Process for reducing the concentration of arsenic in an aqueous solution comprising a fluoroacid

Patent metadata

Field	Value
Publication number	US-11639302-B2
Application number	US-201716348242-A
Country	US
Kind code	B2
Filing date	Nov 9, 2017
Priority date	Nov 10, 2016
Publication date	May 2, 2023
Grant date	May 2, 2023

Abstract

A process for reducing the concentration of one or more arsenic-containing compounds in an aqueous solution comprising at least one fluoroacid, which process comprises: (i) contacting the aqueous solution with an oxidising agent to produce one or more Asv-containing compounds; and (ii) removal of precipitated arsenic-containing compounds; wherein the process comprises a step (iii) the addition of an aqueous alkali solution or slurry, which may take place after step (i) and before step (ii) or after step (ii).

First claim

The invention claimed is:

1. A process for reducing the concentration of one or more arsenic-containing compounds in an aqueous solution comprising at least one fluoroacid to form a treated aqueous solution comprising the fluoroacid, which process comprises:
(i) contacting the aqueous solution with an oxidising agent to produce one or more precipitated As V -containing compounds; and
(ii) removal of precipitated arsenic-containing compounds; and
(iii) the addition of an aqueous alkali solution or slurry, which may take place after step (i) and before step (ii) or after step (ii);
wherein if the step (iii) takes place after step (ii) the process comprises a subsequent step (iv) of the removal of the precipitate resulting from step (iii);
wherein the fluoroacid is present in an amount of from about 1 to about 50% by weight based on the total weight of the aqueous solution;
wherein the addition of the oxidising agent is carried out at a temperature of from 0 to 30° C.;
wherein step (iii) is carried out at a temperature of from about 0° C. to about 30° C.; and
wherein in step (i) is carried out at an acidic pH and the oxidising agent is used in a stoichiometric excess of 20 or more times the quantity of oxidizable arsenic-containing compounds.

2. The process according to claim 1 , wherein the aqueous solution comprises fluorosilicic acid.

3. The process according to claim 1 , wherein the one or more arsenic-containing compounds comprise AsF 3 or a hydrolysed form of AsF 3 .

4. A process according to claim 1 , wherein the oxidising agent is selected from chlorine (Cl 2 ), hypochlorite salts (M + ClO − ), hypochlorous acid (HClO), hydrogen peroxide (H 2 O 2 ) and permanganate salts (M + MnO 4 − ) and mixtures thereof.

5. The process according to claim 1 , wherein the removal of the precipitated arsenic-containing compounds comprises gravity-settling, filtration, anion-exchange resin or a combination thereof.

6. The process according to claim 1 , wherein step (ii) is preceded by the addition of an aqueous alkali solution or slurry.

7. The process according to claim 1 , wherein step (ii) is followed by the addition of an aqueous alkali solution or slurry.

8. The process according to claim 1 , wherein the alkali is calcium hydroxide (Ca(OH) 2 ) or calcium oxide (CaO).

9. The process according to claim 8 , wherein the calcium hydroxide or calcium oxide is present in an amount of from about 15 to about 20% by weight of the aqueous alkali solution or slurry.

10. The process according to claim 1 , further comprising dilution of the aqueous solution to less than 10 wt % fluoroacid prior to the addition of the aqueous alkali solution or slurry.

11. The process according to claim 1 , wherein step (i) is carried out in a time period of from about 1 to about 30 minutes.

12. The process according to claim 11 , wherein step (i) is carried out in a time period of from 2 to 5 minutes.

13. The process according to claim 1 , wherein step (iii) is carried out at a temperature of from about 15° C. to about 30° C.

14. The process according to claim 1 , comprising subsequently recycling all or part of the treated aqueous solution and repeating the process of claim 1 .

15. The process according to claim 1 , wherein from about 50 to about 100% by weight of the arsenic-containing compounds is removed from the aqueous solution.

16. A process according to claim 1 , wherein the treated aqueous solution contains about 5 ppm or less of arsenic-containing compounds.

17. The process according to claim 1 , wherein the treated aqueous solution contains about 1 ppm or less of arsenic-containing compounds.

18. A process for the production of fluorosilicic acid comprising the process as defined in claim 1 , wherein the aqueous solution comprises fluorosilicic acid.

19. A process for the purification of fluorosilicic acid comprising the process as defined in claim 1 , wherein the aqueous solution comprises fluorosilicic acid.

20. The process according to claim 1 , wherein the aqueous solution comprises fluorosilicic acid and hydrofluoric acid.

21. The process according to claim 1 , wherein the aqueous solution comprises fluorosilicic acid and hydrofluoric acid in a combined amount of at least 20% by weight.

22. The process according to claim 1 , wherein the step (i) is carried out at an acidic pH of less than 3.

23. A process for reducing the concentration of one or more arsenic-containing compounds in an aqueous solution comprising at least one fluoroacid to form a treated aqueous solution comprising the fluoroacid, which process comprises:
(i) contacting the aqueous solution with an oxidising agent to produce one or more precipitated As V -containing compounds; and
(ii) removal of precipitated arsenic-containing compounds; and
(iii) the addition of an aqueous alkali solution or slurry, which may take place after step (i) and before step (ii) or after step (ii);
wherein if the step (iii) takes place after step (ii) the process comprises a subsequent step (iv) of the removal of the precipitate resulting from step (iii);
wherein the fluoroacid comprises fluorosilicic acid;
wherein the addition of the oxidising agent is carried out at a temperature of from 0° C. to 30° C.;
wherein step (iii) is carried out at a temperature of from about 0° C. to about 30° C.;
wherein in step (i) the oxidising agent is used in a stoichiometric excess of 20 or more times the quantity of oxidizable arsenic-containing compounds, and the oxidising agent is selected from chlorine (Cl 2 ), hypochlorite salts (M + ClO − ), hypochlorous acid (HClO), hydrogen peroxide (H 2 O 2 ) and permanganate salts (M + MnO 4 − ) and mixtures thereof; and
wherein the alkali is calcium hydroxide (Ca(OH) 2 ) or calcium oxide (CaO).

24. The process according to claim 23 , wherein the step (i) is carried out at an acidic pH of less than 3.

Assignees

• Mexichem Fluor Sa De Cv

Inventors

• Garcia Juan Alberto Juarez
• Castillo Iris Samantha Duran
• Robles Nilo Martinez

Classifications

• C02F1/66

  by neutralisation; pH adjustment (for degassing C02F1/20; using ion-exchange C02F1/42; for flocculation or precipitation of suspended impurities C02F1/52; for removing dissolved compounds C02F1/58) · CPC title

• C01B7/191

  Hydrogen fluoride · CPC title

• C01G28/02

  Arsenates; Arsenites {(C01G28/001 takes precedence)} · CPC title

• C01G28/007

  Halides (C01G28/001 takes precedence) · CPC title

• C02F1/76

  with halogens or compounds of halogens {(C02F1/4674 takes precedence)} · CPC title