| In the field of flotation, there exists a need to develop collectors with higher selectivity. In this respect, chelating agents have potential for use as effective reagents for they can selectively form inner metal-organic complexes with certain metal ions. Another approach to developing selective flotation reagents involves modification of the structure of conventional collectors to suit specific cases.; The collector properties of ten ortho-hydroxyoxime type chelating agents were investigated to determine the effect of the structure of the oxime reagents on the flotation of chrysocolla. The structures of these reagents are modifications of salicylaldoxime, which is a well-known chelating agent for copper. Flotation tests were conducted as a function of reagent concentration, conditioning time, pH and ionic strength, and the results were compared with those obtained using salicylaldoxime. Substitution of the hydrogen in the 5th position of the benzene group with a methoxy, and of the hydrogen attached to the carbon of the oximic group by methyl or butyl increased the collector property, whereas substitution with a benzyl to the latter, or with methyl groups to both positions together, caused a decrease in the collector property. Substitution of either the phenolic or the oximic hydrogen with a methyl group, or the benzene ring with either cyclohexanone or naphthalene was detrimental.; Single-mineral flotation tests were carried out with dodecylamine hydrochloride using purified chromite and its main gangue mineral, serpentine. Good flotation was obtained in the basic pH range where chromite and the reagent are oppositely charged, suggesting strong electrostatic adsorption aided by dimer formation. Collector properties of eight secondary, tertiary and quarternary amines were also investigated. Secondary and tertiary amine salts gave bell shaped flotation recovery curves, the maximum shifting toward lower pH values as the length of the alkyl groups was increased, due to precipitation. Quarternary amines, however, gave flotation recovery curves with maxima at high pH, since they did not precipitate, having no protons to donate. The flotation behavior of the two minerals exhibited some differences, depending on the collector structure and the conditioning pH.; The mineral-solution equilibria were also studied and the results were correlated with those of flotation tests. Chrysocolla was found to be negatively charged in the entire pH range studied (2.5-12); the zeta potential approached zero around pH 2.5 and gave a maximum around pH 5, where maximum flotation was observed for most of the reagents tested. Chromite was found to have very low solubility, and a point of zero charge around pH 6. |
