Enhanced Adsorption of Methylene Blue Using Distilled Water Neutralized Red Mud

This work is aimed at improving the ability of red mud to remove methylene blue from aqueous
solution. The efficiency of methylene blue (MB) removal by untreated red mud was compared to that
of red mud neutralized with distilled water. 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-, SO4
2-, HPO4
2- and HCO3
- on dye removal. Distilled water treated red mud (RMD) had
improved adsorbent properties than raw red mud (RM). For all the parameters tested, RMD showed
higher removals of MB compared to RM. The fitting order for tested isotherm models was: Langmuir >
Dubinin–Radushkevich > Freundlich for RMD and Freundlich > Dubinin–Radushkevich > Langmuir for
RM. Monolayer adsorption capacities of RMD 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 RMD > MB on RM. MB removal was found to be more endothermic, more
spontaneous and more favourable on RMD than on RM. Desorption experiments using acetone gave
good results up to four cycles. MB can easily be removed from waste water using distilled water
neutralized red. Water modified red mud is relatively efficient as other used materials for MB removal
(Table 5), so it was concluded that red mud modified with distilled water can be used for industrial
applications in removing methylene blue from various real effluents released from various types of
industries such as chrome plating, textile dyeing, leather tanning and photolithographic industries.
Furthermore, red mud is very cheap as compared to other adsorbents so easily available. Also
modification of red mud with water is a cheaper process with no risk of introducing other chemicals on
to it as opposed to other neutralization methods that use mineral acid, heat and other chemicals.
Distilled water neutralized red mud is more efficient in removing methylene blue from waste water
than untreated red mud.