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Title: Colloidal and surface properties of illite
Author: Beene, M. G.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1988
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Physico-chemical and colloidal properties of two illites (illite 1 from USA and illite 2 from Australia) are reported herein. Illite 1 is of a platey habit (aspect ratio 2:1, specific surface area 62.34 m2/g). Illite 2 has thicker edges (aspect ratio 2:1 and a specific surface area of 125.64 m2/g). The two clays are mineraologically similar and differ only in their layer composition: illite 1 contains a higher proportion of aluminium in the tetrahedral layer and illite 2 has a higher percentage of iron in the octahedral layer. The significance of adequate surface preparation on the titratable surface charge density of illite (potentiometric titration) is illustrated. Both clays develop a positive charge density at pH lower than the point of zero titration (PZT) and a negative charge density above it. The presence of an electrokinetic potential associated with a permanent negative charge density is manifested by the dependence of the electrophoretic mobility of illite 2 on both the homoionic form (Na-, K- and Cs-) and electrolyte concentration. In dilute electrolyte, the mobility of the three forms of illite is negative and indistinguishable. In concentrated electrolyte, the mobility of K-illite 2 is lower than that of Na-illite 2 at a given pH. Cs-illite 2 exhibits isoelectric points in CsC1 concentrations higher than 10-2 M. The zeta potential calculated from the Dukhin and Derjaguin expression is in good agreement with that obtained from the computer method of O'Brien and White. An electrical double layer (triple layer) model has been developed to predict charge densities and potential of illite. Model calculation show that by allowing capacitances and ionization/complexation constants to vary with pH and salt concentration respectively, the edge charge density and zeta potential can be satisfactorily predicted. Rheological tests have shown that in a given salt concentration, the structure of K-illite 2 dispersions resulting from f-f, f-e, e-e interactions is strongly influenced by pH At 0 = 0.02, low pH and/or electrolyte concentration higher than 10-2 M KC1, the dispersions are elasticoviscous.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available