Removal of elements from coal fly ash
A method for removing elements, including heavy metals, from fly ash and from fly ash resulting from removal of SO x /NO x from flue gas using Na 2 CO 3 /NaHCO 3 /trona, is described. An aqueous suspension of the fly ash and/or a solution of the leachate from the fly ash is treated with dissolved ferrous compounds, such as FeSO 4 .7H 2 O and/or FeCl 2 .4H 2 O, at a chosen initial acidic pH, and the precipitation of the ferrous ions as the solution basifies sequesters the trace elements.
1. A method for removing at least one element from fly ash, comprising:
treating said fly ash with an acidified liquid;
allowing the acidified liquid to become basic by reaction with said fly ash, forming a basified liquid;
dissolving at least one ferrous compound in the basified liquid, forming a precipitate of the ferrous compound, whereby said at least one element is sequestered by the precipitate; and
separating the precipitate from the basified liquid.
2. The method of claim 1 , wherein the at least one ferrous compound is chosen from ferrous chloride, a hydrated form of ferrous chloride, ferrous sulfate, and a hydrated form of ferrous sulfate.
3. The method of claim 2 , wherein said hydrated ferrous chloride comprises FeCl 2 .4H 2 O.
4. The method of claim 2 , wherein said hydrated ferrous sulfate comprises FeSO 4 .7H 2 O.
5. The method of claim 1 , wherein said at least one element comprises selenium.
6. The method of claim 1 , wherein said at least one element comprises arsenic.
7. The method of claim 1 , wherein said at least one element comprises a heavy metal.
8. The method of claim 7 , wherein the heavy metal is chosen from silver, barium, cadmium, cobalt, chromium, copper, manganese, nickel, lead, vanadium, and zinc.
9. The method of claim 1 , wherein the acidified liquid has a pH ≦5.
10. The method of claim 1 , wherein the acidified liquid has a pH ≦2.
11. The method of claim 1 , wherein said fly ash comprises materials chosen from trona, carbonate, bicarbonate, and limestone.
12. The method of claim 11 , wherein said fly ash comprises Na 2 CO 3 /NaHCO 3 /trona.
13. A method for removing at least one element from fly ash, comprising:
treating said fly ash with an acidified liquid comprising at least one soluble ferrous compound;
allowing the acidified liquid to become basic by reaction with said fly ash;
whereby a precipitate of the ferrous compound is formed, said precipitate sequestering said at least one element; and
separating the precipitate from the basic liquid.
14. The method of claim 13 , wherein the at least one ferrous compound is chosen from ferrous chloride, a hydrated form of ferrous chloride, ferrous sulfate, and a hydrated form of ferrous sulfate.
15. The method of claim 14 , wherein said hydrated ferrous chloride comprises FeCl 2 .4H 2 O.
16. The method of claim 14 , wherein said hydrated ferrous sulfate comprises FeSO 4 .7H 2 O.
17. The method of claim 13 , wherein said at least one element comprises selenium.
18. The method of claim 13 , wherein said at least one element comprises arsenic.
19. The method of claim 13 , wherein said at least one element comprises a heavy metal.
20. The method of claim 19 , wherein the heavy metal is chosen from silver, barium, cadmium, cobalt, chromium, copper, manganese, nickel, lead, vanadium, and zinc.
21. The method of claim 13 , wherein the acidified liquid has a pH ≦5.
22. The method of claim 13 , wherein the acidified liquid has a pH ≦2.
23. The method of claim 13 , wherein said fly ash comprises materials chosen from trona, carbonate, bicarbonate, and limestone.
24. The method of claim 23 , wherein said fly ash comprises Na 2 CO 3 /NaHCO 3 /trona.