Adsorption of anionic dye - Orange II - in aqueous solution onto hexadecyltrimethylammonium bromide (HDTMA)-coated zeolite (HCZ) reached 38.96 mg/g compared with 8.13 mg/g onto natural zeolite. Fourier Transform Infrared (FTIR), scanning electronic microscopy (SEM) and X-ray powder diffraction (XRD) data showed that HDTMA-coated zeolite developed surficial positive charges. The adsorption reaction fits the Freundlich isotherm (R-2 = 0.93) and the value of 1/n was less than unity (=0.81) and suggest a multi-layer physi-sorption process. The kinetics of the adsorption is a pseudo-second-order model. The activation energy (E-a) of the reaction is +35.70 kJ/mol to further support a physi-sorption process while the Delta H degrees (+82.79 kJ/mol) is characteristic for an endothermic reaction. The Delta G degrees values of -2.33, -0.98 and -0.37 kJ/mol at 25 degrees C, 30 degrees C and 35 degrees C, respectively implied that the adsorption reaction was feasible and thermodynamically spontaneous. We proposed that both electrostatic interactions and partitioning process are involved in the adsorption mechanisms of Orange II dye onto HCZ. (C) 2014 Elsevier Inc. All rights reserved.