Kinetic and equilibrium isotherm studies for the adsorptive removal of Brilliant Green dye from aqueous solution by rice husk ash

The present study deals with the adsorption of Brilliant Green (BG) on rice husk ash (RHA). RHA is a solid waste obtained from the particulate collection equipment attached to the flue gas lines of rice husk fired boilers. Batch studies were performed to evaluate the influences of various experimental parameters like initial pH (pH0), contact time, adsorbent dose and initial concentration (C0) on the removal of BG. Optimum conditions for BG removal were found to be pH0≈3.0, adsorbent dose ≈6 g L−1 of solution and equilibrium time ≈5 h for the C0 range of 50–300 mg L−1. Adsorption of BG followed pseudo-second-order kinetics. Intra-particle diffusion does not seem to control the BG removal process. Equilibrium isotherms for the adsorption of BG on RHA were analyzed by Freundlich, Langmuir, Redlich–Peterson (R–P), Dubnin–Radushkevich (D–R), and Temkin isotherm models using a non-linear regression technique. Langmuir and R–P isotherms were found to best represent the data for BG adsorption onto RHA. Adsorption of BG on RHA is favourably influenced by an increase in the temperature of the operation. Values of the change in entropy (ΔS0) and heat of adsorption (ΔH0) for BG adsorption on RHA were positive. The high negative value of change in Gibbs free energy (ΔG0) indicates the feasible and spontaneous adsorption of BG on RHA.