Composition for removing arsenic from aqueous streams
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.
1. A composition comprising a mixture of particles of cerium dioxide (CeO 2 ) 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.