Separation of fine-grained zircon and rutile: a study of flotation chemistry and kinetics

George D Wren

Zircon can be separated from rutile with flotation, providing a recovery advantage for fine grained deposits. The combination of fluoride, dodecyl amine acetate (DDA) and starch can achieve good performance, however tight procedures are required due to sensitive reagent interactions. This study considers how these interactions affect flotation kinetics by reviewing previous work, characterising an ore sample, and completing experiments aiming to relate flotation chemistry and kinetics. An ore sample was sourced from WIM100 and characterised, identifying the dominant minerals: zircon, rutile, ilmenite, monazite, xenotime, sillimanite, tourmaline, and quartz. Some interesting surface features were observed, including ilmenite oxidation and inclusions of impurities in rutile. Adsorption results were analysed with kinetics, isotherms, thermodynamic calculations, and by considering the effects of specific changes to solution chemistry. The adsorption of DDA is quick, reaching equilibrium within an hour. For zircon, it is dominated by chemisorption at zirconia sites and enhanced by the addition of NaF and starch, a result of multilayer formation. On rutile, physisorption dominates without significant interactions with fluoride and starch. Zeta potential measurements show strong adsorption of fluoride, DDA and starch, and indicate DDA is chemisorbed on all minerals except rutile and tourmaline. Flotation kinetics are presented graphically and described by a novel first order model with a time dependant rate constant. It provides an improved description when compared with typical kinetic models, demonstrating both good fit and reasonable estimate for maximum recovery. By comparing flotation performance with adsorption results, selectivity is seen to depend on surface and solution chemistry, including surface cleaning and activation by fluoride, starch adsorption on titanium minerals, DDA adsorption on silicate and phosphate minerals and formation of multilayers consisting of DDA, amylose and fluoride. Some metallurgical results are also presented, showing that combining DDA flotation with magnets and gravity can achieve high zircon recovery (> 95%) to an acceptable concentrate. A similar result was obtained with a phosphonic acid collector and starch, without additional physical processing.

Separation of fine-grained zircon and rutile: a study of flotation chemistry and kinetics

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