substances (such as alumina, to form synthetic cryolite). Sodium fluoride is recovered from the aqueous solution (as by evaporation or extraction) and used per se or reacted with sulfuric acid to produce hydrogen fluoride.
Claims13
A process consisting essentially of the steps of:
- (a) reacting in a precipitation zone fluosilicic acid in aqueous solution with a sodium-containing compound selected from the group consisting of sodium hydroxide, sodium carbonate, sodium silicate and combinations thereof, to form an alkaline aqueous slurry comprising silica and dissolved sodium fluoride;
- by maintaining during said reaction the pH of the alkaline aqueous slurry at a value greater than 7 and up to about 9, the alkaline aqueous slurry at least about saturated with sodium fluoride, and the temperature of the alkaline aqueous slurry substantially equal to its boiling point so that an amorphous silica precipitate is formed;
- and
- (b) separating precipitated amorphous silica from the alkaline aqueous slurry leaving an aqueous solution comprising sodium fluoride.
A process for recovering solid amorphous silica from fluosilicic acid consisting essentially of the steps of:
- (a) reacting fluosilicic acid with a material selected from the group consisting of MOH, M.sub.2 CO.sub.3, M.sub.2 SiO.sub.3, and combinations thereof, where M is selected from the group consisting of sodium, potassium, and ammonium, to form an alkaline aqueous slurry comprising silica and a dissolved fluoride salt MF;
- wherein during said reacting the pH of the alkaline aqueous slurry is maintained at a value greater than 7 and up to about 9, the water content of the alkaline aqueous slurry is maintained sufficiently low such that the slurry is at least about saturated with respect to the fluoride salt, and the temperature of the alkaline aqueous slurry is maintained at its boiling point so that an amorphous silica precipitate is formed;
- and
- (b) separating precipitated amorphous silica from the alkaline aqueous slurry.
A process for recovering a low silica content fluoride solution and solid amorphous silica from phosphate plant scrub liquor containing at least about 15% by weight fluosilicic acid, consisting essentially of the steps of:
- (a) combining the scrub liquor with sodium carbonate in a precipitation zone to form an alkaline aqueous slurry comprising precipitated amorphous silica and sodium fluoride by maintaining the pH of the alkaline aqueous slurry at a value greater than 7 and up to about 9, the water content of the alkaline aqueous slurry sufficiently low such that the slurry contains solid sodium fluoride, and the temperature of the alkaline aqueous slurry substantially equal to its boiling point;
- (b) adding sufficient water to the alkaline aqueous slurry in a dissolving zone to dissolve substantially all of the solid sodium fluoride;
- and thereafter
- (c) separating precipitated amorphous silica from the alkaline aqueous slurry leaving an aqueous solution comprising sodium fluoride.
A process for recovering solid amorphous silica from fluosilicic acid consisting essentially of the steps of:
- (a) reacting fluosilicic acid with MOH, where M is selected from the group consisting of sodium and potassium to form an alkaline aqueous slurry comprising silica and a dissolved fluoride salt MF;
- wherein during said reacting the pH of the alkaline aqueous slurry is maintained at a value greater than 7 and up to about 9, the water content of the alkaline aqueous slurry is maintained sufficiently low such that the slurry is at least about saturated with respect to the fluoride salt, and the temperature of the alkaline aqueous slurry is maintained substantially equal to its boiling point so that an amorphous silica precipitate is formed;
- and
- (b) separating precipitated amorphous silica from the alkaline aqueous slurry.
A process for recovering solid amorphous silica from fluosilicic acid consisting essentially of the steps of:
- (a) reacting fluosilicic acid with a material selected from the group consisting of M.sub.2 CO.sub.3, M.sub.2 SiO.sub.3, M.sub.2 CO.sub.3, M.sub.2 CO.sub.3 and M.sub.2 SiO.sub.3 and combinations thereof with MOH, where M is selected from the group consisting of sodium, potassium, and ammonium, to form an alkaline aqueous slurry comprising silica and a dissolved fluoride salt MF;
- wherein during said reacting the pH of the alkaline aqueous slurry is maintained at a value greater than 7 and up to about 9, the water content of the alkaline aqueous slurry is maintained sufficiently low such that the slurry is at least about saturated with respect to the fluoride salt, and the temperature of the alkaline aqueous slurry is maintained at its boiling point so that an amorphous silica precipitate is formed;
- and
- (b) separating precipitated amorphous silica from the alkaline aqueous slurry.
Dependencies are inferred from the claim text.