This paper describes studies of preparation, activation and physical characterization of a Chilean zeolite (Ch-zeolite) employed as adsorbent for manganese ions from aqueous solutions. The zeolite sample, composed mainly of clinoptilolite and mordenite, had a specific surface area of 118 m(2) g(-1) (N-2 adsorption), the particles were negatively charged in a wide pH range and presented a cation-exchange capacity of 1.09 meq NH4+ g(-1). The medium pH influenced significantly the Mn2+ ions adsorption capacity and best results were obtained at pH 6-6.8. The adsorption onto the activated zeolite followed the pseudo-second-order kinetic model and activation of the Ch-zeolite with NaOH resulted in the highest reaction rate. The equilibrium data showed excellent correlation with the Langmuir isotherm model. Ch-zeolite modification by treating it with NaCl (0.77 meq Mn2+ g(-1)), NaCH (0.76 meq Mn2+ g(-1)), Na2CO3 (0.72 meq Mn2+ g(-1)) and NH4Cl (0.67 meq Mn2+ g(-1)) increased its uptake ability when compared with the natural Ch-zeolite (0.26 meq Mn2+ g(-1)). These data contribute to the understanding of mechanisms involved in zeolite activation and provide some practical clues to improve the adsorption efficiency (uptake capacity and kinetics) of manganese ions. (C) 2008 Elsevier Ltd. All rights reserved.