Abstract
Chitosan and keratin were tested as low cost biosorbents to remove phenol from water solutions at variable temperature (20-50 degrees C), initial phenol concentration (10-90 mg L-1) and pH (5.0-10.0), and fixed biosorbent dosage (10 g L-1). The pseudo-second order kinetic model exhibited the best fit to the experimental data and allowed estimating theoretical values of sorption capacity of 4.51 mg g(-1) with keratin and 2.87 mg g(-1) with chitosan. Equilibrium isotherms, described at best by the Freundlich model, pointed out that keratin (K-F = 1.34 mg(1-1/n) L-1/n g(-1)) was more effective than chitosan (K-F = 0.19 mg(1-1/n) L-1/n g(-1)) in phenol removal, although the sorption intensity was almost coincident (n = 1.18-1.19). The results of tests performed at different temperatures suggested a novel thermodynamic approach based on the occurrence of a sorbent inactivation equilibrium, whose changes of enthalpy and entropy were estimated to be 35.7 kJ mol(-1) and 118 J mol(-1) K-1 with chitosan, and 256 kJ mol(-1) and 845 J mol(-1) K-1 with keratin. The main functional groups involved in phenol sorption by both raw and phenol-bound materials were identified by FT-IR spectroscopy.