UBC Theses and Dissertations
Effect of alkali metal cations on adsorption of guar gum onto quartz Ma, Xiaodong
The effect of alkali metal chlorides (LiCl, NaCl, KCl, CsCl) on the adsorption of guar gum, a naturally occurring polysaccharide, onto quartz from dilute aqueous solutions of the electrolytes was investigated. The adsorption of guar gum onto quartz and the resulting colloidal stability of the system were determined through adsorption, zeta potential and turbidity measurements. This thesis analyzes a previously undescribed phenomenon of enhanced polysaccharide adsorption in the presence of cesium and potassium cations. At the same time, lithium and sodium cations show no effect on the polysaccharide adsorption density compared to that observed in distilled water. These differences in the behavior of the simple alkali chlorides are attributed to their water structure breaking or water structure making capabilities. In this approach, since hydrogen bonding is the main adsorption mechanism, the polymer adsorption process is treated as a competition between polymer and water molecules for polar surface sites on the quartz surface. While water structure-breaking cations disturb the interfacial water layer allowing guar gum to more densely adsorb on the exposed surface silanol groups, structure-making cations better fit into the interfacial water layer and do not affect the guar gum-water competition for the polar surface sites. The results strongly suggest that simple alkali metal chlorides are not totally indifferent, and even in dilute solutions their water-structure making/breaking capabilities should be taken into account to better understand the behavior of a model system such as quartz-guar gum. The study is relevant to several industrial flotation processes where polysaccharides are used as selective depressants. This thesis should be a valuable contribution to our understanding of the mechanisms of polysaccharide adsorption on mineral surfaces.