Interaction of exchanged Zn2+-montmorillonite with alkaline and earth alkaline cations

Desorption of Zn2+ by montmorillonite in alkaline and earthalkaline environments was carried out at room temperature and at pH 6.0 using the following techniques: a combination of analytical methods to determine the variation of montmorillonite chemical composition, X-ray powder diffraction (at controlled relative humidity and at controlled temperature in the range 50°C≤T≤400°C) and thermal analysis. The desorption isotherms clearly show that some of the Zn2+cations are retained in the layers, the proportion being greater when the montmorillonite is treated with Na+ and smaller when treated with Mg2+. The d(001) basal spacing, for samples teated with Na+-K+ and Na+-Ca2+ mixed solutions, appears to be mainly affected by the first appearance of K+ and Ca2+. Differential thermal analyses of Zn2+-exchanged samples shows two dehydroxylation reactions at about 380 and 650°C which emphasized that Zn2+ is differently bonded in the layers and hence differently released.