Applied Science, Faculty of
Mining Engineering, Keevil Institute of
DSpace
UBCV
Aboagye, Patrick Ansah
Master of Applied Science – MASc
University of British Columbia
All over the world, the primary economic deposits of rare earths are being exhausted. Finding new sources and methods for the concentration, coupled with a cost-effective extraction of rare earth elements (REEs) is imperative. Alternate and innovative strategies for the extraction and concentration of minerals are being developed continuously. Out of the many physical concentration processes available, the hydrophobic hydrophilic separation (HHS) process has yielded the best result for the pre-concentration of rare earth minerals (REMs). This study explores the possibility of using HHS as a novel process used to physically concentrate REMs of US coals (from 300 ppm to 2 % on ash basis) on BC coals. First, a set of three samples (roof, floor, and parting) were carefully chosen based on the outcome of their correlation coefficient from a study conducted in 2021 to characterize BC coals. A tailings sample (CT) from the plant was also selected to study in this thesis. The results on the roof, floor, and parting showed little to no concentration of REEs. Further investigations were carried out on the CT as most of the roof, floor, and partings would eventually end up as tailings due to processing at the coal preparation plant. The HHS process was affected by pH levels ranging from 7.5 to 9.5, and the results revealed a slight improvement in the final concentrate grade. An increase in collector dosage showed a direct correlation with the increase in concentrate grade, calculated on an ash basis. The reduction of the particle size (P80) of the tailings sample from 20 microns to 8.5 microns also resulted in an increase in the final concentrate grade. The mineralogical examination found that the rare-earth-bearing minerals were monazite, xenotime, and some smaller traces of REEs encapsulated in zircon. The majority of the sample was predominantly composed of quartz and illite/muscovite with minor traces of kaolinite and carbonates with slight traces of monazite and xenotime minerals.
PRELIMINARY ASSESSMENT OF HYDROPHOBIC-HYDROPHILIC SEPARATION FOR PRE-CONCENTRATION OF REE FROM COAL TAILINGS AND ALIKE MATERIAL by Patrick Ansah Aboagye BSc., Kwame Nkrumah University of Science and Technology, 2012 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Mining Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) April, 2023 © Patrick Ansah Aboagye, 2023 ii The following individuals certify that they have read and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance the thesis entitled: Preliminary assessment of hydrophobic-hydrophilic separation for pre-concentration of REE from coal and alike material submitted by Patrick Ansah Aboagye in partial fulfillment of the requirements for the degree of Master of Applied Science in Mining Engineering Examining Committee: Dr. Maria Holuszko, Associate Professor, Mining Engineering, UBC Supervisor Dr. Bern Klein, Professor, Mining Engineering, UBC Supervisory Committee Member Dr. Marek Pawlik, Professor, Mining Engineering, UBC Supervisory Committee Member iii Abstract All over the world, the primary economic deposits of rare earths are being exhausted. Finding new sources and methods for the concentration, coupled with a cost-effective extraction of rare earth elements (REEs) is imperative. Alternate and innovative strategies for the extraction and concentration of minerals are being developed continuously. Out of the many physical concentration processes available, the hydrophobic hydrophilic separation (HHS) process has yielded the best result for the pre-concentration of rare earth minerals (REMs). This study explores the possibility of using HHS as a novel process used to physically concentrate REMs of US coals (from 300 ppm to 2 % on ash basis) on BC coals. First, a set of three samples (roof, floor, and parting) were carefully chosen based on the outcome of their correlation coefficient from a study conducted in 2021 to characterize BC coals. A tailings sample (CT) from the plant was also selected to study in this thesis. The results on the roof, floor, and parting showed little to no concentration of REEs. Further investigations were carried out on the CT as most of the roof, floor, and partings would eventually end up as tailings due to processing at the coal preparation plant. The HHS process was affected by pH levels ranging from 7.5 to 9.5, and the results revealed a slight improvement in the final concentrate grade. An increase in collector dosage showed a direct correlation with the increase in concentrate grade, calculated on an ash basis. The reduction of the particle size (P80) of the tailings sample from 20 microns to 8.5 microns also resulted in an increase in the final concentrate grade. The mineralogical examination found that the rare-earth-bearing minerals were monazite, xenotime, and some smaller traces of REEs encapsulated in zircon. The iv majority of the sample was predominantly composed of quartz and illite/muscovite with minor traces of kaolinite and carbonates with slight traces of monazite and xenotime minerals. v Lay Summary Future demands for REEs and the difficulty of economically extracting them from conventional sources have necessitated the need to find secondary sources like coal and its byproducts to meet this demand. REEs naturally occur in relatively small amounts in the Earth or in any other feedstock, making it imperative to enrich the concentration of REEs to a certain degree to be economical. Gravity, magnetic separation, electrostatic separation, and froth flotation are physical separation techniques applied to beneficiate typical REMs. HHS, developed by Virginia Tech on the principle of oil agglomeration, has shown to be the most effective in increasing the REEs concentration from 300 ppm to about 17,000 ppm in their coals on ash basis. This study examines HHS method to preconcentrate REES on selected coal samples from a BC coal deposit and associated byproducts from coal production. The results from this study will provide an improved understanding of HHS methodology and how this method could be used for processing coal tailings from BC coals and their byproducts. vi Preface This graduate research was carried out in parallel with the study on the “Characterization and bench-scale testing of rare earth elements (REEs) from East Kootenay coalfields” for Geoscience BC (2019–2023), in which I participated. I am also co-author of the final report that has currently been submitted for review to Geoscience BC (March 2023). Since some of the characterization techniques were established during the Geoscience BC project, and because I took part in these experiments, I applied these techniques in my current research. Apart from this, the data in this thesis is derived from experiments I have carried out. Others previously investigated the HHS method, but it has not experimented on coals from BC. In this research, I carried out experiments that replicated conditions of the previously developed HHS process, but the analysis of the data and assessment of the results were conducted by me. In addition, findings from this work were supported by the quantitative mineralogical work, a new feature supplementing the HHS process evaluation. This was an instrumental in deriving final conclusions from this research. vii Table of Contents Abstract ......................................................................................................................................... iii Lay Summary .................................................................................................................................v Preface ........................................................................................................................................... vi Table of Contents ........................................................................................................................ vii List of Tables ................................................................................................................................ xi List of Figures .............................................................................................................................. xii List of Symbols ........................................................................................................................... xiv List of Abbreviations ...................................................................................................................xv Acknowledgements ................................................................................................................... xvii Dedication ................................................................................................................................. xviii Chapter 1: Introduction ................................................................................................................1 1.1 Background ..................................................................................................................... 1 1.2 Research Objectives ........................................................................................................ 3 1.3 Thesis Outline ................................................................................................................. 4 Chapter 2: Literature Review .......................................................................................................5 2.1 Rare Earth Elements (REEs) ........................................................................................... 6 2.2 Applications of REEs ...................................................................................................... 9 2.3 Production Statistics of REEs ....................................................................................... 12 2.4 Factors Affecting REEs Prices ...................................................................................... 15 2.5 Beneficiation of REE-Bearing Minerals ....................................................................... 16 2.6 Rare Earths Minerals (REMs) ....................................................................................... 18 2.6.1 REEs in primary sources and REEs in secondary sources ....................................... 19 viii 2.6.2 Commonly mined minerals for REEs extraction ...................................................... 21 2.6.2.1 Bastnaesite ........................................................................................................ 21 2.6.2.2 Monazite ........................................................................................................... 22 2.6.2.3 Xenotime ........................................................................................................... 23 2.6.2.4 Ion-adsorbed clays and other REMs ................................................................. 24 2.6.3 BC coal deposits characterization ............................................................................. 24 Chapter 3: Beneficiation and Extraction of REEs ....................................................................30 3.1 Primary Sources ............................................................................................................ 30 3.1.1 Physical separation methods ..................................................................................... 30 3.1.1.1 Electrostatic separation ..................................................................................... 31 3.1.1.2 Magnetic separation .......................................................................................... 32 3.1.1.3 Gravity separation ............................................................................................. 33 3.1.1.4 Froth flotation ................................................................................................... 33 3.1.1.5 Hydrophobic Hydrophilic Separation (HHS) ................................................... 34 3.1.1.6 Hydrophobic Hydrophilic process description ................................................. 35 3.2 Secondary Sources ........................................................................................................ 36 3.2.1 Coal and coal byproducts ......................................................................................... 36 3.3 Prior Work .................................................................................................................... 36 Chapter 4: Experimental Methodology and Materials ............................................................42 4.1 Sample Selection ........................................................................................................... 42 4.2 Sample Preparation ....................................................................................................... 43 4.3 Particle Size Distribution .............................................................................................. 44 4.4 Proximate Analysis ....................................................................................................... 45 ix 4.5 Reagents ........................................................................................................................ 45 4.6 Decarbonization of Studied Coal Samples Prior to HHS ............................................. 46 4.6.1 Coal flotation – decarbonization of CT .................................................................... 46 4.6.2 Decarbonization of roof, partings, and floor samples ............................................... 48 4.7 Hydrophobic Hydrophilic Separation (HHS) ............................................................... 48 4.8 Mineralogical Characterization ..................................................................................... 49 4.8.1 Sequential extraction ................................................................................................. 50 4.8.2 Analytical methods ................................................................................................... 51 4.8.2.1 Inductively Coupled Plasma (ICP) ................................................................... 51 4.8.2.2 Quantitative X-ray Diffraction (XRD).............................................................. 52 4.8.2.3 Scanning Electron Microscopy (SEM) – Energy Dispersive Spectroscopy (EDS) 53 4.8.2.4 Mineralogical liberation analysis ...................................................................... 53 4.9 Performance Indicator ................................................................................................... 53 Chapter 5: Results and Discussion .............................................................................................55 5.1 Preliminary HHS ........................................................................................................... 56 5.2 Effect of pH on HHS Process ....................................................................................... 57 5.3 Effect of Collectors and Dosage Rate for HHS Process ............................................... 59 5.4 Effect of Size Reduction (Grinding) ............................................................................. 62 5.5 Characterization Results ............................................................................................... 64 5.5.1 Sequential extraction ................................................................................................. 64 5.5.2 XRD and SEM results ............................................................................................... 65 5.6 Particle Size and REE Distribution Compared with Mineralogy ................................. 71 x Chapter 6: Conclusion and Recommendation ..........................................................................75 6.1 Recommendations ......................................................................................................... 78 Bibliography .................................................................................................................................80 Appendices ....................................................................................................................................94 Appendix A Proximate Analysis Procedure ............................................................................. 94 Appendix B - General Flotation Procedure .............................................................................. 96 Appendix C List of Some REMs and Their Composition ........................................................ 97 xi List of Tables Table 2.1 Essential REEs .............................................................................................................. 19 Table 2.2 Bastnaesite composition in REEs (w.r.t. 100 % REO) ................................................. 21 Table 2.3 REE concentrations (on an ash basis; ppm) in samples of the East Kootenay coalfield’s roof, floor, coal, and partings. ....................................................................................................... 26 Table 2.4 Categorization of REE sources based on REE grade and outlook coefficient ............ 28 Table 2.5 Results of HREE–LREE and outlook coefficient of East Kootenay coalfield samples ....................................................................................................................................................... 28 Table 3.1 Physical separation methods used by mines to recover REOs ..................................... 34 Table 4.1 Sequential extraction procedure used in this study ....................................................... 50 Table 5.1 Proximate analysis of CT samples after flotation. ........................................................ 57 Table 5.2 Observed mineral abundance for sample F1................................................................. 70 Table A.6.1 Some of the REMs found in the traditional RE deposits ......................................... 97 xii List of Figures Figure 2.1 Global REE output, 2011–2020 ................................................................................... 6 Figure 2.2 REE elements circled in red ......................................................................................... 7 Figure 2.3 List of REEs discovered in natural deposits ................................................................. 9 Figure 2.4 REE uses ..................................................................................................................... 10 Figure 2.5 Applications of REEs ................................................................................................. 12 Figure 2.6 Percentages of REOs produced. ................................................................................. 13 Figure 2.7 Resources and reserves of neodymium, praseodymium, terbium, and their geographical distribution ............................................................................................................. 14 Figure 2.8 Map of Canadian REE project sites, showing the status of operations ....................... 15 Figure 2.9 Bastnaesite .................................................................................................................. 22 Figure 2.10 Monazite. ................................................................................................................... 23 Figure 2.11 Xenotime .................................................................................................................. 24 Figure 2.12 Coal mines in British Columbia ............................................................................... 25 Figure 2.13 REE concentration versus ash content of the East Kootenay coalfield, British Columbia ...................................................................................................................................... 27 Figure 3.1 Schematic picture of the HHS procedure ................................................................... 35 Figure 3.2 OHA’s impact on a sample of micronized thickener underflow’s ability to extract REEs ............................................................................................................................................. 37 Figure 3.3 The results of the HHS tests on a micronized thickener underflow sample both with and without decarbonization ........................................................................................................ 38 Figure 3.4 Particle size’s impact on a thickener underflow sample’s ability to recover REEs ... 39 xiii Figure 3.5 SMO’s impact on a sample of micronized thickener underflow’s ability to extract REEs ............................................................................................................................................ 40 Figure 3.6 Comparison of three different separation methods .................................................... 41 Figure 4.1 Schematic of sample preparation for analysis ............................................................. 43 Figure 4.2 Crushers used in the sample preparation a) jaw crusher b) jaw crusher plates c) hammer mill .................................................................................................................................. 44 Figure 4.3 Schematic of flotation test and HHS test on CT sample ............................................. 47 Figure 4.4 Schematic for HHS process used for F1, P1, and R1 samples .................................... 49 Figure 5.1 Schematic for collector dosage test work .................................................................... 55 Figure 5.2 Preliminary HHS test work on roof, floor, and parting (R1, F1 and P1) sample ........ 56 Figure 5.3 Effect of pH on HHS of the CT sample ...................................................................... 58 Figure 5.4 Effect of different collectors on CT sample a) hydroxamate b) sodium oleate ........... 60 Figure 5.5 a) Enrichment factor for both reagents b) concentrate ash for both reagents .............. 61 Figure 5.6 Effect of particle size on CT sample at collector dosage of 1 kg/t .............................. 63 Figure 5.7 Schematic for grind size variation test ........................................................................ 63 Figure 5.8 Sequential extraction results (R1, F1, P1, CT) showing the distribution of REEs in various modes of occurrences ....................................................................................................... 64 Figure 5.9 Quantitative XRD analysis for select samples a) R1 b) P1 c) F1 ................................ 67 Figure 5.10 SEM-EDX mapping of xenotime (YPO4) mineral identified in sample F1 ............. 68 Figure 5.11 Grain size distribution of different REE-bearing minerals in F1 .............................. 70 Figure 5.12 Mineral liberation and association results of sample F1 ........................................... 71 Figure 5.13 TREE distribution by wt (%) in different size fraction for P1, R1, and F1............... 73 xiv List of Symbols Symbol Description Unit Cc Concentrate grade ppm Cf Grade of REE in feed sample ppm Coutl Outlook Coefficient - Cos Cosine - E Energy J EF Enrichment factor - Mc Mass of concentrate (product) g Mf Mass of feed g r radius mm Wt % Weight percent % ℽso Surface energy at solid/oil interface J ℽsw Surface energy at solid/water interface J θ Contact angle radian xv List of Abbreviations AMD Acid Mine Drainage ASTM American Society for Testing and Materials DbD Dewatering by Displacement EDS Energy Dispersive X-ray Spectroscopy EF Enrichment Factor HREE Heavy Rare Earth Elements ICP-MS Inductively Coupled Plasma – Mass Spectrometry ICP-OES Inductively Coupled Plasma – Optical Emission Spectrometry LED Light Emitting Diode LREE Light Rare Earth Elements LTA Low Temperature Ashing NETL National Energy Technology Laboratory NRCan Natural Resources of Canada QXRD Quantitative X-ray Diffraction RE Rare Earth REE Rare Earth Elements REM Rare Earth Minerals REO Rare Earth Oxide ROM Run of Mine SEM Scanning Electron Microscope S&P Standard and Poor xvi TREE Total Rare Earth Elements UCC Upper Continental Crust UF Underflow US DOE United States Department of Energy USGS United States Geological Survey XRD X-ray Diffraction xvii Acknowledgements I offer my immense appreciation to my supervisor, Dr. Maria Holuszko, for her generous support and guidance throughout the program. Her meticulous guidance, exceptional recommendations, constant support, encouragement, and patience helped to enhance my research skills and taught me a great deal about scientific knowledge as well as life in general. I also greatly appreciate the financial support from Geoscience BC (No. 2018–002) for the research project and scholarship support from Geoscience BC in collaboration with Mitacs. I would like to recognize the assistance of and offer my thanks to Aaron Hope, Frank Yan, Libin Tong, and other NBK Institute of Mining Engineering staff for their help in completing my research. I would also like to extend my sincere gratitude to my colleagues and friends, Dr. Amit Kumar, Dr. Vinoth K. Kuppusamy, Francis Tenkorang, Ken J. Roberts, Sandra A. Koranteng, Dr. Kodjo Afewu, Charles Ofori Asare, Samuel Adjartey, and Jennifer Katchen for their moral support all through the challenging times of this research and the COVID-19 pandemic. Last but not least, I would like to express my thanks and eternal gratitude to my parents, Enoch A. Aboagye and Faustina Amoh, and my siblings, Margaret Opare, Daniel A. Aboagye, and Priscilla Anim. I would not be the person I am today without their unwavering love and support. xviii Dedication This thesis is dedicated to God, family, and the academic world. 1 Chapter 1: Introduction 1.1 Background Seventeen elements from the periodic table, 15 lanthanides, and two transition metals make up rare earth elements (REEs). They include scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, and ytterbium, as well as dysprosium (Connelly et al., 2005). Between 1787 and 1941, there was over 160 years’ worth of rare earth discoveries (Szabadvary, 1988; Weeks, 1956). Due to the physical and chemical characteristics of REEs, they have numerous economic and technical uses (Goonan, 2011; Long, 2011). REEs are sometimes classified based on their atomic weight, solubility, demand and consumption pattern, and abundance levels in the earth’s crust (Jonsson et al., 2013; Zhang et al., 2015; Basafa et al., 2016). They are used in production of wind turbines, lasers, fiber optics, electric vehicles, defense systems, motors, and superconductors (Zepf, 2013). As technology develops and more nations switch to green energy, the demand for REES has skyrocketed recently and is expected to continue for the foreseeable future (USGS, 2020). Using traditional mining methods to beneficiate REEs is difficult as they rarely occur in high concentrations in the earth’s crust. Due to the peculiar nature of REEs and the rising need for them worldwide, improved approaches must be developed to extract REEs effectively from both conventional and non-conventional sources. Since the discovery of REEs, extraction and recovery of the elements from conventional sources have received increased focus. Contemporary research aims to eliminate the barriers for the extraction of REEs from non-conventional sources (Meisam et al., 2020). Researchers, including Zhang et al., 2015; Honaker et al., 2016; Ganguli and Cook, 2018; and Kuppusamy et al., 2019 found that coal and its byproducts are augmented with 2 significant quantities of metals and could serve as a likely source of REEs. The research of REEs from these sources is hard-pressed by the abundance of coal reserves and their byproducts, which also have the advantage of having already been mined and having gone through some degree of processing (Hodgkinson and Grigorescu, 2020). Compared to other conventional approaches that are capital-intensive and have an adverse effect on the environment, this added benefit increases the commercial worth of extracting REEs from coal sources. Canada is one of the world’s exporters of metallurgical coal, with a production of 42 million tonnes in 2021. Alberta and British Columbia contributed 83 % of Canada’s coal production in 2020. There are approximately 21.9 billion tonnes of potentially mineable coal reserves in BC. Currently, seven operating open pit coal mines in southeastern and northeastern BC produce between 25–30 million tonnes of coal per year, representing approximately 42.7 %, or $3.97 billion, of the provinces’ mining revenues. More than 17 coal exploration and development projects are planned for the province by 2020. (British Columbia Geological Survey, 2020). Coal production comes with some environmental risks, and as such, the Government of Canada announced in 2018 to phase out coal-fired electricity by 2030 (NRCan, 2022; Statistics Canada, 2022). With these production statistics in mind, it consequently means that a significant amount of coal tailings had already been produced and deposited in the form of fine coal tailings ponds. Coal tailings have already been processed and would be a good source if reprocessing is considered. Several physical and extractive technologies must be used to economically produce REEs from coal and other conventional and unconventional sources (Ozbayoglu et al., 2000; Abdel-Reheim, 2000; Hernandez-Exposito A et al., 2006; Pradip and Faustenau, 2013). The physical separation techniques include gravity separation, magnetic separation, floatation, electrostatic separation, and 3 the fairly novel hydrophobic hydrophilic separation (HHS) method. Amongst these physical separation techniques, only HHS concentrated REEs from 300 ppm to 1,308 ppm on the ash basis (Honaker, 2017). As a result of the coal production in the province, there are about 25–30 million tonnes of tailings in addition to the past historical production of millions of tonnes that could be used to recover REEs (British Columbia Geological Survey, 2020). This study will investigate the possibility of using the HHS approach to pre-concentrate REEs from the coal samples representing tailings and similar material collected from BC coal fields and elaborate on their mineralogy in the context of their physical processing. 1.2 Research Objectives The research objective was to assess whether the HHS process, as introduced by Honaker (2010) from the University of Kentucky and affirmed by Li Biao (2019) from the Virginia Polytechnic Institute and State University, can pre-concentrate REEs from coal flotation tailings and similar to tailings materials from coal production. This involves understanding the nature of REE association in coal-mining products such as tailings and overburdened material from mined seams. These materials will usually end up in the rejects such as tailings, due to being mined with the coal strata. The main research objective was broken down into sub-objectives as follows: • To select the samples that exhibited higher outlook potential for REE extraction from the mine site’s overburden material such as roof, floor, and partings from active seams by coal geologists (Chapter 2) • To prepare flotation tailings for HHS preconcentration of REEs (Chapter 3) • To evaluate the applicability of the HHS process on selected coal samples (Chapter 4) • To evaluate the impact of different criteria and assess the efficacy of the HHS procedure (Chapter 5) 4 • To evaluate the overall effectiveness of the HHS process for the studied samples (Chapter 5) • To derive an understanding of the process’s effectiveness based on mineralogical evaluations (Chapters 5 and 6) 1.3 Thesis Outline The sub-objectives from the core structure of the thesis are divided into six chapters, as described below: Chapter 1 provides the research background and thesis objectives for this study with the outline of individual chapters. Chapter 2 is a literature review on REEs, their application, production statistics, factors affecting global pricing, the beneficiation of rare earth-bearing minerals, and commonly mined REE minerals. It offers a look into BC coalfield REE characterization. Chapter 3 looks at the beneficiation and extraction of REEs from primary sources, the physical separation methods (electrostatic separation, magnetic separation, gravity separation, froth flotation, and HHS) involved and the beneficiation and extraction of REEs from secondary sources. Chapter 4 presents the sample selection, preparation process, characterization techniques (proximate analysis, sequential extraction, and quantitative x-ray diffraction [QXRD]), the HHS methodology, and analytical methods used to characterize the samples. Chapter 5 discusses the results from the experiments, encompassing the preliminary HHS process on selected samples, the effect of particle size, the effect of collector type and dosage, the effect of pH, and the mineralogical characterization of the feed and products. Chapter 6 summarizes the study’s findings and makes suggestions for additional research. 5 Chapter 2: Literature Review Over recent years, a special group of elements has increasingly been in the spotlight, primarily due to their particular importance in manufacturing many modern technological units that have become essential tools in our everyday life. They are referred to as REEs. REEs were first discovered in 1787, and studies on them continued up until the 1940s. (Szabadvary, 1988; Weeks, 1956). Aside from chemists, geologists, and specialized-materials-and-technological engineers, many people were either unfamiliar with these elements or just recognized them as “the higher one of these two rows of elements beneath the main body of the Periodic System of the Elements” (Van Gosen, 2017; Voncken, 2016). This was partly because their wide range of applications was unknown or unfamiliar to the public until 2009. In modern times, REEs have gained considerable prominence because of how important they are in making critical components of our modern technology. This is reinforced by China’s near total control of production and supply, leading to the world’s heavy dependence on China (Long, 2011; Tse, 2011; Hatch, 2012a). In 2009, China introduced production restrictions that increased the demand and affected the costs of REEs on the global market (Geschneider, 2011). This inevitably triggered a worldwide concern among countries and manufacturers of high-tech equipment, as new technological developments were not feasible without REEs. However, in 2014, China agreed to remove the restrictions after complaints from Japan, the United States, European Union members, and the World Trade Organization (Hatch, 2012a). These problems encircle the global supply and demand of the REEs, thus, giving the metals more 6 visibility and importance in modern-day living. This consequently led to exploration efforts by major industrialized countries and companies to discover economic deposits of REEs to reduce the dependence on China’s supply (Van Gosen, 2017). Figure 2.1 Global REE output, 2011–2020 (USGS, Mineral Commodity Summaries, 2021) 2.1 Rare Earth Elements (REEs) REEs are 17 chemically similar elements comprising 15 lanthanides and two transition elements (Spedding, 1978; Connelly et al., 2005). All the lanthanides, which have atomic numbers from 57 to 71, except for promethium, are found in nature. Again, promethium (atomic number 61) is extremely rare and unstable in nature and is mostly excluded from the list. The REEs have comparable chemical properties and, thus, are primarily found in minerals as a single chemical entity. Because of its similar chemical and physical characteristics and affinity for lanthanides, yttrium (atomic number 39) is frequently referred to as an REE. Moreover, it is typically 7 discovered in deposits that contain other REEs. (Van Gosen, 2017). Figure 2.2 depicts them with a red circle around them in the Periodic Table of Elements. Figure 2.2 REE elements circled in red (http://www.redbubble.com/people/seifip/works/5309681-mendeleevs-periodic-table-of-elements?p=poster) Johan Gadolin was the first person to discover the REE yttrium in 1974. (Gadolin, 1794, 1796; Weeks, 1968; Gupta and Krishnamurthy, 2005). By the late 1800s, all but two REEs (lutetium, discovered in 1907, and promethium in 1945) were left to be discovered; (Marinsky et al., 1947). As deceptive as the term “rare” may be, they are quite common in the Earth compared to other metals but not in sufficient quantities to be commercially mined. Cerium is the most prevalent REE, more prevalent than copper or lead. (Lide, 2004, p. 17). Apart from promethium, all other REEs are more abundant than most native elements. (Lide, 2004, p. 17), as shown in Figure 2.3. While it is difficult to concentrate REEs during mining, they are not rare in terms of their occurrences. (Adams and Staatz, 1973). Some peculiar rock types of uncommon minerals containing REEs provide some challenges when finding a suitable method for separating these elements. 8 The bulk of REEs are light rare earths (LREE) (cerium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium) while heavy rare earths (HREE) (gadolinium, lutetium, terbium, dysprosium, holmium, erbium, thulium and yttrium) (Gupta and Krishnamurthy, 1992; Trifonov, 1963) are found in nature in smaller quantities. Scandium, an REE, is excluded from both categories (Gupta and Krishnamurthy, 1992). There have been many classifications based on different variables, but from the perspective of the evolution of REEs, these two classifications are more than enough. (Schoeller and Powell, 1955). The lanthanides (the elements La and Lu), which have seven sub-orbitals (f-orbitals), are atomic structures that accommodate two electrons. This leads to 15 possible fillings for the f-orbitals. This gives rise to elements that have closely related properties. All lanthanides have a valency of 3, with europium, yttrium, and samarium able to form 2+ ions. All the REEs, except for promethium, are not radioactive and has stable isotopes. Promethium is mainly generated during a nuclear reaction. 9 Figure 2.3 List of REEs discovered in natural deposits (Bradley S. et al., 2017) 2.2 Applications of REEs Due to the peculiar physical and chemical characteristics (fluorescent, conductive, and magnetic properties) that make REEs unique, they have a wide range of economic and technical applications. (Goonan, 2011; Long, 2011). After the mid-1900s, after breakthrough developments in the commercial purification of REES, the number of their applications increased tremendously. (Kronholm et al., 2013). This has increased to a considerable extent in the past ten years due to the digitization and development of modern technologies. As a result of their chemical and physical similarities, REEs are described mostly based on application rather than individuality. Typically, 10 HREEs are used less than LREEs because HREEs are more expensive and exist in lower quantities. Holmium to lutetium on the periodic table are very expensive and rare, so they tend to be used for highly specialized high-end-technologies. Permanent magnets are expected to be the largest consumer of REEs in 2020, according to Natural Resources Canada (NRCan). This is followed by catalysts (20.2 %), polishing powder and additives (13.6 %), other products (8.9 %), metallurgy (8.6 %), batteries (7.8 %), glass (7.8 %), ceramics (2.7 %), phosphors (0.6 %), and pigments (0.4 %), as shown in Figure 2.4. For polishing and to give glass its colour and other unique optical qualities, the glass industry uses REEs. For instance, cerium is used to decolourize glass and manufacture glass requiring a specific level of polishing precision. The refractive index of optical glass is raised using REEs like lutetium and lanthanum. In lithography, where a high refractive index is required, the more costly lutetium is used. Glass that requires special colours and glare-reduction qualities utilizes erbium, holmium, neodymium, praseodymium, and ytterbium. Optical fibers use europium as a doping agent. Figure 2.4 REE uses (NRCan, 2020) 11 REEs are also used in making petroleum and automotive industry catalysts (Goonan, 2011). A recent expanding use of REEs is in the making of permanent magnets. One of the strongest magnets, neodymium–iron–boron magnets, are utilized to create space-related devices, hard drives, mobile phones, wind turbines, aviation actuators, and electric motors (Goonan, 2011; Long, 2011). These magnets also include smaller quantities of dysprosium, gadolinium, and praseodymium. These devices also contain small quantities of dysprosium, which increases their capacity to function at high temperatures and decreases their susceptibility to demagnetization. Lanthanum-based alloys are used for making nickel-metal hydride batteries (Kopera, 2004), and it is found in many consumer products like cars and rechargeable products (Anderson and Patiño-Echeverri, 2009). Display screens, incandescent fluorescent, and light-emitting diode lighting all use REEs such as yttrium, cerium, lanthanum, europium, and terbium (Goonan, 2011; Long, 2011). Gadolinium phosphors are used in X-ray imaging and other medical procedures (MRI). Yttrium, lanthanum, cerium, neodymium, and praseodymium are used in ceramic pigments. Further studies are anticipated to uncover more applications for REEs. This is summarized in Figure 2.5. 12 Figure 2.5 Applications of REEs (Dev S et al., 2020; Report CWR, 2016) 2.3 Production Statistics of REEs Rare Earth Oxide (REO) production substantially increased between 1992 and 2017, mainly driven by increased demand for technological applications (British Geological Survey, 2020). According to US Geological Survey (USGS) data, approximately 210,000 tonnes were produced in 2019, representing a 13 % increment from the previous year in 2018. China has been the primary producer of REOs, accounting for 62 % of the total supply in 2019 alone. China has supplied most of the world’s REO contributing 62 % of the supply in 2019 through official production. The United States (12 % of global production), Myanmar (10 %) and Australia (10 %) also contribute their fair share of production. (S&P Global Market Intelligence; USGS, 2020). 13 China is the only producer of valuable HREEs. Figure 2.6 shows that the production of REEs globally is gradually building up, though still not up to the production level of China. In 2011, China produced (105,000 tonnes) as many REEs as the rest of the world (111,000 tonnes). Even though it has been steady throughout the years, China’s production has still been much more than the total production from the rest of the world. (NRCan, 2022). Figure 2.6 Percentages of REOs produced. (USGS, 2020; JRC, 2018) The monopoly of China in the rare earth industry has led many countries to support more geological exploration and mining projects aimed at diversifying the supply chain. This has led to some countries having to reopen past mines to try and reduce the dependency of the world on China. The United States reopened the Mountain Pass mine, and Australia followed with the 14 reopening of Mount Weld mine. Aside from this, many other projects are undergoing a fast-track process to try and reduce China’s lead in the industry (S&P Global Market Intelligence, 2020). Canada is a major candidate for resource abundance of REEs after China. However, the United States and Australia have much stronger position regarding reserves, reevaluating the ambitions to gain some control in the supply chain. About 20 % of the available reserves are accounted for by the European Union’s overseas territory of Greenland and for almost 10 % of the overall global reserves. Figure 2.7 shows the known in situ resources and reserves of neodymium, praseodymium, dysprosium, and terbium and their global distribution. Figure 2.7 Resources and reserves of neodymium, praseodymium, terbium, and their geographical distribution (JRC Report, 2020; S&P Global Market Intelligence, 2020) Canada is not a current commercial REE producer but hosts numerous developed exploration projects. In 2021, Canada started the Nechalacho project, a small-scale demonstration mining project (1.46 % REO, measured, indicated, and inferred), with the ore from the site being sent to Saskatchewan Research Center in Saskatoon for further processing. Several REE explorations in Canada are in the advanced stages and have the potential to produce HREEs that are needed for making high-tech and clean energy applications. (NRCan, 2022). Figure 2.8 shows a map of Canada’s active and exploration sites. 15 Figure 2.8 Map of Canadian REE project sites, showing the status of operations (NRCan, 2022) 2.4 Factors Affecting REEs Prices Since China has significant control over the REE market, China can restrict supplies to boost demand and increase the prices of the REEs, much to the dismay of the rest of the world. This happened in 2010 when China imposed certain restrictions on its production and export of the much-needed REMs (Tse, 2011). These restrictions on REEs led to the Western countries having to change their strategy about these critical elements and necessitated the need to find new and alternative REE deposits. (Chen, 2011). 16 Further issues that prospective producers of REEs must consider include (Delaney, 2010) • insufficient technical expertise (outside of China); • managing radioactive waste created as a byproduct of extracting REEs, the substantial upfront expenses of REE plant construction (conventional plant costs are close to one billion dollars), the lack of easily available market prices, and the erratic demand levels for individual REEs. The imbalance between supply and demand has forced research into new areas to meet the demands, including recycling, scavenging of available waste streams rich in REEs, improved efficiency of REEs extraction processes, development of new rare earths mineral (REM) deposits, finding alternate sources of REEs, and even pursuing alternatives to REEs use entirely. The assessment of REEs uses the classification of REEs depending on the amount of industry demand. (Seredin, 2010). For primary evaluation purposes, the outlook coefficient (Coutl) is used. The proportion of surplus REE to essential REE is what determines this ratio.: Coutl = (Nd + Eu + Tb + Dy + Er + Y)/REE sum: (Ce + Ho + Tm + Yb + Lu)/REE sum. Using this coefficient allows for the early grading of newly discovered deposits and assessing the value of well-known deposits, including those currently mined (Seredin, 2010). 2.5 Beneficiation of REE-Bearing Minerals The principal source of REMs is a variety of geologic bodies and hard rock deposits or placer sands (secondary deposits). Because of the presence of phosphates and carbonates, the 17 composition of the REMs in these deposits varies (Jackson and Christiansen, 1993). According to Jackson and Christiansen (1993), carbonatites are the most dominant source of REEs. Carbonatites contain mostly LREEs and REEs are present in minerals such as bastnaesite, allanite, and apatite (Gupta and Krishnamurthy, 2005). Pegmatites are also another source of REEs (Jackson and Christiansen, 1993). They are hard rocks formed from the re-melting of crustal material. Crystals containing HREEs are formed as the magma cools down, with the LREEs remaining in the residual liquid. As a result, compared to when found in other rocks, monazite and allanite in pegmatites tend to be richer in the HREEs (Gupta and Krishnamurthy, 2005). Hydrothermal deposits can also include REEs (Jackson and Christiansen, 1993). Since they are less soluble than the heavier ones, the LREEs settle out first, leaving the heavier ones in the liquid. Consequently, minerals like xenotime and HREEs can be found in hydrothermal deposits (Gupta and Krishnamurthy, 2005). Chemical weathering causes calcite, dolomite, and apatite to dissolve in carbonatites. Because of its great affinity for phosphate radicals, the REMs that result from this typically produces supergene monazite. Certain minerals are altered by extreme lateritic weathering. Ion adsorption-type deposits occasionally occur because of extremely prolonged weathering with little erosion (Clark and Zheng, 1991). Placer deposits contain high amounts of monazite and xenotime and are known for their high specific gravities and chemical inertness. Tidal actions, currents, waves, and winds on the coast 18 tend to concentrate heavy minerals. As such, important mineable placer deposits are formed along beaches and dunes of coastlines (Gupta and Krishnamurthy, 2005). There are 47.6 million metric tonnes of REO that are thought to be present in REEs deposits worldwide (Hedrick, 1988; Clark and Zheng, 1991; Sabot and Maestro, 1995). These are primarily found in China, the United States, Australia, India, Russia, and South Africa. 2.6 Rare Earths Minerals (REMs) REMs occur in nature as a mixture in many rock formations, unlike other metals that occur in their elemental states. The concentration they are found in ranges from 10 ppm to 300 ppm (Sabot and Maestro, 1995). They are mostly found in oxidic forms due to their strong affinity to oxygen and exist in almost 160 discrete minerals. The mineral in which they exist is not abundant, but there are REEs in these minerals expressed as oxide that could be as high as 60 %. Since 1991, about 200 minerals have been found to contain REEs with at least more than 0.01 % REO (O’Driscoll, 1991). Table 2.1 highlights some REMs (Aplan, 1988; Ferron et al., 1991; Jackson and Christiansen, 1993). Despite the numerous REEs containing minerals in existence, they mostly occur in these three minerals: bastnaesite, monazite, and xenotime. Therefore, they serve as the primary resource for extracting REMs. Bastnaesite, monazite, and xenotime are the ones that are found most often. Other well-known minerals include apatite, brannerite, euxenite, gadolinite, loparite, and uraninite. 19 Table 2.1 Essential REEs (Ferron et al., 1991, Jackson and Christiansen, 1993) 2.6.1 REEs in primary sources and REEs in secondary sources Monazite, xenotime, and bastnaesite are the principal sources of REEs. The total estimated global REEs reserves as of 2019 were 120 million tonnes. China’s reserves are around 44 million tonnes, followed by Brazil and Vietnam, both at 22 million tonnes. Russia was estimated to have 12 million 20 tonnes, India with 6.9 million tonnes, Australia with 3.4 million tonnes, and Greenland and the United States both have 1.5 million tonnes in reserves (NRCan, 2020). Regardless of these reserves being present, efforts have been made to recycle REEs from consumer products. In 2014 alone, an estimated 1200 kg of yttrium, 130 kg of terbium, and 350 kg of lanthanum were used to produce light-emitting diodes (Jowitt et al., 2018). Magnets (containing 20–30 % REEs) are the most significant contributor to electronic waste, followed by fluorescent lamps (containing more than 20 %) (Wilburn, 2012; Venkatesen et al., 2018). Since then, as more consumer goods have been produced, the recycling potential of REEs has expanded (NRCan, 2020). Growing technological advancements means a growing usage of REEs; it’s estimated that the global growth of REE usage is 1 % yearly (Jowitt et al., 2018). Yet, REE recycling can complement harvested REEs rather than replace them. In addition, additional cutting-edge and reasonably priced technologies can assist in easing the environmental difficulties that recycling aims to solve (Mohr, 2009). The year 2019 saw the production of more than 4.6 billion tonnes of mining waste, which may have contained 1.96 million tonnes of REEs. The mining tailings comprise a sizeable amount of REEs in them; however, it is important to determine whether environmental extraction of these elements would be economically viable. REEs may be extracted from mining waste to lessen its environmental impact, save resources, and save the need to start new REEs mining operations. Therefore, it is important to develop efficient ways to collect REEs from various waste sources, including the recycling of electronic waste and other types of industrial waste currently in use. 21 2.6.2 Commonly mined minerals for REEs extraction 2.6.2.1 Bastnaesite In vein deposits, metamorphic zones, and pegmatites, bastnaesite is a fluorocarbonate of a rare earth metal from the cerium group. Bastnaesite’s chemical formula is Ce (CO3) F. The LREEs are found in the ore material containing bastnaesite. There are about 800 million metric tonnes (6 % REO) of bastnaesite in Bayan Obo of China, compared to the 3.3 million metric tonnes (7.7 % REO) in Mountain Pass, United States (Gupta and Krishnamurthy, 2005). This is summarized in Table 2.2 below (Hedrick, 1991). Other locations in Australia, Brazil, Canada, and Burundi contain bastnaesite as the main REO. The REO dissolves and combines with the existing phosphates since bastnaesite is chemically vulnerable to weathering (Voncken, 2016). Table 2.2 Bastnaesite composition in REEs (w.r.t. 100 % REO) 22 Figure 2.9 Bastnaesite Photograph by J.H.L Voncken (1997) 2.6.2.2 Monazite Monazite, with a general chemical formula of CePO4 (Breithaupt, 1829), is a phosphate mineral with an REEs content of about 70 % REO. Like bastnaesite, it is mainly made of cerium, lanthanum, praseodymium, and neodymium, which account for 83.55 % and 94.50 % of the total REO, is regarded as a selective, cerium-type mineral (Cesbron, 1986; Ferron et al., 1991; Gupta and Krishnamurthy, 1992; Gupta and Krishnamurthy, 2005; Trifonov, 1963). Yttrium content varies from 5 % Y2O3 upwards, with a thorium content of 4 % to 12% (Gramaccioli and Segalstad, 1978; Gupta and Krishnamurthy, 2005). The chemical stability of yttrium allows it to form detrital minerals in placer deposits and beach sand. Some amount of uranium is also present in monazite. It may be found in vein deposits in igneous and metamorphic rocks as an accessory mineral (Aplan, 1988). 23 Figure 2.10 Monazite. (Naturalis Biodiversity Center, Leiden, The Netherlands, Sample RGM 412064). In granites and granodiorites, monazites are a minor mineral associated with pegmatites in most metamorphic rocks. 2.6.2.3 Xenotime Xenotime, mostly made up of heavy elements, is an yttrium phosphate with about 67 % REO but is a small component in granite or gneiss (Aplan, 1988). Xenotime also occurs with placer deposits, but not many such deposits exist. Xenotime, relative to monazite, occurs in minute quantities of about 0.5% to 5% of the total monazite content. Despite its scarcity, xenotime houses most of the HREE, and this highlights its importance. Chinese ion-absorbed REE-bearing clays are also a significant source of HREEs (Cheng et al., 1994; Chi et al., 2001). Due to its existence in relative amounts to monazite, it is often a byproduct of monazite processing (Cheng et al., 1994; Ferron et al., 1991). 24 Figure 2.11 Xenotime (Naturalis Biodiversity Center, Leiden, The Netherlands) 2.6.2.4 Ion-adsorbed clays and other REMs There are ion-adsorbed clays that contain close to 60 % REO from the yttrium groups and, thus, serve as an important source for HREEs (Zhang and Edwards, 2012). Due to their nature, they require little to no physical beneficiation and can be processed directly using metallurgical methods. There are other minerals that are sources of REEs. These include allanite (ranges from 3 % to 51 % REO, depending on the source), apatite (from trace to about 10 % REO), brannerite, and eudialyte (1 % to 3 % REO). 2.6.3 BC coal deposits characterization The National Energy Technology Laboratory in the United States studied the potential of coal as a source of REEs (Bryan et al., 2015). The investigation concentrated on samples with at least 300 ppm of total REEs at 2 % by weight in the process streams (U.S. Department of Energy, 2016). 25 In BC, Goodarzi (1988), Birk and White (1991), and Goodarzi et al. (2009) initiated studies of trace elements when they proved that coals, especially in BC coalfields, contained REMs in them. Some have comparable REE concentration to traditional commercial REEs deposits (Seredin and Dai, 2012). Kuppusamy and Holuszko’s research sought to identify the most promising coal sources for REE while also attempting to create a database of REE occurrence in the East Kootenay coalfields (Kuppusamy and Holuszko, 2019). The initial phase of the research was published in 2019 paper, in which 49 samples (comprising roof, floor, partings, and coal) were characterized based on a simplified version of the United States Geological Survey (USGS) Coal Quality survey (COALQUAL). The USGS COALQUAL characterization included coal type, proximate analysis, ultimate analysis, major-, minor-, and trace-elements analysis (Finkelman et al., 1994). The parameters used for BC coals classification included type, rank, and major-, minor-, and trace-element concentrations (Kuppusamy and Holuszko, 2021). Figure 2.12 Coal mines in British Columbia (BC Geological Survey, 2019) 26 Kuppusamy and Holuszko’s analysis was most recently updated in 2021 report, with an additional 55 samples. Coal, also known as coal seams, and the resulting roof, floor, and partings from the coal seams under inspection were all subjected to the research. REEs in these samples were quantified using ash content and coal sample REEs concentration (REE concentration in the ash of the coal sample). According to studies by Kuppusamy and Holuszko (2021), all the coals may be classed as low-to-medium volatile bituminous coals and have metallurgical applications. Five elements (cerium, lanthanum, neodymium, yttrium, and scandium) accounted for more than 77 % of the total REEs, with REE concentrations ranging from 91 ppm to 686 ppm on an ash basis (Kuppusamy and Holuszko, 2021). Table 2.3 provides an overview of the highest, lowest, and average REE concentrations for each kind of geological material on an ash basis. Table 2.3 REE concentrations (on an ash basis; ppm) in samples of the East Kootenay coalfield’s roof, floor, coal, and partings. (Kuppusamy and Holuszko, 2021). According to the results from the study, coal samples indicated a higher concentration of REEs relative to other geological types. It was observed that the REEs concentration increased with increasing ash content, suggesting an REE association with mineral matter (Kuppusamy and Holuszko, 2021). 27 Figure 2.13 REE concentration versus ash content of the East Kootenay coalfield, British Columbia (Kuppusamy and Holuszko, 2021) Due to the beneficiation of coal, coal tailings streams have a significant percentage of mineral matter content (ash). Bench scale flotation experiments by Kuppusamy and Holuszko (2019) revealed that almost all the REEs by weight ended up in the middlings and the tailings streams, as shown in Figure 2.13 above. Dai et al. (Dai et al., 2017) developed an economic evaluation technique that utilized the outlook coefficient to prepare a sensitivity plot. The outlook coefficient is the ratio of the sample’s excess REEs concentrations to its relative levels of crucial REEs concentrations (Seredin and Dai, 2012). The outlook coefficient indicates the market price for the REEs in the coal; since the concentration of the critical REEs increase with the index (Dai et al., 2017). Table 2.4 summarizes the minimum, maximum, and average outlook coefficients for the different material types. The evaluation led to 28 five categories being developed for the analyzed samples (outlook categories in Table 2.4 and analyzed samples in Table 2.5) based on the US Department of Energy’s (2016) proposed classification. Table 2.4 Categorization of REE sources based on REE grade and outlook coefficient (US Department of Energy, 2016) Categories REE range (ash basis), ppm Outlook coefficient (Coutl) Unpromising source REE < 300 Coutl < 0.7 Promising source 300 < REE < 720 0.7 < Coutl < 2.4 Highly promising source 300 < REE < 720 Coutl > 2.4 Promising source REE > 720 0.7 < Coutl > 2.4 Highly promising source REE > 720 Coutl > 2.4 Table 2.5 Results of HREE–LREE and outlook coefficient of East Kootenay coalfield samples (Kuppusamy and Holuszko, 2021) Kuppusamy and Holuszko (2021) observed that most of the samples had a Coutl of > 1, suggesting that the critical REE concentration is significant in most of the samples, while the HREE concentration was generally more concentrated in coal compared to the floor, roof, and partings (see Table 2.5). Furthermore, some partings in the samples indicated enriched HREE 29 concentrations, resulting in high outlook coefficients. The statistics of partings were enhanced generally as a result of HREE enrichment in select samples. The ratio of HREE–LREE obtained for these samples was comparable to that of coals. Globally reported Coutl (Zhang et al., 2015; Dai et al., 2017) is 0.64, and with these results from the study, BC coals show signs of being a potential source of REE extraction if appropriate mining processes are developed by Kuppusamy and Holuszko, (2021). 30 Chapter 3: Beneficiation and Extraction of REEs 3.1 Primary Sources 3.1.1 Physical separation methods To guarantee that the financial sustainability of commercial REE production from primary and secondary sources is reached, a series of physical separation techniques must be used and usually followed by hydrometallurgical extractions or pyrometallurgical processing (Ozbayoglu et al., 2020; Abdel-Rehum, 2022; Hernadez-Exposito et al., 2006; Gupta and Krishnamurthy,1992; Fuerstanau, 2013). Most mineral concentrates undergo several extraction processes to separate individual REOs. Gravity separation, magnetic separation, and electrostatic separations are a few of the physical separation techniques utilized for REEs recovery. This is mostly combined with increasing their efficiency, they are intended to increase the value of the mineral of interest by removing the gangues utilizing those elements' physical and chemical properties (Ferron et al., 1991). A combination of these methods has been exploited to beneficiate traditional REMs (Jordens et al., 2012). However, not much research has been conducted using these methods to beneficiate REEs from coal. Blissett et al. (2014) examined the viability of concentrating REEs in coal fly ash using a complex processing method. This involved the use of flotation, magnetic separation, and hydrocyclone classification. Unfortunately, only about 26 % enrichment was achieved with this combination, mainly because of size reduction. In a different work presented by Soundarrajan et al. (2015), float-sink, magnetic, and electrostatic separation techniques were utilized to enhance REEs recovery from coarse pit tailings and other refuse samples. Each method was found to be 31 different in terms of the method’s efficiency and the type of feedstock. In summary, there was no substantial increment in REE grade using these methods. Honaker et al. (2014) looked at how well three coal sample separation methods (density-based separation, froth flotation, and magnetic separation) recovered REEs. The results showed that flotation was the best among the three methods. Zhang et al. (2017) used this result to further investigate two forms of flotations: conventional flotation cell and column flotation. When comparing column flotation to the traditional flotation cell, it showed more potential. An enrichment ratio of 10:1 was achieved, indicating that column flotation is a good physical separation candidate. As was expected, though, the recovery took a hit and was just about 4 %. In summary, all the various physical separation methods did not show substantial evidence of pre-concentrating REEs for coal and its byproducts. This could be partly attributed to size limitation for each method since REMs are very small grains. (Honaker et al., 2014). 3.1.1.1 Electrostatic separation Electrostatic separation has been used to concentrate some REE-bearing minerals, such as xenotime or monazite. Due to similarities in gravity and magnetic properties, xenotime is concentrated chiefly with ilmenite; hence, both can be upgraded using electrostatic separation (Gupta and Krishnamurthy,1992; Jordens et al., 2013). Additionally, gangue minerals, which have similar magnetic properties, can be separated from xenotime and monazite using this same method. However, the gangue minerals must have different electrical conductivity from the monazite or xenotime minerals (Ferron et al., 1991; Mat Suli et al., 2017). The only drawback to this application is that the feed material must be dried (Hagashiyama et al., 1998), in most cases prior 32 to processing by electrostatic separation. This leads to incurring a high energy cost due to the drying of fine-sized ore prior to performing the electrostatic separation process, and thus, not a feasible option on an industrial scale (Kelly and Spottiwood, 1989; Jordens et al., 2017). 3.1.1.2 Magnetic separation Magnetic separation is widely used to remove highly magnetic gangue or to concentrate the desired paramagnetic REMs, such as monazite or xenotime (Gupta and Krishnamurthy, 1992). Generally, REMs tend to be magnetic in nature due to the electrons in the 4f subshell (Spedding, 1975). Ito et al. (1991) calculated the magnetic susceptibility of REMs and used it to predict their susceptibility to magnetic attraction based on their chemical composition. His results explained why xenotime showed a three-fold magnetic susceptibility increase. This is largely due to the high concentrations of gadolinium, dysprosium, and erbium in the mineral. The magnetic susceptibility recorded was high for gadolinium to erbium (Ito et al., 1991). The findings were coherent with other reference works, which confirmed the paramagnetic strength of gadolinium, terbium, dysprosium, holmium, and erbium (Spedding and Daane, 1961; Topp, 1965). In China, magnetic separation is employed as a cleaning step before the flotation of feeds and concentrates containing REEs and to remove iron-bearing gangue (Chi et al., 2001; Zhang and Edwards, 2012). Gravity and magnetic separation techniques are used to extract bastnaesite before flotation at China’s second largest REEs deposit (Chi et al., 2001). Research has indicated that, before using a more selective technique, paramagnetic monazite must be removed by magnetic separation from heavy mineral gangues, such as zircon and rutile (Ferron et al., 1991; Tran, 1991; Zhang and Edwards, 2012). 33 3.1.1.3 Gravity separation Gravity separation techniques are generally the most cost-effective beneficiation method. It is based on the principle of Newton’s law, where the separation of particles in a viscous medium occurs based on particle size (Khanchi et al., 2014). REEs have a relatively high specific gravity (4.9 and 5.5), and thus, gravity separation works very well in its beneficiation (Mat Suli et al., 2017). 3.1.1.4 Froth flotation Flotation is the most widely utilized and effective separation method in commercial REEs beneficiation (Abaka-Wood et al., 2016). Several investigations on the flotation of REEs found in bastnaesite have been undertaken in the United States and China. For the flotation of bastnaesite, collectors such as hydroxamates, fatty acids, sodium silicate, and sodium hexafluoro silicate are typically utilized (Jordens et al., 2013; Mat Suli et al., 2017; Hourt et al., 1991; Anderson et al., 2017). Different mineral processing facilities utilize various physical separation methods, such as flotation (see Table 3.1), to extract REMs from gangue minerals (Abaka-Wood et al., 2016). However, the reason for not commonly using froth flotation to concentrate REEs from coal fine rejects is the complexity of the floating fine coal tailings; fine coal rejects are usually obtained from the unsuccessful flotation response of coal at the plant. In addition, one must design a suitable process for floating many different REMs from coal tailings at their very low concentrations and minute grain sizes. 34 Table 3.1 Physical separation methods used by mines to recover REOs 3.1.1.5 Hydrophobic Hydrophilic Separation (HHS) Drs. Yoon and Luttrell of Virginia Tech created the HHS process in 1995 from the dewatering-by-displacement (DbD) concept when they patented a novel technique for dewatering tiny coal particles (Yoon and Luttrell, 1995). The procedure entails the dispersion of mineral particles by gravity in a dense chlorofluorocarbon media from coal that has been clumped together. The low-boiling-point organic liquid is then recovered by low-temperature heating for recycling (Keller, 1982). The spherical agglomeration process was invented by Capes in the 1960s in Canada, where the idea of separation of coal due to its affinity to hydrocarbon oils was utilized to successfully separate fine coal from very fine gangue minerals forming ash in coal (Capes et al., 1971). In 1984, Keller changed the low-boiling-point organic liquid to pentane, particularly due to the high recovery cost and environmental concerns (Seaman, 1992). The process resulted in the production of very low ash coal with a very high moisture content (Keller, 1985). This peculiar problem led to the discontinuation of the process around the year 1990. Advancements in oil 35 agglomeration technology led by Drs. Yoon and Luttrell from Virginia Tech led to the production of low ash and low moisture coal. This became known as HHS. 3.1.1.6 Hydrophobic Hydrophilic process description The HHS process was developed to clean and dewater ultrafine coal. The process, as shown in Figure 3.2, is described in the following steps: • Step 1: Droplets of a low-boiling-point solvent (oil) are introduced into a slurry stream of coal and selectively coat the hydrophobic particles. • Step 2: The coated coal particles coalesce to produce an agglomerate that can be split from mineral matter. • Step 3: The agglomerates are broken in the presence of a high solvent concentration. Coal with a higher affinity for the solvent remains with the solvent, while the ash stays within the water. • Step 4: The spent solvent is retrieved by filtration and evaporation for recycling in the process. Figure 3.1 Schematic picture of the HHS procedure (Yoon et al., 2016) 2 1 4 3 36 3.2 Secondary Sources 3.2.1 Coal and coal byproducts Recent research has shown that coal and coal byproducts contain REEs. REEs concentrations were 2000 ppm in coal seams and coal preparation plant rejects, compared to the usual value of 445 ppm in coal fly ash (Ketris et al., 2009; Sacahn et al., 2018; Zhang et al., 2015). Hower et al.’s (2013) investigation revealed that samples of coal ash from several power stations had between 187 ppm and 600 ppm of REEs. REOs levels in coal ash samples from Poland and the UK ranged from 297 ppm to 579 ppm and 371 ppm to 432 ppm, respectively (Blisset et al., 2014). Several places have revealed that coal contains more REEs than fly ash does. Alunite supergroup sulphates, carbonates, and aluminum phosphates are a few REMs found in coal (Dai et al., 2012). 3.3 Prior Work HHS related work started in 1995 at Virginia Tech from the concept of DbD. This process was later elaborated by Yoon and Luttrell in 2016. In the early days, this process was studied on bituminous coal, using butane as the hydrophobic liquid. Sohn et al. (1997) noted that an agitated coal-butane mixture forms dry powder, but only in the presence of high volumes of oil. Enrichment by froth flotation has always been a challenge as the REE-enriched monazite grains (< 5 μm) are too small to be recovered (Zhang et al., 2017). Therefore, Biao Li (2019) explored the feasibility of using HSS instead of flotation to recover REMs associated with coal byproducts. The study focused on thickener underflow from a coal preparation plant in Kentucky. Several HHS tests were conducted to examine the impacts of collector dosage and type, decarbonization (removal of organic carbonaceous material), liberation, depressant—such as sorbitan monooleate, 37 and sample aging. Another aspect of the research compared forced air flotation against the HHS process. The HHS process showed superior results, with an assayed Total REE (TREE) grade of 17,590 ppm on ash basis compared to 8,279 ppm on ash basis for the forced air flotation. Each enrichment was from a feed assay of ~350 ppm TREEs. The representative sample of the thickener underflow used in the study assayed ~ 56 % ash. The low ash value required the decarbonization of the feed sample prior to undertaking the grinding and HHS tests. After, the samples that passed 35 μm with an ash content of more than 91 % were subjected to further grinding to a particle size of 8 μm and 3.9 μm. Approximately 10–25% solids of decarbonized slurry were conditioned for 15 minutes at natural pH and subsequently conditioned for five minutes using octanohydroxamic acid (OHA). This is recognized industry wide as the best collector for the flotation of monazite. Heptane was added to the conditioned slurry and run at low shear for five minutes to help form coal agglomerates. Figure 3.2 OHA’s impact on a sample of micronized thickener underflow’s ability to extract REEs (Biao Li, 2019) 38 The study showed that, as the collector dosage increased, there was a corresponding increment in the recoveries, but there was a drop in the REE grade of the final product. This was attributed to the recovery of more clay particles at the higher dosage rate (Zhang et al., 2018; Zhang, 2017). This was further verified by the relationship between the OHA dosage and concentrate ash (Figure 3.2b). Furthermore, the study investigated the effects of removing coal (decarbonization) prior to REMs recovery. The samples were subjected to grinding before removing hydrophobic carbonaceous material (coal). The removal of coal was achieved via flotation. Using a decarbonization process before the HHS test led to an improvement in REEs recovery and an increase in REEs grades in the HHS concentrate product on a foundation of coal and ash (Figure 3.3). Figure 3.3 The results of the HHS tests on a micronized thickener underflow sample both with and without decarbonization (Biao Li, 2019) 39 The study also explored the effect of further liberation on the samples and realized an improvement in both recovery and grade. Further grinding resulted in more REEs, and REMs being exposed; thus, the grade of the final concentrate increased by 2.5 with a corresponding increase in recovery also, about 4.6 times. Figure 3.4 shows the results of this test. Figure 3.4 Particle size’s impact on a thickener underflow sample’s ability to recover REEs (Biao Li, 2019) Studies by Yoon (2005) showed that increasing a mineral’s hydrophobicity using a non-ionic surfactant increased its floatability. These reagents are selected based on their hydrophobic-hydrophilic balance (HLB) numbers. Any non-ionic surfactant with an HLB of less than 15 would be sufficient for this purpose. Sorbitan monooleate (SMO) with an HLB of 4.3 was used. A number of HHS tests was conducted on two micronized (d80 = 8 μm and 3.9μm) thickener underflow 40 samples, both with 0 kg/t SMO and 0.9 kg/t SMO. The results showed that both the TREE grade and recovery increased at a dosage rate of 0.9 kg/t (Figure 3.5). Figure 3.5 SMO’s impact on a sample of micronized thickener underflow’s ability to extract REEs (Biao Li, 2019) Another aspect of the study was comparing the conventional and column flotation to the HHS process. The conventional and column flotation showed very good results in terms of the grade of the final concentrate and recovery, but the HHS process proved to be the superior of the three. Figure 3.6 depicts the results of this experiment. 41 Figure 3.6 Comparison of three different separation methods (Biao Li, 2019) Based on the success of the results from Biao Li, (2019) the procedures and methods were replicated for this research. The main objective of this thesis was to investigate the efficiency of HHS, a process promoted as being an effective one for fine particles in the recovery REMs in BC coal and coal byproducts. 42 Chapter 4: Experimental Methodology and Materials To determine the practicality and effectiveness of the HHS method to create REEs concentrate from coal tailings, this chapter details the experimental approach as well as the tools and materials employed. Several experimental techniques are employed to decarbonize coal tailings and release minerals containing REEs. Various reagents were used both during the decarbonization and for follow-up steps for hydrophilizing the REEs for their separation. 4.1 Sample Selection The East Kootenay coalfield in southeast BC served as the source of the samples used in this investigation, as shown in Figure 2.13. Coal seams in the East Kootenay coalfields are largely of metallurgical quality and predominantly classified as medium volatile bituminous coals with volatile matter ranging from 20.7 % to 33 % (Kuppusamy and Holuszko, 2019). The samples were collected from respective mines and plants by site geologists and plant operators. Over 100 samples were analyzed by Kuppusamy and Holuszko (2021) to develop an REEs database for the region of interest. The samples were characterized based on a few factors discussed in Section 2.6 of this thesis. Three samples, one roof, floor, and partings, were each selected based on the coefficient outlook and the number of TREEs present in that sample for further analysis. The ratio of the sample’s relative quantities of excessive REEs to its relative amounts of crucial REEs is known as the coefficient outlook (Seredin and Dai, 2012). From now on, the samples will be denoted by R1 for roof sample, F1 for floor sample, and P1 for parting sample. The three samples, R1, F1, and P1, had an outlook coefficient falling with 300< REE > 700 ppm, indicating a promising resource for extraction. Another sample defined as coal tailings (CT) was also used during the initial tests. It was selected based on the same criteria. 43 4.2 Sample Preparation In summary, samples received from the mine were screened using a 1”-inch (25.4 mm) sieve. The samples coarser than 1”-inch (25.4 mm) size was crushed using a jaw crusher to obtain 100 %, passing 1”-inch (25.4 mm) size to satisfy plant practice for the top size of the feed to the plant. The crushed sample was mixed with the rest of the samples and homogenized by mixing the samples thoroughly. The homogenized sample was split into eight portions using a rotary splitter to obtain an approximately 35 kg to 40 kg sample. Except for the sample further processed, the remaining samples were double bagged and stored in a closed bucket to avoid sample weathering. The 1" (25.4 mm) samples were further crushed using a hammer mill, passing 4.75 mm and riffle split into 5 kg representative sample aliquots. Each was labelled appropriately, double bagged, and stored in closed buckets for use. Depending on the requirements, these 5 kg sample batches were further crushed or split to obtain a representative sample of the required size for analysis. Figure 4.1 Schematic of sample preparation for analysis 44 Figure 4.2 Crushers used in the sample preparation a) jaw crusher b) jaw crusher plates c) hammer mill 4.3 Particle Size Distribution Particle size separation of samples was performed using a series of sieves and a Ro-tap shaker on select samples. A representative sample of 200 g passing 500 μm was wet sieved to separate ultra-fines (-45 µm) from the rest of the sample. Both fractions (-45 µm and +45 µm) were filtered, dried at 65°C, and weighed. Dry screening was conducted on the coarser fraction (+45 μm) using Ro-tap for 20 minutes and separated into five more fractions: +300 µm; -300 µm +212 µm; -212 µm +106 µm; -106 µm +53 µm; -53 µm. All the fractions were collected, weighed, and sent for REEs analysis in each size fractions. The mass loss during the experiment was less than 1 %. 45 4.4 Proximate Analysis American Society for Testing Minerals (ASTM) standard procedures (ASTM, 2017b; ASTM 2012b; ASTM 2017c; ASTM 2013) were followed to determine the proximate analysis of the sample and are described in Appendix A. 4.5 Reagents • Hydrophobic Hydrophilic Separation (HHS) Heptane (𝐶7𝐻16), with specs High Performance Liquid Chromatography (HPLC) Grade 99+ %, was used as a hydrophobic oil phase (hydrophobic liquid for emulsion formation) for the REEs test work for this research. In all stages of the test work, where necessary, sodium silicate was added to disperse the gangue material during the HHS process. A collector was also added during the HHS process to aid in the recovery of REE-bearing minerals. This study focused on sodium alkyl hydroxamic acid and sodium oleate as primary collectors (C-18 fatty acid). • Flotation For coal flotation, Methyl Isobutyl Carbinol (MIBC) was used as the frother, and kerosene was used as the collector. A detailed procedure is provided in Section 4.6 below. • Oil agglomeration for decarbonization of the roof, floor, and partings (R1, F1, P1) Pentane was used during the decarbonization for oil agglomeration of R1, F1, and P1 samples. A detailed procedure is provided in Section 4.7 • Sequential extraction The reagents used for the sequential extraction are ammonium sulfate, sodium acetate, hydrochloric acid, and nitric acid. The detailed purpose of each reagent is provided in Section 4.8.1. 46 4.6 Decarbonization of Studied Coal Samples Prior to HHS Both types of studied coal samples needed to be decarbonized before proceeding with the HHS procedure for REEs separation. The reason for decarbonization was to reduce the content of carbonaceous (organic) matter in the samples collected from the coal seams R1, F1 and P1 and CT, as they still contained a significant amount of coaly material, and to increase the mineral matter (ash) content for improving the extraction of REE-bearing minerals. Two methods for decarbonization were applied. Coal flotation for CT was used because the coal was still highly floatable, and flotation, as shown from previous research on these samples, could be easily applied to remove clean coal and increased ash content in these tailings. Oil agglomeration was selected for the R1, F1 and P1 samples because the coal in these samples was less floatable, as found from previous test work (Kuppusamy and Holuszko, 2019). 4.6.1 Coal flotation – decarbonization of CT The sample (CT) was used for REMs concentration using HHS. Before conducting HHS, the feed sample was subjected to coal flotation to remove any excess carbonaceous (decarbonization) material present in the feed sample. After removing carbonaceous material, the CT sample was later used for HHS in all the tests. For the flotation test, a representative feed sample of CT was crushed to obtain a size of -500 µm and a standard Denver laboratory cell was used to conduct the batch test. The cell was filled to ¾ height with water, and the impeller speed was adjusted to 1300 r/min. The feed sample was placed in the cell and conditioned for five minutes to wet the sample thoroughly. Using a high-speed laboratory blender, the reagent emulsion was prepared separately by pouring 200 mL of water into 47 the blender. The reagent emulsion of 240 g/t of kerosene (collector) and 200 g/t of MIBC (frother) was used for concentrate collection according to the previous work on similar types of samples (Kuppusamy, 2022). The appropriate amount of collector (kerosene) and half of the necessary volume of the frother (MIBC) were also added to the blender, which was then run at high speed for 30 seconds. The produced emulsion was swiftly introduced into the cell and was allowed to condition there for 15 minutes. At the end of 15 minutes of conditioning time, the other half of the frother volume is introduced to the cell and conditioned for an additional minute. The concentrate was collected at this time at an aeration rate of 4.5 L/min until the foam was barren. After being pressure filtered, the concentrate and filtered tailings were both dried at 65 °C. The HHS process later utilized the tailings produced by this stage test. Figure 4.3 shows the schematic of the process. Figure 4.3 Schematic of flotation test and HHS test on CT sample 48 4.6.2 Decarbonization of roof, partings, and floor samples The decarbonization process was conducted on the three samples (R1, P1, and F1) to ascertain if this step was necessary prior to HHS test work for REEs recovery to remove as much carbonaceous material as possible. Decarbonization was achieved for the three samples (R1, P1, and F1) via oil agglomeration, while flotation was used for the decarbonization of the CT sample, as discussed in the previous section. A 500 mL beaker was used as the mixing vessel for the oil agglomeration, with an impeller for the agitation. Around 25 g of the sample was added to the beaker, which had 200 mL of water in it, and it was then exposed to high-shear agitation in the presence of oil to encourage the attachment of oil droplets to the coal particles. For coal oil agglomeration, pentane was employed as the hydrophobic liquid oil, and 50 mL was used for each batch run. By agitating the micro-agglomerates with low shear, the recovery of the micro-agglomerates is improved. The coal agglomerates are then screened off using a standard 100 mesh screen (150 µm), resulting in a product that could be processed using HHS. It is worth noting that this stage was omitted after it was found that it could not remove much of the clean coal and collected very little of the REE in a very small mass of the sample. 4.7 Hydrophobic Hydrophilic Separation (HHS) REEs are associated with inorganic mineral matter, so carbonaceous material must be removed from the various coal samples (R1, F1, P1 and CT being tested for REE recovery. The REEs HHS-associated process (Figure 4.4) can be considered a two-stage process; HHS recovery of low ash coal and REE recovery from the high ash tailings. 49 In this procedure, the decarbonized slurry is conditioned for 15 minutes using a known dosage of sodium silicate (Table 4.1), and a dispersant is added to hinder the hydrophilization of non-REE-bearing gangue minerals. After this, the slurry is conditioned for an additional 15 minutes using a collector to target the REE-bearing minerals. After this, a large volume of heptane oil (hydrophobic liquid for emulsion formation) is added and subjected to high shear conditions to form emulsions. The resulting slurry is transferred to a separatory funnel, and the tailings are removed. The samples were then dried and sent for analysis. Figure 4.4 Schematic for HHS process used for F1, P1, and R1 samples 4.8 Mineralogical Characterization This section details the mineralogical characterization methods used for the experiments. Solvent extraction is used to determine the mineral or various chemical species association of REEs, 50 Inductive Coupled Plasma (ICP) is used to measure and identify the various elements, X-ray Diffraction (XRD) is used to identify the crystalline phases and then followed mineral liberation analysis using the Tescan Integrated Mineral Analyzer (TIMA). 4.8.1 Sequential extraction Sequential extraction, developed by Tessier in 1979, was used to analyze trace (Tessier et al.,1979) and was later modified for coal applications (Finkelman, 1994; Finkelman et al., 1990). Dai et al. (2002) successfully employed the sequential extraction procedure for REEs in coal. A parallel extraction method was also employed for other trace elements in coal (Bai et al., 2011; Dai et al., 2004; Zhang et al., 2007; Zheng et al., 2008; Zhou et al., 2016). Based on these studies, a simplified four-step procedure is adopted and used, as shown in Table 4.1. Table 4.1 Sequential extraction procedure used in this study Stage Mode of occurrence Procedure 1 Ion-exchangeable phase 250 mL of 1M ammonium sulphate and 25 g of the material were added to a 500 mL beaker. The slurry mixture was filtered using Whatman-grade 42 filter papers after being magnetically agitated for 24 hours at room temperature. The solid was dried at 65°C after the liquid was discarded. A solid weighing around 3–4 g was removed and preserved for REE analysis. 2 Weak acid soluble form Following the addition of 200 mL of 1M sodium acetate, 20 g of the dried material from Step 1 was pH-adjusted to 5 using acetic acid. The slurry mixture was filtered using grade 42 filter papers after being magnetically agitated for 18 hours at room temperature. The solid waste was dried at 65°C after the liquid 51 was discarded. A sample of the solid residue weighing around 3–4 g was obtained and preserved for REE analysis. 3 REE associated with carbonates (calcites and monosulphides) 15 g of the solids residue from stage 2 was mixed with 200 mL of 3 M hydrochloric acid. The slurry mixture was filtered using Whatman-grade 42 filter papers after being magnetically agitated for 20 hours at room temperature. The solid was dried at 65°C after the liquid was discarded. A sample of the solid residue weighing around 3–4g was obtained and preserved for REE analysis. 4 REE associated with disulphides (pyrites) 10 g of the solids residue from stage 3 was mixed with 200 mL of 2 M nitric acid. Using Whatman-grade 42 filter papers, the slurry mixture was magnetically swirled for 20 hours at room temperature. The liquid was discarded, and 65°C drying was applied to the solid residue. A sample of the solid, weighing around 3–4g, was saved for REE analysis. 5 REE associated with silicates & aluminosilicates REE in the residual solids 4.8.2 Analytical methods 4.8.2.1 Inductively Coupled Plasma (ICP) Feed and test product samples (0.2 g) were introduced to lithium metaborate and lithium tetraborate flux and adequately mixed to measure the TREE. The samples were then fused at 1025°C in a boiler. After cooling, the melts were digested in a solution of nitric, hydrochloric, and hydrofluoric acids. When the solutions had been digested, inductively coupled plasma-mass spectrometry was used to examine them (ICP-MS). The analytical results were corrected for inter-52 elemental spectral interference. This analysis was conducted by ALS Geochemistry in North Vancouver, British Columbia and MS Analytical Laboratory in Langley, British Columbia. In this study, REEs in coal are expressed as follows: whole-coal basis (REEs concentration in the coal sample) and ash basis (REEs concentration in the ash of the coal sample). To ensure the accuracy of the method, the results were compared against a certified reference material and calibration standards. Further, samples are analyzed in duplicates or triplicates, where possible, and average values are used for the data analysis. For replicates, the standard deviation of TREE analysis was less than 5 ppm. 4.8.2.2 Quantitative X-ray Diffraction (XRD) The samples were subjected to quantitative phase analysis using the Rietveld method. X-ray powder diffraction data (QXRD) were gathered on a subset of the samples to determine the principal mineral phases. Each sample was ground into a fine powder with grains within the ideal range for X-ray analysis (<10 m). The diffraction data was collected over a range of 3–80° of 2Ɵ with CoKα radiation on a Bruker D8 Advance Bragg-Brentano diffractometer equipped with a LynxEye-XE detector and operated at 35 kV and 40 mA, using a take-off angle of 6°. The X-ray diffractogram was analyzed using the International Centre for Diffraction Database PDF-4 using Search-Match software by Bruker. The QXRD of the sample was refined with the Rietveld program Topas 4.2 (Bruker AXS). 53 4.8.2.3 Scanning Electron Microscopy (SEM) – Energy Dispersive Spectroscopy (EDS) In order to study the finely dispersed REE-bearing minerals and ascertain their mineral associations and size, a Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) examination of the chosen samples was performed in the Materials Engineering department at the University of British Columbia using a FEI Company Quanta 650 SEM. The system was run at 20 kV with a 10 mm operating distance. 4.8.2.4 Mineralogical liberation analysis For select samples, mineral liberation analysis was also carried out by Process Mineralogical Consulting Limited, based in Vancouver. This automated mineral analysis system can identify minerals in polished sections and be used to quantify grain size, mineral association, and liberation. A single polished block section was prepared from each sample and systematically measured with the Hitachi FLEXSEM, equipped with the AMICS software to collect information on the deportment of REE-bearing minerals, their modal abundance, degree of liberation, and association with gangue minerals. A second measurement with the TIMA system was completed to validate the results, complete elemental mapping for REEs, and generate particle maps. 4.9 Performance Indicator The recovery (R) of REE for the physical extraction process was calculated using the following equation: R = 𝑴𝑪∗𝑪𝑪 𝑴𝑭∗𝑪𝑭 * 100 % Equation 4.1 54 Where MF and MC are the masses of the feed and concentrate (product) (g), respectively. CF and CC are the concentrations of REE in the feed and concentrate (product) (μg/g), respectively. Other than recovery, the Enrichment Factor (EF) was calculated for physical extraction process, which indicates the quality of the concentrate in terms of REE concentration. EF was calculated as follows: EF = 𝑪𝑪 𝑪𝑭 * 100 % Equation 4.2 CF and CC are the same as defined above for Equation 4.1. 55 Chapter 5: Results and Discussion This chapter discusses the results and the outcomes of the experiments conducted on the selected samples; F1, R1, P1, and CT. The first section presents the preliminary results from the HHS process carried on F1, R1, and P1, followed by the test work on CT investigating the effect of particle size and reagent type (collectors), and the effect of reagent dosage and pH. The schematic representation of the test work related to the effects of the collectors’ dosage. Figure 5.1 Schematic for collector dosage test work 56 5.1 Preliminary HHS To enhance the liberation of REMs, the samples were subjected to grinding prior to conducting the HHS test. This should have liberated some of the REMs and carbonaceous material. The R1, P1, and F1 samples had an REE concentration of 273.94 ppm, 224.24 ppm, and 226.46 ppm on ash basis, respectively. The ash contents of the feedstock were also 92.30 %, 86.45 %, and 88.45 % for R1, P1, and F1, respectively. Even though the feedstock samples had a high ash content, removing additional coal from the ground sample prior to HHS recovery of REMs minerals was studied in this preliminary assessment. This was done on the R1 sample only and is denoted by R1* in the results. Decarbonization by agglomeration using pentane oil to capture the carbonaceous material was used in this case. After decarbonization, the concentrate was sieved to separate a clean coal concentrate from tailings containing mineral matter. Fifty millilitres of pentane were utilized in the decarbonization process, and a 75 µm sieve was used for the agglomerate recovery step. The HHS test was then conducted on the tailings resulting from the decarbonization process. Figure 5.2 Preliminary HHS test work on roof, floor, and parting (R1, F1 and P1) sample 57 The conditions of HHS were 1.0 kg/t of hydroxamate, 2 kg/t of sodium silicate as the dispersing agent, and 100 mL of heptane as the hydrophilizing liquid. The results from the decarbonization of the R1 sample, now referred to as R1*, show a lower recovery of 38 %, compared to 43 %, 40 %, and 45 % for R1, P1, and F1, respectively (see Figure 5.2). However, the REEs concentrate grade was higher for R1* (236 ppm on ash basis as compared to the other samples: F1 [215 ppm], P1 [218 ppm], and R1 [227 ppm]). Due to insufficient sample mass for the roof, floor, and partings, tailings samples were used for further exploratory test work. The assumption was that roof, floor, and parting samples would end up as tailings after processing. Thus, the CT sample was used for further study. The initial ash of CT was 40 % and REEs grade of 126 ppm on ash basis. 5.2 Effect of pH on HHS Process The CT sample was ground to a d80 of 25 µm and then underwent flotation to remove as much carbonaceous material from the feed sample as possible. The flotation was conducted at 240 g/t of kerosene and 200 g/t of MIBC, according to a previous study on similar samples (Kuppusamy, 2022). The resulting tails from the flotation were then dried and used as feed material to investigate the effect of pH, grinding, and dosage on the HHS process. The results of the CT sample after flotation are shown in Table 5.1. The rest of the experiments used the CT as feedstock. Table 5.1 Proximate analysis of CT samples after flotation. Sample ID Mass (g)Moisture (%)Volatile Matter (%)Ash (%)CT feed 500 1.43 18.31 40.32CT Conc (Clean coal) 297.7 1.67 26.86 18.33CT Tailings 202.3 1.28 17.34 72.4458 Approximately 50 g of the CT sample was taken for the HHS test work. The HHS process was carried out at 15 % solids content with 1.0 kg/t of hydroxamate and 2.0 kg/t of sodium silicate as a dispersing agent. Also, 250 mL of heptane was used as the hydrophobic liquid. The process is described in detail in Section 4.7. Every other condition was kept constant except for the pH. The HHS was conducted at pH 7.5 and 9.5; the results are shown in Figure 5.3. Figure 5.3 Effect of pH on HHS of the CT sample It was observed that at a pH of 9.5, a recovery of 8.2 % was achieved, as opposed to the 6.32 % recorded for pH 7.5. The REE grade on ash basis was also slightly higher for pH 9.5 (260.9 ppm) compared to 251 ppm at a pH of 7.5. Theoretically, it is expected that increasing the pH of the 59 slurry would help modify the surface of most of the REMs and increase their recovery and the grade of REEs. There was just about a 1.9 % increment in recovery. 5.3 Effect of Collectors and Dosage Rate for HHS Process Two different collectors were used for HHS on CT samples to see how each affected the concentration of REEs and their recovery. Aside from varying the collectors, their dosages varied from 1.0 kg/t to 2.0 kg/t. Figures 5.4 a and b show the correlation between the grade (REE concentration) and recovery for both collectors at increasing dosages. 60 Figure 5.4 Effect of different collectors on CT sample a) hydroxamate b) sodium oleate 61 Figure 5.5 a) Enrichment factor for both reagents b) concentrate ash for both reagents As the collector dosage for both sodium oleate and hydroxamate increased from 1.0 kg/t to 2.0 kg/t, the REEs recoveries also increased from 2.86 % to 7.18 % for sodium oleate and 4.32 % to 4.77 % for hydroxamate (see Figure 5.4 a and b). The highest REEs grade calculated on ash basis was 271 ppm for sodium oleate and 365 ppm for hydroxamate, both at 1.0 kg/t. Previous research revealed that the clay minerals that are finely scattered in the coal organic matrix might occasionally be linked to REMs and REEs. (Zhang et al., 2018; Zhang, 2017). This leads to the recovery of more clay particles that effectively dilutes the REE concentrate grade as the dosage increases. This theory is supported by the link between dose and concentrate ash content seen in Figure 5.5b. The enrichment factor that indicates the quality of the REE concentrate decreases for both reagents as the dosage rate increases supports the theory of dilution effect, as discussed above (see Figure 5.5a). However, the decline of the enrichment factor (Section 4.9) is less drastic for 62 the sodium oleate, even though the ash contents in the concentrates for both collectors are the same. 5.4 Effect of Size Reduction (Grinding) The findings of HHS testing on CT samples at two different grind sizes—d80 of 8.5 µm and d80 of 25 µm—are displayed in Figure 5.6. Figure 5.7 shows the experimental approach. It is important to note that the sample was decarbonized using flotation to remove the majority of the coal. As shown in Figure 5.6, as the particle size was decreased from d80 of 25 µm to 8.5 µm, the grade and recovery marginally improved. The HHS procedure yielded a concentrate with REEs of 248.3 ppm on an ash basis at a recovery of 5.21 % at a d80 of 25 µm. When the CT sample was ground further to d80 = 8.5µm, the HHS produced a concentrate assay of 342.5 ppm reported on ash basis at an 11.42 % recovery. The grade and recovery were both boosted by 0.9 and 2.1 times, respectively, by the improved REMs liberation. To compare results, the collector dosage was not varied and was kept at 1.0 kg/t. However, as the particle size decreases, a higher dosage of collector would be required to make the particles hydrophobic due to the increased surface area of the particles. Thus, an improved separation would theoretically be expected as the collector dosage increases. However, further fine grinding would be much more energy intensive; hence, it would be more costly. 63 Figure 5.6 Effect of particle size on CT sample at collector dosage of 1 kg/t Figure 5.7 Schematic for grind size variation test 64 5.5 Characterization Results 5.5.1 Sequential extraction REEs are expected to be associated with inorganic minerals. As such, the four samples, R1, P1, F1, and CT, were subjected to sequential chemical extraction, as described in Chapter 4 (Section 4.81), to establish REEs mineral species association. The step-by-step sequential extraction allows us to determine the REEs association with various species, possibly indicating an association with various minerals. These can be categorized into five groups: (Stage 1) ion-exchangeable REEs could be implying an association with clay minerals or organic matter; (Stage 2) weak acid soluble form; (Stage 3) REEs bound to carbonates and mono-sulfides; (Stage 4) REEs associated with disulfides; and (Stage 5) REEs association with silicates and aluminosilicates. The results are shown below in Figure 5.8. Figure 5.8 Sequential extraction results (R1, F1, P1, CT) showing the distribution of REEs in various modes of occurrences 65 It can be observed from Figure 5.8 that more than 65 % by weight of REEs are associated with silicates and aluminosilicate minerals for all the samples (Stage 5). REEs associated with acid-soluble forms (Stage 2 and Stage 3) account for about 30 %, 13 %, 17 %, and 21 %, respectively for samples R1, F1, P1, and CT. Ion-exchangeable modes can be extracted using monovalent salt solutions such as ammonium sulfate, as suggested by Moldoveanu and Papangelakis (2012 and 2013). The results from stage 1 extraction indicated that ion-exchange forms were 3.5 %, 2 %, 3 %, and 4 % for R1, F1, P1, and CT, respectively. This represents the loosely bound REEs with ions that may be organically combined with a coal matrix or ions absorbed on clay. 5.5.2 XRD and SEM results Mineralogical analysis using XRD, and SEM-EDS analysis was conducted to identify the major mineral phase and REMs in the selected three samples (P1, F1, and R1). Quantitative phase analysis of the samples was done using the Rietveld method, and QXRD was collected on selected samples (P1, F1, and R1) to identify major mineral phases. For this purpose, all the samples were ground into a fine powder to obtain an optimal grain size suitable for the range for XRD analysis (< 10 μm). The phase identification results for P1, F1, and R1 are shown in Figure 5.7. It can be demonstrated that clay minerals like kaolinite and illite, which made up around 33 % to 35 % of the identified crystalline phases in the sample, were the most common minerals found in all three samples. Approximately 47 % to 58 % of the crystalline phase was provided by quartz. Moreover, trace levels of other minerals such as pyrite, anatase, rutile, carbonates, and anatase were detected. The concentration of REMs is below the XRD analysis detection limit; hence, the XRD analysis was 66 unable to identify them. SEM-EDS characterization was also conducted on all three samples (P1, F1, and R1). 67 Figure 5.9 Quantitative XRD analysis for select samples a) R1 b) P1 c) F1 68 Elements observed in the highlighted grains are as follows: Top Left (R1): Yt, Y, Ca, Si, O; Top Right (F1): Ba, Fe, Cl, Al, Si, O Bottom Left (P1): La, Ce, Y, Sc, Al, Si, Na, P, O Figure 5.10 SEM-EDX mapping of xenotime (YPO4) mineral identified in sample F1 69 An SEM-EDS analysis of the selected samples was carried out to examine the spread of REMs and to determine the mineral associations and size. An automated liberation analysis was conducted for sample F1. Two size fractions (-106 +75 μm and -53 +25 μm) of the F1 sample were analyzed, and the results are depicted in Figure 5.9 and Figure 5.10. The two fractions of sample F1 consist predominantly of quartz (52.9–56.5 wt.%) and muscovite/illite (39.3–45.6 wt.%) with minor amounts (<5 wt.%) of kaolinite (0.81–1.73 wt.%) and carbonates (0.2–1.1 wt.%), and trace amounts of (<0.05 wt.%) REE-bearing phases (monazite and xenotime), without a significant difference between the two fractions. Five monazite grains ranging in size from 5 µm to 25 µm were detected, as well as one occurrence of the Y-phosphate xenotime. Most monazite was observed in the +75-fraction associated with quartz and muscovite/illite. The most abundant accessory phase is zircon, with 73 observed grains. Zircon, which occurs as Zr (SiO4), may also contain minor traces of uranium, thorium, lead, yttrium-REE, phosphorous and other REEs. 70 Figure 5.11 Grain size distribution of different REE-bearing minerals in F1 Table 5.2 Observed mineral abundance for sample F1 The mineral liberation analysis (Table 5.3) indicates the presence of three grains of monazite, one grain of xenotime, and 34 grains of zircon below ten microns. There was just one grain of monazite mineral in the ≥15 ≤20 microns. Most of these three REE-bearing minerals were locked in illite/muscovite and kaolinite. The sequential analysis results show that about 33–35% of the REEs Mineral Monazite Xenotime Zircon≥2.00<5.00 µm 0 0 0≥5.00<10.00 µm 3 1 34≥10.00<15.00 µm 1 0 16≥15.00<20.00 µm 0 0 7≥20.00<25.00 µm 1 0 3≥25.00 µm 0 0 13Total 5 1 73Grains Observed - F1 Sample71 are associated with aluminosilicate mineral species that could be clays. From the SEM images (Figure 5.11), it could be inferred that the REE-bearing minerals were less than five microns, and, as such, the REMs were not liberated enough since the d80 was 25 microns. It can be concluded that the HHS process did not work because the REE-bearing minerals were tiny and locked up in clays. This suggests that the reagent/collector had difficulty reaching the surface of the REM, making it hydrophobic, making it difficult to concentrate by HHS procedure. Figure 5.12 Mineral liberation and association results of sample F1 5.6 Particle Size and REE Distribution Compared with Mineralogy Three sample types (R1, F1, and P1) were sieved to obtain different-size fractions. Each of these size fractions was weighed to obtain the weight distribution of the sample in each of these size fractions, and the representative sample was sent for REE analysis. The TREE (15 lanthanides plus scandium and yttrium, except promethium distribution in each size fraction are shown in Figure 5.13, along with the sample weight distribution for each size fraction. 72 It can be noted that the weight percentage of the TREE in each size fraction and sample weight distribution was similar for the size fractions (+300 µm, +212µm, +53µm, +25µm, and -25 µm), indicating that REEs are evenly distributed between these size fractions. About 25 % of REE was found in the +106 µm size fraction for all three samples, while the -25 µm accounted for about 30 % of REE for all three samples analyzed. Both size fractions account for over 50 % of the REE content in all three samples tested. Since 30 % of REEs are found in the finest fraction (<45µ), this may indicate that REE-bearing minerals are very fine (clays, monazite grains found in SEM), while 25 % of REE-bearing minerals are locked in the coarser fraction (+106 µ). The relatively even distribution of REEs in the remaining size fractions indicates association with different minerals when it above 10%. The particle size distribution supports mineral liberation analysis indicating that a significant portion (30–35%) of the REE-bearing minerals are in the -45 µ as in sample F1 (Figure 5.12); therefore, they are fine, with possibly more in the -25 µ fraction, while another >60 % are locked in the coarser fractions. These may not be well liberated for successful concentration. 73 Figure 5.13 TREE distribution by wt (%) in different size fraction for P1, R1, and F1 From the automated mineralogy (liberation analysis) results, it appears that zircon mineral grains are found both in the coarse fraction and fines (see Table 5.2), but in the coarse fraction, they appeared as very fine grains. They could accumulate in the coarser size fractions when they are coarse or associated with coarse particles. Also, in Figure 5.10, the SEM image with the example of the xenotime grain (REE-bearing mineral), one can notice that the mineral that hosts xenotime is much larger. This could be another example of a smaller REE-bearing mineral being associated with a much larger mineral, forming a fairly large particle together. On the other hand, illite/muscovite minerals appear to be found in the coarser sizes +63 µ (Figure 5.10), while some of the larger quartz particles in the same size interval are shown to carry zircon grains. It is very likely that in the studied samples, most of the REE-bearing minerals like xenotime and monazite were locked in larger clay or quartz particles, while zircon was mostly accumulating in very fine fractions as liberated particles with only some portion of larger +25 µm (13 out of 73) 74 particles; however, these are still considered very fine particles when it comes to physical separation such as HHS. Also, looking at the mineral composition of the F1 sample (automated liberation analysis results), the major mineral phases present in this sample were clays and quartz. Since these minerals only carried few xenotime and monazite mineral grains locked in their particles, it is not surprising that HHS separation was not successful. Specifically, the collector that was used in the HHS separation was targeting monazite and xenotime minerals, while both minerals were physically inaccessible for the reagents due to their inclusion in larger clays and quartz particles. Simply, there were too few minerals to make the separation beneficial. The sequential extraction tests for the F1 sample also indicated that ~80 % of REEs (Figure 5.8) were extracted from silicate and aluminosilicate minerals by the sequential extraction test; thus, this supports this conclusion. Modal mineralogy derived from XRD analysis also confirms that quartz and illite/muscovite in the F1 sample accounted for close to 80 %. 75 Chapter 6: Conclusion and Recommendation This study was carried out to assess the feasibility of using the HHS process for the pre-concentration of REMs from coal and coal byproducts. From a previously developed database (Kuppusamy and Holuszko, 2021), three samples (one roof, one floor, and partings from the active seam) were selected for the study. These samples were collected directly from the coal seam. The samples were characterized based on their outlook coefficient and found to be a potential source of REEs. Samples R1, P1, and F1, roof, floor, and seam samples, would be processed through the plant and end up as tailings. Subsequently, the coal tailings sample (CT) was subjected to various testing regimes to determine the amenability of a pre-concentration of REMs by the HHS process. The test work involved investigating the effect of the reagent dosage, reagent type, pH, and mineral particle size. . The significant findings of the research are listed below: • The decarbonization (removal of carbonaceous-coal organic material) yielded a lower recovery but resulted in a much higher grade if performed prior to the HHS process. • The variation of pH from 7.5 to 9.5 for the HHS process improved the efficiency of the process by about 1.9 %. At a pH of 7.5, a recovery of 6.32 % and REE grade of the concentrate of 251 ppm on ash basis was achieved, while at a pH of 9.5, a recovery of 8.2 % and 260.9 ppm on ash basis was achieved. • Particle size improves the efficiency of the HHS process. However, there was a slight improvement in the recovery of REE-bearing minerals as the grind size was reduced to 8.5 microns. At a d80 of 25 µm, the HHS process produced a concentrate that assayed 248.3 ppm at a recovery of 5.21 %. When the CT sample was ground further to d80 of 8.5µm and maintained the same collector dosage of 1.0 kg/t, the HHS produced a concentrate 76 assay of 342.5 ppm on ash basis at an 11.42 % recovery. The improved liberation of REMs increased the grade by 0.9 times and the recovery by 2.1 times. • Collector type and dosage affect the recovery and concentration of REEs in the product stream. As the collector dosage for both sodium oleate and hydroxamate increased from 1.0 kg/t to 2.0 kg/t, the REE recoveries also increased: from 2.86 % to 7.18 % for sodium oleate and from 4.32 % to 4.77 % for hydroxamate. The highest REE grade achieved was 271 ppm for sodium oleate and 365 ppm for hydroxamate at 1.0 kg/t collector dosage. • Mineralogical analysis of the selected samples has shown that monazite and xenotime were identified as the main REE-bearing minerals initially identified in SEM and later confirmed by the automated liberation analysis. REMs were generally locked either in the clay matrix or quartz, while only a few grains were counted in the F1 sample. SEM showed that the REE-bearing minerals were smaller than ten microns and, as such, not well liberated for physical concentration. It was found that clays such as kaolinite and illite made up the majority of the three samples (F1, R1, and P1), accounting for between 33 % and 35 % of the sample’s detectable crystalline phases. Quartz made up between 47 % and 58 % of the crystalline phase. There were also sporadic reports of other minerals such as pyrite, anatase, rutile, carbonates, and others. Two size fractions (-106+75 μm and -53+25 μm) of the F1 sample were analyzed using SEM-EDS and TIMA mineral liberation system. The two fractions of sample F1 were shown to consist of predominantly quartz (52.9–56.5 wt.%) and muscovite/illite (39.3–45.6 wt.%), with minor amounts (<5 wt.%) of kaolinite (0.81–1.73 wt.%), carbonates (0.2–1.1 wt.%), and trace amounts of (<0.05 wt.%) REE-bearing mineral phases (monazite and xenotime), without a significant difference between the two fractions. Five monazite grains ranging in size from 5 µm to 25 µm were detected, as well 77 as one occurrence of the Y-phosphate xenotime. Most monazite was observed in the +75-fraction associated with quartz and muscovite/illite. The most abundant accessory phase is zircon, with 73 observed grains. Zircon, which occurs as Zr (SiO4), could also contain minor traces of uranium, thorium, lead, yttrium, phosphorous and other REEs, possibly contributing to the higher REE grade. Overall, the HHS process could not concentrate to an appreciable degree (anywhere close to 2 % of TREE) to be the successful process of treating studied samples. The mineral liberation analysis revealed that zircon mineral grains are found both in the coarse fraction (see Table 5.2) and as very fine grains. The particle size distribution supports the mineral liberation analysis that a significant portion (30–35 %) of the REE-bearing minerals are either in the -45 µ, as in sample F1 (Figure 5.12) or -25µ fraction, while another >60 % are locked in the coarser fractions; and these may not be well liberated for successful concentration. Most REE-bearing minerals were locked in clays of illite/muscovite and quartz mineral phases. Illite/muscovite minerals appear to be found in the coarser sizes +63 µ (Figure 5.10), while some of the larger quartz particles in the same size interval are shown to carry zircon grains. It is possible that in the studied samples, most of the REE-bearing minerals like xenotime and monazite were locked in larger clay or quartz particles, while zircon was mostly accumulating in very fine fractions as liberated particles with only some portion of larger +25 µm (13 out of 73) particles; however, these are still considered very fine particles when it comes to physical separation such as HHS. The sequential analysis results show that about 33–35 % of the REE associated with clays supports this reasoning. From the SEM diagrams (Figure 5.8), it could be 78 inferred that the REE-bearing minerals were less than five microns, and, as such, the REEs were not liberated enough since the d80 was 25 microns. The mineral composition of the F1 sample’s (TIMA analysis) major mineral phases present in this sample were clays and quartz; since these minerals only carried few xenotime and monazite mineral grains locked in their structure, and the collector that was used in the HHS separation was specifically targeting monazite and xenotime minerals, both minerals were physical inaccessible for the reagents. This was due to their association with larger clays or quartz particles. Simply, there were too few minerals to make the separation beneficial. In conclusion, since most of the REMs were generally locked in the clay matrix or quartz grains, desliming the feedstock and then subjecting the clay minerals to fine grinding (less than five microns) to liberate the REMs prior to carrying out the HHS process would be something to consider. 6.1 Recommendations Based on the current study, advancements in the following areas will enhance the study of fully understanding the benefits of the HHS process. • In this study, most of the REMs were generally locked in the clay matrix, and, as such, desliming the feedstock and then subjecting the clay minerals to further grinding to liberate the REMs prior to HHS would significantly improve the liberation of the REE-bearing minerals. 79 • A further increase in pH for the HHS process and adding various cleaning stages (like having multiple flotation cleaner banks) of the product could possibly help improve the grade of the REEs. • In this study, REM characterization and association were carried out using XRD and SEM-EDS mapping. 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Here, it is described in brief: Weight loss resulting from oven-drying a 1 g sample at 104 °C to 110 °C for an hour was used to calculate the sample’s moisture content (ASTM, 2017b). The moisture content was calculated as follows: Moisture content (%): (𝑊𝑖−𝑊𝑓/𝑊𝑖)*100 Where Wi represents the initial weight of the sample used (g), and Wf denotes the weight of the sample after drying (g). The dried sample from the moisture analysis was heated in a vented boiler over the course of an hour to attain a temperature of 500 oC to measure the amount of ash present. The furnace’s temperature was also raised, reaching 750 +/- 15 °C after two hours. Until the bulk of the residue achieved a consistent weight, the sample was kept at 750 +/- 15 °C for an additional two hours. The residue mass was divided by the initial dry sample mass to determine the ash content. (ASTM, 2012b). The ash content of the sample was computed as follows: Ash content (%): (𝑊𝑐−𝑊𝑒/𝑊𝑠) *100 Where Wc represents the weight of the capsule, cover, and ash (g), We denotes the weight of the empty capsule and cover (g), and Ws is the weight of the sample used for analysis. Mass loss after heating 1 g of the sample at 950 o C for seven minutes in a dry crucible was used to calculate the sample’s volatile matter content. The volatile matter was obtained by adjusting the 95 predicted mass loss for the moisture content (ASTM, 2017c). The volatile matter of the sample was determined as follows: Mass loss (%): (𝑊𝑖−𝑊𝑓)/(𝑊𝑖− 𝑊𝑒)*100 Where We denotes the weight of the empty capsule and cover (g), Wi represents the weight of the capsule, cover, and sample before heating (g), and Wf is the weight of the capsule, cover, and sample after heating (g). Volatile matter (%): Mass loss (%) – Moisture content (%) The percentages of moisture, ash, and volatile matter were subtracted from 100 to determine the fixed carbon (ASTM, 2013). The relation used for computing fixed carbon is shown below: Fixed carbon (%): 100 – [Moisture (%) + Ash (%) + Volatile Matter (%)] 96 Appendix B - General Flotation Procedure For the flotation test, a representative feed sample was crushed to obtain a size of -500 μm, and a standard Denver laboratory cell was used to conduct a batch test. The cell was filled to 3/4 height with water, and the impeller speed was adjusted to 1300 r/min. The feed sample was placed in the cell and conditioned for five minutes to wet the sample completely. Using a high-speed laboratory blender, the reagent emulsion was prepared separately by pouring 200 mL of water into the blender. The appropriate amount of collector (kerosene) and half of the necessary volume of the frother (methyl isobutyl carbinol, or MIBC) were also added to the blender, which was then run at high speed for 30 seconds. The produced emulsion was swiftly introduced into the cell and was allowed to condition there for 15 minutes. After 15 minutes of conditioning, the second half of the frother volume was added, and the cell was conditioned for an additional minute. The concentrate was collected until the froth was barren at a rate of 4.5 L/min air aeration. The concentrate and filtered tailings were dried at 65 °C after being pressure filtered. Following drying, representative samples were divided from the concentrate, and rejects were gathered from several flotation batches for examination. 97 Appendix C List of Some REMs and Their Composition Table A.6.1 Some of the REMs found in the traditional RE deposits (Long et al., 2010; Verplanck et al., 2014) 98
Thesis/Dissertation
eng
Mining Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Holuszko, M. E.
Preliminary assessment of hydrophobic-hydrophilic separation for pre-concentration of ree from coal tailings and alike material
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