Treatment of blast furnace wastewater
First Claim
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.
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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.
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Citations
5 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.
Specification