Abstract
Adsorption tests of Congo Red, a commercial azo dye, by acid mine drainage (AMD) sludge were carried out at different pH, temperature, dye concentration, contact time, and adsorbent dosage. Precoat filtration was conducted to test if the dye could be removed during continuous filtration by a precoated AMD sludge layer. Adsorption of Congo Red onto AMD sludge followed the Langmuir isotherm model with a maximum adsorption capacity of 389.1mg∕g. Based on thermodynamic studies, adsorption was found to be exothermic, and an increase in temperature led to a decline in dye removal. Dye removal decreased with an increasing pH. Through metal leaching tests, it was observed that most metals associated with AMD sludge remained insoluble when adsorption occurred at pH 6–10. A rather rapid process was observed for the adsorption of Congo Red onto AMD sludge with more than 80% adsorption taking place within 5min. Adsorption kinetics followed pseudo-second-order model. Precoat filtration continuously removed Congo Red from aqueous solution with success, and dye removal mechanism via precoat filtration was adsorption. The adsorption and precoat filtration studies showed dye removal could be a beneficial use of AMD sludge prior to its final disposal.
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