Date of Award
Doctor of Philosophy
The relationship between Ba/Mg exchange selectivity and crystalline swelling was investigated with a synthetic fluorohectorite. Changes in the slope of the exchange isotherm were related to changes in basal spacing. To explain these observations, a model is proposed in which the same hydration and coulombic free energies that determine ion specificity also control the extent of crystalline swelling. The various layer hydrates that occur during crystalline swelling are assumed to be stabilized by an activation energy. This activation energy causes hysteresis in both crystalline swelling and ion exchange;A method is presented for determining the relative interlayer anionic field strength of expanding 2:1 phyllosilicates. The method is based on the extent of crystalline swelling of samples equilibrated with an atmosphere controlled at 54% relative humidity after treatment with various mixed K-Mg salt solutions. An index of interlayer anionic field strength was derived from the relationship between the potassium mole fraction of the treatment solution and the extent of crystalline swelling. The validity of the index was confirmed by the linear relationship between the index and layer charge density for a series of nearly isostructural reduced charge clays. Crystal structure, chemical composition and layer charge density were all found to influence the interlayer anionic field strength of reference clays. This was particularly evident for Llano vermiculite where basal hydroxyls lower the interlayer anionic field strength;The alkylammonium method gave a good relative measure of layer charge density for both reference and soil clays. However, the results were systematically lower than the layer charge determined by chemical analysis. The alkylammonium method was used to determine the layer charge of iron rich beidellites in three soils of an Argialboll-Argiaquoll sequence. For these soils horizon differentiation did not effect the beidellite layer charge. Use of the alkylammonium method with soil clays results in partial potassium depletion of soil illites. The K-depleted illites produce low angle X-ray diffraction peaks which are easily misinterpreted as evidence of soil vermiculite.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
David Alan Laird
Laird, David Alan, "Layer charge and crystalline swelling of expanding 2:1 phyllosilicates " (1987). Retrospective Theses and Dissertations. 8554.