UBC Theses and Dissertations
Floatability of jarosites in the presence of anionic surfactants Payne, Avery
Five jarosite samples were synthesized and their surface properties relevant to froth flotation were examined. Sodium jarosite, low-silver sodium jarosite (3.47 % Ag), high-silver sodium jarosite (12.84% Ag), potassium jarosite, and high-silver potassium jarosite (5.56% Ag) were synthetized in an autoclave. No significant differences in zeta potential characteristics [pH 2-10] were observed between the samples, with a common isoelectric point at pH 5. Reagent adsorption and Hallimond tube (single mineral) flotation experiments were conducted with three anionic surfactants at pH 3.5 and at pH 10. The three reagents were: sodium laurate, sodium dodecyl sulfate, and octanohydroxamic acid. These surfactants represented different classes of flotation collectors: weak-electrolyte type (lauric acid and hydroxamic acid), strong-electrolyte type (dodecyl sulfate), highly soluble in water (dodecyl sulfate and hydroxamate) and poorly soluble in water (lauric acid). The experimental results were analyzed in terms of correlations between zeta potential, surfactant adsorption, and flotation results in order to enhance the fundamental understanding of surfactant-jarosite interactions. It was found from the adsorption and flotation results that the floatability of jarosites in the presence of the tested reagents followed two main trends. For several jarosite-reagent-pH combinations, the floatability of the mineral increased steadily with the increasing adsorption density of the reagent. In other cases, a minimum concentration of the reagent was required to initiate flotation even though the adsorption density of the surfactant continuously increased. It was postulated that in the latter case, the transition from poor to good flotation coincided with a change in the adsorption mechanism of the surfactant, while in the former case, one mechanism dominated the interaction. It was concluded that the adsorption of the anionic surfactants was driven by chemical interactions with iron sites on the jarosite surfaces regardless of the jarosite type. When analyzing the adsorption data, it was recognized that the jarosite surface at pH 10 was coated by a goethite (FeO(OH)) layer, while at pH 3.5 the surfactants adsorbed on a clean jarosite surface. No systematic trends were observed as a function of the silver content. Based on all the data, recommendations on the most promising flotation conditions were also made.
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