US 4,765,822 A · Recovery of fluorine from waste gases

Abstract

Fluorine in phosphate ores is present as the mineral fluorapatite. When the ores are digested with sulfuric acid a slurry is formed which can be filtered to make wet-process phosphoric acid. But fluorine compounds are discharged into the surrounding air during digestion and filtration. The fluorine-containing air is scrubbed with water to prevent air pollution. Scrubber water is cooled in ponds and is recycled to the scrubber. However, fluorine compounds are emitted from the cooling ponds and cause air pollution. In the present invention, processes are disclosed for treating fluorine-containing gases without use of cooling ponds thereby eliminating the air pollution problem. A facility is provided for treating fluorine-containing gases wherein fluosilicic acid or fluosilicate salts are converted to a fluoride salt by the addition of an alkaline substance. A slightly acidic scrubber water is concentrated in an absorption tower. When the scrubber water contains nutrients, ammonium is the preferred alkaline substance and the scrubber water is recovered in solid ammonium phosphate fertilizers or in suspension fertilizers. Sodium hydroxide or sodium carbonate are the preferred alkaline substances when sodium cryolite or aluminum fluoride are produced.

Claims40

Dependent claims

A process for the production of suspension fertilizers, said process comprised of the following steps:

(a) treating fluorine-laden gas with ammonia and water containing fluosilicates in a reactor to form an alkaline aqueous mixture containing ammonium fluoride;
(b) prepipitating silica from the aqueous mixture formed in said reactor in step (a);
(c) separating silica precipitated in step (b) from a clarified liquid by sedimentation;
(d) pumping the clarified liquid prepared in step (c) to a vessel;
(e) adding phosphoric acid to the vessel in step (d);
(f) adding ammonia to vessel in step (d);
(g) treating the gas from step (a) in an absorption tower wherein liquid from step (d) is the scrubbing medium;
(h) recycling the liquid from the absorption tower in step (g) to vessel in step (d);
(i) bleeding off a stream of liquid from step (h);
(j) dissolving monoammonium phosphate in liquid from step (i) to form a mixture;
(k) adding ammonia to the mixture in step (j);
(l) adding silica separated in step (c) to the mixture in step (k);
(m) agitating the mixture in step (l);
(n) adding gelling clay to the mixture in step (m) to prepare suspension fertilizer;
and
(o) pumping suspension fertilizer prepared in step (n) to storage.

13 more elements

A process for the production of suspension fertilizer, said process comprised of the following steps:

(a) treating fluorine-laden gas with ammonia and water containing fluosilicates in a reactor to form an alkaline aqueous mixture containing ammonium fluoride;
(b) precipitating silica from the aqueous mixture formed in said reactor step (a);
(c) separating silica precipitated in step (b) by sedimentation;
(d) pumping clarified liquid prepared in step (c) to a vessel;
(e) adding phosphoric acid to the vessel in step (d);
(f) adding ammonia to the vessel in step (d);
(g) treating gas from step (a) in an absorption tower wherein liquid from step (d) is the scrubbing medium;
(h) recycling the liquid from the absorption tower in step (g) to the vessel in step (d);
(i) bleeding off a stream of liquid from step (h);
(j) pumping phosphoric acid to a preneutralizer;
(k) adding ammonia to the preneutralizer in step (j) to form a partially neutralized mixture;
(l) pumping the partially neutralized mixture in step (k) to a granulator;
(m) ammoniating the partially neutralized mixture in step (l);
(n) granulating the mixture in step (m) to prepare a granular solid;
(o) drying the granular solid prepared in step (n);
(p) dissolving dry solid from step (l) in the bleedoff stream from step (i) to form a mixture;
(q) adding phosphoric acid to the mixture in step (p);
(r) adding silica separated in step (c) to the mixture in step (q);
(s) adding ammonia to the mixture in step (r);
(t) agitating the mixture in step (s);
(u) adding gelling clay to the mixture in step (t) to prepare suspension fertilizer;
and
(v) pumping suspension fertilizer prepared in step (u) to storage;

20 more elements

Dependencies are inferred from the claim text.

Recovery of fluorine from waste gases

Life of this patent

Recovery of fluorine from waste gases

Life of this patent

Abstract

Claims40