Montmorillonite as a Model Substance

Before discussing the interfacial reactions of montmorillonite, we have to define what we call montmorillonite in practice. As known, most minerals are not found in pure forms they are present in rocks together with other minerals. Montmorillonite is the main component of bentonite rocks, so bentonites with high montmorillonite content are frequently called montmorillonite. For scientific studies, we use bentonite with high montmorillonite content in natural form after purification with sedimentation. Usually, the fraction 2 pm is the clay fraction containing montmorillonite. 

In the literature, different commercial montmorillonites are used, especially for catalytic purposes (KSF or K10 montmorillonites). They are usually acid-treated clays, montmorillonite content of which is rather low. Our x-ray diffraction studies show 44% Ca-montmorillonite content of K10 montmorillonite, and 53% Na-montmorillonite content of KSF montmorillonite the CEC of KSF montmorillonite was found to be 30 meq/100 g by the ammonium acetate method (Richards 1957). A similar value has been given by Abollino et al. (2003). So, in a strict clay science sense, they cannot be considered as montmorillonite. Naturally, this causes no problems in organic chemistry when the main objective is the catalysis of a given reaction. 

In our studies, the model substance (montmorillonite) was a calcium bentonite (Istenmezeje, Hungary), the characteristic features of which are given here. X-ray diffraction (intensity of the basal reflection) and thermoanalytical (weight loss upon heating) data show 91% montmorillonite content. The other constituents are 5% calcite, 3% kaolinite, 1% x-ray amorphous silicates, and a trace of quartz. The amorphous phase is silicate particles, which are not crystalline for 

---

USE OF MONTMORILLONITE AS A MODEL SUBSTANCE THE IMPORTANT INTERFACIAL PROCESSES ON MONTMORILLONITE... 

---