On the removal of Mn2+ ions by adsorption onto natural and activated Chilean zeolites

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 m2 g−1 (N2 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), NaOH (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.