Adsorption Isotherms and Kinetics Studies of a Cationic and Anionic Dye Removal from Aqueous Solution Onto Raphia Farinifera Biomass

Abstract

The adsorption of methylene blue (MB) a cationic dye and methyl orange (MO) an anionic dye from aqueous solution onto Raphia farinifera as an inexpensive and renewable biosorbent, was investigated in this study through batch experiments in order to determine the effect of pH, contact time and initial dyes concentration at a temperature of 27°C. The process proved to be pH-dependent reaching optimum at pH 12 and 4 for methylene blue and methyl orange dyes respectively within 90 min. Also, the adsorption percentage decreased with increased dye concentration. Five adsorption isotherm models namely: Langmuir, Freundlich, Dubinin Radush-kevich, Temkin and Scatchard isotherm models were applied to analyze the relationship between the amount of dye adsorbed and the remaining in solution. From the result, both Langmuir and Freundlich isotherm models suitably described the mechanism of the sorption process, but the Freundlich isotherm provided a better fit, indicating multilayer adsorption onto heterogeneous binding sites. The non-linear conformity of the Scatchard isotherm plot to the equilibrium adsorption data further supported this fact. Kinetic analysis showed that both dyes followed the pseudo second-order and Elovich kinetic mechanisms. However, MO adsorption kinetics also aligned with the intra-particle diffusion model to a reasonable extent. All these findings suggest that Raphia farinifera is useable as an effective material for separation of MB and MO dyes from aqueous systems.