Preparation of activated carbon from black wattle bark waste and its application for phenol adsorption

Abstract Black wattle bark waste is generated in large amounts by tannin extraction industries, which leads to an environmental problem. In literature there are few reports about reusing this waste, mainly in adsorption processes. An activated carbon from black wattle bark waste was produced, characterized and applied for phenol adsorption. Activated carbon was produced under different carbonization and activation conditions, being characterized and applied as an adsorbent for phenol removal from aqueous solution. The results showed that phenol adsorption capacity increased with the increase of carbonization temperature and of activating agent ratio and, decreased with the increase of carbonization time. Activated carbon presented a micro/mesoporous structure and the surface area was 414.97 m2 g−1. FTIR analysis showed that lactone and quinone groups compose the surface chemistry of the activated carbon. The adsorption kinetics followed the pseudo-second order model. The Weber-Morris model showed that the adsorption occurred by film and intra-particle diffusion, and the increase in stirring rate led to an increase in film diffusion. Temperature increase led to an increase in phenol adsorption capacity, and the highest value was around 98.57 mg g−1, obtained at 55 °C. The Freundlich isotherm model was the more suitable to represent the equilibrium data. Thermodynamic study indicated that phenol adsorption onto the developed activated carbon was a spontaneous, favorable, endothermic and entropy-controlled process. The activated carbon can be used in two cycles with a slight decrease in the equilibrium adsorption capacity and presented a good efficiency to remove phenolic compounds in a simulated industrial effluent.