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 Clˉ, SO₄²ˉ, HPO₄²ˉ and HCO₃ˉ 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.
Department of Chemistry, Higher Teachers’ Training College Maroua, P.O.Box 55 Maroua, Cameroon and Laboratoire des Matériaux et Chimie Inorganique Industrielle, University of Ngaoundere, Cameroon.
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