Method and apparatus for cleaning contaminated particulate material

• US 5,268,128 A
• Filed: 01/31/1991
• Issued: 12/07/1993
• Est. Priority Date: 05/25/1990
• Status: Expired due to Term

• Current Assignee: Duratek Services Inc (Rockwell Holdco, Inc.)
• Original Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Inventors: Lahoda, Edward J., Grant, David C.
• Primary Examiner(s): Walsh, Donald P.
• Assistant Examiner(s): Jenkins, Daniel
• Application Number:
  US07/648,673
• Time in Patent Office: 1,041 Days
• Field of Search: 252/626, 209/2, 209/18, 209/456, 209/457
• US Class Current: 588/20
• CPC Class Codes: B09C 1/02 Extraction using liquids, e.g. washing, leaching , flotation
• CPC Class Codes: G21F 9/04 Treating liquids

Abstract

Particulate material is treated by first washing the contaminated material with a contaminant mobilizing solution comprising a leaching agent, a surfactant or a mixture thereof. Large particles, typically greater than 5 mm are mechanically separated, washed with water and returned to the site as recovered soil. Fines, along with contaminants dissolved or dispersed in the contaminant mobilizing solution are separated from intermediate sized particles by a countercurrent flow of the contaminant mobilizing solution, preferably in a mineral jig. The intermediate sized particles are then abraded in an attrition scrubber to dislodge attached mineral slimes or fines. These additional fines are separated from the intermediate sized particles with a countercurrent flow of wash water in a second mineral jig. The preferred oxidizing agent is chlorine, and hydrogen is the preferred reducing agent.

Claims

1. A method for removing contaminants comprising heavy metals and radioactive compounds, singly and in combination, from a process stream used in removing said contaminants from contaminated particulate material, said method including the steps of:

washing said contaminated particulate material with said process stream, thereby removing said contaminants from said particulate material, said process stream containing an oxidizing agent selected from the group Cl₂, ClO₂ and O₃ and/or a reducing agent, said oxidizing or reducing agent rendering at least one of said contaminants more soluble in said process stream;

separating clean particulate material from said process stream;

treating said process stream with a precipitant to remove said contaminant rendered more soluble in said process stream by said oxidizing or reducing agent; and

recycling said process stream for washing additional contaminated particulate material.

2. The method of claim 1 wherein said heavy metals are selected from the group Hg, U, Pb, Ag, As, Cd, Cr, Cu, Ra, Th.

3. The method of claim 1 wherein said process stream is water-based.

4. The method of claim 3 wherein said process stream further includes a leachate for the removal of said contaminants from said particulate matter.

5. The method of claim 3 wherein said process stream further includes a surfactant for the removal of said contaminants from said particulate matter.

6. The method of claim 5 wherein said surfactants are removed from said process stream following washing of said particulate matter.

7. The method of claim 6 wherein said surfactants are precipitated from said process stream.

8. The method of claim 7 wherein CaCl₂ is used for precipitating said surfactants.

9. The method of claim 8 wherein said contaminant rendered more soluble comprises said heavy metals.

10. The method of claim 8 wherein following removal of said clean particulate matter, said heavy metals are precipitated from said process stream with a precipitant.

11. The method of claim 10 wherein said precipitant comprises Na₂ SiO₃.

12. The method of claim 11 wherein fines are recovered from said process stream prior to precipitation of said heavy metals.

13. The method of claim 12 wherein following removal of said fines said process stream is pH adjusted to about 8-10 to assist in precipitation and removal of said heavy metals from said process stream.

14. The method of claim 13 wherein said precipitated heavy metals are used as a feedstock for mining or smelting operations to recover said heavy metals.

15. The method of claim 13 wherein said precipitated heavy metals are mixed with a fixative material for disposal.

16. The method of claim 11 wherein fines are recovered with said precipitated heavy metals.

17. The method of claim 16 wherein said process stream is pH adjusted to 8-10 to assist in precipitation of said heavy metals.

18. The method of claim 17 wherein said precipitated heavy metals are used as a feedstock for mining or smelting operations to recover said heavy metals.

19. The method of claim 17 wherein said precipitated heavy metals and fines are mixed with a fixative material for disposal.

20. The method of claim 8 wherein said heavy metals are precipitated and removed from said process stream and said process stream is recycled for washing said particulate matter.

21. The method of claim 8 wherein additional oxidizing or reducing agent is added to said process stream following removal of said heavy metals.

22. The method of claim 21 wherein said contaminated particulate material further includes contaminants that are organic compounds and said additional oxidizing or reducing agent destroys said organic compounds.

23. The method of claim 22 wherein said process stream includes an aliphatic surfactant which is recycled for washing said contaminated particulate matter.

24. The method of claim 22 wherein said surfactants are removed from said process stream prior to treating said stream with a heavy metal precipitant and said surfactants are aliphatic when a reducing agent is used and are non-aliphatic when an oxidizing agent is used.

25. The method of claim 1 wherein said reducing agent is H₂ and said oxidizing agent is Cl₂.

26. The method of claim 1 wherein prior to treating said process stream with said precipitant fines are removed from said process stream.

27. A method for removing contaminants comprising heavy metals, radioactive compounds and organic compounds, singly and in combination, from a water-based process stream used in removing said contaminants from contaminated particulate material, said process stream containing a leachate and/or a surfactant, said process stream further including an oxidizing and/or a reducing agent, said oxidizing agent increasing the solubility of said heavy metal in said process stream, said method including the steps of:

washing said contaminated particulate material with said process stream, thereby removing said contaminates from said particulate material;

separating clean particulate material from said process stream, while retaining said heavy metals in solution in said process stream;

adjusting the pH of said process stream to 8-10;

adding a precipitant to precipitate said heavy metals from said process stream;

removing said heavy metals from said process stream; and

recycling said leachate and/or said surfactant for washing additional contaminated particulate matter.

28. The method of claim 27 wherein said reducing agent is H₂ and said oxidizing agent is Cl₂.

29. The method of claim 27 wherein said heavy metals are selected from the group Hg, U, Pb, Ag, As, Cd, Cr, Cu, Ra, Th.

30. The method of claim 27 wherein said precipitant comprises Na₂ SiO₃.

31. The method of claim 27 wherein said oxidizing agent comprises Cl₂, fines are removed from said process stream prior to precipitation of said heavy metals and prior to adjusting said pH, said precipitated heavy metals are removed from said process stream yielding a recycle process stream, and makeup Cl₂ is added to said recycle process stream, which is recycled for washing said contaminated particulate material.

32. The method of claim 27 wherein said oxidizing agent comprises Cl₂, said precipitant flocculates any metal hydroxides and fines, precipitated heavy metals, flocculated metal hydroxides and fines are removed from the process stream, yielding a recycle stream, and makeup Cl₂ is added to said recycle process stream, which is recycled for washing said contaminated particulate material.

33. The method of claim 27 wherein said oxidizing agent is used and comprises Cl₂, and organic contaminants are precipitated with CaCl₂ prior to precipitation of said heavy metals, and said precipitated heavy metals, organics and fines are removed from the process stream, yielding a recycle process stream, which is recycled for washing said contaminated particulate material.

34. The method of claim 27 wherein said oxidizing agent comprises Cl₂ and, wherein prior to adding said heavy metal precipitant, organic contaminants are precipitated with CaCl₂ and said precipitated organic contaminants and fines are removed, after which said heavy metal precipitant is added, said heavy metals are precipitated and removed from said process stream, yielding a recycle process stream, which is recycled for washing said contaminated particulate matter.

35. An apparatus for removing contaminants comprising heavy metals, organics and radioactive compounds, singly and in combination, from a process stream used in removing said contaminants from contaminated particulate material, said apparatus comprising:

means washing said contaminated particulate material with said process stream, thereby removing said contaminates from said particulate material;

means introducing an oxidizing and/or reducing agent to said process stream, said oxidizing agent increasing the solubility of said heavy metals in said process stream;

means separating clean particulate material from said process stream following removal of said contaminants from said particulate material by said process stream;

means treating said process stream with a heavy metal precipitant following removal of said clean particulate material therefrom;

means removing precipitated heavy metal from said process stream following precipitation of said heavy metal;

means treating said process stream after removal of said heavy metal therefrom with makeup oxidizing and/or reducing agent;

means recycling said process stream to said means washing said contaminated particulate material.