Sorption characteristics of methylene blue onto Nypa fruiticans lignin

Abstract

The sorption characteristics of soda lignin extracted from Nypa fruiticans for the removal of methylene blue dye from aqueous solution was investigated in this study, as an ethically sound way of utilizing this unexploited abundant natural resource. Equilibrium data were fitted to the Langmuir and Freundlich isotherm equations while the sorption dynamics were examined with the pseudo-first and second-order kinetic models. The influence of operational variables, namely, time, temperature, liquor-to-solid ratio and temperature, on the removal efficiency was determined using a second-order factorial equation. The Langmuir adsorption isotherm satisfactorily described the sorption of methylene blue dye unto the lignin matrix with a monolayer adsorption capacity of 16.67 mg/g. The sorption kinetics followed the pseudo-second-order kinetic model. The factorial equation derived reproduces the experimented data with errors less than 5%. The influence of the operational variables showed that the maximum variation in the highest uptake of methylene blue was caused by changes in concentration of methylene blue (a change of 32.7 units) while the liquor-to-solid ratio has little or no effect on
the dye uptake.

Keywords: adsorption, methylene blue, lignin, factorial design, isotherms, sorption kinetics