Adsorption of direct dye on palm ash: Kinetic and equilibrium modeling

Palm ash, an agriculture waste residue from palm-oil industry in Malaysia, was investigated as a replacement for the current expensive methods of removing direct blue 71 dye from an aqueous solution. The experimental data were analyzed by the Langmuir and Freundlich models of adsorption. Equilibrium data fitted well with Freundlich model in the range of 50–600 mg/L. The equilibrium adsorption capacity of the palm ash was determined with the Langmuir equation and found to be 400.01 mg dye per gram adsorbent at 30 °C. The rates of adsorption were found to conform to the pseudo-second-order kinetics with good correlation. The results indicate that the palm ash could be employed as a low-cost alternative to commercial activated carbon.