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Abstract
The removal by adsorbing colloid flotation of Cr(III), Ni(II), and Zn(II) from chromium stream electroplating wastewater was investigated. Adsorbing colloid flotation involves the stripping of contaminants by adsorption or coprecipitation onto added colloidal material and its subsequent flotation by column flotation. The added colloid may be prepared prior to the adsorption step or, as in this case, prepared in situ by the hydrolysis of added metal [Fe(III)] ions. Adsorbing colloid flotation using a single surfactant (SDS) in the batch mode was shown to result in poor results for “real” industrial samples, presumably due to the chemical complexity of such samples. However, a dual surfactant system [sodium dodecylsulfate (SDS) + dodecanoic acid (DA)] provided encouraging results. By using such a dual surfactant system, chromium stream electroplating wastewater was treated, successfully lowering metal ion contamination levels to below that required for discharge into typical metropolitan drainage systems. Flotation was found to be successful at near neutral pH conditions (7.5) and for several different (electroplating) industrial samples. Adsorbing colloid flotation in the continuous mode was investigated by using the dual surfactant system optimized in batch experiments. At flow rates encouraging to full-scale commercial applications, toxic metal ions [Cr(III), Ni(II), Zn(II)] were stripped from contaminated industrial samples to below the 10 ppm typically required for metropolitan discharge. A two-stage continuous processing scheme was investigated where once-treated effluent was passed through a second “polishing” column. Use of this two-stage process typically resulted in the stripping of toxic metal ions (from similar samples) to well below the 1 ppm level typically required for environmental discharge.