Treatment of blast furnace wastewater

• US 4,366,064 A
• Filed: 11/05/1981
• Issued: 12/28/1982
• Est. Priority Date: 10/30/1980
• Status: Expired due to Fees

• Current Assignee: United States Steel Corporation (U.S. Steel)
• Original Assignee: United States Steel Corporation (U.S. Steel)
• Inventors: Mihelic, Edward L., Schlosberg, Samuel B.
• Primary Examiner(s): Therkorn, Ernest G.
• Application Number:
  US06/318,303
• Time in Patent Office: 418 Days
• Field of Search: 210/694, 210/739, 210/743, 210/746, 210/754, 210/755, 210/756, 210/663, 210/664, 210/668, 210/669
• US Class Current: 210/668
• CPC Class Codes: C02F 1/76 with halogens or compounds of halogens C02F1/4674 takes precedence

Abstract

Wastewater, particularly blowdown from a recycle gas-scrubbing and gas-cooling system of a blast furnace, is treated in a two-stage chlorination unit, the first stage including a chlorine addition at a pH of about 8.5 to about 10, preferably 9-9.5, and the second stage continuing the chlorination reaction at a pH of about 6 to about 8, preferably 7-7.5, while monitoring the oxidation-reduction potential of the second stage to utilize as a control point for chlorine addition in the first stage. Various contaminants, notably the nitrogen-containing compounds, are destroyed in the chlorination steps. A caustic or lime pretreatment is preferred for scale control at a pH of about 10.5 to about 11, preferably 10.7, while lime pretreatment is performed at a pH of about 9.6 to about 10, preferably 9.8. After chlorination, the process stream is preferably passed through activated carbon to remove organics.

Claims

1. Method of treating blast furnace and other wastewater containing ammonia, cyanide and phenol by breakpoint chlorination comprising chlorinating said wastewater maintained at a pH of about 8.5 to about 10 in an initial vessel by the addition of a chlorinating compound in response to the redox potential measured in a second vessel, flowing said wastewater from said initial vessel to said second vessel, mixing said wastewater, and maintaining the pH in the second vessel from about 6 to about 8, and the redox potential of the second vessel at a value of from about +625 millivolts to about +750 millivolts.

2. Method of claim 1 followed by passing said wastewater through activated carbon to remove residual contaminants.

3. Method of claim 1 in which the retention time of the wastewater in the second vessel is at least about thirty minutes.

4. Method of claim 1 in which the pH of the first vessel is maintained from about 9-9.5.

5. Method of claim 1 in which the pH of the second vessel is maintained from about 7-7.5.