Removal of cationic dyes by modified waste biosorbent under continuous model: Competitive adsorption and kinetics

Abstract

Modified waste sugarcane bagasse (SCB) was prepared to remove cationic dyes: methylene blue and rhodamine B from aqueous solution by using a continuous mode. Effects of flow rate on adsorption of the two dyes in fixed bed column were studied. Competitive adsorption kinetics of the two dyes in binary system was investigated in detail. Results showed that the adsorption capacities of the modified sorbent for methylene blue and rhodamine B in one component system were 1.7 and 0.4 mmol g−1, respectively. Competitive adsorption process in the binary system could be divided into three phases: free adsorption, substitution adsorption and adsorption equilibrium. 0.19 mmol of rhodamine B absorbed was replaced by 0.35 mmol of methylene blue in the second phase. Simple modified Yoon–Nelson model was used to predict the adsorption kinetics for the first time. The obtained adsorption rate constants for the two dyes in the three phases both followed the order: phase I > phase III > phase II, demonstrating that substitution adsorption phase is the rate determining step. Desorption experiment showed that the loaded two dyes could be separated and recycled by using the mixture solution of HCl (0.1 mol L−1) and ethanol as eluent. The prepared fixed bed column had great potential in industrial wastewater treatment. Keywords: Sugarcane bagasse, Fixed bed column, Competitive adsorption, Methylene blue, Rhodamine B