Rice husk ash as an effective adsorbent: Evaluation of adsorptive characteristics for Indigo Carmine dye

Present study explored the adsorptive characteristics of Indigo Carmine (IC) dye from aqueous solution onto rice husk ash (RHA). Batch experiments were carried out to determine the influence of parameters like initial pH (pH0), contact time (t), adsorbent dose (m) and initial concentration (C0) on the removal of IC. The optimum conditions were found to be: pH0 = 5.4, t = 8 h and m = 10.0 g/l. The pseudo-second-order kinetic model represented the adsorption kinetics of IC on to RHA. Equilibrium isotherms were analyzed by Freundlich, Langmuir, Temkin and Redlich–Peterson models using a non-linear regression technique. Adsorption of IC on RHA was favorably influenced by an increase in the temperature of the operation. The positive values of the change in entropy (ΔS0) and heat of adsorption (ΔH0); and the negative value of change in Gibbs free energy (ΔG0) indicate feasible and spontaneous adsorption of IC on to RHA.