Acid/base treatment of Al-PILC in KCl solution

The ion-exchange properties of Na+ montmorillonite and its Al-pillared form have been investigated. Electrolyte solutions of (KCl/HCl), (KCl/KOH) and (KCl/NaOH) at two different concentrations of 0.05 M and 0.1 M were used. T he results obtained on the original clay are compared with those on the pil lared form to see the impact of the ion exchange on the stability of the pi llars. The study was performed by using X-ray diffraction (XRD), nitrogen-a dsorption measurements, elemental analysis of the solids before and after m odification and atomic absorption spectroscopy (AAS) as a tool to analyze t he supernatant. The recorded pH curves of the base substrate montmorillonit e and the Al-PILC give an indication of the anion and cation uptakes as a f unction of the pH of the solutions utilized. The results show a significant increase in ion-exchange capacity after intercalation of alumina pillars. However, by X-ray diffraction an appreciable decrease of the interlayer spa cing is noticed from about 18.3 Angstrom to 14 Angstrom at pH 1.73 and to 1 6 Angstrom at pH 12.45 for Al-PILC although no structural breakdown occurs. In contrast, the surface area and the micropore volume decrease significan tly in highly acidic or basic medium. For instance, a surface area of 232 m (2) g(-1) for the Al-PILC decreases after treatment at pH 2.63 to 215 m(2) g(-1) and to 71 m(2) g(-1) at pH 1.73. The same observation is made under b asic conditions. Moreover, a considerable amount of Al3+ is leached out fro m the modified Al-PILC, Therefore, it is reasonable to assume that the alum ina pillars are attacked during this treatment, leading to partial destruct ion or dissolution of the pillars. (C) 1998 Elsevier Science B.V. All right s reserved.