Treatment of Red Mud with Distilled Water to Improve Its Efficiency to Remove Methylene Blue from Aqueous Solution

Abstract

In this work, raw red mud was treated with distilled water and its methylene blue (MB) removal efficiency from aqueous solution evaluated and compared to that of raw red mud. The pH, surface charge, particle size distribution, chemical composition, infrared spectrometry and morphology analyses were used to characterize the adsorbents. Batch experiments without agitation and filtration were conducted to determine the influence of contact time, solution pH, temperature, initial dye concentration, adsorbent dose and presence of Cl-, SO42-, HPO42- and HCO3- on dye removal. Distilled water treated red mud (RMW) had improved adsorbent properties than raw red mud (RM). For all the parameters tested, RMW showed higher removals of MB compared to RM. The fitting order for tested isotherm models was: Langmuir > Dubinin–Radushkevich > Freundlich for RMW and Freundlich > Dubinin–Radushkevich > Langmuir for RM. Monolayer adsorption capacities of RMW and RM were found to be 17.123 and 4.221 mg/L respectively. Pseudo-second-order kinetic model suited well than other tested kinetic models. Equilibrium was attained in 24 hours, and the order of shifting of equilibrium to the right as well as the rate of uptake is: MB on RMW > MB on RM. MB removal was found to be more endothermic, more spontaneous and more favourable on RMW than on RM. Desorption experiments using acetone gave good results up to four cycles. These findings revealed that treating red mud with distilled water significantly enhanced its ability to easily remove MB from aqueous solutions.