Method for removing metals from acid mine drainage

• US 20040094484A1
• Filed: 11/15/2002
• Published: 05/20/2004
• Est. Priority Date: 11/15/2002
• Status: Active Grant

• Current Assignee: NORAM Engineering and Constructors Ltd.
• Original Assignee: NORAM Engineering and Constructors Ltd.
• Inventors: Zhuang, J. Ming
• Granted Patent: US 7,033,507 B2
• Time in Patent Office: Days
• US Class Current: 210/721
• CPC Class Codes: C02F 1/52 by flocculation or precipitation of suspended impurities C02F1/463 takes precedence
• CPC Class Codes: C02F 1/5236 using inorganic agents
• CPC Class Codes: C02F 1/5263 using natural chemical compounds
• CPC Class Codes: C02F 1/66 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 Class Codes: C02F 1/74 with air aeration of stretches of water C02F7/00
• CPC Class Codes: C02F 2101/203 Iron or iron compound
• CPC Class Codes: C02F 2101/206 Manganese or manganese compounds
• CPC Class Codes: C02F 2103/10 from quarries or from mining activities
• CPC Class Codes: Y10S 210/912 Heavy metal

Abstract

A method for removing metal contaminants from acidic mine wastewater using lignin derivatives, such as lignosulfonates and kraft lignin, an alkali coagulant, such as a lime compound, and an alkaline composition for increasing the pH. The lignin derivatives are dispersed in the wastewater and the coagulant is added, increasing the pH to about 4.5-8.5 and causing the formation of a floc. The alkaline composition is then added to bring the pH to about 9 to 10, causing the further formation of a floc. Optionally, air oxidation is carried out, reducing the pH to about 8.1-8.6. Optionally, a ferric or ferrous salt may also be added. The flocs comprise metal-lignin colloids, metal hydroxides and metal salts. The flocs coagulate to form a sludge. Optionally, fly ash or diatomaceous earth may be added to increase the density and stability of the sludge. The sludge that is formed contains the metals and is separated from the treated water by filtration.

Claims

1. A method for removing metals from metal-containing acidic mine wastewater, comprising the steps of:

(a) dispersing lignin derivatives in said wastewater;

(b) dispersing an alkali coagulant in said wastewater, thereby increasing the pH of said wastewater;

(c) after steps (a) and (b), dispersing an alkaline composition in the wastewater, thereby increasing the pH of said wastewater and causing the formation of a floc; and

(d) separating metal-containing flocs formed in said wastewater from said wastewater.

2. A method according to claim 1 further comprising, after step (c), the step of causing oxidation of said wastewater.

3. A method according to claim 2 wherein said oxidation is done by introducing air into said wastewater.

4. A method according to claim 1 wherein said metals comprise one or more of aluminum, cadmium, cobalt, copper, manganese, nickel, lead and zinc.

5. A method according to claim 1 wherein said lignin derivatives comprise lignosulfonates.

6. A method according to claim 1 wherein said lignin derivatives comprise sulfonated kraft lignin salts.

7. A method according to claim 1 wherein said lignin derivatives comprise sulfonated kraft lignin salts.

8. A method according to claim 5 wherein said lignosulfonates comprise one or more of:

(i) ammonium lignosulfonates;

(ii) calcium lignosulfonates;

(iii) sodium lignosulfonates;

(iv) potassium lignosulfonates; and

(v) magnesium lignosulfonates.

9. A method according to claim 6 wherein said sulfonated kraft lignin salts comprise sulfonated kraft lignin salts of ammonium, calcium, sodium, potassium or magnesium.

10. A method according to claim 1 wherein the amount of said lignin derivatives is in the range of 0.0002 to 0.05 grams per liter of said wastewater.

11. A method according to claim 1 wherein said alkali coagulant is a lime compound.

12. A method according to claim 11 wherein the amount of said lime compound is about 0.1 to 0.8 g (as CaO) per liter of said wastewater.

13. A method according to claim 11 wherein the amount of said lime compound is about 0.15 to 0.5 g (as CaO) per liter of said wastewater.

14. A method according to claim 11 wherein said lime compound comprises hydrated lime, quick lime, limestone, dolomitic lime, dolomitic hydrated lime, dolomitic limestone, or mixtures thereof.

15. A method according to claim 1 wherein the pH is increased to a pH in the range of 4.5 to 8.5 in step (b).

16. A method according to claim 1 wherein the pH is increased to a pH in the range of 6.0 to 7.5 in step (b).

17. A method according to claim 1 wherein the pH is increased to a pH in the range of 9 to 10 in step (c).

18. A method according to claim 1 wherein the pH is increased to a pH in the range of 9.3 to 9.6 in step (c).

19. A method according to claim 1 wherein said alkaline composition comprises caustic soda, soda ash or soluble hydroxides or a mixture thereof.

20. A method according to claim 1 wherein said alkaline composition comprises a lime compound.

21. A method according to claim 1 wherein said step of separating comprises coagulating said flocs to form a sludge and separating said sludge from said aqueous filtrate.

22. A method according to claim 1 wherein said step of separating said sludge is done by filtration.

23. A method according to claim 3 wherein said oxidation reduces the pH to about 8.0-8.6.

24. A method according to claim 3 wherein said oxidation reduces the pH to about 8.3-8.5.

25. A method according to claim 1 further comprising the step of adding fly ash or diatomaceous earth to said wastewater.

26. A method according to claim 25 wherein the amount of said fly ash or diatomaceous earth is 0.5 grams or less per liter of said wastewater.

27. A method according to claim 25 wherein the amount of said fly ash or diatomaceous earth is in the range of 5 to 10 percent by weight of the weight of said alkali coagulant.

28. A method according to claim 25 wherein said step of adding fly ash or diatomaceous earth is carried out at the same time as step (a).

29. A method according to claim 25 wherein said step of adding fly ash or diatomaceous earth is carried out at the same time as step (b).

30. A method according to claim 25 wherein said step of adding fly ash or diatomaceous earth is carried out at the same time as step (c).

31. A method according to claim 25 wherein said fly ash is one of class C or class F fly ash.

32. A method according to claim 2 further comprising the step of adding a ferric or ferrous salt.

33. A method according to claim 2 further comprising the step of adding a ferric salt to said water after said step of air oxidation.

34. A method according to claim 2 wherein said oxidation reduces the pH of said water to about 8.7-8.9, further comprising the step of adding a ferric salt to said water after said step of air oxidation, reducing the pH to 8.0-8.6.

35. A method according to claim 33 wherein said ferric salt is ferric chloride and the amount of ferric chloride added is in the range of 0.01 to 0.12 g per liter of wastewater.