Adsorptive removal of malachite green dye from aqueous solution by bagasse fly ash and activated carbon-kinetic study and equilibrium isotherm analyses

Adsorption of malachite green (MG) was studied using three adsorbents namely, bagasse fly ash (BFA), a sugar industry waste, and activated carbons commercial grade (ACC) and laboratory grade (ACL). Batch adsorption studies were conducted to evaluate the effect of various parameters such as pH, adsorbent dose, contact time and initial MG concentration on the removal of MG. The initial pH of the dye solution strongly affected the chemistry of both the dye molecules and adsorbents in an aqueous solution. The effective pH was 7.0 for adsorption of MG by the three adsorbents. Equilibrium reached in about 4 h contact time. Optimum BFA, ACC and ACL dosages were found to be 1, 20 and 4 g l−1, respectively. The adsorption followed pseudo-second-order kinetics. Equilibrium adsorption data on BFA, ACC and ACL were analyzed by Freundlich, Langmuir, Dubnin–Radushkevich, Redlich–Peterson and Temkin isotherm equations using regression analysis. Non-linear error analysis showed that the Freundlich isotherm best-fits the equilibrium data for adsorptive removal of MG by BFA and ACC and Redlich–Peterson best follows the equilibrium data for ACL. Thermodynamic study showed that MG adsorption on BFA was comparable to that obtained with ACC or ACL.