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Hydrophobic Surface State of Talc and How It Is

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Hydrophobic Surface State of Talc and How It Is HYDROPHOBIC SURFACE STATE OF TALC AND HOW IT IS INFLUENCED BY POLYSACCHARIDE ADSORPTION by Venkata Veeren Babu Atluri A dissertation submitted to the faculty of The University of Utah in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Metallurgical Engineering The University of Utah May 2019 Copyright © Venkata Veeren Babu Atluri 2019 All Rights Reserved The University of Utah Graduate School STATEMENT OF DISSERTATION APPROVAL The dissertation of Venkata Veeren Babu Atluri has been approved by the following supervisory committee members: Jan D Miller , Chair 01/15/2019 Date Approved Xuming Wang , Member 01/15/2019 Date Approved Michael L. Free , Member 01/15/2019 Date Approved Vladimir Hlady , Member 01/15/2019 Date Approved York R. Smith , Member 01/15/2019 Date Approved and by Michael Simpson , Chair/Dean of the Department/College/School of Metallurgical Engineering and by David B. Kieda, Dean of The Graduate School. ABSTRACT Talc is both an important industrial mineral product recovered by flotation, and also in other cases, a gangue mineral of concern in the flotation of certain sulfide ores, such as the PGM ores in South Africa and in the United States. The talc face surface is naturally hydrophobic with a contact angle of nearly 80º, which accounts for its flotation recovery in one case, and its contamination of sulfide mineral concentrates in other instances. High- quality talc structures were investigated using surface analysis techniques including contact angle analysis, high-speed video bubble attachment measurements, atomic force microscopy, molecular dynamics simulation (MDS), microflotation, and film thickness measurements by Synchronized Triwavelength Reflection Interferometry Microscopy (STRIM). The presence of aluminum, which replaces silicon in the silica tetrahedral layer of the talc structure, results in a charge imbalance on the face surface because Si+4 is replaced by Al+3. Experimental sessile drop contact angles were found to decrease with increased aluminum content, decreasing from about 80º for no substitution (talc) to 0º for extensive substitution (phlogopite). For a hydrophilic phlogopite surface, the water film is stable with an equilibrium film thickness (he) of 25 nm. However, for a hydrophobic talc surface, air bubbles readily attach to the talc face surface with a critical rupture thickness (hc) of 56 nm. Further, the wetting characteristics and water film stability at the talc surface have been studied, regarding the effect of polysaccharides such as guar gum, starch, and dextrin. In the presence of polysaccharides, there was a significant increase in bubble attachment time at the talc surface but only a slight change in contact angle, which suggests that polysaccharide depression of talc was due to the slow rate of bubble attachment and not due to a change in contact angle. The adsorption state of the polysaccharides can be described as being due to a hydrophobic interaction between the nonpolar mineral surface and the hydrophobic portion of the polysaccharide molecule. Interestingly, it was found that the critical and equilibrium film thickness values do not change significantly with the polysaccharide type or concentration. iv Dedicated to my family and friends TABLE OF CONTENTS ABSTRACT ....................................................................................................................... iii LIST OF TABLES ............................................................................................................. ix LIST OF FIGURES ........................................................................................................... xi ACKNOWLEDGMENTS ............................................................................................... xiv Chapters 1. INTRODUCTION .......................................................................................................... 1 1.1 Flotation of Sulfide Minerals ............................................................................... 2 1.2 Phyllosilicate Minerals ........................................................................................ 6 1.3 Background on Talc ........................................................................................... 11 1.4 Polysaccharide Depressants ............................................................................... 13 1.5 Research Objectives ........................................................................................... 17 1.6 Dissertation Organization .................................................................................. 18 2. WETTING CHARACTERISTICS OF TALC ............................................................. 21 2.1 Introduction ........................................................................................................ 21 2.2 Materials and Methods....................................................................................... 24 2.2.1 Minerals and Reagents ........................................................................... 24 2.2.2 X-Ray Photoelectron Spectroscopy ....................................................... 24 2.2.3 Experimental and Simulation Sessile Drop Contact Angle ................... 25 2.2.4 MDS Interfacial Water Analysis ............................................................ 26 2.2.5 Experimental and Simulation Bubble Attachment Time ....................... 26 2.2.6 Synchronized Triwavelength Reflection Interferometry Microscopy ... 29 2.2.7 Atomic Force Microscopy ..................................................................... 31 2.3 Sessile Drop Contact Angle Results .................................................................. 31 2.3.1 Experimental .......................................................................................... 32 2.3.2 MD Simulation....................................................................................... 32 2.4 MDS Interfacial Water Analysis........................................................................ 34 2.4.1 Relative Number Density ....................................................................... 37 2.4.2 Water Dipole Moment and Hydrogen Bonding ..................................... 37 2.5 Bubble Attachment Results ............................................................................... 40 2.5.1 Experimental .......................................................................................... 40 2.5.2 MD Simulation....................................................................................... 42 2.6 Film Thickness Results ...................................................................................... 44 2.6.1 Synchronized Triwavelength Reflection Interferometry Microscopy ... 44 2.6.2 Discussion .............................................................................................. 46 2.7 Atomic Force Microscopy Results .................................................................... 49 2.8 Summary ............................................................................................................ 51 3. SIGNIFICANCE OF ALUMINUM SUBSTITUTION................................................ 53 3.1 Introduction ........................................................................................................ 53 3.2 Materials and Methods....................................................................................... 55 3.2.1 Minerals and Reagents ........................................................................... 55 3.2.2 X-Ray Photoelectron Spectroscopy ....................................................... 57 3.2.3 Experimental and Simulation Sessile Drop Contact Angle ................... 57 3.2.4 MDS Interfacial Water Analysis ............................................................ 58 3.2.5 Experimental and Simulation Bubble Attachment Time ....................... 60 3.3 X-ray Photoelectron Spectroscopy Results........................................................ 60 3.4 Sessile Drop Contact Angle Results .................................................................. 62 3.4.1 Experimental .......................................................................................... 62 3.4.2 MD Simulation....................................................................................... 65 3.5 Interfacial Water Analysis ................................................................................. 67 3.5.1 Relative Number Density ....................................................................... 75 3.5.2 Water Dipole Moment and Hydrogen Position ..................................... 77 3.6 Bubble Attachment Results ............................................................................... 79 3.6.1 Experimental .......................................................................................... 79 3.6.2 MD Simulation....................................................................................... 81 3.7 Summary ............................................................................................................ 87 4. ADSORPTION OF POLYSACCHARIDES ON TALC .............................................. 90 4.1 Introduction ........................................................................................................ 90 4.2 Materials and Methods....................................................................................... 93 4.2.1 Minerals and Reagents ..........................................................................
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