Removal of methylene blue from aqueous solution using by untreated lignite as potential low-cost adsorbent: Kinetic, thermodynamic and equilibrium approach

摘要: Abstract The adsorption mechanism of the cationic methylene blue dye to abundant and inexpensive lignite as an adsorbent from aqueous solutions was investigated a function ionic strength, pH, temperature, initial concentration, contact time stirring speed. capacity increased with increasing pH although it not affected by value zeta potential decreased pH. Experimental data were modelled different equilibrium isotherms such Langmuir, Freundlich, Temkin, Dubinin–Radushkevich (D–R), BET, Halsey, Harkins–Jura, Smith Henderson isotherms. process fitted well pseudo-second-order kinetics Langmuir model. Activation energy processes found be 49.81 kJ mol −1 concentration 80 mg L using Arrhenius equation, indicating strong electrostatic interactions between dye. isosteric enthalpy entropy changes calculated 58.19 kJ mol −0.186 kJ mol  K , respectively, that endothermic orderliness system slightly decreases molecules surface. FT-IR results revealed several functional groups on coal surface are responsible for adsorption. observed differences in reflection SEM images adsorbed due presence blue, which adsorbed. BET isotherm nitrogen-adsorption–desorption analysis implied is heteroporous material exhibiting microporous properties.