REMOVAL OF CYANIDE FROM AQUEOUS STREAMS

• US 20100307977A1
• Filed: 11/17/2008
• Published: 12/09/2010
• Est. Priority Date: 11/15/2007
• Status: Abandoned Application

• Current Assignee: Maelgwyn Mineral Services Africa (Pty) Ltd.
• Original Assignee: Maelgwyn Mineral Services Africa (Pty) Ltd.
• Inventors: Singh, Adrian
• Application Number:
  US12/743,145
• Publication Number:
  US 20100307977A1
• Time in Patent Office: Days
• US Class Current: 210/669
• CPC Class Codes: B09C 1/02 Extraction using liquids, e.g. washing, leaching , flotation
• CPC Class Codes: C02F 1/283 using coal, charred products, or inorganic mixtures containing them
• CPC Class Codes: C02F 1/74 with air aeration of stretches of water C02F7/00
• CPC Class Codes: C02F 2101/18 Cyanides
• CPC Class Codes: C02F 2103/10 from quarries or from mining activities
• CPC Class Codes: C02F 2209/04 Oxidation reduction potential [ORP]
• CPC Class Codes: C02F 2209/05 Conductivity or salinity
• CPC Class Codes: C22B 11/08 by cyaniding
• CPC Class Codes: C22B 15/0076 Cyanide groups
• CPC Class Codes: C22B 3/24 by adsorption on solid substances, e.g. by extraction with solid resins
• CPC Class Codes: C22B 7/008 by an alkaline or ammoniacal leaching
• CPC Class Codes: Y02P 10/20 Recycling

Abstract

This invention relates to a method of removing cyanide in the form of free cyanide (cyanide ions i.e. CN′) and weak acid dissociable cyanide (WAD) from an aqueous stream. WAD is cyanide complexed with metals such as Cu. The method finds particular application in removing cyanide from a tail stream from a carbon in leach (CIL) mining operation. The method of the invention is carried out by contacting an aqueous stream containing cyanide with carbon, under conditions wherein the Eh (oxygen reduction potential (ORP) measured in mV) of the aqueous stream is O or above. Advantageously the pH of the solution is buffered to from 7-9.

Claims

1. A method for removing cyanide from an aqueous stream, wherein:

the aqueous stream is contacted with carbon under conditions wherein the Eh (oxygen reduction potential (ORP) measured in mV) of the aqueous stream is 0 or above, to remove cyanide from the stream;

or

the aqueous stream is treated to control the Eh to 0 or above, and thereafter the aqueous stream is contacted with carbon, to remove cyanide from the stream.

2. The method as claimed in claim 1, wherein the aqueous stream is a tail stream from a carbon in leach (CIL) mining operation.

3. The method as claimed in claim 1, wherein WAD cyanide is removed from the aqueous stream.

4. The method as claimed in claim 1, wherein the Eh is from 0-500 mV.

5. The method as claimed in claimed in claim 4, wherein the Eh is from 0-300 mV.

6. The method as claimed in claim 5, wherein the Eh is from 0-200 mV.

7. The method as claimed in claim 1, wherein the carbon is in particulate form.

8. The method as claimed in claim 7, wherein the particles are 2-3 mm in size.

9. The method as claimed in claim 1, wherein the carbon is activated carbon.

10. The method as claimed in claim 1, wherein the carbon is added in an amount of 5-100 g/l of the stream containing cyanide.

11. The method as claimed in claim 10, wherein the carbon is added in an amount of 10-60 g/l of the stream containing cyanide.

12. The method as claimed in claim 11, wherein the carbon is added in an amount of 20-60 g/l of the stream containing cyanide.

13. The method as claimed in claim 1, wherein the pH of the aqueous stream is buffered to from 7-9.

14. The method as claimed in claim 13, wherein the buffering takes place over a period of 0.5-1.5 hours.

15. The method as claimed in claim 14, wherein the buffering takes place over a period of about an hour.

16. The method as claimed in claim 1, wherein the Eh of the stream is controlled by passing the stream through an oxygenating device in multiple passes, before or after the addition of cyanide to the stream.

17. The method as claimed in claim 16, wherein the oxygenating device is operated at a pressure of from above 1 bar up to about 10 bar.

18. The method as claimed in claim 17, wherein the oxygenating device is operated at a pressure of about 2.5 bar.

19. The method as claimed in claim 16, wherein oxygen is introduced into the oxygenating device in the form of bubbles.

20. The method as claimed in claim 19, wherein the bubbles have a size of from 1 micron to 1000 microns.

21. The method as claimed in claim 20, wherein the bubbles have a size of from 1 to 500 microns.

22. The method as claimed in claim 19, wherein the bubbles have an average size of 100 microns.

23. The method as claimed in claim 16, wherein the oxygenating device provides high shearing to the stream.

24. The method as claimed in claim 16, wherein the oxygen line pressure at the point of injection of oxygen is above the pressure of the oxygenating device.

25. The method as claimed in claim 24, wherein the oxygen line pressure at the point of injection of oxygen is above the pressure of about 10 bar.

26. The method as claimed in claim 16, wherein the oxygen consumption of the oxygenating device is from 0.25 kg/t to 200 kg/t liquid.

27. The method as claimed in claim 16, wherein the aqueous stream is re-circulated through the oxygenation device in 2 or more passes.

28. The method as claimed in claim 27, wherein the aqueous stream is re-circulated through the oxygenation device in 2 to 300 passes.

29. The method as claimed in claim 28, wherein the aqueous stream is re-circulated through the oxygenation device in 2 to 200 passes.

30. The method as claimed in claim 29, wherein the aqueous stream is re-circulated through the oxygenation device in 2 to 50 passes.

31. The method as claimed in claim 30, wherein the aqueous stream is re-circulated through the oxygenation device in 2 to 10 passes.

32. The method as claimed in claim 31, wherein the aqueous stream is re-circulated through the oxygenation device in 2 to 5 passes.

48. The method as claimed in claim 32, wherein the aqueous stream is re-circulated through the oxygenation device in 2.5 passes.

49. The method as claimed in claim 17, wherein the contact with carbon takes place in a tank separate from the oxygenation device.

50. The method as claimed in claim 17, wherein the cyanide removal takes place in multiple stages.

55. The method as claimed in claim 6, wherein the Eh is controlled by passing the stream through an oxygenation device in multiple passes, before or after the addition of cyanide to the stream.

56. The method as claimed in claim 55, wherein the aqueous stream is re-circulated through the oxygenation device in 5 to 15 passes.

57. The method as claimed in claim 56, wherein the aqueous stream is re-circulated through the oxygenation device in 10 passes.

59. A method for treating an aqueous stream containing metal values comprising the following steps:

treating the stream in an accelerated leach, wherein 0.1-20 kg/t (as required) cyanide is added to the stream and the stream is treated in an oxygenating device in multiple passes in a method as defined in claim 7.

60. The method as claimed in claim 59, wherein the aqueous stream is re-circulated through the oxygenation device in 5 to 10 passes.

61. The method as claimed in claim 60, wherein the aqueous stream is re-circulated through the oxygenation device in 5 passes.

62. The method as claimed in claim 59 wherein the Eh of the stream in the oxygenating device is greater than 0.

63. An integrated process for leaching an aqueous stream containing metal values comprising the following steps:

1) subjecting the stream to an optional pre-oxidation first stage by passing the stream through an oxygenating device in multiple passes;

2) subjecting the stream to an optional accelerated leach stage;

3) subjecting the stream to a carbon in leach (CIL) process and;

4) subjecting a tail stream from the CIL process to a cyanide removal stage as defined in claim 1.

33-47. -47. (canceled)

51. A method for treating an aqueous stream containing metal values comprising the following the steps:

treating the stream in a pre-oxidation stage; and

subjecting the stream to a CIL process;

wherein the pre-oxidation stage is conducted under conditions to provide an Eh (oxygen reduction potential (ORP) measured in mV) of the aqueous stream in the CIL process of 0 or above.

52. The method as claimed in claim 51, wherein the Eh is controlled to from 0-500 mV.

53. The method as claimed in claim 52, wherein the Eh is controlled to from 0-300 mV.

54. The method as claimed in claim 53, wherein the Eh is controlled to from 0-200 mV.

58. The method as claimed in claim 51, wherein the pre-oxidation takes place at a pH of 9 to 10.