Flotation behaviour of zircon with sodium oleate as a collector was studied in a modified Hallimond tube over a wide pH range from 3 to 11. Electrokinetic, surface tension and infrared studies were performed to suggest mechanisms for the collector action in view of oleate species diagrams. Maximum flotation recoveries of zircon were obtained at around neutral pH values with a sharp decline towards the alkaline region. The effect of pH on the flotation recovery was found to be more significant at lower sodium oleate concentrations even though the peak recovery values were unsatisfactorily low at low concentrations. Electrokinetic and solution surface tension measurements indicated that pH was effective on both the surface charge of the mineral and the surface tension of sodium oleate solutions. The isoelectric point of untreated zircon was found at pH = 4.4. Zircon surface acquired a net negative charge in sodium oleate solutions and no isoelectric point was observed over the pH range from 2.5 to 11. Ion-molecular oleate species and colloidal neutral oleic acid precipitates were suggested as being responsible for the flotation of zircon in the near neutral and acidic pH values, respectively.
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