Calcium-montmorillonite prepared from

The structural parameters of cation-exchanged montmorillonites prepared from calcium-montmorillonite (Istenmezeje) are listed in Table 2.3. As seen in Table 2.3, the basal pacing of monovalent montmorillonite is approximately 1.25 nm, and the water content is approximately 1%. It means that there is one layer of water in the interlayer space. For bivalent montmorillonite, both basal spacing (>1.5 nm) and water content (>10%) are higher, showing two layers of water molecules in the interlayer space. The basal spacing of Pb-montmorillonite is 1.254 nm, which is similar to the value characteristic of monovalent montmorillonite (1.241 nm). However, it does not mean that lead is sorbed on the surface of montmorillonite as monovalent cation since the other parameters that are determined by the distance between the layers (hydration entropy, charge/ion radius value, water content in the interlayer space) lie between the values for bivalent and monovalent cations (Foldvari et al. 1998). 

The Structural Parameters of Cation-Exchanged Montmorillonites Prepared from Calcium-Montmorillonite (Istenmezeje, Hungary)... 

The most important industrial example of cation exchange is the preparation of sodium-montmorillonite/bentonite from calcium bentonite. As seen in Table 2.2, calcium ions have greater affinity to the layer charge than sodium ions, so the calcium-sodium cation exchange must be performed in the presence of carbonate ions. It means that calcium-montmorillonite/bentonite is suspended in sodium carbonate solution. Calcium ions precipitate with carbonate ions, so sodium ions can occupy the interlayer space. This process is known as soda activation of bentonite. The disadvantage of soda activation is that sodium-montmorillonite is contaminated with calcium carbonate. 

Work by Shishan et al. [20] illustrates the importance of utilizing montmorillonite that has sodium as the counterion for the preparation of the organomontmorillonite for successful exfohation by melt blending with a polymer. The montmorillonite in this work had calcium as the counterion. Calcium compromises the full exfohation of montmorillonite in water. Hence, the organomontmorillonite prepared from octadecyla-mine hydrochloride does not fully exchange with montmorillonite. 

The major constituents of soils are sesquioxides and clay minerals. Iron oxide (goethite) was synthesized by a method described by Gerth [4] and manganese oxide (manganite) was prepared by a method described by McKenzie [5]. The clay mineral montmorillonite was obtained from Wyoming, USA, while kaolinite was obtained from Ward Corp., USA. Organic substances were destroyed by a pretreatment of the clay minerals with HjOj. The surfaces were loaded with calcium chloride and adjusted to pH 7. 

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