Journal
JOURNAL OF HAZARDOUS MATERIALS
Volume 302, Issue -, Pages 468-474Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.jhazmat.2015.10.013
Keywords
Coking wastewater; Cyanide; Ferrous sulfate; Complexation; Biodegradability
Categories
Funding
- National Science Foundation of China [21207040, 51278199]
- Chinese Postdoctoral Science Foundation [2012M521607]
- K.C. Wong Magna Fund in Ningbo University
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The effect of ferrous sulfate (FeSO4) treatment on the removal of cyanide compounds and the improvement of biodegradability of coking wastewater were investigated by varying Fe:TCN molar ratios. Results suggested that the reaction between FeSO4 and coking wastewater was a two-step process. At the first step, i.e., 0 <= Fe:TCN <= 1.0, the reaction mechanisms were dominated by the precipitation of FeS, the complexation of CN-, and the coagulation of organic compounds. The COD of coking wastewater decreased from 3748.1 mg/L to 3450.2 mg/L, but BOD5:COD (B/C) was improved from 0.30 to 0.51. At the second step, i.e., 1.0 < Fe:TCN <= 3.2, the immobilization of soluble metal-cyanide compounds by ferrous ions was the dominating mechanism. The COD showed a continuous increase to 3542.2 mg/L (Fe:TCN = 3.2) due to the accumulated ferrous ions in coking wastewater. Moreover, B/C decreased progressively to 0.35, which was attributed to the negative effects of excess ferrous ions on biodegradability. To improve coking wastewater's biodegradability, a minimum ferrous dosage is required to complete the first step reaction. However, the optimum ferrous dosage should be determined to control a safe residual TCN in coking wastewater for the further biological treatment. (C) 2015 Elsevier B.V. All rights reserved.
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