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 triphenylmethane classification of dye chemicals are widely used during the manufacture of leather. The spent dyestuffs in wastewater escape biological treatment owing to their poor biodegradability. An adsorption procedure was used in this study for the removal of dyes from aqueous solution using Rice Bran-based Activated Carbon (RBAC). The molecular weight of the dye chemicals, the mass of RBAC and the diameter of RBAC particle had positive effects on the rate of adsorption. Initial concentration of dye chemicals, pH of the dye solution and temperature of adsorption showed a negative impact on adsorption. The enthalpies of adsorption for Direct Red 31, Acid Black 1 and Acid Green 16 were -32.1, -23.4 and -21.7 KJ mol -1 respectively, indicating the adsorption was an exothermic physical process. The entropies of adsorption 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 adsorption process.