Acid/base treatment of Al-PILC in KCl solution

Abstract

Abstract 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. The results obtained on the original clay are compared with those on the pillared form to see the impact of the ion exchange on the stability of the pillars. The study was performed by using X-ray diffraction (XRD), nitrogen-adsorption measurements, elemental analysis of the solids before and after modification and atomic absorption spectroscopy (AAS) as a tool to analyze the supernatant. The recorded pH curves of the base substrate montmorillonite and the Al-PILC give an indication of the anion and cation uptakes as a function 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 spacing is noticed from about 18.3 A to 14 A at pH 1.73 and to 16 A at pH 12.45 for Al-PILC although no structural breakdown occurs. In contrast, the surface area and the micropore volume decrease significantly 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 basic conditions. Moreover, a considerable amount of Al 3+ is leached out from the modified Al-PILC. Therefore, it is reasonable to assume that the alumina pillars are attacked during this treatment, leading to partial destruction or dissolution of the pillars.