LAUSR

Abstract The adsorption of methyl orange (MO) onto goethite (G), chitosan beads (CSB) and goethite impregnated with chitosan beads (GCSB) as a new and potential adsorbents have been studied. Batch adsorption studies were conducted to evaluate the effect of various parameters such as pH, contact time, initial dye concentration and temperature. The adsorbents are characterized by using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Brunner-Emmet-Teller (BET) analysis, respectively. FTIR results revealed that hydroxyl, amine and carboxyl functional groups present on the surface of adsorbents. Experimental equilibrium data for adsorption of MO was analyzed by the Langmuir, Freundlich and Dubinin-Radushkevich models. The results showed that the best fit was achieved with the Langmuir isotherm equation with maximum adsorption capacities of 55, 73 and 84 mg/g for G, CSB and GCSB, respectively. The pseudo-first-order and pseudo-second-order model equations were used to analyze the kinetic data of the adsorption process and the data was fitted well with the pseudo-second-order kinetic model. The calculated thermodynamic parameters, namely ΔG o , ΔH o and ΔS o showed that adsorption of MO was spontaneous and endothermic in the temperature range 298–338 K. Desorption experiments were carried out to explore the feasibility of regenerating the adsorbent and the adsorbed MO from G, CSB and GCSB were desorbed using 0.1 M NaOH with an efficiency of 91, 94 and 96%, respectively, recovery. Findings of the present study indicated that G, CSB and GCSB can be successfully used for removal of MO from aqueous solution.