Ion exchange mechanism of Cr+3 on naturally occurring clinoptilolite

Abstract

Ion exchange isotherms are very important tools to achieve a better comprehension of cation removal by means of zeolite treatment. In this work, three isotherms were obtained (at 298K, at 313K and at 333K) from natural pretreated Na+ clinoptilolite. The ion exchange was carried out with Cr+3 ions. The isotherms' shape is similar to the classical type 'b' isotherm, according to the arrangement proposed by Breck (1984). Mathematical fitting was applied to the experimental points (Table Curve software) to obtain a representative curve thereof. From such fittings, points were simulated and then used to construct the Kielland plots, whose shape was associated with an ion exchange mechanism. Straight lines were obtained as an indication that, although the zeolite used is of natural occurrence and presents impurities such as mordenite and clays, only one site is involved in the ion exchange process.