Fly ash and red mud have been emplo

Fly ash and red mud have been employed as adsorbents for the removal of methylene blue dye from aqueous solutions by Wang et al.. It was found that fly ash generally showed higher adsorption capacity than red mud. The adsorption capacity of 1.4 × 10−5 and 7.8 × 10−6 mol/g, for raw fly ash and red mud, respectively, have been reported. Red mud was explored as low-cost adsorbent for the removal of phenol, 2-chlorophenol, 4chlorophenol, and 2,4-dichlorophenol from wastewater by Gupta et al.. It was reported that 2,4-dichlorophenol and 4chlorophenol were adsorbed by the developed adsorbent up to 94–97%, while the removal of 2-chlorophenol and phenol was up to 50–81%. The order of removal was 2,4-dichlorophenol > 4chlorophenol > 2-chlorophenol > phenol. It was suggested by them that the removal of phenols took place through a particle diffusion mechanism. The adsorption was found to be endothermic in nature and followed both Langmuir and Freundlich models. Neutralized red mud was used for phenol removal from aqueous solution. The experiments demonstrated that maximum phenol removal was obtained in a wide pH range of 1–9 and it took 10 h to attain equilibrium. Namasivayam and Arasi investigated the adsorption potential of red mud for congo red dye removal from aqueous solution. The removal capacity of the red mud for the dye was 4.05 mg/g. Wang et al. have discussed the novel applications of red mud as coagulant, adsorbent and catalyst for environmentally benign processes in their comprehensive review.