Batch adsorption of basic dye using acid treated kenaf fibre char: Equilibrium, kinetic and thermodynamic studies

An adsorbent (H-KFC) was prepared from kenaf fibre char by acid treatment using HCl (3 M). The treatment caused an increase in the BET surface area and as a result there was an increase in the adsorption of Methylene blue dye (MB) in batch system studies. The adsorption process was investigated by varying the initial dye concentration, adsorbent dose, pH and temperature. The highest percentage removal of Methylene blue dye (MB) was found to be 95 wt% at a concentration of 50 mg/L. At a pH of 8.5, the sorption of dye was favourable. The equilibrium data was analysed using the Langmuir, Freundlich and Temkin isotherm models. It was found that the equilibrium data was best represented by the Langmuir isotherm model. The kinetic data obtained was analysed using a pseudo-first-order and pseudo-second-order equation. The experimental data fitted well the pseudo-second-order kinetic model. The intraparticle diffusion model showed three steps where intraparticle diffusion was not the only rate controlling step of the adsorption process. Thermodynamic studies indicated that the adsorption was endothermic, increasing in randomness of adsorbed species and spontaneous at high temperatures.

► The maximum removal was obtained at pH 8.5.
► The adsorption isotherm data were fitted well to Langmuir isotherm.
► The adsorption kinetic described well by the pseudo-second-order model.
► The intraparticle diffusion was not the only rate controlling step of adsorption process.
► The adsorption was found to be endothermic, increasing randomness and spontaneous at high temperature.