Problems Associated with Layer Charge Characterization of 2:1 Phyllosilicates
A. R. Mermut, 1994. "Problems Associated with Layer Charge Characterization of 2:1 Phyllosilicates", Layer Charge Characteristics of 2:1 Silicate Clay Minerals, A. R. Mermut, S. A. Boyd, W. J. Farmer, W. F. Jaynes, G. Lagaly, D. A. Laird, A. R. Mermut
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The layer charge is, perhaps, the single most important characteristic of 2:1 phyllosilicates. The layer charge indicates a mineral's capacity to retain cations and to adsorb water and various polar organic molecules. It influences the affinity of organo-clays for sorption of organic contaminants in aqueous system (Lee et al., 1990). Studies on structural chemistry also confirm the importance of the layer charge for the characterization of the silicate clays (Newman and Brown, 1987).
It is been suggested that the classification of 2:1 silicate clays, which remains to be a problem, may be resolved by taking into account the magnitude of the layer charge, charge distribution between tetrahedral and octahedral sheets, dioctahedral versus trioctahedral and the type of the adsorbed cation(s) (Bailey et al., 1971). The International Association for the Study of Clays (AIPEA) nomenclature committee considers the layer charge as one of the primery criteria for classification of 2:1 silicate clays.
Based on basal spacings of clays saturated with known cations and cation exchangecapacities (CEC), four groups of swelling 2:1 silicate clay minerals can be identified (Lagaly and Weiss, 1969). These are: