Chemically modified sunflower stalks as adsorbents for color removal from textile wastewater

Quaternary ammonium groups were chemically grafted onto sunflower stalks in order to improve their adsorption performance to anionic species in wastew ater. The chemically modified sunflower stalks were evaluated as adsorbents for two basic dyes (Methylene Blue and Basic Red 9) and two direct dyes (C ongo Red and Direct Blue 71) in aqueous solutions by using equilibrium isot herms and kinetic adsorption. Before the modification, sunflower stalks exh ibited relatively low adsorption to the direct dyes but very high adsorptio n to the basic dyes. The modified sunflower stalks showed increased adsorpt ion to the anionic dyes, but slightly reduced adsorption to the cationic dy es, due to the existence of quaternary ammonium ions on the surface of the residues. The maximum adsorption capacities of two direct dyes on the modif ied sunflower stalks are 191.0 and 216.0 mg g for Congo Red and Direct Blue 71 at 50 degrees C, respectively, which were at least four times higher th an that of the unmodified residues. The adsorption rates of two direct dyes tuffs are much higher on the modified residues than on the unmodified ones. Within 30 min, about 80% of direct dyes were removed from the solutions by the residues. (C) 1999 John Wiley & Sons, Inc.