Applied Science, Faculty of
Mining Engineering, Keevil Institute of
DSpace
UBCV
Zafar, Geety
Master of Applied Science - MASc
University of British Columbia
Microplastic pollution is a serious environmental concern, which requires innovative solutions. This study investigates the incorporation of high-density polyethylene (HDPE) and polycarbonate (PC) microplastics into the products of coal processing, specifically clean coal concentrates from flotation, to evaluate their effect on coal coking properties. After flotation, microplastics were blended with the flotation concentrates at varying concentrations and tested for caking properties by Free Swelling Index (FSI) and fluidity by Gieseler Fluidity (GF). The results show that while FSI remained largely unaffected, fluidity was significantly reduced, indicating that coal concentrates mixed with plastic will not be suitable for metallurgical coke production. However, blending the microplastics with coal middlings reduced ash content while maintaining high calorific value. This suggests a promising alternative for use in thermal coal applications such as power generation, gasification, or even hydrogen production.
Mitigation of Microplastic Pollution by Blending with Products of Metallurgical Coal Processing by Geety Zafar BA, Balkh University, Mazar-i-Sharif, Afghanistan, 2018 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) June 2025 © Geety Zafar, 2025 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, the thesis entitled: Mitigation of Microplastic Pollution by Blending with Products of Metallurgical Coal Processing submitted by Geety Zafar in partial fulfilment of the requirements for the degree of Master of Applied Science in Mining Engineering Examining Committee: Dr. Maria Holuszko, Mining Engineering, UBC Supervisor Dr. Scott Dunbar, Mining Engineering, UBC Supervisory Committee Member Dr. Marek Pawlik, Mining Engineering, UBC Supervisory Committee Member iii Abstract Microplastic pollution is a serious environmental concern, which requires innovative solutions. This study investigates the incorporation of high-density polyethylene (HDPE) and polycarbonate (PC) microplastics into the products of coal processing, specifically clean coal concentrates from flotation, to evaluate their effect on coal coking properties. After flotation, microplastics were blended with the flotation concentrates at varying concentrations and tested for caking properties by Free Swelling Index (FSI) and fluidity by Gieseler Fluidity (GF). The results show that while FSI remained largely unaffected, fluidity was significantly reduced, indicating that coal concentrates mixed with plastic will not be suitable for metallurgical coke production. However, blending the microplastics with coal middlings reduced ash content while maintaining high calorific value. This suggests a promising alternative for use in thermal coal applications such as power generation, gasification, or even hydrogen production. . iv Lay Summary Microplastics are small plastic particles that harm ecosystems and health, prompting researchers to explore new ways to manage them. This study investigates a novel approach of blending microplastics with metallurgical coal products to assess their potential for either improving metallurgical coal quality or for using such blends for energy generation and/or possibly for other industrial applications. The results show that while microplastics reduced the fluidity of coal, making it unsuitable for producing high-quality coke required in steelmaking, their addition to middlings, generated as intermittent product between clean coal and tailings (reject) from flotation could improve its potential as a cleaner fuel for energy generation. Specifically, samples with microplastics maintained sufficient calorific value while lowering ash content, which are indicating their suitability for thermal coal applications. This research explores mixing microplastics with coal waste to reduce pollution, create useful coal products, and cut down on coal mine waste disposal. v Preface This thesis is the original work of the author, Geety Zafar, completed under the supervision of Professor Dr. Maria Holuszko and Professor Dr. Scott Dunbar. No Generative Artificial Intelligence tools were used in the research and development of this thesis. The development of the research questions and the methodology design were done in collaboration between me and my supervisor, Professor Dr. Maria Holuszko. Based on these questions, I was responsible for identifying and designing the research, conducting the literature review, and performing the experimental work, including coal and microplastic grinding, flotation tests, sample preparation, and ash analysis of coal. I also analyzed the research data with guidance from my supervisors. The Gieseler fluidity and Free Swelling Index (FSI) tests were conducted at GWIL-Birtley Coal Testing in Calgary, which I attended in person. These tests were carried out under the supervision of Heather Dexter, Operations Manager, and I observed the experimental procedures and equipment. The data analysis presented in Figures 14, 15, 16, 17, and 19 in Chapter 3 was visualized with the help of Professor Dr. Scott Dunbar. The visual for Figure 19 was created with support from both Professor Dr. Scott Dunbar and my supervisor, Professor Dr. Maria Holuszko. Dr. Dunbar also assisted in reviewing the formatting and structure of the thesis. vi Table of Contents Abstract .......................................................................................................................................... iii Lay Summary ................................................................................................................................. iv Preface............................................................................................................................................. v Table of Contents ........................................................................................................................... vi List of Tables ............................................................................................................................... viii List of Figures ................................................................................................................................ ix Acknowledgements ......................................................................................................................... x Dedication ...................................................................................................................................... xi 1 Introduction .................................................................................................................................. 1 1.1 Metallurgical Coal Production in Canada and British Columbia .................................... 2 1.2 Coal and Microplastic Interactions in Industrial Processes............................................. 3 1.3 Coal as a Potential Medium for Microplastic Utilization................................................ 5 2 Literature Review......................................................................................................................... 6 2.1 Microplastic Pollution and its Environmental Impact ..................................................... 6 2.2 Co-Carbonization as a Potential Solution for Microplastic Waste Mitigation ................ 8 2.3 Thermal Behavior of Microplastic in Industrial Carbonization Processes ................... 11 2.4 Environmental and Industrial Benefits of Co-Carbonization ........................................ 12 2.5 Compatibility of Thermal Properties of Plastic and Coal ............................................. 13 2.6 Plastic Recycling Process at Nippon Steel .................................................................... 14 2.7 Summary of Literature Review ..................................................................................... 17 2.8 Knowledge Gaps and Research Objectives ................................................................... 18 3 Methodology and Experimental Results .................................................................................... 21 3.1 Coal Sample Sourcing and Sample Preparation ............................................................ 21 3.1.1 Sample Sourcing ......................................................................................................... 22 3.1.2 Crushing and Grinding .............................................................................................. 22 3.1.3 Plastic Selection and cryogenic grinding ................................................................... 22 3.2 Flotation and Ash Analysis ........................................................................................... 23 3.3 Free Swelling Index ...................................................................................................... 24 3.4 Gieseler Fluidity Test .................................................................................................... 26 3.5 Feasibility of Clean Fuel Production ............................................................................. 30 3.6 Key Findings ................................................................................................................. 31 4 Addition of Microplastics at Processing Plant ........................................................................... 32 4.1 Scope and Objective ...................................................................................................... 32 4.2 Proposed Integration Pathway: Mine-Site Blending ..................................................... 33 4.2.1 Technical Feasibility .................................................................................................. 34 4.2.2 Environmental and Logistical Benefits ...................................................................... 35 4.3 Combustion, Gasification, and Hydrogen Production from Microplastics and Coal Blend ................................................................................................................................... 35 4.4 Risks, Challenges and Benefits ..................................................................................... 37 5 Conclusion and Recommendations ............................................................................................ 38 5.1 Impact of Adding Microplastics to Metallurgical Coal Products ................................. 39 5.2 Integration at Mine Sites ............................................................................................... 39 5.3 Limitations .................................................................................................................... 40 References ..................................................................................................................................... 42 Appendix A Plastometer results.................................................................................................... 48 vii Appendix B Ash and moisture content of flotation stages ........................................................... 53 Appendix C Results for clean coal product .................................................................................. 54 Appendix D Calorific Value and Density of HDPE and PC ........................................................ 55 Appendix E Particle Size Distributions of Coal Feed and HDPE ................................................ 57 viii List of Tables Table 1: Ash Content of Flotation Products ................................................................................. 24 Table 2: FSI Results ...................................................................................................................... 25 Table 3: Ash Content, FSI, for Feed and Concentrate with Microplastics ................................... 26 Table 4: Ash Content, and Calorific Value ................................................................................... 31 ix List of Figures Figure 1: Chemical characteristics of microplastics. ...................................................................... 1 Figure 2: Metallurgical coal processing flowsheet with the points of interest for this study. ....... 3 Figure 3: Properties of synthetic polymers. ................................................................................... 4 Figure 4: How Microplastics Affect the Environment and Human Health .................................... 6 Figure 5: Sources of microplastics .................................................................................................. 7 Figure 6: Effects of Microplastics on Human Health ..................................................................... 8 Figure 7: Recycling waste plastics at Nippon Steel ...................................................................... 15 Figure 8: How waste plastics and coal are processed in coke ovens. ........................................... 17 Figure 9: Freezer/Mill Cryogenic Grinder used to grind microplastics ........................................ 23 Figure 10: Flotation flowsheet showing 2 stages of flotation; S1 rougher and S2 cleaner stage to obtain <10% ash product. Feed-F, TP – 1st stage tailings; CP- 1st concentrate C-final concentrate, T- final tailings .............................................................................................................................. 23 Figure 11: Flotation products: Left-Concentrate, Right-Tailings samples ................................... 24 Figure 12: Equipment used for FSI tests at GWIL laboratory (Calgary) ..................................... 25 Figure 13: The Gieseler Fluidity equipment at GWIL laboratory (Calgary) ................................ 27 Figure 14: Gieseler fluidity test results for C (top) and C + 1%HDPE (bottom) ......................... 28 Figure 15: Gieseler fluidity test results for CCP (top) and CCP + 1%HDPE (bottom) ............... 29 Figure 16: Gieseler fluidity test results for CCP + 1% PC ........................................................... 30 Figure 17: Effects of HDPE microplastic addition on ash content and calorific value of middlings....................................................................................................................................................... 31 Figure 18: Effects of increased microplastics addition (up to 60%) on ash and calorific value. .. 32 Figure 19: Suggested configuration of system to manufacture blend of coal and microplastic ... 33 x Acknowledgements I would like to express my deepest gratitude to Dr. Maria Holuszko for accepting me as her student, guiding my research, and supporting my scholarship at UBC. Her expertise, patience, and encouragement have been invaluable throughout this journey. I am also sincerely thankful to Dr. Scott Dunbar for his kindness, insightful guidance, and unwavering support whenever I needed direction. His mentorship has played a crucial role in shaping this research. A special thanks to Libin Tong for his invaluable assistance in the lab, particularly with flotation experiments, and to Frank Yan for his guidance in operating lab equipment. I am also grateful to Aaron Hope and Christopher McElligott for providing microplastic samples, which were essential to this study. Finally, I extend my heartfelt appreciation to Heather Dexter, Operations Manager GWIL-Birtley Coal Testing and her team for their kind contribution in this research to make it happen which I am truly thankful for. I am fortunate to have my family, friends, and colleagues who supported and encouraged me throughout this challenging yet rewarding journey. Their belief in me has been my greatest source of motivation. xi Dedication I dedicate this thesis to my mother whose unwavering love and sacrifices made my education possible. Her strength and resilience continue to inspire me every day. I also dedicate this work to my professors, Dr. Maria Holuszko and Dr. Scott Dunbar, for their invaluable guidance, encouragement, and belief in my potential. Their mentorship has been instrumental in shaping my academic journey. 1 1 Introduction Microplastic pollution is a growing environmental concern, affecting both aquatic and terrestrial ecosystems. These tiny plastic particles, typically less than five millimeters in size, originate from industrial waste, degraded consumer plastics, and synthetic fibers. As Figure 1 shows due to their persistence and resistance to natural degradation, microplastics accumulate in water bodies, soils, and even the food chain, posing risks to both environmental and human health. Traditional microplastic waste management methods struggle to effectively address microplastic contamination, necessitating alternative strategies for mitigation. Source: (Raza et al., 2022) Figure 1: Chemical characteristics of microplastics. One emerging approach is the integration of microplastics into the industrial processes, particularly attractive approach could be to integrate microplastic into metallurgical coal carbonization, called co-carbonization. This study explores blending of microplastic with metallurgical coal processing products from British Columbia to assess their suitability for the co-carbonization. The goal is to determine whether microplastics can be safely incorporated without compromising the ability of coal to form high-quality coke, a material essential for steel production or if this blend can be utilized for other alternative uses. 2 1.1 Metallurgical Coal Production in Canada and British Columbia In 2024, Canada’s coal production was 42.5 mln metric tonnes, while coal production can be split almost 50/50 between thermal for energy-electricity generation and metallurgical for coke making used in steel production. About 90% of Canada’s coal is produced in just two provinces: Alberta and British Columbia, while over 90% of the exported coal is of metallurgical coal quality and most of the coal is exported to Asian countries and Europe. The main countries that buy Canadian metallurgical coal are Japan, China, South Korea, and India (Natural Resources Canada, 2025). In 2020, Canada exported about 64% of the coal and since then, coal exports have increased to 80.7%, meaning that more and more coal produced in Canada has been exported abroad (Statistics Canada, 2025). The British Columbia coal production accounted for 64% of total Canada’s coal production in 2023 according to Statistics Canada, (2024). The coal production significantly contributes to the local economies of the coal producing provinces while the metallurgical coal is an important raw material for transition to the clean and renewable energy. This is because metallurgical coal is used for steel production which is an essential component of many technologies that are part of this green transition. It is common practice in Canada that coal extracted in open pit mining operations is cleaned at the preparation plants. The coal preparation plants in British Columbia treat coal in three streams, coarse, intermediate and fines (<0.5 mm). Generally, Dense Medium Cyclones (DMC) are used for treating coarse coal (50mm - 1mm), while intermediate stream (1mm-0.3mm) is cleaned by water-based gravity units such as Water Only Cyclones (WOC) in combination with spirals for better results, while the fine coal (-0.3mm) is treated by froth flotation. The rejects from each stream are disposed of separately, while the fine coal rejects are usually disposed of in form of coal slurries into the tailings ponds and these tailings ponds present the most challenging aspects for coal handling from the environmental point of view therefore, they pose the greatest challenges for the coal mining industry. Figure 2 shows the example of the coal processing plants cleaning metallurgical coal in British Columbia. 3 Figure 2: Metallurgical coal processing flowsheet with the points of interest for this study. 1.2 Coal and Microplastic Interactions in Industrial Processes Metallurgical coal, also known as metallurgical or coking coal, plays a vital role in the steel industry. When heated under controlled conditions, it undergoes carbonization, producing coke that serves as both a fuel and iron ore reductant in the blast furnace used for steel production. However, incorporating microplastics into this process presents both challenges and opportunities. On one hand, the high temperatures and controlled atmosphere of carbonization may allow for the thermal decomposition of microplastics, potentially repurposing them in industrial applications rather than allowing them to persist in the environment. On the other hand, microplastics could alter the physical and chemical properties of coke, affecting its suitability for steelmaking (Adeleke et al. 2023). Microplastics are classified as primary or secondary based on their origin. Primary microplastics are intentionally manufactured as small particles and are commonly found in personal care products (e.g., polyethylene in microbeads, polymethyl methacrylate in abrasives) or synthetic textiles (e.g., nylon fibers released during washing). Secondary microplastics, by contrast, form when larger plastic materials, such as bottles, containers, and synthetic fibers and break down 4 through environmental exposure and physical degradation. The common polymers such as high-density polyethylene (HDPE), polycarbonate (PC), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and low-density polyethylene (LDPE), were used before to assess their behavior in the coal carbonization process (Nomura et al. 2003; Chen et al., 2020; Bambalaza et al. 2023; Koskela et al., 2023); Figure 3 shows the common physical and chemical properties of these plastics as per (Frontier Lab, n.d.). Source: Frontier Lab, n.d. Figure 3: Properties of synthetic polymers. Understanding the thermal properties of synthetic polymers and different plastics is critical for their integration with coal. The melting point (Mp) of a polymer determines the temperature at which it transitions from a solid to a liquid, affecting its decomposition behavior during carbonization. Polymers with lower melting points (e.g., LDPE and polypropylene) may integrate more easily into thermal processes, while those with higher melting points (e.g., PET and polycarbonate) require greater energy input for breakdown. Additionally, the glass transition temperature (Tg), which marks the point at which a polymer changes from a rigid state to a more flexible, rubber-like form, is an important factor in evaluating the thermal compatibility of microplastics with coal. 5 1.3 Coal as a Potential Medium for Microplastic Utilization Coal is a carbon-rich sedimentary rock used for both energy production and other industrial applications. It is classified into four main types: lignite, sub-bituminous, bituminous, and anthracite, with increasing carbon content and energy efficiency from lignite to anthracite. Bituminous medium-rank coal, is widely used in electricity generation while only certain medium volatile bituminous coals are used in metallurgical applications due to their favorable thermo-plastic properties. Coking or metallurgical coal, a subset of bituminous coal, possesses unique properties that allow it to soften, liquefy, and re-solidify into a hard, porous structure called coke when subjected to high-temperature carbonization. Coke is a solid carbon material used in steelmaking and this coke is essential in steel production, serving as both a fuel and a reducing agent in blast furnaces. (Ram River Coal Corp., n. d.). The steel industry may provide an opportunity for repurposing microplastics by incorporating them into the carbonization process. This process provides a controlled thermal environment that could facilitate the degradation of microplastics while potentially even further increasing carbon content in such a blend. However, it is critical to assess how the inclusion of microplastics affects key coking coal parameters, such as coal fluidity as measured by Geisler Fluidity (GF), and Free Swelling Index (FSI), which influence the strength and structural integrity of the resulting coke. This work is the first attempt to test whether BC metallurgical coal products could become a medium for incorporation of different types of plastics or microplastics for reutilization purposes. 6 2 Literature Review 2.1 Microplastic Pollution and its Environmental Impact Microplastics, defined as plastic particles smaller than five millimeters, have become a persistent environmental concern. Their presence in water bodies, soil, and even atmospheric systems highlights the difficulty of managing plastic waste through conventional recycling methods (Raza et al., 2022). These pollutants originate from both primary sources (e.g., microbeads in personal care products, synthetic fibers from textiles) and secondary sources (e.g., plastic fragmentation due to environmental degradation) (Beckingham & Ghosh, 2017). Numerous studies indicate that microplastics absorb toxic substances, potentially transferring harmful chemicals into the food chain. As shown in Figure 4, microplastics are found in oceans, rivers, soil, and in the air. These small plastic particles enter the environment through different sources. Boats and ships release plastic waste into the ocean, while factories produce pollution that includes plastic particles. Littering and improper waste disposal also add plastics to the natural environment. Over time, sunlight and weather help break plastic into even smaller pieces, making them harder to remove. Source: Osman et al., 2023 Figure 4: How Microplastics Affect the Environment and Human Health 7 Microplastics eventually enter the food chain, mainly through seafood. In the ocean, fish and other marine animals mistake these plastics for food and eat them. When humans consume seafood, they may also ingest microplastics as a result. These small plastic particles can also be carried in the air, which means people can breathe them in. Microplastics can come from everyday items like bottles, bags, clothes, and even from ships and fishing gear in the ocean. Factories, urban pollution, and waste-burning release microplastics into the atmosphere, making air contamination another major concern. These small plastic pieces can enter the environment from both land and sea, polluting water and harming nature as illustrated in Figure 5. Source: Osman et al., 2023 Figure 5: Sources of microplastics Figure 6 illustrates how microplastics enter the human body and what health problems they might cause. On the left side, it shows that people can ingest microplastics through food or drink. Once inside the human body, microplastics can spread to different organs and cause serious health issues. Figure 6 (right) shows the possible health effects. Based on a review of research, Osman et al (2023) suggest that microplastics may cause lung problems (pulmonary diseases), heart problems (cardiovascular diseases), inflammation, can induce or mediate cancer, and inflict long- 8 term damage. They can also weaken the immune system (called immunotoxicity), increasing the risk of infections, and possibly affect pregnant women and their babies. Source: Osman et al., 2023 Figure 6: Effects of Microplastics on Human Health Since microplastics are everywhere, it is important to find ways to reduce plastic waste and prevent further pollution. Efforts such as improving waste management, reducing plastic production, and using alternative industrial processes to mitigate their presence can help limit the spread of microplastics in the environment. Because of the limitations of traditional plastics recycling and waste management approaches, alternative solutions, such as industrial repurposing of microplastics, needs to be explored. Currently, researchers are also looking for more effective ways to reduce microplastic pollution and remove these particles from the environment, especially microplastic, one that can’t be efficiently recycled. One promising approach could be the co-carbonization of microplastics with metallurgical coal, a process that could potentially mitigate plastic pollution while producing valuable coke for the steel industry. 2.2 Co-Carbonization as a Potential Solution for Microplastic Waste Mitigation Coal carbonization is a high-temperature process used in the steel industry to convert metallurgical coal into coke, a critical material for blast furnace operation. The coke making process involves heating coal in the absence of oxygen, breaking it down into volatile compounds and leaving 9 behind a carbon-rich solid. Given that microplastics are composed of hydrocarbon polymers, researchers have investigated their potential to be thermally degraded or transformed within this process to become part of the coke product (Chen et al., 2020). Bambalaza et al. (2023) explored the co-carbonization of waste polyethylene terephthalate (PET) with discard coal, finding that PET could be effectively converted into a carbon-rich material suitable for industrial use. The process increased the fixed carbon content of the resulting coke, making it comparable to conventional metallurgical coke. These findings support the hypothesis that certain plastics, when processed under controlled conditions, could be integrated into coal carbonization without compromising coke quality. Further research by Nomura et al. (2003) investigated how adding different types of plastics to coal during carbonization affects coal caking properties and coke strength. Their findings show that the impact varies depending on the type of plastic used. Aliphatic polymers such as polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC) had little to no effect on coal caking properties or coke strength. In some cases, PE even improved coke strength. However, polystyrene (PS), polyethylene terephthalate (PET), and terephthalic acid (TFA) negatively affected the process. These plastics hindered coal expansion and fusion, reduced fluidity and total dilatation, and weakened coke strength. Nomura et al. (2003) suggested that the negative effect of PS and PET is due to their thermal decomposition, thereby reducing its ability to form strong coke. These findings emphasize the importance of carefully selecting plastic types when blending them with coal to avoid compromising coke quality. Carpenter (2010) examined how waste plastics can be injected into blast furnaces (BFs) alongside coal to reduce the need for coke and lower environmental impact. The study found that properly processed plastics can replace some of the pulverized coal, providing the heat and gases needed to turn iron ore into metal. However, not all plastics are suitable, for example those with high chlorine content can cause corrosion, slag contamination, and harmful emissions. According to Carpenter (2010) to make plastic injection work efficiently, oxygen levels and furnace temperatures must be carefully controlled to ensure complete combustion and minimize unburned residues. The researcher concludes that using plastics in this way reduces coke consumption, extends the life of 10 coke ovens, and cuts CO₂ emissions. However, challenges remain in collecting, processing, and maintaining a consistent and stable plastic feedstock to keep blast furnace operations running smoothly. Koskela et al., (2023), investigated whether adding high-density polyethylene (HDPE) plastic to coal could improve the strength of metallurgical coke. Metallurgical coke must be strong enough to support the weight of materials inside a blast furnace while allowing gases to flow through it efficiently. In their experimental process, the researchers added small amounts of HDPE (3% to 5%) to coal blends and then subjected the mixture to carbonization in a laboratory coke oven. After the coke was formed, they tested its compressive strength to evaluate how well it could withstand pressure. The results were then compared to coke produced without plastic additives to determine if the HDPE had any significant effects. The results of Koskela et al. (2023) indicated that adding HDPE improved the strength of the coke, particularly when 5% HDPE was used. The compressive strength increased, and the coke showed less breakage under high pressure. Additionally, microscopic analysis revealed that large pores in coke can reduce its strength, meaning that optimizing the plastic-to-coal ratio is essential to maintaining coke quality. Koskela et al. (2023) suggests that HDPE can be used as an additive in coke production without significantly weakening the coke’s structure. This finding is important because it provides a potential method for recycling plastic waste while also enhancing the mechanical properties of coke. In the steel industry, blast furnaces need strong coke to allow proper airflow and support heavy loads. However, some types of coal do not produce strong coke on their own. To fix this, steel manufacturers use molded coal, which is made by compressing coal into a solid shape with a binder. Ishii et al. (2019) explored a new way to make molded coal stronger and cheaper by using recycled plastic as a binder instead of traditional coal tar binders. They mixed plastic waste with heavy coal tar and tested how well it worked as a binder. Then they tested different plastic mixing ratios (0.3, 0.5, and 0.8) and heated the mixture to 200°C to see how the plastic melted. After that, they made molded coal using different binders and checked its strength and durability. 11 They compared the results with molded coal made using traditional binders. The researchers found that the molded coal made with plastic binders was stronger than coal mixed with traditional binders and using plastic waste reduced CO₂ emissions, making the process more environmentally friendly and their method provides a cheaper and more sustainable way to produce high-strength coke. In steelmaking, strong coke is needed to support heavy material load inside a blast furnace and allow gases to flow through. If the coal used to make coke is too weak, the coke will break apart and will not work properly. A binder helps coal hold its shape, making the final coke stronger and more effective. This showed another way that plastic can be used in improving the coke quality in steel making process. 2.3 Thermal Behavior of Microplastic in Industrial Carbonization Processes The effectiveness of co-carbonization depends on the thermal compatibility of plastics with coal. Each plastic type has a specific melting point and thermal degradation profile, which determines its behavior during carbonization. Research by Chen et al. (2020) explain that plastics like polyethylene (PE) and polypropylene (PP) break down easily at lower temperatures, making them easier to mix with coal during heating. However, plastics with higher melting points, like polyether ether ketone (PEEK) and polycarbonate (PC), need much higher temperatures to decompose, so they do not blend well with coal when it softens and hardens. This might mean that low-melting-point plastics, such as polyethylene (PE) and polypropylene (PP), decompose at temperatures compatible with coal’s thermoplastic range, allowing for better integration. In contrast, high-melting-point plastics, such as polyether ether ketone (PEEK) and polycarbonate (PC), require higher temperatures and may not fully blend with coal’s softening and resolidification process. Additionally, studies on the thermal properties of coal indicate that its plasticity, swelling behavior, and fluidity play crucial roles in determining how well microplastics can be integrated. Ng et al. (2024) analyzed coal thermal behavior using Gieseler and Sapozhnikov tests, demonstrating that the maximum fluidity of coal correlates with its ability to bind additives during carbonization. Studies on hydrothermal and pyrolytic processing provide further insight into microplastic transformation. Sun et al. (2022) demonstrated that microplastics can be converted into porous carbon materials through controlled carbonization under specific thermal conditions. Their research highlights how modifying factors such as temperature, the use of molten salts, and 12 reaction conditions can enhance carbon yield and surface area. However, their focus was on using the resulting porous carbon as a catalyst for pollutant degradation, rather than for coke formation or steelmaking applications. Understanding how microplastics can be turned into porous carbon under controlled conditions shows how different reaction conditions affect porous carbon quality, which can be an important when considering microplastics as a potential additive in coal carbonization. 2.4 Environmental and Industrial Benefits of Co-Carbonization Beyond its potential to reduce plastic waste, co-carbonization offers economic and environmental benefits for the steel industry. Adeleke et al. (2023) reviewed the use of waste plastics in coke production, showing that plastics can reduce the need for traditional coking coal. They suggest this could improve process efficiency and contribute to more sustainable steel production, but they do not provide a full cost analysis. Their review supports the economic feasibility of co-carbonization by showing that plastics can partially replace expensive, high-quality coking coal, helping to reduce costs for steel manufacturers. Although it does not provide a full financial analysis, it suggests that incorporating plastics into coke production can improve efficiency, which may lead to lower production costs over time. This aligns with the idea that industries can achieve cost savings by reducing their dependence on scarce and high-cost coal while still maintaining high-quality coke production. Moreover, converting microplastics into porous carbon could also be a useful strategy for managing plastic waste and reducing environmental pollution. The resulting carbon material showed potential applications in environmental remediation, particularly as a catalyst for breaking down organic pollutants in wastewater (Sun et al., 2022). This study demonstrates that plastics-derived carbon can be used for the environmental applications. However, despite these potential benefits, scalability remains a key challenge. While, laboratory experiments have demonstrated feasibility, large-scale implementation requires further research into the process optimization, emissions control, and the regulatory considerations. Beyond its technical feasibility, the co-carbonization of plastics with coal presents potential economic and environmental benefits. A study by Adeleke et al. (2023) reviewed how adding plastics to coke 13 production can help reduce plastic waste, improve process efficiency, and lower carbon emissions. They suggest that plastics could replace part of the coal used in steelmaking. Their study supports the environmental benefits of co-carbonization by demonstrating that using plastic waste in coke production helps reduce plastic and microplastic pollution, preventing it from ending up in landfills or being incinerated. In addition, it also highlights how replacing part of the coal with plastics can lower carbon emissions, making steel production more environmentally friendly. From an industrial standpoint, incorporating plastics into coke production can improve energy efficiency and increase coke yield, benefiting steel manufacturers by making the process more sustainable and potentially reducing energy consumption. Additionally, using waste plastics as a carbon source supports circular economy initiatives, diverting plastic waste from landfills and reducing the carbon footprint of steel production. The International Energy Agency (IEA) has emphasized the need for innovative carbon mitigation strategies in heavy industries, suggesting that repurposing plastic waste through processes like co-carbonization could contribute to decarbonization efforts. However, regulatory and operational challenges remain. For instance, studies on emissions from plastic pyrolysis indicate that certain plastics may release volatile organic compounds (VOCs) and other hazardous byproducts if not carefully controlled. Bambalaza et al. (2023) highlight that optimizing reaction temperatures and using catalytic additives can minimize these emissions, ensuring a cleaner and more sustainable process. Form the reviewed literature only few types of plastic would be the suitable candidates for mixing with the metallurgical to improves its quality. 2.5 Compatibility of Thermal Properties of Plastic and Coal A key factor in the co-carbonization is making sure that the thermal properties of plastics match how coal behaves during carbonization. As coal turns into coke, it goes through different thermal stages, including softening, forming a plastic layer, releasing volatile gases, and finally solidifying into coke. Ng et al. (2024) studied coal plasticity and contraction behavior using the Gieseler, Sapozhnikov plastometer, and Ruhr dilatometer tests. Their research shows that these tests help to understand how coal behaves when heated and this information is useful for evaluating whether a type of coal is suitable for coke production. 14 When introducing plastic into this process, the thermal decomposition temperature of plastics must complement the plasticity range of coal. Levchik and Weil (2004) provide important insights into how certain plastics break down under heat, which helps in understanding their compatibility with coal during carbonization. Their study shows that when PET and PBT plastics are added to coal, they are more likely to increase gas emissions rather than contribute to the solid structure of coke. The study also found that PET has a high activation energy (160-200 kJ/mol), meaning it needs higher temperatures to break down compared to other plastics. This suggests that PET may not soften and mix well with coal at typical carbonization temperatures, making it less suitable for co-carbonization. Additionally, the PET plastics behaves differently in an air environment versus an inert (oxygen-free) one, producing more oxygen-rich gases when exposed to air. This could affect how coal softens and melts during heating. These findings highlight the importance of selecting plastics that not only break down within the right temperature range but also form enough solid carbon to enhance coke quality. Compatibility of thermal properties of coal and plastic is very important aspect of co-carbonization that needs to be evaluated. Although, there are still significant environmental challenges in considering carbonization as a net-zero plastic pollution mitigation industrial process, some countries proceed with the carbonization as a method for recycling or reutilizing plastic in steel making industries. In the following section, examples of recycling waste plastic at the steel plants are explained in a greater detail. 2.6 Plastic Recycling Process at Nippon Steel In the year 2000, Nippon Steel started using coke ovens to recycle waste plastics at their Nagoya and Kimitsu plants. These plants are capable of processing 40,000 tons of plastic waste per year. This process is part of Japan’s energy-saving plan, helping reduce energy use and repurpose plastic waste. (Figure 7) shows how Nippon steel is processing the mixing of coal and plastics with each step and pictures. 15 Source: https://www.nipponsteel.com/en/csr/env/circulation/waste.html (accessed March 2025) Figure 7: Recycling waste plastics at Nippon Steel When plastics are heated in coke ovens, they break down into different products. Around 20% turns into coke, 40% becomes tar and light oil, which can be used as liquid fuels. The remaining 40% is converted into gas, which can be used as a cleaner energy source. Before mixing with coal, plastics must be properly treated: metal contaminants are removed using magnets, and the plastics are crushed and filtered to eliminate impurities, compacted into larger particles using an agglomerator, and finally pelletized for easy blending. Once the treated plastics are blended with coal and fed into the coke oven, the mixture undergoes carbonization. This method of co-carbonizing plastics with coal presents an effective solution for plastic waste management. It not only diverts plastics from landfills and incineration but also contributes to energy efficiency and reduces CO₂ emissions. Ultimately, it supports a circular economy by turning waste into valuable resources for industrial use. Meanwhile, using waste plastics in coke ovens is a promising way to recycle plastic while producing valuable industrial materials. However, it is important to find the right balance of plastic-to-coal ratio to ensure the quality of 16 coke remains high. If used correctly, this process can help reduce plastic pollution, save energy, and support a more sustainable steel industry. The Japan Iron & Steel Federation (JISF) started an energy-saving plan to reduce energy consumption by 10% by 2010, using 1990 levels as a reference. As part of this effort, they also introduced a method to save an additional 1.5% of energy by using waste plastics in steel production. Instead of throwing plastic waste away, it can be used as a raw material in steel manufacturing. In addition, the steel industry has traditionally focused on recycling plastics in blast furnaces. However, researchers found that coke ovens could also be used for this purpose. Coke ovens heat coal at high temperatures (about 1,100°C) in a low-oxygen environment, turning it into coke, gas, tar, and other useful by-products. Their study found that adding 1% waste HDPE (High-Density Polyethylene) plastic to coal did not weaken the strength of the coke, meaning this method could be a new way to recycle plastic without harming coke quality. Krishnan et al. (2006) found that waste plastics can be co-carbonized with coal in stamp-charged coke ovens to produce coke, tar, light oil, and gas without harming coke quality. Laboratory and plant trials at Tata Steel showed that adding up to 1% of waste HDPE (High-Density Polyethylene) plastics did not reduce coke strength, making this a viable method for plastic waste recycling. Figure 8 shows how waste plastics and coal are processed in coke ovens, producing coke (used in blast furnaces for steelmaking), tar and light oil (sent to chemical plants), and coke oven gas (COG) (used for energy in power plants). The Nippon Steel Nagoya and Kimitsu plants started using this technology in 2000, showing that it works in real industrial settings. By recycling plastics this way, the steel industry can reduce waste, lower energy use, and create a more sustainable production process. . 17 Based on Kato et al., 2002 Figure 8: How waste plastics and coal are processed in coke ovens. 2.7 Summary of Literature Review Microplastic pollution has become a widespread and persistent environmental problem. Defined as plastic particles smaller than five millimeters, microplastics are now found in oceans, rivers, soil, and even the air. They originate from both primary sources like microbeads and synthetic fibers, and secondary sources such as the breakdown of larger plastics. Numerous studies, including Osman et al. (2023), have shown that microplastics can enter the human body through seafood consumption or inhalation, potentially leading to cell damage, inflammation, weakened immune systems, and other serious health issues. Their tiny size and widespread distribution make them extremely difficult to remove from the environment through traditional recycling and waste management methods. Due to the challenges of recycling and the omnipresence of microplastics, researchers have been exploring alternative solutions. One promising approach is co-carbonization and blending microplastics with coal during the coke-making process in the steel industry. Studies such as those by Chen et al. (2020), Bambalaza et al. (2023), and Koskela et al. (2023) demonstrate that certain types of plastics, particularly low-melting-point polymers like polyethylene (PE) and polypropylene (PP), can be thermally degraded and successfully incorporated into coke without 18 compromising its quality. Research showed that, depending on the plastic type and proportion used, it was even possible to enhance coke strength or at least maintain acceptable coke quality for industrial applications. Real-world examples further support these laboratory findings. For instance, Nippon Steel in Japan has successfully integrated waste plastics into coke production since 2000. Their plants process up to 40,000 tons of waste plastic per year, turning it into valuable coke, tar, light oils, and gas, while maintaining coke strength when plastic addition remains around 1%. This demonstrates that with careful preparation and processing, large-scale recycling of plastics through coke ovens is not only feasible but also beneficial for reducing plastic pollution, lowering CO₂ emissions, and improving the sustainability of steel production. In conclusion, microplastic pollution poses a serious threat to both the environment and human health, and conventional recycling methods are not sufficient to address it. Co-carbonization presents a promising, scalable, and industrially proven method to mitigate microplastic pollution by converting plastic waste into valuable materials used in steelmaking. However, careful selection of plastic types and operational optimization are essential to ensure the success of this approach without compromising coke quality and by providing win-win situation in terms of environmental aspects. The products of the flotation such as the flotation concentrate and fine tailings which represent important yet underutilized by-products in metallurgical coal processing are particularly relevant to the waste utilization efforts in the mining industry and can possibly be used for mitigation of microplastic or in general environmental plastic pollution. 2.8 Knowledge Gaps and Research Objectives While existing studies offer useful insights into the effect of blending of coal with plastic or microplastic on co-carbonization and their industrial potential, there are still significant knowledge gaps. One major limitation is the lack of validation of controlled experiments to see how plastic or microplastics affect coking properties of coal and what is the chemical and physical interaction between coal and plastic during the carbonization. Another is a lack of correlation between small scale and large-scale experiments or industrial application, namely correlation between fluidity, caking and coke strength of coal and plastic blends. Most of the research has focused either on 19 small scale experimental work using FSI or fluidity tests (GF or Sapozhnikov) which are performed on small samples under specific conditions or on a large industrial-scale, such as adding plastic or plastic-coal blend straight into the industrial coke oven or blast furnace during the steel making process. As a result, some conflicting results were reported, in some studies adding plastic was shown to not having any effects while in others deterioration of either coke or coking properties of coal was evidenced. Another challenge is the lack of consistent information on the plastic-to-coal ratios, making it unclear how much plastic and what kind of plastic can be safely added without worsening coke quality. Additionally, there is uncertainty about the best point for integrating plastics or microplastic into the carbonization process or whether it should be rather blended with coal at an early stage such as coal processing stage. Specifically, when microplastic is being considered, where would be the best to blend with coal? Could it be at the processing plant where the fine coal is being prepared before being sent to the steel plant? Another gap in knowledge is that nobody looked at the effects of adding plastic for the low fluidity coals to see whether there will be any improvement in their coking characteristics, while most study were only concerned with the maintaining the good coking characteristics of the blend that already has good fluidity. British Columbia (BC) is the main exporter of metallurgical coal in Canada and these coals are generally characterized by low fluidity and there was an opportunity to study whether adding plastic in form of microplastic would improve the fluidity of these coals. Nobody has studied this before for these coals. In the context of this thesis, the focus is explicitly on blending the plastic in form of microplastic where the coal is being processed at the mine site. In terms of processing of metallurgical coal in BC, the process begins with run-of-mine being crushed, which is first treated in a rotary breaker to separate larger waste rock from the coal. The material is then separated into three size streams: coarse, intermediate, and fines. Each of the streams follows a specific processing pathway as discussed in chapter 1. The flotation concentrate which is combined with the clean coal from other cleaning units (coarse and intermediate) to form final “clean coal”, coarse and intermediate tailings are disposed separately while the fine tailings 20 are sent to the tailings’ ponds. In this research, the focus is on the flotation process with two products; concentrate and fine tailings as indicated in Figure 2 and marked by red stars. To explore a new approach for mitigating microplastic pollution, this thesis investigates the integration of microplastics into the flotation concentrate first. In the experimental phase, crushed and fine ground coal was subjected to flotation in UBC lab to obtain a clean coal product. This clean coal was then dried and blended with microplastics (ground plastic) to evaluate its behavior during Gieseler plastometry and the Free Swelling Index (FSI) testing. These tests aim to understand how the microplastics interact with the metallurgical coal during these tests and assess whether they can be viably incorporated into the coal-based products without degrading coking coal quality. The findings from these experiments are presented in the subsequent section of this thesis, with detailed discussion on how this approach contributes to the beneficial resource recovery and the microplastic pollution mitigation at the same time. 21 3 Methodology and Experimental Results Laboratory experiments were used to generate flotation products for testing to find out whether adding microplastics to these products will not deteriorate coking characteristics of the tested coal, focusing on their impact on fluidity and swelling properties. Given the importance of maintaining high-quality coking coal for steelmaking, this research also explores whether microplastic addition could be better suited for alternative applications, such as clean coal production for energy generation. Specifically, this study evaluates the effects of blending of the high-density polyethylene (HDPE) and the polycarbonate (PC) microplastics with coal on the metallurgical and thermal coal characteristics through two main approaches: 1. Blending microplastics with flotation concentrate products to assess their effect on coking properties such as Free Swelling Index (FSI), ash content, and Gieseler Fluidity (GF). 2. Mixing microplastics with middlings and flotation tailings to evaluate their potential for producing low-ash thermal coal products suitable for energy generation by assessing their Calorific Value (CV). Namely, the research aims to evaluate how this integration impacts key coal quality parameters such as Free Swelling Index (FSI), ash content, and GF-fluidity, which are usually good indicators of metallurgical coal quality. It also explores the potential of incorporating microplastics into coal middlings/tailings to produce lower-emission thermal coal products, where ash reduction and calorific value (CV) are key considerations. 3.1 Coal Sample Sourcing and Sample Preparation A series of steps were needed to prepare and analyze coal and microplastic samples, generate flotation products, and assess the feasibility of integrating microplastics into coal and providing good coking coal blend through a preliminary study with each step detailed below. 22 3.1.1 Sample Sourcing Fresh coal samples used in this study were sourced from Elk Valley Resources from active mining operation. The coal was of metallurgical quality. The coal was shipped directly to the Coal and Mineral Processing laboratory (CMPL) at the University of British Columbia. These samples represent typical BC coking coal used in metallurgical applications and will serve as the base material for testing microplastic integration. 3.1.2 Crushing and Grinding The raw coal samples were crushed and ground into fine particles sizes. The samples were initially crushed in hammer mill then ground in the pulverizer to achieve a particle size distribution (PSD) suitable for flotation and other analyses. The particles were ground to the sizes smaller than 0.3mm (100% passing 300µ) to match the flotation particle sizes at the operating mines, the coal feed for flotation was P80=130µ (80% of particles passing) and d50=55µ (50% of particles passing) obtained from Particle Size Distribution (PSD) analysis by sieving (Appendix E). 3.1.3 Plastic Selection and cryogenic grinding Two types of plastics were selected based on the most commonly used plastics, and these included Hard Density polyethylene (HDPE), and Polycarbonate (PC). These types represent the variety of plastics commonly used and will allow for an evaluation of microplastic-coal integration. The selected plastics were ground in a cryogenic grinder. Figure 9 shows the Cryogenic Grinder machine to produce fine microplastic particles The produced microplastic had P80=255µ and d50=175µ obtained from Particle Size Distribution (PSD) analysis by sieving (Appendix E). 23 Figure 9: Freezer/Mill Cryogenic Grinder used to grind microplastics 3.2 Flotation and Ash Analysis Flotation was necessary to prepare coal samples for the follow up evaluation of coking and thermal coal properties. In this flotation experiment, the recommended reagent dosages were followed to assess the separation performance of bituminous coal. For a 500 g coal sample, 25 milligrams of MIBC (methyl isobutyl carbinol) were added as the frother, which corresponds to the standard dosage of 50 g/t of coal. 2 drops of kerosene, was also added as a commonly used oily collector. In order to achieve an ash content of 10% or less, a typical ash content for a final clean coal product, two stages of flotation were performed (see Figure 10). The moisture and ash contents of flotation products were determined and ash contents are shown in Table 1. It can be seen that the ash content of first concentrate (CP) was 12 .6%. The ash in final concentrate (C) was 9.2% while an ash content of 24.9% was in the tailings of the second flotation (T) which can be considered “middlings”, i.e., they are not clean, but they are not tailings. Figure 10: Flotation flowsheet showing 2 stages of flotation; S1 rougher and S2 cleaner stage to obtain <10% ash product. Feed-F, TP – 1st stage tailings; CP- 1st concentrate C-final concentrate, T- final tailings 24 Figure 11: Flotation products: Left-Concentrate, Right-Tailings samples Table 1: Ash Content of Flotation Products 3.3 Free Swelling Index Free Swelling Index (FSI) measures the caking properties of coal, indicating how well it can form a coherent mass upon heating in the absence of air. FSI is used to assess the swelling properties of the coal. One-gram sample of pulverized coal is heated in a covered ceramic crucible. In this test, the temperature is raised up to 820 ºC in 2.5 minutes, according to a prescribed in ASTM standard (ASTM D720/D720M). After the coal has been transformed into the so called “coke button” then its shape is compared against a series of standard shapes. This property is one of the coal’s characteristics to determine its suitability for coke making in the metallurgical processes such as steel production. Since FSI is used in several coal classification systems including International Coal Classification system, FSI test was used here on the blend of coal and microplastics in order to determine whether the presence of microplastics has any effect on the coal's ability to form acceptable coke button. 25 Figure 12 shows the FSI equipment and this approach assesses the feasibility of using microplastics as a supplementary material in coal used for coke production, potentially offering an innovative solution to plastic waste management. Figure 12: Equipment used for FSI tests at GWIL laboratory (Calgary) The experimental results in Table 2 provide insights into how adding different types of microplastics affects FSI value for blends of coal with different types of plastic. The primary focus was on using high-density polyethylene (HDPE) and polycarbonate (PC), which were tested at varying concentrations to determine their impact on the coal quality of the concentrate from flotation. It is observed that when PC was added to the concentrate the FSI value dropped, but rather insignificantly. Table 2: FSI Results Sample FSI Concentrate C 8 C + HDPE 0.5% 7.5 C + HDPE 1% 8 C + PC 0.5% 7.5 C + PC 1% 8 C + HDPE 3% 7.5 C + PC 3% 8 26 The coal ash analysis results indicate that adding microplastics to coal concentrate from flotation does not significantly reduce ash content in the samples as shown in Table 3. For instance, the concentrate which is clean coal product, initially had an ash content of 9.29% and when blended with 1% HDPE or 1% PC, the ash content remained at comparable levels (9.31% and 9.26%, respectively) while maintaining a stable Free Swelling Index (FSI) of 8.0, which is within the range required for a good metallurgical coal. This suggests that small amounts of microplastics do not negatively impact coal ash content a non-carbon impurities. Further on, concentrate was used to study the effect of adding plastic on the fluidity which is discussed in the next section. Table 3: Ash Content, FSI, for Feed and Concentrate with Microplastics Sample ID ASH% FSI Feed F 25.34 7.5 Concentrate C 9.29 8.0 F + HDPE 0.5% 26.29 7.0 F + HDPE 1% 25.77 8.0 C + HDPE 0.5% 9.29 7.0 C + HDPE 1% 9.31 8.0 F + PC 0.5% 26.29 7.5 F + PC 1% 26.05 7.5 C + PC 0.5% 9.34 7.5 C + PC 1% 9.26 8.0 3.4 Gieseler Fluidity Test The Gieseler fluidity test measures how coal softens, melts, and flows when heated. The more fluid the coal is, the more chance that particles in the coal will be distributed uniformly through the coal when it hardens. A uniform distribution leads to stronger coke, an essential characteristic for iron ore production where the coke has to support the weight of the iron ore in the blast furnace. Metallurgical coal melts at about 400°C, exhibits maximum fluidity at about 450°C, and then re-solidifies at about 480°C. Figure 13 shows the equipment used for the fluidity test. 27 Figure 13: The Gieseler Fluidity equipment at GWIL laboratory (Calgary) Figure 14 shows the results of GF tests carried out on the flotation concentrate C and with the addition of 1% HDPE microplastics. Without the microplastics the maximum fluidity (measured in Dial Division Per Minute, DDPM) of C is 12 DDPM, but there is a notable decrease in the coal fluidity to 7.6 DDPM when the microplastics are introduced. The 1% plastic addition was based on previous test work carried out by Nippon steel in 2000, as discussed in the literature review, which indicated that 1% plastic addition was shown not to significantly affect coke properties. However, Krishnan et al. (2006) showed in contrary to the previously reported results, that a notable decrease was observed in the coal fluidity when the microplastics are introduced at higher than 1%, therefore the highest plastic addition was kept at 1% for the experiments in this study. Figure 14 depicts results for GF versus time and temperature, where, maximum fluidity is expressed in division dials per minute (DDPM) which is considered a key parameter in coking coal. 28 Figure 14: Gieseler fluidity test results for C (top) and C + 1%HDPE (bottom) It has been noticed that after adding 1% of plastic to concentrate, the DDPM value dropped significantly. However, this particular coal had very low fluidity to start with (12 DDPM) but the DDPM value still dropped to much lower after adding plastic (7.6 DDPM). To determine whether the decrease in fluidity was characteristic of this particular coal, a clean coal product (CCP) with higher fluidity was requested from the mine. The results of GF tests on CCP are shown in Figure 16 where it can be seen that without the microplastics the maximum fluidity of CCP was 145 DDPM, but when 1% HDPE was added, the maximum fluidity dropped to 78 DDPM, a similar effect as in the case of the flotation concentrate C. When 1% of PC microplastic was added the same was observed, fluidity decreased to 82.5 DDPM (Figure 16). 12.405101501002003004005006000 20 40 60dial divisions per minuteTemperature °CTime (min)Flotation Concentrate CTemperatureddpm7.605101501002003004005006000 10 20 30 40 50 60 70dial divisions per minuteTemperature °CTime (min)Flotation Concentrate C + 1%HDPETemperatureddpm 29 Figure 15: Gieseler fluidity test results for CCP (top) and CCP + 1%HDPE (bottom) 144.602040608010012014016001002003004005006000 10 20 30 40 50 60 70dial divisions per minuteTemperature °CTime (min)Clean Coal Product CCPTemperatureddpm77.102040608010012014016001002003004005006000 20 40 60 80dial divisions per minuteTemperature °CTime (min)CCP + 1%HDPETemperatureddpm 30 Figure 16: Gieseler fluidity test results for CCP + 1% PC This decline in DDPM suggests that microplastic additives interfere with coal softening and fusion behavior, potentially impacting coking coal characteristics regardless of type of coal, whether it has low fluidity or higher fluidity, there was the same end effect, decrease in fluidity after plastic addition is shown in Figure 14, 15 and 16. This finding aligns with previous studies indicating that plastic decomposition during carbonization alters the fluidity of coal, likely due to interactions between plastic and coal particles during thermal process. 3.5 Feasibility of Clean Fuel Production The addition of microplastics negatively affected fluidity when the clean coal such as concentrate was blended with microplastic, while the results on the blending microplastics with coal processing products such as flotation tailings could provide an alternative pathway for clean fuel preparation. The tailings from the second flotation (cleaner stage to reduce the concentrate ash to less than 10%) which are referred here as middling’s because it is not “clean” enough to be the concentrate but not “dirty” enough to be called tailings (<65% ash) was mixed with 10%, 30% and 40% HDPE microplastic and analyzed for calorific value (CV) as shown in Table 4 and illustrated in Figure 17. It was shown that such blend (coal + HDPE) although not having good fluidity, maintained reasonable energy values (26.213 MJ/kg and 26.263 MJ/kg) while calorific value for pure HDPE is approximately 40.6 MJ/kg, suggesting that these blends may be highly suitable as an energy source in thermal coal applications. Also, this opens the possibility of using coal-microplastic 82.502040608010012014016001002003004005006000 10 20 30 40 50 60 70dial divisions per minuteTemperature °CTime (min)CCP + 1%PCTemperatureddpm 31 blends as a cleaner fuel alternative, repurposing plastic waste while reducing disposal of fine coal waste stream. Table 4: Ash Content, and Calorific Value Sample ID ASH% CV Middlings + 10% HDPE 22.43 26.213 Middlings + 30% HDPE 17.49 26.263 Middlings + 40% HDPE 14.92 26.181 Figure 17: Effects of HDPE microplastic addition on ash content and calorific value of middlings 3.6 Key Findings  The addition of microplastics reduces coal fluidity, making it not suitable for forming high-quality coke in steelmaking.  Potential for alternative fuel applications of fine coal tailings/middlings because of a decrease in ash content and exceptionally good calorific value.  Despite its limitations in in the use for coke production, microplastic-blended coal may be useful for thermal energy generation.  Fine coal tailings mixed with HDPE retained acceptable energy values, suggesting that the microplastics could be utilized to produce cleaner-burning coal products. 32 4 Addition of Microplastics at Processing Plant 4.1 Scope and Objective This study evaluates the feasibility of incorporating microplastics into metallurgical coal products, specifically flotation tailings or middlings if such are available at the processing plant, to produce a secondary (value added) thermal coal product for power generation. The aim is to assess technical suitability, relative economic viability, and environmental advantages of this approach using existing mine-site infrastructure. The data in Table 4 show that adding 40% HDPE microplastics to the middlings reduced the ash content from over 25% to less than 15%, while the trend of the ash content versus plastic concentration line suggests that ash content could be reduced even more, to 10% or less, with about 60% plastic addition as shown in Figure 18. Figure 18: Effects of increased microplastics addition (up to 60%) on ash and calorific value. This is important because lower ash content means even higher calorific value (CV) hence the better thermal coal product. While added microplastics maintained the CV above 23.8 MJ/kg, which is a good target for high-quality thermal coal. This means that the coal mixed with microplastics can be used to generate electricity or heat, making it a viable clean energy product. This also, can indicate that if the flotation tailings from the plant have an ash content between 40 and 50% ash, by adding more plastic one will be able to reduce ash content in such a blend 33 warranting high CV for their clean coal product. More importantly, this can be done without any processing, meaning that by simply adding plastic or microplastic to flotation tailings one can obtain high quality thermal coal product. In addition, this also means that instead of disposing of fine coal rejects from flotation circuits into the tailing’s ponds, which are difficult to handle, and costly to manage, there is a possibility to mix them with microplastics to create a cleaner fuel. This approach not only provides a sustainable way to reduce plastic waste in form of microplastic, but also helps mining operations make better use of coal byproducts that would otherwise go to waste. 4.2 Proposed Integration Pathway: Mine-Site Blending Figure 19 presents possible configuration of system for producing blend consisting of fine coal and microplastic. According to the proposed scenario, the flotation tailings could be sent to the thickener for settling of the fine coal rejects, once coal slurry (tailings) are thickened, microplastic could be added before filter press to remove water. Figure19 shows a scheme for blending of coal flotation tailings with microplastic. Figure 19: Suggested configuration of system to manufacture blend of coal and microplastic 34 This could be beneficial, because if the microplastic is dry, it would further remove moisture from the filter cake which usually has a moisture content of about 30%. Alternatively, if dry microplastics are added to the thickened coal tailings, it may suffice to reduce the final moisture to less than 9% hence there will be no need for further dewatering. However, if this is not achieved, the coal and microplastic mixture is then passed through a filter press, a machine that squeezes out the remaining water and turns the wet mixture into a drier product in the solid form like a filter cake product then this material could be handled short distance to the nearby power plant facility. The advantage is that this coal and microplastic blend can be catered according to the power plant requirements in terms of ash and moisture content, as long as this material is handleable between mine and power plant facility. The end result is a clean coal product containing microplastics, which can be handled and transported more easily. This solid product can then be shipped for use as a thermal coal energy source, such as for power generation or for industrial heating applications. What makes this idea even more attractive is that it can be done with only a few modifications to the existing coal processing plant facility. Instead of discarding the fine tailings into mining ponds, where they’re difficult to manage, this approach allows fine tailings to be reused, along with microplastic waste in order to create a useful product. In the end, this approach leads to less waste, reduced microplastic pollution, and a more sustainable use of the coal byproducts or rejects. Also, it will reduce coal mine environmental footprint by utilizing their most troublesome waste such as fine coal tailings. This proposed intergradation pathway can be accomplished at the mine site. In summary, turning coal tailings and microplastics into thermal coal product which can be referred to as cleaner fuel could be both environmentally and economically beneficial. 4.2.1 Technical Feasibility Using microplastics in coal tailings presents a technically feasible approach, especially since tailings cannot be used for coke-making. The mixing process itself is relatively simple and does not require heavy machinery because low-energy mixers or conveyor-based systems are generally sufficient to achieve an even distribution of microplastics into the coal slurry. The microplastic can be introduce either into the coal slurry (flotation tailings) or immediately before filter press. Alternatively, this integration of microplastic can be done before after the filter press, which produces a dry coal “cake” that is ideal for blending with crushed microplastics. For effective 35 mixing, the microplastics used should be finely ground to particles smaller than 1 mm, allowing them to match the particle size distribution of fine coal fractions. Additionally, the use of flocculants may be not be necessary following the thickening stage, because the microplastic could possibly act as flocculant, but this aspect would need to be further researched. Overall, the infrastructure and technology required for blending microplastics at mine sites are either already available or can be easily implemented with minimal amendments. 4.2.2 Environmental and Logistical Benefits This approach offers several environmental and logistical advantages. First, it provides a practical pathway for reducing plastic waste by transforming it into a usable energy product instead of sending it to landfills or incinerators. At the same time, it avoids fine coal tailings disposal, which are typically discarded as waste, hence, it provides an opportunity for converting them into fuel suitable for energy generation. Since the microplastics are mixed directly on site, there is no need to transport them separately, which saves on fuel and logistics costs. This solution aligns well with broader sustainability initiatives, including British Columbia’s CleanBC strategy and circular economy goals. Furthermore, projects like this may be eligible for a 19% carbon tax rebate under CleanBC’s 2024 guidelines, providing an additional economic incentive to adopt microplastic integration at the industrial level. 4.3 Combustion, Gasification, and Hydrogen Production from Microplastics and Coal Blend To ensure that the coal and microplastic-blend can be used safely without generating toxic emissions as an energy source, it is essential to match this type of fuel with appropriate power generation technologies. From the combustion point of view, another possible and more environmental option is the Circulating Fluidized Bed (CFB) boiler, which operates at lower temperatures of around 850°C (Babcock & Wilcox, n.d.). CFB boilers are widely used in clean coal power plants and are capable of handling a variety of fuel types, including coal blended with microplastics. They also reduce harmful emissions such as nitrogen oxides (NOx) and sulfur dioxide (SO₂), which makes them environmentally favorable. 36 One of the most effective and the most environmental option would be to use the Integrated Gasification Combined Cycle (IGCC) system (Homolka, 2019). This method gasifies the coal and plastic mixture at temperatures between 815°C and 1926°C under high pressures of up to 1600 psi. The process produces syngas, a mixture of carbon monoxide and hydrogen, which powers gas turbines. The heat generated during this process is also used to produce steam, driving steam turbines for additional power. IGCC systems are known for their high efficiency (up to 50%) and low emissions, making them particularly suitable for mixed feedstocks that include plastics. Even more advanced but higher-cost technology is Plasma Gasification. This technology exposes waste to extremely high temperatures (over 3,000°C) using a plasma arc. It effectively breaks down even hazardous or mixed plastics like PVC and polycarbonate into clean syngas, while leaving behind a vitrified, non-toxic slag. Plasma gasification is known for producing minimal ash and exceptionally clean emissions, though its higher capital cost makes it suitable mainly for high-value or highly contaminated waste streams. Hydrogen production is another promising application of plastic-coal co-gasification. In systems like IGCC or standalone gasification units, the syngas produced can be further processed through water-gas shift reactions to increase its hydrogen content. The resulting hydrogen can then be purified using pressure swing adsorption or membrane separation. This hydrogen could serve as a clean fuel for industrial use, transportation, or be fed into green steelmaking processes and helping reduce dependency on fossil fuels and significantly lowering CO₂ emissions. Using microplastics as a feedstock for hydrogen production not only reduces plastic waste but also contributes to the growing global hydrogen economy. Lastly, advanced incineration with flue gas cleaning is another viable route (Carlsson, n.d.). This method combusts the coal-plastic blend in specialized boilers equipped with systems like Flue Gas Desulfurization (FGD), Selective Catalytic Reduction (SCR), and Electrostatic Precipitators (ESP). These technologies ensure tight control over emissions of dioxins, hydrochloric acid (HCl), and heavy metals, making the process environmentally compliant and safer for human health. 37 4.4 Risks, Challenges and Benefits Despite the promising potential, certain risks must be managed carefully. Each type of plastic needs to be tested for its combustion behavior, emission characteristics, and reactivity. Plastics containing chlorine or benzene should be avoided, as they can overload thermal systems or produce hazardous byproducts. Therefore, it is crucial to conduct pilot-scale trials before any large-scale deployment to validate the gas composition, energy output, and system performance. Additionally, plastics of unknown or mixed composition, such as those sourced from household or municipal waste, should undergo pre-treatment or be restricted to gasification processes where high-temperature breakdown is more controlled and predictable. In conclusion, the integration of microplastics with mine-site tailings and their conversion into clean fuel or energy generation is technically feasible and environmentally promising. The process benefits from low-cost infrastructure, and when combined with advanced energy technologies such as IGCC, CFB boilers, plasma gasification, or hydrogen production systems, it can deliver clean energy with lessened environmental impact. Further research is recommended to explore different plastic types, measure emissions under various operating conditions, and evaluate the scalability of this solution in real-world industrial environments. 38 5 Conclusion and Recommendations This research explored the feasibility of mitigating microplastic pollution by incorporating microplastics into the byproducts of metallurgical coal processing, particularly blending with the clean coal and flotation tailings. Through a series of laboratory-scale experiments, this study assessed the impact of blending common plastic types, such as high-density polyethylene (HDPE) and polycarbonate (PC), with different coal products and evaluating changes in Free Swelling Index (FSI), fluidity, ash content, and calorific values (CV) for these blends. Additionally, there may some opportunities in adding microplastic and avoid use of flocculant as there may be a possibility that microplastics may act as a flocculant, however, this needs to be further researched. Plastic production is an extremely energy-intensive process, requiring between 62–108 MJ of energy per kilogram, which is significantly higher than for materials like paper, wood, glass, or metals. In 2015 alone, plastic manufacturing used approximately 6% of the global electricity generated from coal. If current trends continue, by 2050, plastic production and processing could consume up to 20% of the world’s oil supply and 15% of the allowable annual global carbon emissions (Che & Heynderickx, 2024, p. 2). Given these high energy demands and the resulting environmental burden, the upgrading plastic waste into energy-rich solid fuels offers a valuable alternative. When plastics are converted into usable fuels or energy materials, they can partially replace the coal in industrial processes and help reduce reliance on the fossil fuels. This approach not only offsets emissions from the coal but also contributes to cleaner energy production. Since 73% of the human-made greenhouse gases (GHGs) come from energy, using the microplastics waste as fuel could also lower GHG emissions overall (Che & Heynderickx, 2024, p. 2). The accumulation of microplastics waste, has become a major global concern due to its environmental persistence and lack of efficient management strategies. Traditional disposal methods, like landfilling or incineration, can still contribute to more pollution and are unsustainable. At the same time, the growing push for a circular economy and alternative energy 39 sources has led scientists to explore ways to repurpose the plastic waste into clean energy products through innovative feedstocks (Che & Heynderickx, 2024, p. 3). In conclusion, repurposing microplastics into the carbon-rich solid fuels supports both environmental goals and industrial needs. For the coal industry, especially in metallurgical coal processing, this creates a viable pathway to blend microplastics waste with coal waste or by-products, improving fuel quality while reducing pollution are directly supporting the aims of this thesis. 5.1 Impact of Adding Microplastics to Metallurgical Coal Products The findings indicate that blending microplastics with high-quality metallurgical coal (such as flotation concentrate) negatively affects its fluidity, which is critical for coke formation. Although the addition of plastics did not significantly alter the FSI, the reduced fluidity makes the blend unsuitable for coking applications. As a result, this approach is not recommended for BC steelmaking-grade coal. However, when large amounts of microplastic was blended with fine coal flotation tailings (middlings) it was shown that by simply mixing microplastic with tailings there is a potential for alternative fuel applications. As shown in this work, blending HDPE with tailings led to a steady reduction in ash content and maintenance of high calorific value due to the high calorific value of HDPE plastic itself. As a result, samples blended with 10%–30% HDPE maintained or slightly showed an improved energy content. This indicates that microplastics can act not just as a filler but as a secondary energy contributor, enhancing the fuel’s heat output during combustion. 5.2 Integration at Mine Sites The proposed blending system as discussed in previous chapter, demonstrates the practical feasibility of this approach at the mine site. After flotation, the tailings are passed through a thickener, and then send to a filter press to form a dry cake. Crushed microplastics can be added either before or after that stage, requiring only minor modifications to existing coal preparation facilities. This blended product is then ready for transport and can be used in modern power plants, gasification systems, or even hydrogen production units. 40 This approach has multiple environmental and logistical benefits. It reduces the volume of plastic waste, minimizes the need for fine tailings disposal, and adds value to a waste stream that is otherwise challenging to handle due to high water content and low energy value. Fine coal particles typically retain moisture and are difficult to manage, but blending them with dry plastics improves handling while avoiding disposal in tailings ponds. Further research is required to optimize microplastic-coal blending ratios and explore adding different types of plastic, mixture of plastic from sources as plastic recycling facilities, or microplastic recovered at the waste water treatment plants. 5.3 Limitations One of the main limitations of this research is that only polycarbonate (PC) and high-density polyethylene (HDPE) were tested for blending with the coal. While the results indicate that these plastics contribute to reduced ash content and demonstrate potential for the integration, other common microplastic types still need to be examined to determine whether they produce similar results or not. Furthermore, microplastics in the environment are typically found as complex mixtures rather than as isolated polymer types. This diversity presents a challenge, as testing each type individually before further analysis and large-scale implementation is both time-consuming and resource-intensive. Future research should focus on evaluating a broader range of microplastics, including mixed compositions, to better understand their collective impact on the coal processing and further their effects on the carbonization. Understanding the interactions between various polymers and coal under thermal conditions will help establish clear guidelines for safe and effective blending. A pilot-scale trial at a coal preparation plant would be needed to validate the process beyond laboratory conditions. This would involve testing the performance of the microplastic-blended tailings in actual filter presses and observing their handling, drying behavior, and at the same time generating high-quality fuel in a real time. Another aspect of this type of trial could be to use the coal preparation plant as an investigational site to explore possibility of separating various mixtures of plastics by gravity because plastics like HDPE and PC have different densities 41 (Appendix D) or even by the froth flotation as both of these units are already being employed at these plants. This could facilitate not only separation of various plastics from each other, but possibly eliminating ones that are not desirable for blending with coal processing products at the plant or simply aid in segregation of various plastics from each other for further utilization elsewhere. From an energy recovery standpoint, further investigation into the most suitable combustion and gasification technologies, like circulating fluidized bed (CFB) boilers, plasma gasification units, or integrated gasification combined cycle (IGCC) systems is very essential. These systems vary in cost, efficiency, and environmental performance depending on the plastic type and fuel blend. Lastly, a more detailed techno-economic and lifecycle analysis (LCA) would help quantify the full environmental and financial impact of this approach, including greenhouse gas emissions, waste reduction, and long-term cost savings. This analysis should consider policy incentives, such as carbon credits or waste diversion programs, which may improve the viability of implementation at industrial sites. In conclusion, while this study shows that microplastics can be integrated into coal processing byproducts to create usable thermal fuels, a number of technical, environmental, and economic questions remain unanswered. Addressing these through further research and pilot testing will help unlock the full potential of this innovative and sustainable solution. 42 References Adeniyi, A. G., Amusa, V. T., Iwuozor, K. O., & Emenike, E. C. (2023). 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Procedia Earth and Planetary Science, 1, 807–813. https://core.ac.uk/download/pdf/82348877.pdf Zhou, M., Liu, C.-h., Meng, L., Wei, X.-m., & Zheng, Z.-l. (2009). Estimate research on co-carbonization of blend coal with waste plastics. Procedia Earth and Planetary Science, 1, 807–813. https://core.ac.uk/download/pdf/82348877.pdf 48 Appendix A Plastometer results 49 50 51 52 53 Appendix B Ash and moisture content of flotation stages Two stages of flotation were required to reduce the ash content of the coal to less than 10%. In the first stage three samples of the feed F, three samples of the concentrate CP and three samples of the tailings were taken and analyzed for moisture and ash content. The results are shown below. The ash content of CP is seen to be about 12%. First flotation stage In the second stage four samples of the concentrate C and two samples of the tailings T were taken and analyzed for moisture and ash content. The results are shown below. The ash content of C is less than 10% with an average of 9.24%. Second flotation stage Sample Crucible Crucible and coal Crucible and coal after drying for 1 h at 105-110 degreeCrucible and coal after treatement for 3h at 750Mass before Mass dried % Moisture M_ash M_Sample % AshF1 18.0451 19.0459 19.038 18.3019 1.0008 0.9929 0.7894 0.2568 0.9929 25.864F2 19.5921 20.5922 20.584 19.8483 1.0001 0.9919 0.8199 0.2562 0.9919 25.829F3 17.4222 18.4228 18.3806 17.6706 1.0006 0.9584 4.2175 0.2484 0.9584 25.918CP1 18.8005 19.8034 19.7934 18.9227 1.0029 0.9929 0.9971 0.1222 0.9929 12.307CP2 16.1551 17.1554 17.1463 16.2819 1.0003 0.9912 0.9097 0.1268 0.9912 12.793CP3 16.9027 17.9025 17.8941 17.0312 0.9998 0.9914 0.8402 0.1285 0.9914 12.961CP4 18.5584 19.5592 19.5506 18.6803 1.0008 0.9922 0.8593 0.1219 0.9922 12.286TP1 18.2411 19.2412 19.2344 19.0355 1.0001 0.9933 0.6799 0.7944 0.9933 79.976TP2 17.1326 18.1333 18.1262 17.7758 1.0007 0.9936 0.7095 0.6432 0.9936 64.734TP3 17.9244 18.9248 18.9169 18.701 1.0004 0.9925 0.7897 0.7766 0.9925 78.247Sample Crucible Crucible and coal Crucible and coal after drying for 1 h at 105-110 degreeCrucible and coal after treatment for 3h at 750Mass before Mass dried % Moisture M_ash M_Sample % AshC1 18.5569 19.5579 19.5502 18.6499 1.001 0.9933 0.7692 0.093 0.9933 9.363C2 18.2396 19.2404 19.2345 18.3362 1.0008 0.9949 0.5895 0.0966 0.9949 9.71C3 17.9229 18.9247 18.9177 18.0118 1.0018 0.9948 0.6987 0.0889 0.9948 8.936C4 16.9015 17.903 17.8971 16.9908 1.0015 0.9956 0.5891 0.0893 0.9956 8.969T1 18.0437 19.0459 19.0403 18.2856 1.0022 0.9966 0.5588 0.2419 0.9966 24.273T2 16.1545 17.1561 17.1492 16.4081 1.0016 0.9947 0.6889 0.2536 0.9947 25.495 54 Appendix C Results for clean coal product 55 Appendix D Calorific Value and Density of HDPE and PC According to technical documentation from Qenos eXsource, the calorific value of solid HDPE is approximately equivalent to 40.6 MJ/kg. The calorific value of polycarbonate (PC) is reported to be 30.34 MJ/kg according to Pillay et al. (2023), which analyzed the environmental impact and material properties of polymeric spectacle lenses. According to the data provided by Professional Plastics (n.d.), the specific heat of polycarbonate (PC) is approximately 1200 J/kg·K, and its thermal conductivity ranges between 0.19–0.22 W/m·K, with an upper working temperature of 115–130°C. For high-density polyethylene (HDPE), the specific heat is higher, around 1900 J/kg·K, and the thermal conductivity is also slightly higher, ranging between 0.45–0.52 W/m·K, with an upper working temperature between 55–120°C. (Professional Plastics, n.d.). The density of HDPE ranges between 0.954 and 0.960 g/cm³ (or 954 to 960 kg/m³), depending on the specific polymer grade and crystallinity (eXsource, n.d.). The density of unfilled polycarbonate (PC) is reported as 1.2 g/cm³ (or 1200 kg/m³) according to ASTM D792, as listed in the technical datasheet provided by International Polymer Solutions Inc. (n.d.). This reflects the compact and heavy molecular structure of PC, which includes aromatic rings and oxygen-containing carbonate groups. HDPE has a higher calorific value but lower density, while PC has a lower calorific value but higher density. These differences are rooted in their molecular structure and elemental composition. Calorific value measures energy released per unit mass during combustion, whereas density reflects mass per unit volume. Therefore, HDPE which usually consists only carbon and hydrogen atoms would allow for energy-enrich combustion as compare to PC, releasing more energy per kilogram. On the other hand, PC contains oxygen atoms (in carbonate groups) and aromatic rings, which are already partially oxidized. This results in lower net energy when burned because less additional oxidation (i.e., less energy release) is possible. 56 In terms of density, the opposite trend is observed: despite its name, HDPE has lower density because its molecular chains are long, straight, and lightweight, with no bulky atoms. PC has higher density due to its heavy molecular structure, which includes oxygen atoms and rigid aromatic (benzene-like) rings. These features increase the mass per unit volume, making PC denser than HDPE, even though it stores less energy per kilogram. 57 Appendix E Particle Size Distributions of Coal Feed and HDPE The particles were ground to the sizes smaller than 0.3mm (100% passing 300µ) to match the flotation particle sizes at the operating mines, the coal feed for flotation was P80=130µ (80% of particles passing) and d50=55µ (50% of particles passing) obtained from Particle Size Distribution (PSD) analysis by sieving and plotted on cumulative basis. The produced microplastic had P80=255µ and d50=175µ obtained from Particle Size Distribution (PSD) analysis by sieving and plotted on cumulative basis.
Thesis/Dissertation
eng
Mining Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Holuszko, M. E.
Mitigation of microplastic pollution by blending with products of metallurgical coal processing
Text