Effect of Heating on Swelling and Dispersion of Different Cationic Forms of a Smectite
The effect of heat treatments on the swelling, dispersion, particle charge and particle aggregation of Li-, Na-, K-, Mg-, Ca- and Al-Wyoming bentonite was investigated. Before thermal treatment, unheated (25 °C) Li-, Na- and K-clays showed increased d001 spacing on glycerol solvation and dispersed spontaneously in water. Mg-, Ca- and Al-clays did not disperse spontaneously in water, but the d001 spacing increased upon glycerol solvation. After heating at 300 °C or above, none of these clays dispersed spontaneously. However, swelling varied with the type of cation and the temperature of heating.
The results generally suggested that swelling and dispersion of homoionic Wyoming bentonite after heating at various temperatures depended upon the nature of bonding between clay particles and the cations. Enhanced swelling and dispersion of clays indicated the more ionic character of the cationic bonding than cases where heating resulted only in swelling, with polar covalent bonding of cations to clay surfaces allowing limited hydration. It is also suggested that, when both swelling and dispersion as a result of thermal treatment are absent, a covalent bond is formed between cation and clay surface.
Thermal treatment apparently affects the bonding in different ways. It appears that the smaller cations (ionic radius <0.7 Å) Li, Mg and Al migrate to octahedral vacant sites and form covalent bonds after heating at 400 °C; this drastically reduces the negative charge. This process for Li-clays occurred even at 200 °C. The larger cations (ionic radius > 0.9 Å) Na, K and Ca apparently did not migrate into the lattice sites after heating to 400 °C; a high proportion of them were exchangeable. The data for exchangeable cation, particle charge and clay particle size were consistent with the postulated effect of the nature of cationic bonding upon swelling and dispersion properties.
Key WordsCationic Clay Bonding Dispersion Particle Charge Swelling Thermal Treatment X-ray Diffraction
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- Christenson HK, Horn RG. 1985. Solvation forces measured in non-aqueous liquids. Chemica Scripta 25:37–41.Google Scholar
- Glaeser R, Mering J. 1968. Homogeneous hydration domains of the smectites. CR Acad Sci Paris 46:436–466.Google Scholar
- Greene-Kelly R. 1955. Dehydration of the montmorillonite minerals. Mineral Mag 30:604–615.Google Scholar
- Horvath I, Novak I. 1975. Potassium fixation and the charge of montmorillonite layer. In: Bailey SW, editor. Proceedings of the International Clay Conference; Mexico City. Wilmette, Illinois: Applied Publishing, p 185–189.Google Scholar
- Huheey JE, Keiter EA, Keiter RL. 1994. Inorganic chemistry.New York: Harper Collins, p 130–135.Google Scholar
- Jackson ML. 1969. Soil chemical analysis—advanced course. 5th printing. Madison, WI: ML Jackson, Univ of Wisconsin. 894 p.Google Scholar
- Jenkins HDB, Hartman P. 1982. A new approach to electrostatic calculations for complex silicate structures and their application to vermiculites containing a single layer of water molecules. In: van Olphen H and Veniale F, editors. Proceedings of the Internationa] Clay Conference; 1981; Bologna, Pavia. Amsterdam: Elsevier Science, p 87–95.Google Scholar
- Rengasamy P, Sumner ME. 1996. Processes involved in sodic behaviour. In: Sumner ME and Naidu R, editors. Sodic soils: distribution, processes, management and environmental consequences.New York: Oxford Univ Pr. 265 p.Google Scholar
- Tettenhorst RT. 1962. Cation migration in montmorillonites. Am Mineral 47:769–773.Google Scholar