Composition for removing arsenic from aqueous streams

• US 7,686,976 B2
• Filed: 10/26/2007
• Issued: 03/30/2010
• Est. Priority Date: 01/29/2003
• Status: Active Grant

• Current Assignee: Rare Earth Acquisitions LLC
• Original Assignee: Molycorp Minerals LLC (Oaktree Capital Management LP)
• Inventors: Witham, Richard Donald, Burba, John Leslie III, McNew, Edward Bayer
• Primary Examiner(s): Hruskoci; Peter A
• Application Number:
  US11/925,247
• Publication Number:
  US 20080093580A1
• Time in Patent Office: 886 Days
• Field of Search: 252/175
• US Class Current: 252/175
• CPC Class Codes: C02F 1/28 by sorption using ion-exchange C02F1/42; sorbent compositions B01J
• CPC Class Codes: C02F 1/281 using inorganic sorbents
• CPC Class Codes: C02F 1/42 by ion-exchange ion-exchange in general B01J
• CPC Class Codes: C02F 1/5236 using inorganic agents
• CPC Class Codes: C02F 1/5245 using basic salts, e.g. of aluminium and iron
• CPC Class Codes: C02F 1/62 Heavy metal compounds
• CPC Class Codes: C02F 1/72 by oxidation C02F1/4672 takes precedence
• CPC Class Codes: C02F 2101/103 Arsenic compounds
• CPC Class Codes: C02F 2201/006 Cartridges
• CPC Class Codes: C02F 2305/12 Inert solids used as ballast for improving sedimentation C02F3/1226 takes precedence
• CPC Class Codes: C02F 9/00 Multistage treatment of water, waste water or sewage
• CPC Class Codes: Y10S 210/911 Cumulative poison

Abstract

Arsenic is removed from water and other aqueous feeds by (1) treating the feed with a compound containing cerium in the +4 oxidation state, preferably cerium dioxide, to oxidize arsenic in the +3 oxidation state to arsenic in the +5 oxidation state and (2) removing the arsenic in the +5 oxidation state from the aqueous phase, normally by contacting the treated feed with alumina or other precipitating agent containing cations in the +3 oxidation state.

Claims

1. A composition comprising a mixture of particles of cerium dioxide (CeO₂) to oxidize arsenic in the +3 oxidation state to arsenic in the +5 oxidation state and a rare earth precipitating agent in the +3 oxidation state to precipitate, from an aqueous solution, the arsenic in the +5 oxidation state, wherein said cerium dioxide and rare earth precipitating agent are in the form of a slurry or physical mixture.

2. The composition defined by claim 1, further comprising particulate solids and wherein said particulate solids comprise alumina.

3. The composition defined by claim 2 essentially devoid of lanthanum, and wherein the particles in said mixture range in diameter from about 0.25 to 1.5 millimeters.

4. The composition defined by claim 2 essentially devoid of all rare earths except cerium.

5. The composition defined by claim 2, wherein the particles in said mixture range in diameter from about 0.5 to 1.0 millimeters.

6. The composition of claim 1, wherein the rare earth precipitating agent comprises a rare earth compound and wherein the composition comprises from about 8 to about 60 wt. % of the cerium oxidizing agent in the form of an oxide.

7. The composition of claim 1, wherein the rare earth precipitating agent is compounded with arsenic in the +5 oxidation state.

8. A composition, comprising:

(a) a cerium oxidizing agent to oxidize arsenic in the +3 oxidation state to arsenic in the +5 oxidation state, the cerium in the cerium oxidizing agent having a first oxidation state of +4; and

(b) a cerium precipitating agent to precipitate, from an aqueous solution, the arsenic in the +5 oxidation state, the cerium in the cerium precipitating agent having a second oxidation state of +3.

9. The composition of claim 8, wherein the cerium oxidizing agent and precipitating agent are substantially water insoluble.

10. The composition of claim 9, wherein the cerium oxidizing agent is supported on a substrate selected from the group consisting of alumina, gamma-alumina, activated alumina, acidified alumina, metal oxides comprising labile anions, crystalline alumino-silicates, amorphous silica alumina, ion exchange resins, clays, ferric sulfate, porous ceramics, and mixtures thereof.

11. The composition of claim 9, wherein the cerium oxidizing agent and precipitating agent are in the form of a slurry or physical mixture.

12. The composition of claim 9, wherein the cerium oxidizing agent comprises cerium dioxide, ceric ammonium nitrate, ceric ammonium sulfate, ceric sulfate, or ceric nitrate.

13. The composition of claim 8, wherein the cerium oxidizing agent and precipitating agent are substantially water soluble.

14. The composition of claim 8, wherein the cerium oxidizing agent oxidizes arsenite to arsenate and wherein the cerium precipitating agent is compounded with arsenic in the +5 oxidation state.

15. The composition of claim 8, wherein the composition comprises from about 8 to about 60 wt. % of the cerium oxidizing agent in the form of an oxide.

16. The composition of claim 8, wherein the composition is in the form of a particulate and wherein at least most of the particulate has a diameter of from about 0.25 to about 1.5 mm.

17. The composition of claim 8, wherein the cerium precipitating agent comprises cerous carbonate.

18. A composition, comprising:

a cerium oxidizing agent to oxidize arsenic in the +3 oxidation state to arsenic in the +5 oxidation state, the cerium in the cerium oxidizing agent having a first oxidation state of +4;

a rare earth precipitating agent, the rare earth in the rare earth precipitating agent having a second oxidation state of +3 and the rare earth precipitating agent being capable of forming a precipitate with arsenic; and

arsenic compounded with the rare earth precipitating agent, the arsenic having an oxidation state of +5.

19. The composition of claim 18, wherein the cerium oxidizing agent and rare earth precipitating agent are substantially water insoluble.

20. The composition of claim 19, wherein the cerium oxidizing agent is supported on a substrate is selected from the group consisting of alumina, gamma-alumina, activated alumina, acidified alumina, metal oxides comprising labile anions, crystalline alumino-silicates, amorphous silica alumina, ion exchange resins, clays, ferric sulfate, porous ceramics, and mixtures thereof.

21. The composition of claim 19, wherein the cerium oxidizing agent and rare earth precipitating agent are in the form of a slurry or physical mixture.

22. The composition of claim 19, wherein the cerium oxidizing agent comprises ceric ammonium nitrate, cerium dioxide, ceric ammonium sulfate, ceric sulfate, or ceric nitrate.

23. The composition of claim 18, wherein the cerium oxidizing agent and rare earth precipitating agent are substantially water soluble and.

24. The composition of claim 18, wherein the rare earth precipitating agent is lanthanum oxide.

25. The composition of claim 18, wherein the rare earth precipitating agent is cerous carbonate.

26. The composition of claim 18, wherein the cerium oxidizing agent oxidizes arsenite to arsenate.

27. The composition of claim 18, wherein the precipitating agent comprises a rare earth compound and wherein the composition comprises from about 8 to about 60 wt. % of the cerium oxidizing agent in the form of an oxide.

28. The composition of claim 18, wherein the composition is in the form of a particulate and wherein at least most of the particulate has a diameter of from about 0.25 to about 1.5 mm.

29. A composition, comprising:

a water-soluble cerium oxidizing agent to oxidize arsenic in the +3 oxidation state to arsenic in the +5 oxidation state, the cerium in the cerium oxidizing agent having an oxidation state of +4, and

a cerium precipitating agent to form a precipitate with the arsenic in the +5 oxidation state, the cerium in the cerium precipitating agent having an oxidation state of +3.

30. The composition of claim 29, wherein the cerium precipitating agent is compounded with arsenic in the +5 oxidation state.

31. The composition of claim 29, wherein the cerium oxidizing agent comprises ceric ammonium nitrate, ceric ammonium sulfate, ceric sulfate, or ceric nitrate.

32. The composition of claim 29, wherein the cerium precipitating agent comprises cerous carbonate and further comprising:

a particulate material comprising alumina, gamma-alumina, activated alumina, acidified alumina, metal oxides comprising labile anions, crystalline alumino-silicates, amorphous silica alumina, ion exchange resins, clays, ferric sulfate, or porous ceramics.