Azo Dye Removal from Aqueous Solutions Using Laccase-modified Red Mud: Adsorption Kinetics and Isotherm Studies

Removal of acid red 37 from aqueous solutions has been studied using red mud waste material after its modification with laccase from Russulaceae (Lactarius volemus). Laccase was purified by using saturated precipitate (NH4)2SO4, diethylaminoethyl celulose (DEAE-cellulose) and immobilized on red mud. The removal of acid red 37 by the laccase-modified red mud has been demonstrated in order to explore its potential use as low-cost adsorbent. The adsorption kinetics of acid red 37 dye on the laccase-modified red mud with respect to pH, contact time, temperature and adsorbent dose were investigated. The optimum results were obtained at pH 4, contact time of 60 min and temperature of 30ºC. The Freundlich equation was found to have the highest value of R2 compared with the Langmuir model. Thermodynamic parameters including the Gibbs free energy, enthalpy and entropy changes indicated that the adsorption of acid red 37 onto laccase-modified red mud was feasible, spontaneous and endothermic.