SURFACE CHEMISTRY AND FLOTATION BEHAVIOR OF MONAZITE, APATITE, ILMENITE, QUARTZ, RUTILE, AND ZIRCON USING OCTANOHYDROXAMIC ACID COLLECTOR By Josue Nduwa Mushidi A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in fulfillment of the requirement of the degree of Master of Science (Metallurgical and Material Engineering). Golden, Colorado Date: _________________ Signed: __________________________________ Josue Nduwa Mushidi Signed: ___________________________________ Dr. Corby Anderson Thesis Advisor Golden Colorado Date: ______________ Signed: ___________________________________ Dr. Ivar Reimanis Head of MME Department ii ABSTRACT Global increase in rare earth demand and consumption has led to further understanding their beneficiation and recovery. Monazite is the second most important rare earth mineral that can be further exploited. In this study, the surface chemistry of monazite in terms of zeta potential, adsorption density, and flotation response by microflotation using octanohydroxamic acid is determined. Apatite, ilmenite, quartz, rutile, and zircon are minerals that frequently occur with monazite among other minerals. Hence they were chosen as gangue minerals in this study. The Iso-Electric Point (IEP) of monazite, apatite, ilmenite, quartz, rutile, and zircon are 5.3, 8.7, 3.8, 3.4, 6.3, and 5.1 respectively. The thermodynamic parameters of adsorption were also evaluated. Ilmenite, rutile and zircon have high driving forces for adsorption with ΔGads. = 20.48, 22.10, and 22.4 kJ/ mol respectively. The free energy of adsorption is 14.87 kJ/mol for monazite. Adsorption density testing shows that hydroxamate adsorbs on negatively charged surfaces of monazite and its gangue minerals which indicates chemisorption. This observation was further confirmed by microflotation experiments. Increasing the temperature to 80°C raises the adsorption and flotability of monazite and gangue minerals. This does not allow for effective separation. Sodium silicate appeared to be most effective to depress associated gangue minerals. Finally, the fundamentals learned were applied to the flotation of monazite ore from Mt. Weld. However, these results showed no selectivity due to the presence of goethite as fine particles and due to a low degree of liberation of monazite in the ore sample. iii TABLE OF CONTENTS ABSTRACT ................................................................................................................................................... iii TABLE OF CONTENTS ............................................................................................................................... iv LIST OF FIGURES ...................................................................................................................................... vii LIST OF TABLES ......................................................................................................................................... xi ACKNOWLEDGMENT ............................................................................................................................... xv CHAPTER 1: INTRODUCTION ................................................................................................................... 1 CHAPTER 2: BACKGROUND ..................................................................................................................... 2 2.1 Rare Earth Minerals and deposits ..................................................................................................... 2 2.2 Rare Earth Elements and Applications ............................................................................................. 4 2.2.1 Rare earth elements ...................................................................................................................... 4 2.2.2 Chemistry of rare earth elements ................................................................................................. 6 2.2.3 Applications of rare earth elements.............................................................................................. 7 2.3 Monazite ............................................................................................................................................ 7 2.4 Physical concentration of monazite ................................................................................................. 10 2.5 Review on the flotation of monazite ................................................................................................ 11 2.6 Processing of monazite concentrate. ................................................................................................ 13 The thorium problem ............................................................................................................................ 16 2.7 Surface chemistry of flotation .......................................................................................................... 16 CHAPTER 3: MATERIALS AND EXPERIMENTAL METHODS ........................................................... 25 3.1 Materials .......................................................................................................................................... 25 3.2 Reagents ........................................................................................................................................... 25 3.3 Experimental Methods .................................................................................................................... 27 3.3.1 Mineral Characterization ............................................................................................................ 27 3.3.2 Zeta Potential Measurement ....................................................................................................... 28 3.3.3 Adsorption Density Experiments ............................................................................................... 30 iv 3.3.4 Microflotation Experiments ....................................................................................................... 33 CHAPTER 4: EXPERIMENTAL RESULTS AND DISCUSSION ............................................................ 36 4.1 Mineral Characterization.................................................................................................................. 36 4.1.1 Pure Minerals ............................................................................................................................. 36 4.1.2. Mt. Weld Ore .............................................................................................................................. 46 4.2 Streaming potential measurements .................................................................................................. 58 4.3 Adsorption Density .......................................................................................................................... 67 4.3.1 Solid – Liquid Ratio Determination ........................................................................................... 68 4.3.2 Kinetics of Adsorption ............................................................................................................... 71 4.3.3 Adsorption Isotherm at room temperature ................................................................................. 74 4.3.4 Effect of Temperature ................................................................................................................ 76 4.3.5 Effect of pH on Adsorption ........................................................................................................ 78 4.4 Microflotation experiments ............................................................................................................. 80 4.4.1 Effect of Concentration .............................................................................................................. 81 4.4.2 Effect of pH ................................................................................................................................ 82 4.4.3 Effect of Temperature ................................................................................................................ 84 4.4.4 Effect of Depressant Addition ................................................................................................... 85 CHAPTER 5: FLOTATION OF LYNAS MT. WELD MONAZITE ORE ................................................. 90 5.1 Background ...................................................................................................................................... 90 5.2 Flotation Results .............................................................................................................................. 91 5.3 Discussion of the Results ................................................................................................................. 95 CHAPTER 6: CONCLUSIONS ................................................................................................................... 98 REFERENCES ........................................................................................................................................... 100 APPENDIX A: SUPPLEMENTAL CHARACTERIZATION DATA ...................................................... 103 APPENDIX B: ZETA POTENTIAL DATA .............................................................................................. 109 v APPENDIX C: ADSORPTION DATA .....................................................................................................