FUNDAMENTAL SURFACE CHEMISTRY AND FROTH FLOTATION BEHAVIOR USING QUEBRACHO TANNINS by Jordan Rutledge 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: _______________________ Jordan Rutledge Signed: _______________________ Dr. Corby G. Anderson Thesis Advisor Golden, CO Date __________________ Signed:________________________ Dr. Angus Rockett Professor and Head Department of Metallurgical and Materials Engineering ii ABSTRACT With an increasing emphasis on minimizing the impact and downstream treatment of metallurgical processes, a focus on utilizing less harmful and easier to handle reagents is occurring. Tannins, a naturally occurring, non-toxic reagent, have shown promise in metallurgical and mineral processing applications. This research was performed to investigate the use of tannins (specifically two types of quebracho: Tupasol ATO and Tupafin ATO) in the froth flotation process as a depressant for gangue minerals. Two ore types, copper and fluorite, were researched. The primary gangue mineral of interest was calcite for the fluorite ore, while it was pyrite for the copper ore. Surface chemistry studies including zeta potential, adsorption density, and microflotation were undertaken to provide fundamental knowledge about the behavior of tannins interacting with the mineral surface. Adsorption studies indicate that the mechanism for Tupasol ATO adsorption onto calcite and fluorite surfaces is chemisorption, as an increase in adsorption occurred with increasing temperature. The same adsorption behavior is true for Tupafin ATO adsorption onto pyrite surfaces, although Tupafin ATO adsorption did not increase with increasing temperature onto chalcopyrite surfaces, suggesting the adsorption mechanism may be physical. Thermodynamic calculations for adsorption including Stern-Grahame free energy, entropy and enthalpy were determined. All four minerals tested were found to be thermodynamically favorable. Fluorite, calcite, and pyrite were endothermic in nature, while chalcopyrite was found to be exothermic. Microflotation experiments were completed on pure minerals to determine the suitable operating parameters for bench flotation; a number of statistical models were generated to predict the outcomes of changing parameters. Three different tannins (Tupasol ATO, chestnut, and wattle) were compared for the microflotation of calcite and fluorite; Tupasol ATO was found to have the best performance. Bench flotation was performed on three different ores, a Mexican fluorite ore, a Peruvian copper ore, and Morenci copper ore. With the addition of Tupasol ATO, the recovery and grade of the fluorite concentrate was seen to increase. Tupafin ATO was shown to provide a dramatic increase in recovery and doubling the grade for the Morenci copper concentrate. Tupafin ATO also demonstrated a positive effect on the grade and recovery of the Peruvian copper ore. This suggests that tannins not only work as a depressant but as a dispersant. An economic analysis was completed to explore some of the fiscal benefits of using tannins for froth flotation. iii TABLE OF CONTENTS ABSTRACT ................................................................................................................................... iii LIST OF FIGURES ..................................................................................................................... viii LIST OF TABLES ....................................................................................................................... xiii ACKNOWLEDGEMENTS ......................................................................................................... xxi DEDICATION ............................................................................................................................ xxii CHAPTER 1 INTRODUCTION .................................................................................................... 1 1.1 Background .................................................................................................................... 1 1.2 Motivation ...................................................................................................................... 1 1.3 Approach ........................................................................................................................ 1 CHAPTER 2 TANNINS IN MINERAL PROCESSING AND EXTRACTIVE METALLURGY2 2.1 Introduction .................................................................................................................... 2 2.2 Flotation .......................................................................................................................... 3 2.2.1 Jamesonite ............................................................................................................. 3 2.2.2 Strontium ............................................................................................................... 5 2.2.3 Rare Earth Oxides ................................................................................................. 6 2.2.4 Scheelite ................................................................................................................ 6 2.2.5 Fluorite .................................................................................................................. 9 2.2.6. Sulfides: Copper-Lead-Zinc-Nickel Ores .......................................................... 15 2.3 Precipitation .................................................................................................................. 21 2.3.1 Germanium .......................................................................................................... 21 2.4 Precious Metals Recovery ............................................................................................ 25 2.4.1 Gold Bacterial Oxidation ..................................................................................... 25 2.4.2 Tannin Gel Adsorption ........................................................................................ 26 2.5 Pressure Leaching ......................................................................................................... 28 2.5.1 Zinc and Nickel ................................................................................................... 28 iv CHAPTER 3 FLOTATION FUNDAMENTALS ........................................................................ 30 3.1 Electrical Double Layer and Zeta Potential ................................................................. 30 3.2 Adsorption Density ....................................................................................................... 32 3.3 Microflotation ............................................................................................................... 34 3.4 Bench Scale Flotation ................................................................................................... 34 CHAPTER 4 EXPERIMENTAL MATERIALS AND METHODS ............................................ 35 4.1 Materials ....................................................................................................................... 35 4.1.1 Materials: Fluorite Study ..................................................................................... 35 4.1.2 Materials: Polymetallic Sulfide Study ................................................................. 35 4.2 Reagents ....................................................................................................................... 35 4.2.1 Reagents: Fluorite Study ..................................................................................... 35 4.2.2 Reagents: Polymetallic Sulfide Study ................................................................. 36 4.3. Experimental Methods ................................................................................................ 37 4.3.1 Mineral Characterization ..................................................................................... 38 4.3.2 Zeta Potential ....................................................................................................... 38 4.3.3 Adsorption Density .............................................................................................. 39 4.3.4 Microflotation and Stat-Ease Design Expert ....................................................... 41 4.3.5 Bench Flotation ................................................................................................... 43 CHAPTER 5 EXPERIMENTAL RESULTS AND DISCUSSION FLUORITE STUDY .......... 48 5.1 Mineral Characterization .............................................................................................. 48 5.1.1 Mexican Fluorite Ore .......................................................................................... 48 5.2 Adsorption Density ....................................................................................................... 56 5.3 Zeta Potential ................................................................................................................ 61 5.3.1 Fluorite ................................................................................................................ 61 5.3.2 Calcite .................................................................................................................. 63 5.4 Microflotation ..............................................................................................................