Removal of diazo and triphenylmethane dyes from aqueous solutions through an adsorption process

Direct Red 31, Acid Black 1 and Acid Green 16 belonging to diazo and triphe nylmethane classification of dye chemicals are widely used during the manuf acture of leather. The spent dyestuffs in wastewater escape biological trea tment owing to their poor biodegradability. An adsorption procedure was use d in this study for the removal of dyes from aqueous solution using Rice Br an-based Activated Carbon (RBAC). The molecular weight of the dye chemicals , the mass of RBAC and the diameter of RBAC particle had positive effects o n the rate of adsorption. Initial concentration of dye chemicals, pH of the dye solution and temperature of adsorption showed a negative impact on ads orption. The enthalpies of adsorption for Direct Red 31, Acid Black 1 and A cid Green 16 were -32.1, -23.4 and -21.7 KJ mol(-1) respectively, indicatin g the adsorption was an exothermic physical process. The entropies of adsor ption for Direct Red 31, Acid Black 1 and Acid Green 16 were -96.94, -59.92 and -26.96 J K-1 mol(-1) respectively, suggesting that RBAC favours the ad sorption process. (C) 1999 Society of Chemical Industry.