School of Chemistry - Theses
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ItemOleic acid adsorption at the goethite-water interface( 1976)The adsorption of oleate at the goethite-water interface has been studied. In addition, the interactions of oleate at other mineral-water interfaces were considered. Mainly by means of a literature review, a bulk equilibrium solubility diagram for oleic acid in water was constructed, as a function of total oleate concentration and pH. The competing bulk precipitation equilibria for oleic acid mineral phases such as iron (III) oxides, barite, calcite and fluorite and the relevant metal oleates, were considered graphically. Literature, adsorption, flotation recovery, electrokinetic and infrared work was examined in the light of this bulk precipitation data. It was found that many of these studies have been carried out in pH-concentration regions where bulk equilibrium phase changes were occurring, such as precipitation of oleic acid or of metal oleates. Adsorption behaviour in these systems was obscured by the bulk precipitation effects. Adsorption experiments were carried out with oleate in the presence of goethite, choosing pH and concentration such that bulk precipitation effects were not important. Electrostatic and hydrophobic interactions as well as chemisorption, appeared to be of importance in the adsorption process. A new approach for surfactant adsorption, a multiple equilibrium model, was suggested to describe quantitatively, the adsorption of oleate at the goethite-water interface. This approach considers oleic acid solution equilibria. The adsorption process is represented by the reaction of neutral goethite surface sites with oleate and protons in the manner of solution equilibria. A good fit was obtained to the experimental data. The model predicts that the acid-soap species HOI2 is the most important adsorbed species.