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Chromate reduction by waste iron from electroplating wastewater using plug flow reactor.
Shiao-Shing Chen1, Bao-Chrung Hsu, Li-Wei Hung
1Institute of Environmental Engineering and Management, National Taipei University of Technology, No. 1, Section 3, Chung-Hsiao East Road, Taipei 106, Taiwan. f10919@ntut.edu.tw <f10919@ntut.edu.tw>
Journal of Hazardous Materials
|September 11, 2007
Summary
Waste iron effectively removes high chromate concentrations from electroplating wastewater in a plug flow reactor. This simultaneous waste treatment approach lowers pH and reduces the need for base addition to meet discharge standards.
Area of Science:
- Environmental Chemistry
- Wastewater Treatment
Background:
- Electroplating wastewater contains high concentrations of toxic chromate.
- Simultaneous treatment of waste iron and chromate offers a sustainable solution.
- Low pH of electroplating wastewater facilitates the reaction.
Purpose of the Study:
- To investigate the use of waste iron for chromate reduction in electroplating wastewater.
- To evaluate the efficiency of a plug flow reactor (PFR) for this treatment.
- To determine the optimal hydraulic retention time (HRT) and pH for chromate removal.
Main Methods:
- Utilizing a plug flow reactor (PFR) to treat high-concentration chromate wastewater with waste iron.
- Adjusting influent pH and hydraulic retention time (HRT) to achieve complete chromate reduction.
- Analyzing effluent characteristics, including pH and turbidity.
- Employing X-ray diffraction (XRD) to identify precipitate species.
Main Results:
- Complete chromate reduction was achieved at various pH and HRT combinations (e.g., pH 1.7/98 min, pH 1.5/40 min, pH 1.3/20 min).
- Elevated effluent pH was observed, reducing the requirement for base addition.
- Turbid effluent (pH 3-5) indicated precipitation of chromium oxides/hydroxides, enhanced by iron coagulation.
- X-ray diffraction identified chromium oxides, hydroxides, and an iron-chromium complex (Cr2FeO4).
Conclusions:
- Waste iron is an effective reductant for high-concentration chromate in electroplating wastewater.
- The PFR system facilitates simultaneous waste treatment and pH adjustment.
- The process minimizes post-treatment base requirements and forms stable chromium precipitates.
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