Process for the removal of heavy metals from a phosphoric acid containing composition using a flocculating agent

Patent metadata

Field	Value
Publication number	US-12545582-B2
Application number	US-202118008812-A
Country	US
Kind code	B2
Filing date	Jun 16, 2021
Priority date	Jun 16, 2020
Publication date	Feb 10, 2026
Grant date	Feb 10, 2026

Abstract

Improved methods for the removal of heavy metals, in particular cadmium, from an aqueous phosphoric acid containing composition, wherein an ionic polymeric flocculating agent is added to a phosphoric acid containing composition subsequent to the addition of an organothiophosphorous heavy metal precipitating agent to said composition, particularly under gentle mixing conditions, such as between 100 and 300 rpm. The flocculating agent promotes the formation of agglomerates of the heavy metal containing precipitate, thus facilitating their removal from the composition. More in particular, the phosphoric acid containing composition is obtained by the acid digestion of phosphate rock, preferably by nitric acid, sulfuric acid, or a combination thereof.

First claim

The invention claimed is:

1 . A process for the removal of heavy metals from a phosphoric acid containing composition, comprising the steps of
(a) providing a phosphoric acid containing composition comprising dissolved heavy metals; (b) precipitating the dissolved heavy metals by adding a heavy metal precipitating agent to the composition of step (a), at a pH of 1.6 to 2.2 measured after a 13-fold dilution by volume using water, thereby obtaining a heavy metal precipitate in a phosphoric acid containing composition, wherein the heavy metal precipitating agent comprises a diorgano-dithiophosphinic acid or an alkali metal or ammonia salt thereof, represented by Formula 1

wherein R is a linear or branched hydrocarbon group selected from alkyl, aryl, alkylaryl, or aralkyl, and wherein the hydrocarbon group contains 3 to 20 carbon atoms, and M is H, alkali metal or ammonia;
(c) adding a first flocculating agent having a molecular weight of 4×10 6 Dalton to 8×10 6 Dalton, to the composition obtained in step (b), wherein said first flocculating agent is a cationic polymer wherein 20% to 80% of the moieties making up the cationic polymer are cationic charged moieties, an anionic polymer wherein 10% to 50% of the moieties making up the anionic polymer are anionic charged moieties, or a mixture thereof, thereby obtaining agglomerates comprising the heavy metal precipitate in a phosphoric acid containing composition; and
(d) separating the agglomerates comprising the heavy metal precipitate from the phosphoric acid containing composition, and wherein
the phosphoric acid containing composition is an acidic aqueous composition comprising from 6-21 wt % nitric acid, from 25 to 33 wt % phosphoric acid, from 3.5 to 5 wt % calcium and dissolved heavy metals, where the wt % is based on the total weight of the composition.

2 . The process according to claim 1 , wherein step (a) further comprises the steps of
(i) adjusting the pH of a phosphoric acid containing composition comprising dissolved heavy metals to a pH of 1.6 to 2.2 measured after a 13-fold dilution by volume using water, thereby obtaining a phosphoric acid containing composition comprising a sludge fraction; (ii) optionally adding a second flocculating agent having a molecular weight of 4×10 6 Dalton to 8×10 6 Dalton, to the composition of step (i), wherein said second flocculating agent is a cationic polymer wherein 20% to 80% of the moieties making up the cationic polymer are cationic charged moieties, an anionic polymer wherein 10% to 50% of the moieties making up the anionic polymer are anionic charged moieties, or a mixture thereof; and (iii) separating the sludge fraction from the composition of step (i) or (ii).

3 . The process according to claim 2 , wherein the first and, optionally, the second flocculating agent is a copolymer of (meth) acrylamide and a chloro-methylated monomer or a copolymer of (meth) acrylamide and (meth) acrylic acid.

4 . The process of claim 3 wherein the first and, optionally, the second flocculating agent is a copolymer of (meth) acrylamide and dimethylaminoethyl (meth) acrylate or (meth) acrylic acid.

5 . The process of claim 2 wherein the pH of the phosphoric acid containing composition is adjusted by the addition of ammonia.

6 . The process of claim 2 wherein the second flocculating agent is a cationic polymer wherein 20% to 60 wt % of the moieties making up the cationic polymer are cationic charged moieties, or an anionic polymer wherein 10% to 40% of the moieties making up the anionic polymer are anionic charged moieties, or a combination thereof.

7 . The process according to claim 1 , wherein the first flocculating agent is added in a dose of 3 to 30 g/m 3 acid composition.

8 . The process of claim 5 wherein the dose is 3 to 20 g/m 3 acid composition.

9 . The process according to claim 1 , wherein the precipitation and/or flocculation steps are performed at a temperature of 5 to 50° C.

10 . The process according to claim 1 wherein the phosphoric acid containing composition is an acid digest of phosphate rock.

11 . The process of claim 10 wherein the phosphate rock is digested by nitric acid, or a combination of sulfuric acid and nitric acid.

12 . The process according to claim 1 , wherein R in Formula 1 is selected from the group consisting of cyclohexyl, isopropyl, isobutyl, n-propyl, octyl, hexyl, phenylethyl and 2,4,4-trimethylpentyl.

13 . The process of claim 12 wherein the heavy metal precipitation agent is sodium diisobutyldithiophosphinate.

14 . The process according to claim 1 , wherein the heavy metals are selected from cadmium, copper, nickel, mercury, zinc, arsenic, manganese and/or lead.

15 . The process of claim 1 wherein the dissolved heavy metal is cadmium.

16 . The process of claim 1 wherein the first flocculating agent is a cationic polymer wherein 20% to 60% of the moieties making up the cationic polymer are cationic charged moieties, or an anionic polymer wherein 10% to 40% of the moieties making up the anionic polymer are anionic charged moieties, or a combination thereof.

Assignees

• Yara Int Asa

Inventors

• Kita Patrycja
• Vojnovic Tanja
• Jørgensen Tom Rames
• Jordbræk Per Arne

Classifications

• C01B25/234 Primary

  Purification; Stabilisation; Concentration (purification concomitant with preparation C01B25/22; preparation involving solvent-solvent extraction C01B25/46) · CPC title

• C02F2209/06

  pH · CPC title

• B03D3/06

  Flocculation · CPC title

• C01P2006/80

  Compositional purity · CPC title

• C02F9/00

  Multistage treatment of water, waste water or sewage · CPC title