Investigation of applicability of the various adsorption models of methylene blue adsorption onto lignite/water interface

Methylene blue adsorption isotherms for raw and pyrolysed coal samples were determined at 20 °C. The raw coal sample showed the highest adsorption capacity. It was observed that adsorption capacity generally decreased with increasing pyrolysis temperature. The sample pyrolysed at 700 °C exhibited the lowest adsorption capacity. The experimental data obtained were applied to the Freundlich, Langmuir, BET, Halsey, Harkins-Jura, Smith and Henderson isotherm equations to test the fitness of these equations to raw and pyrolysed coal samples. By considering the experimental results and adsorption models applied in this study, it can be concluded that adsorption of methylene blue occurs through physical interactions, and the lignite sample has a mesoporous structure.