~) Pergamon Minerals Engineering, Vol. 7, No. 9, pp. 1085-1098, 1994 Elsevier Science Ltd Printed in Great Britain 0892-6875194 $7.00+0.00 0892-6875(94)00054-9 THE SURFACE PROPERTIES AND FLOTATION BEHAVIOUR OF XENOTIME TA-WUI CHENG, A.C. PARTRIDGE, TAM TRAN and P.L.M. WONG Centre for Minerals Engineering, University of New South Wales, P.O. Box 1, Kensington, 2033, NSW, Australia (Received 18 Januasy 1994; accepted 1 March 1994) ABSTRACT Smface properties and flotation behaviour of xenotime using sodium oleate as a collector have been investigated. Adsorption isotherm attd flotation studies in combination with chemical modelling were conducted to investigaie the surface properties of xenothne and mechanisms of the interactions of the smface with the collector and the collector-treated stnface with air bubbles. It was foutwl that the adsot.'ption process on a xenotime sulface is very much pH dependent. The amount of active sites on the sulface available for reacting with the collector is related to the distribution of hydroxyl species. Front both experimental observations and chemical modelling, sulface precipitation is believed to play an important role its governing the mechanisms of flotation its acidic and alkaline media. Surface precipitation may render the mineral sulface more hydrophilic. From the adsotption isotherm at 25°C, the orientation of oleate molecules was found to be vertical, having a cross-sectional area of 21,~ 2. On the other hand, at a higher temperature of 70°C, the cross-sectional area changed to a higher vahse of 42e~ 2, indicating a combination of vertical and flat orientations. Keywords Flotation; xenotime; adsorption; sodium oleate INTRODUCTION With the development of advanced technological applications of rare-earth elements and new uses based on their unique chemical and physical properties, the demand for rare-earth elements has increased rapidly. Xenotime, a major source for heavy rare-earth dements, is recovered as a by-product from the concentration of heavy minerals such as monazite, zircon, ruffle, ilmenite and garnet. With some heavy mineral deposits, the valuable constituents are in a fine size range, for which standard physical processing methods are less efficient and heavy losses occur. Therefore, for technical and economic reasons, flotation is an attractive method and offers a better alternative for xenotime recovery. The separation of rare earth minerals from each other is difficult due to their similar atomic structures and surface characteristics. The effectiveness of flotation is primarily controlled by the surface properties of the minerals and is significantly related to the collector adsorption at the mineral-water interface. The most extensively used collectors in rare-earth mineral separation are the long-chain fatty acids and their alkaline salts, especially oleic acid and sodium oleate. It is therefore necessary to systematically investigate the surface chemistry of xenotime in oleate solution. This paper reports results of adsorption isotherms, flotation and physico-chemical modelling studies, and discusses the mechanisms of xenotime flotation in the presence of sodium oleate. 1085