# US 4,399,110 A · Process for reducing the radioactivity of calcium sulfate prepared from phosphate rock

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- Number: US 4,399,110 A
- Document ID: US4399110A
- Status: Granted
- Kind: A
- Application number: 06/272,681
- Filed: 1981-06-11
- Granted: 1983-08-16
- Earliest claimed: 1980-06-11
- Assignees: Chemische Werke Huls Aktiengesellschaft
- Inventors: Hans-Friedrich Kurandt
- Web page: https://patentgrep.com/patent/US4399110A

## CPC

- C01F 11/46: Sulfates (dehydration of gypsum {for the production of calcium sulfate cements} C04B11/02)
- G21F 9/10: by flocculation
- C01P 2006/42: Magnetic properties
- C01F: COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS (metal hydrides {monoborane, diborane or addition complexes thereof} C01B6/00; salts of oxyacids of halogens C01B11/00; peroxides, salts of peroxyacids C01B15/00; sulfides or polysulfides of magnesium, calcium, strontium, or barium C01B17/42; thiosulfates, dithionites, polythionates C01B17/64; compounds containing selenium or tellurium C01B19/00; binary compounds of nitrogen with metals C01B21/06; azides C01B21/08; {compounds other than ammonia or cyanogen containing nitrogen and non-metals and optionally metals C01B21/082; amides or imides of silicon C01B21/087}; metal {imides or} amides C01B21/092, {C01B21/0923}; nitrites C01B21/50; {compounds of noble gases C01B23/0005}; phosphides C01B25/08; salts of oxyacids of phosphorus C01B25/16; carbides C01B32/90; compounds containing silicon C01B33/00; compounds containing boron C01B35/00; compounds having molecular sieve properties but not having base-exchange properties C01B37/00; compounds having molecular sieve and base-exchange properties, e.g. crystalline zeolites, C01B39/00; cyanides C01C3/08; salts of cyanic acid C01C3/14; salts of cyanamide C01C3/16; thiocyanates C01C3/20; {double sulfates of magnesium with sodium or potassium C01D5/12; with other alkali metals C01D15/00, C01D17/00})
- G21F: PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR (radiation protection by pharmaceutical means A61K8/00, A61Q17/04; in cosmonautic vehicles B64G1/54; combined with a reactor G21C11/00; combined with X-ray tubes H01J35/16; combined with X-ray apparatus H05G1/02)
- C01P: INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS

## Abstract

The level of radioactivity in gypsum produced from phosphate rock can be reduced by adding to the slurry of acid and phosphate rock in the conventional process for producing phosphoric acid a combination of concentrated nitric acid or hydrochloric acid and an ammonium salt, especially ammonium nitrate or ammonium phosphate, before the precipitation of the calcium sulfate.

## Claims

### Claim 1

A process for producing calcium sulfate having low levels of radioactivity from phosphate rock comprising:
(1) reacting said phosphate rock with sulfuric acid, whereby a slurry is produced;
(2) adding to said slurry a concentrated mineral acid selected from the group consisting of nitric acid and hydrochloric acid, and an ammonium salt selected from the group consisting of ammonium nitrate and ammonium phosphate; and
(3) separating calcium sulfate from the soluble reaction products and phosphoric acid in said slurry.

### Claim 2 (depends on 1)

The process of claim 1, wherein said calcium sulfate is digested after step 2 at a temperature of 60.degree.-110.degree. C. for a period of 5-10 hours before separating from the soluble reaction products in said slurry.

### Claim 3

A process for producing calcium sulfate having low levels of radioactivity from phosphate rock comprising:
(1) reacting said phosphate rock with a mineral acid selected from the group consisting of nitric acid and hydrochloric acid, whereby a slurry is produced;
(2) adding to said slurry an ammonium salt selected from the group consisting of ammonium nitrate and ammonium phosphate;
(3) precipitating calcium sulfate by the addition of sulfuric acid or an inorganic sulfate to said slurry; and
(4) separating calcium sulfate from the soluble reaction products and phosphoric acid in said slurry.

### Claim 4 (depends on 3)

The process of claim 3, wherein said calcium sulfate is digested at a temperature of 60.degree.-110.degree. C. for a period of 1-10 hours before separating from the soluble reaction products in said slurry.