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Introduction

Coal is the most abundant type of fossil fuel, accounting for 64% of globally recoverable resources in the world, compared to oil (19%) and natural gas (17%). Coal is traditionally used in the energy sector, generating about 40% of the world's electricity. The demand for coal is expected to increase by over 60% from 2006 to 2030, of which developing countries will account for over 90%. Coal-fired electricity generation is still a major energy source in North America and Australia. In addition, coal is also used in the metallurgical sector, where 70% of the world's steel industry depends on it. The challenge here has been in how to maximize productivity, reduce energy consumption, and drastically reduce carbon dioxide (CO2) emissions (Osborne and Gupta 2013). Efforts have been made to offer a more efficient and cleaner use of coal, including its use in the production of electricity, steel and its associated products, and energy-related chemicals, as well as increasing the use of coal byproducts (Osborne et al. 2013). While significant progress has been made, it is still worth seeking new environmentally friendly and efficient usages of coal beyond these well-known applications. Such usages are not set to immediately replace the existing applications of coal, however, but instead provide alternatives so that whenever the opportunity arises, new market sectors can be generated and expanded as quickly and efficiently as possible.

Among different coal materials, low-rank coal has been one of the most discussed and has seen its popularity grow in recent years. This is in part because of its unique yet challenging nature, and because of its versatile applications. Low-rank coal contains lower calorific values than those of anthracite, bituminous, and subbituminous. However, it is rich in organic matter (OM) and humic substances (HS, or "humic") that have been proven to be beneficial for several different purposes. Unfortunately, these purposes have so far been largely unrecognized or misunderstood. This is chiefly because they fall outside of the scope of the usages that people are more familiar with when it comes to coal materials. In the province of Alberta, for example, low-rank coal has been recommended as a source of calories for electricity generation (Alberta Energy 2017).

The main purpose of this book is to show that low-rank coal can be commercialized and marketed in sectors beyond those in which it is currently employed, such as electricity generation. Consequently, the new usages of this type of coal should be championed as a more efficient and cleaner way forward. As summarized below, at least four alternative usages have been identified, while others are possibly to follow in the near future.

The first alternative usage of low-rank coal is in oil/gas drilling. In this sector, drilling fluid is required to protect the stability of the wellbore from fractures, pores, and other openings. It is needed to transport cuttings for their separation at the surface, suspend solids within the fluid, and maintain stability of uncased sections of the borehole. In the water-based drilling fluid system, colloidal materials (i.e. clay) are added to the fluid to reduce water loss through the porous media of the formation. However, this may result in an increase in the drilling fluid viscosity, reducing its rate of penetration. This can be compensated for by adding low-rank coal to deflocculate the fluid, reducing both its viscosity and also reducing water loss. In the oil-based drilling fluid system, low-rank coal is added as an emulsifier, resulting in smaller droplets of a high film strength. A reduction of water loss is achieved with a minimal increase in viscosity (Dearing et al. 2004 and Caenn et al. 2017). Low-rank coal has been used more commonly in the water-based system as a thinning/dispersant and secondary filtration control agent. At high temperatures, this material performs better than that of lignosulfonates (Canamara-United Supply Ltd. 2001).

The second alternative usage of low-rank coal is in mining remediation. This sector deals with the presence of inorganic and organic contaminants that lead to a decline in soil quality. There are two in-situ treatment methods available for the contaminated soil: bioremediation and phytoremediation. Bioremediation relies on microbial metabolism of contaminants, while phytoremediation relies on uptake and processing by plants (Fangueiro et al. 2018). Low-rank coal has been found to be effective when added as a soil amendment, enhancing the growth of soil organisms and accelerating the breakdown of organic contaminants (Liem et al. 2003a). It has been found to be effective in increasing plant cover grown in mining tailings ponds after several years of treatment (Szczerski et al. 2013). In the laboratory, low-rank coal has been reported to improve the chemical and physical properties of soil (Bekele et al. 2013; Liem et al. 2003a and 2003b).

The third alternative usage of low-rank coal is in foundry. This sector concerns metal casting, which includes melting, molding, casting, solidification control, and other post-casting processing operations. Greensand (clay and water) is a molding material commonly used in the industry, in which impressions of the molten material can be formed (Campbell 2015). Between uses, water is added to the sand and later mulled (mixed and smashed) in order to regenerate it. During this step, when low-rank coal is added to the blend, it has been found to reduce clay viscosity, as well as improving mulling efficiency, mold permeability, water retention, and shakeout efficiency. This material does not affect clay durability, and in fact lowers foundry emissions by reducing the amount of smoke in the cooling line (Van Leirsburg 1999).

The fourth alternative usage of low-rank coal is in agriculture. This usage is what this book is all about. In this context, agriculture is defined as any practices related to the improvement of soil, crops, and livestock productivity. The emphasis is on the content of HS within the material, in which commercial products can be manufactured, i.e. soil amendments and feed supplements. HS are active ingredients that have been scientifically proven to enhance the productivity of soil, crops, and livestock. The main objective of this book is to show that not only does low-rank coal benefit agriculture, but also that avoiding its use in electricity generation will result in the reduction of CO2 emissions. This can be seen as a win-win scenario with respect to both the coal and agricultural sectors, thus improving environmental credentials of the coal industry.

Before going into the detail of this proposal, it is essential to understand the properties of different coal materials. Those who are not familiar with the sector will most likely associate low-rank coal with other coal materials (especially with their potential hazards) and therefore question the feasibility of its having a green use. Chapter 2 discusses the unique physical and chemical properties of low-rank coal. In this book, low-rank coal is defined as a type of coal with lower calorific values (19 300 kJ/kg or less) compared to those of anthracite, bituminous, and subbituminous (with calorific values of 19 300 to 34 900 kJ/kg). This material falls under the category of lignite (including its weathered/oxidized form, i.e. leonardite), which is in the bottom rank among all coal materials. The main information in this book comes from a concern with low-rank coal from Alberta (also identified as humalite), which is in the author's line of work. It contains only small impurities and is therefore a good-quality material. This material has been found to be non-hazardous with respect to its contents as well as its handling.

While low-rank coal contains lower calorific values, it is rich in OM and HS. These are the determining parameters with respect to the benefit of this material in agriculture. Since HS are complex in nature and have unique physical and chemical properties, the various methods for their analysis must be understood and compared with respect to their accuracy and practicality. The colorimetric and gravimetric methods are the most popular in the commercial community due their (relative) simplicity and accuracy, while others are more popular within a theoretical or research context. Different low-rank coal materials are analyzed for their humic components and compared to one another. The main focus of Chapter 3 is on original work completed using both the colorimetric and gravimetric methods, which resulted in the modification of the International Organization for Standardization (ISO) 19822 method. This chapter also presents work on the comparison of various commercial OM products available on the market. Products to be evaluated include dry and liquid humic products, biochar, calcium lignosulfonate, soybean extract, peat moss, and molasses. These are humic and non-humic products of similar properties, which are commonly mistaken for one another.

Chapter 4 summarizes the benefits of HS in agriculture and includes information on their background science. Due to the vast collection of information and existing data on soil, crops, and livestock available from public domains, a literature review is provided. Firstly, saline and compacted soils have commonly been problematic in commercial fields in that they lower productivity. The use of HS has been found to improve the...