Removal of ferricyanide ions from aqueous solutions using modified red mud with cetyl trimethylammonium bromide

The reuse of red mud, an industrial waste found in alumina productions, is an efficient method to decrease the disadvantages of the industrial operation. In this study, red mud has been modified (ABC) with the surfactant of cetyl trimethylammonium bromide (CTAB) and used as a new adsorbent for the removal of ferricyanide anions from aqueous solution. The CTAB changed the charge of red mud to positive charge in a concentration above the critical micelle concentration that efficiently reduced the negative charge repulsion force between the adsorbent surface and ferricyanide anions. The equilibrium studies using two- and three-parameter models showed that the adsorption process followed the Freundlich model in which ferricyanide adsorption onto ABC was heterogeneous with a multilayer adsorption. The kinetic studies have been carried out with the consideration of pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models, which displayed the chemisorption interaction by intraparticle diffusion as a controlling step. Thermodynamic studies indicated that the ferricyanide adsorption process onto ABC was endothermic and spontaneous.