Removal of Basic Dye From Aqueous Solution By Adsorption On Melon Husk In Binary And Ternary Systems

Abstract

The adsorption behaviour of a cationic dye (methylene blue)   in binary and ternary solutions on the husk of melon (Citrullus lanatus) seed was investigated in order to elucidate the effects of competitive adsorption on the kinetics and thermodynamics of the sorption process.  The experimental findings showed that adsorption equilibrium was reached within 120 min either in single, binary or ternary mixtures; and the   adsorption processes in all the systems studied were described by the pseudo-second order kinetics with the initial rate constant increasing as the  concentrations of the competing dyes were increased.  Five different equilibrium isotherm models ( Freundlich, Temkin, Langmuir, Harkin-Jura and Dubinin-Radushkevich) were applied and  Langmuir was the best-fitting one for the adsorption of methylene blue dye in single system (R² > 0.99), while the binary and ternary systems were best described by Freundlich model (R² > 0.99). The sorption processes were thermodynamically feasible as ?G values were negative. Adsorption in both single and binary systems was exothermic while that of ternary system was endothermic.

Keywords: melon husk, binary dye system, ternary dye system, methylene blue,                       Competitive adsorption, isotherms, thermodynamics, basic dye