Adsorptive removal of methylene blue dye wastewater from aqueous solution using citric acid activated red mud

The activated red mud was prepared as the adsorbent for the removal of methylene blue (MB), from aqueous solution by the batch adsorption technique under different operational parameters including adsorbent dosage, pH, initial dye concentration, contact temperature and time. The results demonstrate that the adsorption percentage of the citric acid activated red mud is improved evidently, and increases with the increase of activated red mud dosage, white decreases with the increase of initial MB concentration and temperature. The red mud activated by using dilute citric acid is quite effective to improve its adsorption efficiency for the dye molecules from the aqueous solution. The uptake capacity for MB is evaluated as 30 mg/g and the equilibrium data fits well to the Langmuir model, and the adsorption kinetic follows the pseudo-second-order equation with its apparent activation energy equal to 9.88 kJ/mol. The thermodynamic parameters, such as the changes in enthalpy and entropy, were determined, revealing the adsorption to be an exothermic yet spontaneous process.