Adsorption Kinetics of Methylene Blue onto Clay Fractionated from Bijoypur Soil, Bangladesh

The adsorption kinetics of methylene blue (MB) from aqueous solution onto clay fractionated from Bijoypur (Netrokona) soil based on particle size (≤53µm) has been investigated. Batch studies were carried out to investigate the effect of contact time, initial dye concentration and temperature on adsorption kinetics. Kinetic studies showed a rapid adsorption during the first thirty minutes. Application of pseudo first order, pseudo second order and intra particle diffusion model equations showed that the experimental results are well expressed by pseudo second order kinetic equation. Adsorption isotherm was constructed from the pseudo second order kinetic data. Maximum adsorption capacity, calculated from well fitted Langmuir equation, is 6.93 mg/g which increased with increase in temperature. The positive value of enthalpy change (∆H o =20.98 kJ/mol) and negative free energy change (∆G o ) indicated that the adsorption of MB on clay is endothermic and involve chemical process. Verification of intra-particle diffusion model showed that intra-particle diffusion could be one of the rate determining steps but pseudo second order mechanism is predominant. Overall adsorption process appears to be controlled by more than one step.