Natural zeolite (NZ) obtained from the Manisa-Demirci region of Turkey was modified by NaOH aqueous
solutions (0.5–2.0 mol/dm3) and the adsorption capacity of natural and modified forms was determined for
manganese removal. The characterisations of the zeolites were carried out by XRD, N2 sorption, FTIR, NH3-TPD
and SEM-EDS. Treatment of the NZ with NaOH leads to a significant decrease of its silica content by desilication
and an increase of its Na content by formation of hydroxysodalite. It was seen from the NH3-TPD results that
NaOH treatment alters the acidity of zeolite.While the number of weak and medium Brønsted/Lewis acid sites
decreases, the number of strong acid sites increases through the introduction of Na+ and the removal of silica.
Treatmentwith NaOH has the effect ofmultiply by two themanganese adsorption capacity of the natural zeolite.
The maximum manganese adsorption capacity was achieved with the zeolite treated with 1.5 M of NaOH. More
than this concentration of NaOH leads not only to a decrease in adsorption capacity of natural zeolite formanganese,
but also to a significant deformation of the zeolite structure. The Langmuir isothermmodel fits wellwith the
results obtained from manganese adsorption on natural zeolite, while the Freundlich isotherm model fits well
with the results obtained on NaOH modified zeolites.