Equilibrium uptake, isotherm and kinetic studies of Cd(II) adsorption onto iron oxide activated red mud from aqueous solution

In this study, iron oxide activated red mud (IOARM) was used effectively to adsorb Cd(II) from aqueous solution. The optimized adsorption parameters were: pH 6.0, dose 6.0 g/L, contact time 90 min, initial concentration 400 mu g/L and temperature 300 K. Adsorption followed Freundlich isotherm model. Langmuir monolayer adsorption capacity was 117.64, 11628 and 107.53 mu g/g, while Freundlich adsorption capacity, k(F), was 3.83, 3.68 and 3.07 mu g/g at 293,298 and 308 K, respectively, The adsorption capacities in both isotherms decreased with temperature indicating exothermic nature of process. Change in Gibb's free energy was -9.93, -10.97 and -1136 kJ/mol at 293,298 and 308 K, respectively, indicating spontaneity and feasibility of the process. The enthalpy change was found to be 7.27 kJ/mol indicating physical adsorption of Cd(II) onto IOARM. Adsorption followed pseudo-second order kinetics with intraparticle and film diffusion mechanisms. The exhausted IOARM was regenerated using 0.1 HNO3 and used five times. The results indicated that IOARM is a promising adsorbent for removal of Cd(II) from water under natural conditions. (C) 2014 Elsevier B.V. All rights reserved.