Coconut Coir Activated Carbon ─ A Novel Adsorbent for Heavy Metal Remediation in Aqueous Environment

The objective of this study was to prepare a low-cost activated carbon from an agricultural solid waste and assess its effectiveness in heavy metal remediation in the aqueous environment. Activated carbon was prepared from coconut coir and its characteristics were compared with that of a commercial bituminous coal-based activated carbon. The coconut coir activated carbon possessed higher surface and micropore area, micropore volume and average pore diameter, and well-developed meso- and micro-pores. Adsorption of hexavalent chromium from aqueous solution by the coconut coir activated carbon was examined. Batch adsorption test showed that extent of adsorption was dependent on chromium concentration, contact time, pH and carbon dose. Maximum adsorption occurred at pH 1.5-2.0 and equilibrium adsorption was attained in 2.5 h. Chromium adsorption followed a pseudo second-order kinetics. Equilibrium chromium adsorption data for the coconut coir activated carbon and commercial activated carbon were described by the Langmuir and Freundlich isotherm models, and indicated higher chromium adsorption capacity of the coconut coir activated carbon. Hexavalent chromium adsorption capacity of the coconut coir activated carbon was compared with that of activated carbon prepared from different waste material and bituminous coal. The coconut coir activated carbon showed high limiting capacity for adsorption of hexavalent chromium. Coconut coir activated carbon is a suitable substitute for commercial activated carbon in the adsorptive removal of hexavalent chromium from water.