ADVANCED BENEFICIATION OF BASTNAESITE ORE THROUGH CENTRIFUGAL CONCENTRATION AND FROTH FLOTATION by Doug Schriner A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science (Metallurgical and Materials Engineering). Golden, Colorado Date ______________ Signed: ________________________ Doug Schriner Signed: ________________________ Dr. Corby Anderson Thesis Advisor Golden, Colorado Date ______________ Signed: ________________________ Dr. Ivar Reimanis Professor and Head Department of Metallurgical and Materials Engineering ii ABSTRACT Gravity separation and flotation studies have been conducted on Molycorp bastnaesite ore in order to determine if new beneficiation schemes present a more selective and more economical alternative than that which is currently employed at Mountain Pass. Literature on bastnaesite, monazite, barite, and calcite flotation and gravity concentration principles was surveyed. Flotation reagent additions were determined using components that have shown preferential floatability of bastnaesite and monazite over the gangue minerals. Hallimond Tube microflotation tests were performed on crushed and ground ore samples. Heavy liquid separation with sodium polytungstate was used to investigate the effectiveness of gravity separation on the ore. Shaking table and Falcon concentrator tests were performed to gravity concentrate the ore. A gravity-concentrated feed was floated and compared with a non-concentrated ore feed to illustrate the benefit of preconcentration. An economic analysis was generated for flotation plants operating with and without gravity preconcentration that would sell products with two distinct grades and recoveries. Qualitative microflotation tests produced little selective separation of the rare earth minerals (bastnaesite, parisite, and monazite) from the gangue (calcite, barite, dolomite, and quartz). Heavy liquid tests illustrated the sink/float behavior of the minerals at different specific gravities of separation. Their results suggest that at higher specific gravities the calcite floats while the bastnaesite and barite sink. Shaking table tests showed potential to effect such a separation, but optimum conditions were not determined. A Falcon centrifugal concentrator was used to carry out tests according to a Design of Experiments matrix generated with Stat Ease Design Expert 9. The best conditions from those trials were determined, and the tests were repeated to verify the desirability of those parameters. Bench flotation was then used to compare the standard feed at plant conditions to a feed consisting of the blended gravity concentrates. The flotation results showed that the preconcentrated feed outperformed the typical plant feed. Economic analysis of a plant with and without gravity preconcentration shows that gravity preconcentration, although more capital-intensive, will yield a higher annual profit and a better 10-year net present value. iii TABLE OF CONTENTS ABSTRACT ............................................................................................................. iii LIST OF FIGURES ..........................................................................................................vi LIST OF TABLES ............................................................................................................xi CHAPTER 1: INTRODUCTION .................................................................................. 1 CHAPTER 2: LITERATURE REVIEW ........................................................................ 9 2.1 Flotation Surface Chemistry and Analysis Techniques ......................... 9 2.1.1 Hydrophobicity and Contact Angle ..................................... 10 2.1.2 Hydrolysis Reactions .......................................................... 11 2.1.3 Zeta Potential and Point of Zero Charge ............................ 13 2.1.4 Adsorption Density ............................................................. 17 2.1.5 Hallimond Tube Flotation.................................................... 19 2.1.6 Temperature Effects ........................................................... 19 2.2 Minerals .............................................................................................. 21 2.2.1 Bastnaesite ......................................................................... 21 2.2.2 Monazite ............................................................................. 22 2.2.3 Calcite and Barite ............................................................... 22 2.3 Reagents ............................................................................................ 23 2.3.1 Collectors ........................................................................... 23 2.3.1.1 Fatty Acids ......................................................... 23 2.3.1.2 Hydroxamates .................................................... 26 2.3.2 Modifiers and Depressants ................................................. 29 2.3.2.1 Soda Ash ............................................................ 29 2.3.2.2 Lignin Sulfonate .................................................. 29 2.3.2.3 Metal Salts ......................................................... 29 iv 2.3.2.4 Sodium Silicate ................................................... 31 2.4 Gravity Concentration ......................................................................... 33 2.4.1 Heavy Liquid Separation .................................................... 37 2.4.2 Shaking Tables ................................................................... 37 2.4.3 Knelson and Falcon Concentrators .................................... 39 CHAPTER 3: EXPERIMENTAL METHODS ............................................................. 43 3.1 Characterization and Mineralogy Procedures ..................................... 43 3.2 Microflotation ...................................................................................... 43 3.3 Magnetic Separation ........................................................................... 46 3.4 Gravity Concentration ......................................................................... 46 3.5 Bench Flotation .................................................................................. 48 CHAPTER 4: RESULTS AND DISCUSSION ........................................................... 49 4.1 Characterization and Mineralogy ........................................................ 49 4.2 Microflotation ...................................................................................... 55 4.3 Magnetic Separation ........................................................................... 61 4.4 Gravity Concentration ......................................................................... 62 4.5 Bench Flotation .................................................................................. 70 CHAPTER 5: ECONOMIC ANALYSIS ..................................................................... 71 CHAPTER 6: CONCLUSIONS ................................................................................. 76 CHAPTER 7: SUGGESTIONS FOR FUTURE WORK ............................................. 78 REFERENCES ........................................................................................................... 79 APPENDIX A: FIRST LOT MINERALOGY .................................................................... 83 APPENDIX B: SECOND LOT MINERALOGY ............................................................... 91 APPENDIX C: EXPERIMENTAL DATA ........................................................................ 98 APPENDIX D: ECONOMIC ESTIMATES .................................................................... 101 v LIST OF FIGURES Figure 1.1. Beneficiation Flowsheet at Mountain Pass (as of 1991) [2] .................. 2 Figure 1.2. Molycorp REO Flotation Circuit ............................................................ 3 Figure 1.3. REO Export Prices from China. Data retrieved from www.metal- pages.com ............................................................................................ 4 Figure 1.4. Sichuan Mianning REE Deposit Flowsheet. [10] .................................. 7 Figure 1.5. Egyptian Beach Sand Beneficiation Flowsheet. The first percentage given relates to the original weight and the second represents the assay of monazite. [12] ......................................................................... 8 Figure 2.1. Visual Representation of Young's Equation, showing the contact angle of a hydrophobic (left) and hydrophilic (right) surface. [19] ....... 10 Figure 2.2. Illustration of the geometry used to determine the contact angle of water on carbon. [19] .......................................................................... 11 Figure 2.3. Aqueous Equilibria of cerium species. [22] ......................................... 12 Figure 2.4. Schematic of electrical double layer (from Somasundaran 1975). [23] ..................................................................................................... 13 Figure 2.5. Zeta Potential of bastnaesite and monazite. (Luo Jiake 1984, from [16]) .................................................................................................... 15 Figure 2.6. Zeta potential of barite, bastnaesite, and calcite in pure water. (Smith 1986, from [16]). ...................................................................... 16 Figure 2.7. Oleate adsorption onto bastnaesite as