Removal of methylene blue from aqueous waste using rice husk and rice husk ash

Present study investigates the potential use of pretreated rice husk (RH) and rice husk ash (RHA) for the removal of methylene blue (MB) from wastewater. A series of batch experiments were carried out to determine the influence of different system variables. Neutral pH was optimum for the removal of MB. Adsorption of MB on RH and RHA was favorably influenced by an increase in the temperature of the operation. The comparative studies of these two adsorbents, RA and RHA with the earlier reported adsorbents obtained from agricultural and industrial waste products, inorganic materials and bioadsorbents, reveals that RH and RHA have maximum adsorption capacity. Adsorption data was fitted to the Langmuir, and Freundlich adsorption model. The former model achieved best fit with the experimental data and its calculated maximum monolayer adsorption capacity have a value of 1347.7 mg g− 1 for adsorption on RH and 1455.6 mg g− 1 for adsorption on RHA at a temperature of 323 K. The change in heat of adsorption (ΔHo) and entropy (ΔSo) values for MB adsorption on RH as well as RHA were positive. The high negative values for Gibbs free energy (ΔGo) indicate the feasible and spontaneous adsorption of MB on RH and RHA.