Lecture 8

Piero m armenante njit cyanide removal via alkaline

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Unformatted text preview: troyed before the metals are precipitated. • Wastewaters containing cyanides (up to 1000 mg/L) are often treated with sodium hypochlorite (NaClO) or chlorine gas mixed with sodium hydroxide (to form sodium hypochlorite) in a two-step process. PIERO M. ARMENANTE NJIT Cyanide Removal Via Alkaline Chlorination (continued) • The first step is the conversion of cyanide (CN-) to cyanate ion (OCN-) in a two-reaction sequence at a pH above 10 (reaction time: 30 min. to 2 h): CN − + H2O + ClO − ⇔ CNCl + 2 OH − CNCl + ClO − ⇔ OCN − + Cl − + H2O • The second step is the oxidation of cyanate with hypochlorite at pH 8.5 to increase the kinetics (reaction time: 10 min. to 1 h): 2 OCN − + 3 ClO − + H2O ⇔ 2CO2 + N2 + 3Cl − + 2 OH − PIERO M. ARMENANTE NJIT Treatment Plant for Wastewaters Containing Heavy Metals Caustic Coagulant Acid Cyanide Wastewater Caustic Chlorine Cyanide Oxidation Chrome Wastewater Neutralization Precipitation Acid Coagulation Flocculation Clarification Treated Wastewater Sulfur Dioxide Equalization and Partial Neutralization Wastewater Recycle Chrome Reduction Acid Wastewater Alkaline Wastewater Sludge Thickening Filtration Sludge to Final Disposal After EPA, Environmental Regulations and Technology: The Electroplating Industry, 1985 PIERO M. ARMENANTE NJIT Additional Information and Examples on Metal Precipitation Additional information and examples can be found in the following references: • Corbitt, R. A. 1990, The Standard Handbook of Environmental Engineering, McGraw-Hill, New York, pp. 6.92; 9.25. • Eckenfelder, W. W., Jr., 1989, Industrial Water Pollution Control, McGraw-Hill, New York, pp. 98-110 • Freeman, H. M. (ed.), 1989, Standard Handbook of Hazardous Waste Treatment and Disposal, McGraw-Hill, New York, pp. 7.21-7.31. PIERO M. ARMENANTE NJIT Additional Information and Examples on Metal Precipitation • Haas, C. N. and Vamos, R. J., 1995, Hazardous and Industrial Waste Treatment, Prentice Hall, Englewood Cliffs, NJ, pp. 147-152. • Sundstrom, D. W. and Klei, H. E., 1979, Wastewater Treatment, Prentice Hall, Englewood Cliffs, NJ, pp. 327-330. • Wentz, C. W., 1995, Hazardous Waste Management, Second Edition, McGraw-Hill, New York, pp. 155-157. PIERO M. ARMENANTE NJIT Filename: Cls06-21.doc Directory: D:\TEMP Template: C:\WINWORD\OVERHEAD.DOT Title: Subject: Author: Piero M. Armenante Keywords: Comments: Creation Date: 02/21/97 9:12 AM Change Number: 49 Last Saved On: 03/02/97 6:14 PM Last Saved By: Piero M. Armenante Total Editing Time: 280 Minutes Last Printed On: 08/31/99 11:21 AM As of Last Complete Printing Number of Pages: 41 Number of Words: 2,263 (approx.) Number of Characters: 12,902 (approx.)...
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