Preparation of Na-P1 and sodalite octahydrate zeolites from interstratified illite–smectite

The clay of Aidoudi (South Tunisia) which is an interstratified illite–smectite corresponding to the following analysis: SiO2: 54.0%; Al2O3: 19.4%; Fe2O3: 6.7%; CaO: 0.2%; MgO: 1.5%; Na2O: 2.3%; K2O: 1.1% and a fire loss of 14.6% has been treated with 1 to 5 M NaOH solutions. Reaction has been performed on reflux during 2 to 24 h. The zeolitic products have been characterized by X-ray diffraction (XRD), infrared (IR) absorption, chemical analysis and SEM observations. For 1 and 1.5 M NaOH solutions zeolite Na-P1 was formed. It represents 47 and 58%, respectively, of the final solid corresponding to a reaction time of 24 h. For 2 to 5 M alkaline solutions sodalite octahydrate zeolite was obtained with yields up to 76% of the final solid. Cation exchange capacities towards ammonium cations have been determined. The final sodalite octahydrate zeolite has a CEC which increases from 167 to 367 mEq/100 g when temperature rises from 25 to 75°C whereas the Na-P1 zeolite presents a constant CEC equal to 270 mEq/100 g.