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About this book

This book presents the state of art of the several advanced approaches to beneficiation of coal. The influence of recent technology attains the advantages of processing coal, purification studies, rheological behavior, and the mineral beneficiation. The experts collected in this volume have contributed significantly to the enrichment in the in depth knowledge not only in context of working knowledge, but also future prospects of clean coal technology.

Table of Contents


Chapter 1. Mineral Beneficiation and Processing of Coal

Coal plays a vital role in steel production and electricity generation. In recent times, coal production has been increased multiple times as the demand for steel and energy increased. Presently, about 41% of the world’s electricity requirements are met by thermal coals. Increased utilization of coal doubled carbon dioxide emission to the atmosphere, which necessitates the development of green methods for coal utilization. The coal preparation techniques are eco-friendly and are advantageous in mitigating the release of harmful toxic gases into the atmosphere. In this chapter, coal preparation techniques employed in the generation of clean coal for various applications are briefly discussed. Present-day coal washeries are equipped with various advanced equipment related to the sizing, concentration, clarification, and drying. The prime objective of the coal preparation is to separate the clean coal at the coarsest possible size. Conventional gravity separators, such as Jigs and dense media cyclones, are very common for treating coarse particles. Whereas, processing of fine particles could be achieved following advanced gravity concentrators and froth flotation techniques. Processing fine particles is a challenging task, which adds to the operating cost and increases associated handling problems. The chapter also sheds light on the plant practices adopted to treat different coals and modular plants.
Tonmoy Kundu, Surya Kanta Das, Dinesh Kumar Biswal, Shivakumar I. Angadi

Chapter 2. Natural Dispersant in Coal Water Slurry Stabilization

The stabilization of a coal-water slurry, which is a concentrated mixture of powdered coal and water, is popularly known as coal-water liquid fuel, and the maintenance of its suitable rheological characteristics necessitates the production of well-dispersed solid coal particles in water. The development of the chemical dispersant or natural dispersant is highly essential for coal water slurry (CWS) stabilization as CWS is gaining importance due to versatility and simplicity of technology involved during the process. This chapter describes the preparation and stabilization CWS by using two natural surfactant. Detail about isolation and characterization of natural surfactant Sapindous laurifolia and Sapindous mukorossi has been discussed. The non-Newtonian nature of the slurry is discussed by variation of coal concentration, natural dispersant concentration, temperature, pH and surface charge of the slurry. Interaction between coal surface and saponin of natural dispersant has been discussed by a suitable mechanism.
Debadutta Das, Prativa Kar, Bijnyan Ranjan Das, Ranjan Kumar Mohapatra, Subrata Narayan Das, Pankaj Kumar Parhi, Umakanta Behera

Chapter 3. Application of Biotechnological Approach for Making Coal an Environmentally Friendly Fuel

Coal is one of the prime sources for energy generation across the globe. The environmental concern with coal is accompanied by sulphur dioxide emission from its combustion. The SO2 emission can be minimized by reducing sulphur concentration of coal before the combustion process. Out of physical, chemical and biological approaches, the latter is considered to be more feasible for sulphur removal due to its economical-viability and environmentally friendly endeavour. Coal contains sulphur in organic and inorganic forms (mainly as pyrite) which can be removed by heterotrophs and acidophiles, respectively. Acidophiles that thrive in acidic environment are iron oxidizers and solubilize pyritic through Fe3+ generation whereas heterotrophs remove organic sulphur by converting it to sulphite form via 4S pathway. The prominent acidophiles for pyrite removal are Acidithiobacillus ferrooxidans (A. ferrooxidans) and Leptospirillum ferrooxidans (L. ferrooxidans) while Rhodococcus erythropolis (R. thryopolis) is a major heterotroph for organic sulphur removal. Several biological studies have been performed reporting about 50–80% of pyritic sulphur removal and 46–90% of organic sulphur removal. However, the biological process being a slow process needs to be considered for further improvements, viz., improvement in the metabolic pathway of sulphur removal, development of improved microbes by recombinant DNA technology, integration of different relevant process along with bio-desulphurization, use of modified or biphasic nutrient medium for making the process more relevant for industrial and field-scale application.
Haragobinda Srichandan, Puneet Kumar Singh, Pankaj Kumar Parhi, Snehasish Mishra

Chapter 4. Oil Agglomeration Towards Quality Enhancement of High-Ash Coals: The Indian Scenario

Beneficiation of high-ash coals has been a topic of great concern around the world. There has been considerable research aimed at development of highly effective yet economically viable ways to perform coal beneficiation. At present, coal cleaning is primarily accomplished through physical separation of mineral matter from coal particles. However, the known processes like jig, density separation and froth flotation typically demineralizes coarse coal particles. The only two techniques which can handle coal fines are froth floatation and oil agglomeration; nevertheless froth flotation fails for ultra-fine coals (<6 μm). Oil agglomeration is an excellent and versatile technique to beneficiate ultra-fine coals which utilizes the difference in surface hydrophobicity of coal particles and mineral matter. The growth of agglomerates is essentially determined by acceleration and particle velocity of water and oil molecules. Our chapter will be discussing the several physical parameters on which the process of oil agglomeration largely depends on. In particular, focus will be given on the present scenario in India with respect to the research and development of oil agglomeration.
Saswati Chakladar, Ashok Kumar Mohanty, Sanchita Chakravarty

Chapter 5. Preparation of Coal-Derived Activated Carbon and Its Application for Adsorption of Metals from Aqueous Solutions

This chapter compiles the studies on the preparation of coal-derived activated carbon (AC) and its application for adsorption of metal ions in aqueous solutions. The general methods for preparation of coal-derived activated carbon can be divided into two categories: physical and chemical methods. The effects of pretreatment of the coals, coal and activating agent types and thermal treatment parameters (temperature, heating rate, reagent dosage, and holding time) on the properties of the produced activated carbon were reviewed. The kinetic aspects while compiling the mathematical models of the carbonization and activation of coals were also presented. It is evident that coal is an excellent activated carbon precursor for the advantages of high carbon content, inexpensive, large availability in nature, and readily primary pores; the obtained activated carbon is successful to be applied for adsorption of metal ions in such aqueous solutions. Perspectives were also discussed with pertinent issues in the preparation of coal-derived activated carbon as the guideline for future works. Using coals as the activated carbon precursor could be part of contributors towards clean coal technology.
Kurniawan, Sookyung Kim

Chapter 6. Characteristic and Equilibrium Adsorption Studies of Biochar

In this chapter, response to the elimination from their water flows of carbofuran was checked by the dried capsicum annuam biochar (CABC). Char at 300 °C is produced from capsicum annuam stem to eradicate carbofuran from the watershed system. Capsicum annuam (CA) and capsicum annuam biochar (CABC) were tested for their physicochemical characteristics. The experiments were performed for different carbofuran concentrations, with varying CABC dosages, pH values, and adsorption time. Different isotherms and kinetic models were investigated to determine the adsorption equilibrium.
Vijetha Ponnam, Subbaiah Tondepu, Rajesh Kumar Jyothi

Chapter 7. Bio-Desulfurization of Coal Using Biotechnological Approach, Making Coal a Less Harmful Fuel

Combustion of raw coal can generate energy which can be used for commercial purpose. As energy from natural gas or crude oil is available in high price, the demand of harvesting of coal for energy is high. So many countries have high resource of coal but they cannot utilize it because of high amount of sulfur oxides emission which can be the cause of serious environmental problems. Combustion of coal generates high amount of sulfur dioxides which also incite the acid rain by mixing with in the atmosphere. To use the coal as energy it is required to reduce the emission of toxic sulfur oxides which can be useful to contribute in sustainable development. The removal of sulfur from coal is difficult for so many reasons, mainly for the complicated structures. Many technologies have been developed to clean coal for improving and encouraging the utilization of coal. Recently, biological process of desulfurization took a big step towards the development of clean coal technology. The basic concept of different technologies for desulfurization has been discussed in this study.
Hafiz Ahmad Ishfaq, Ayantika Banerjee, Sanaullah Qamar

Chapter 8. Environmental Benign Biochar Technologies: Strategic Utilization for CO2 Capture and Wastewater Treatment

Water pollution particularly caused by heavy metal ions and anionic contaminants even in trace amount can pose catastrophic impact on all living organisms. As these contaminants are mostly non-biodegradable and can transformed into complexes, adsorption is a most auspicious technique in recent times. Biochar, a sustainable and low-lost product, synthesized from thermochemical conversion of biomass has attracted research attention with its adsorption prospects of wide range contaminants. However, challenging recovery and often deficient adsorptions forced researchers to develop modification techniques to upgrade the physicochemical characteristics of biochar. These modifications can enhance biochar chemical interactions such as electrostatic attraction, surface complexation, ion exchange, and induction of functional groups. This chapter mainly focussed on the effectiveness of different thermochemical conversion techniques, biochar modifications, and an overview of biochar applications for the efficient removal of heavy metal ions and anionic contaminants from wastewater.
Mohd Danish Khan, Ji Whan Ahn

Chapter 9. Role of Nanomaterials: Enhancing the Adsorption Efficiency of Activated Carbon in Wastewater Treatment

Water is a vital source for every living organism, and it is very much concerned that it is getting depleted in both surface and groundwater. In the present scenario, the waste from both point and non-point sources increases, thereby increasing pollutants’ levels in the water. It is very much needed to this hour that the removal of pollutants with an efficient process could be cost-effective. Many processes have been used to remove pollutants such as activated carbon, limestone, clay, alumina, and silica gel. However, our view mainly focuses on activated carbon. This chapter gives a brief view of the nanoparticle role in enhancing activated carbon efficiency to remove both inorganic and organic pollutants. Discussion includes the current use of activated carbon or modified granular activated carbon (GAC), various nanoparticles, and their combination in wastewater treatment. A significant analysis of the literature is presented, giving weightage on recent advances that may lead to the more complete and feasible use of AC to remove pollutants (both organic and inorganic) from polluted water.
Kiranmai Reddy Majji, Venkata Naga Suresh Reddy Kachireddy, Shashi Kumar Kuruva Nandyal, Sreenivasa Rao Battula

Chapter 10. Adsorption of Metals Using Activated Carbon Derived from Coal

Many industrial activities adversely affect the human health and environmental system. Wastewater containing high levels of pollutants such as metals is one of them. Nowadays metal pollution is the most concerned environmental problem. Various metals mainly mercury, cadmium, chromium, lead, copper, and arsenic present in wastewater are toxic and carcinogenic in nature. Coal-based activated carbon is favourable candidate for removing of toxic metals because of its high adsorption capacity compared to activated carbon (AC) derived from other sources. In this chapter, adsorption of metals present in wastewater using activated carbon is discussed. Furthermore, adsorption isotherm models, i.e. Langmuir or Freundlich, and adsorption kinetics model, i.e. pseudo-first order or pseudo-second order that commonly describe adsorption behaviour, are discussed. Further, the various factors affecting performance of AC to adsorb metals like the pH of solution, activated carbon impregnation, oxidation state, and temperature are discussed.
Parag Girhe, Divya Barai, Bharat Bhanvase

Chapter 11. Generation, Transportation and Utilization of Indian Coal Ash

This chapter describes the generation of coal ash from Indian thermal power plants, its stabilization for pipeline transportation and its utilization as fly ash bricks. For the disposal of coal/fly ash (high concentration) a detail investigation of rheological behaviour is required. The rheological characteristics of fly ash (FA) samples are studied with some natural and synthetic surfactant systems. Presence of surfactant reduces viscosity of the slurry and also increases the wetting properties of solid particles. Moreover, the surfactant role of bottom ash as a viscosity reducing agent is also discussed herewith. Furthermore, the detailed characterization and its utilization as fly ash bricks (FAB) have also been discussed.
Ranjan Kumar Mohapatra, Pradeep Kumar Das, Dulal C. Kabiraz, Debadutta Das, Ajit Behera, Md. Kudrat-E-Zahan

Chapter 12. Studies on Extraction of Heavy Metal (s) from Fly Ash through Hydroprocessing Approach

Management of fly ash is a global challenge at present scenario due to its huge generation from various industries. Due to direct disposal into the environment process, it becomes serious concern in context contamination vis-a-vis loss of valuable metals. To overcome these issues the valuable metal as well as toxic heavy metals can be recovered and/or removed through various environmental friendly hydrometallurgical methods. The key economical prospective of fly ash caused by claiming of rich resources of valuable metals though concentration profile is limited unlike other secondary phases. The leaching method is often adapted to extract the metals utilizing mineral and organic acids. The characterization of fly ash sources is studied to ascertain physical and chemical properties. The two major aspects on treatment of fly ash are illustrated that includes (a) removal of toxic heavy metals and (b) extraction of valuable metals. This chapter is intended to bring the insight on critical analysis on physico-cum-chemical nature of fly ash, its effect towards environment and mainly of leaching process optimization studies on extraction of numerous heavy and toxic metals. The present status of fly ash treatment through hydrometallurgical extraction of metal values in Indian context as well as global scenario has been extensively overviewed and reported.
Saroj Sekhar Behera, Surendra Hansdah, Debadutta Das, Pankaj Kumar Parhi, Rajesh Kumar Jyothi

Chapter 13. Investigation on Extraction and Recovery of Rare Earth Elements from Coal Combustion Products

The present chapter displays an overview of rare earth elements properties, deposits, trend charts about global REEs production, reserves from 2009 to 2019, and shows a comprehensive review on the REEs production and consumption of the lead countries like China. In the second part, the author describes how the rapid surge in global energy needs has augmented the demand on coal-based energy and consequently the production of coal combustion products. This chapter further provides the trend charts associated with global volume of coal combustion products (CCPs), their utilization, total production in countries such as the USA from 2009 to 2018, and how this waste could be a potential resource to recover rare earth elements.
From an environmental point of view, the author presents a review about the impact of air emissions and water contamination owing to the inadequate management of the disposal of CCPs as well as limits and regulations for CCPs in the principal producer and consumer countries. Finally, the author emphasizes on the current necessity to make an effort to find new alternative resources for the extraction of REEs. In addition, the chapter present a systematic summary of the primary methods to recover the REEs from CCPs such as alkaline-acid leaching, roasting, physical separation, bioleaching, and ion extraction processes and their advantages and disadvantages were discussed.
Verónica Cristina Arellano Ruiz, Pankaj Kumar Parhi, Jin-Young Lee, Rajesh Kumar Jyothi

Chapter 14. Recovery of Rare Earth and Some Other Potential Elements from Coal Fly Ash for Sustainable Future

Coal is considered as an important fossil fuel to produce electricity and contributes for the production of nearly 40% of the total electricity worldwide. The coal fly ash generated from combustion of coal is an important source of valuable metals, especially rare earth elements but leads to environmental hazard if left untreated. Therefore, treatment of CFA helps to minimize environmental risk and provide an alternative way to support the demand and supply of valuable metals in order to conserve primary resources. In the last decade, many reports have appeared in the literature for the REE and some other metals recovery from CFA. In this chapter, the methods developed by researchers over the last decade for the recovery of REE and some other elements have been described with their achievements and shortcomings.
Harshit Mahandra, Brendan Hubert, Ahmad Ghahreman

Chapter 15. Coal Fly Ash Utilisation and Environmental Impact

The global power generation is dominated by coal (38%) followed by natural gas (23%), hydro (16%), nuclear (11%), wind (5%), oil (3%), solar (2%) and biofuel (2%) in 2019. The coal-fired power generation creates coal ash (fly ash—85% and bottom ash—15%) nearly 1 billion tonne annually. Although the coal ash was considered waste and dumped as land fill, the application of fly ash in various fields has created around 4 billion US dollar global market in 2020 with the predicted annual increase of 6%. Despite industrial-scale utilisation, limited information is available on potential value-added material extraction from the coal fly ash. This book chapter reviews the current industrial-scale utilisation of coal ash. The paper also undertakes a case study of coal ash utilisation in an emerging nation, as most emerging nations are expected to leverage coal as cheap energy source for power generation to accelerate their industrial and economic development. Furthermore, an analysis on potential metal (including rare earth element) value contained in coal fly ash has also been undertaken to highlight its economic value. The increased industrial-scale utilisation and potential extraction of metal from coal ash ensures a win–win situation for environment, economy, and supplementation of global rare earth element stock.
Shanjida Sultana, Saifuddin Ahsan, Sakib Tanvir, Nawshad Haque, Firoz Alam, Mohan Yellishetty

Chapter 16. Utilization of Circulating Fluidized Bed Combustion Fly Ash for Simultaneous Recovery of Rare Earth Elements and CO2 Capture

Rare earths is an intrinsic requisite for clean-efficient technologies. The unsecured supplying source and the necessity making rare earth elements are critical. Accordingly, numerous hunts commence toward exploration of minable ore deposits, unconventional sources, and substitutions. However, conventional rare earths production seems to be unrealistic due to various economic and environmental obstructions, whereas, the unconventional sources have proposed potential alterations for rare earths. Coal fly ash are universally perceived to be the most viable source of rare earths recovery within all kinds of possibly alternative sources. This chapter intentionally studies the properties of coal fly ash with respect to rare earths occurrence. Ongoing techniques regarding rare earths recovery from Circulating Fluidized Bed Combustion coal fly ash and the incorporation of carbon mineralization process were reviewed.
Quang Tuan Lai, Thriveni Thenepalli, Ji Whan Ahn

Chapter 17. Developments in Characterization and Mineral Processing of Coal Fly Ash for Recovery of Rare Earth Elements

Coal Fly Ash (CFA) is a promising technospheric resource of rare earth elements some of which are designated as critical metals in various countries due to their role in materials of contemporary significance, particularly in green energy technologies. The average REE content in CFA is about 0.05%. Due to the availability of huge volumes of CFA worldwide, focussed R&D efforts are being made to extract REEs from them along with various other valuable metals. It is the endeavour of all researchers involved to develop process schemes which are environmentally benign. Attaining such objective necessitates deeper understanding on the deportment of REEs in the feedstocks, possibility of pre-concentrating the valuables by physical beneficiation techniques and use of hydrometallurgical techniques which deploy bio-degradable or green solvents, enhancing the recyclability of reagents and conserving the process water. An important aspect in CFA utilization is to preserve the pozzolanic properties of CFA intact such that its bulk uses are not destroyed during the process of REE extraction. This chapter gives an overview on the developments in characterization of REEs in coal fly ash, strategies explored for their extraction and conceptual flowsheets developed on various feedstocks of CFA in different countries with added emphasis on Indian scenario.
Tumuluri Sreenivas, Md Serajuddin, Ramkaran Moudgil, Kacham Anand Rao

Chapter 18. Coal Burn Ash: A Sustainable Future Resource for Critical Metals Production

In view of increasing global demand of rare earth metals (REMs), less availability and limited natural resources compelled the researchers to develop the feasible processes to recover REMs from alternative secondary resources. Present book chapter is focused to explore possibility of coal bottom ash utilization for REMs extraction as well as highlights the hydrometallurgical processes for the selective separation and recuperation of REMs from alternative sources carried out at CSIR-NML, India, in collaboration with KIGAM, South Korea. REMs containing coal and its by-products are need to be beneficiated, thus require grinding to release the encapsulated REMs which are interlocked with host particle. REMs recovery process consists of beneficiation-leaching and advance hydrometallurgical separation processes. Coal ash will have tremendous possibility for commercial exploitation of REMs after scale-up and pilot trials.
Manis Kumar Jha, Archana Kumari, Rekha Panda, Rukshana Parween, Sanchita Chakravarty, Rajesh Kumar Jyothi

Chapter 19. Characterization and Utilization of Coal Ash for Synthesis of Building Materials

During the thermal power production, the combustion of coal results in coal ashes as waste products, viz. fly ash (FA) and bottom ash (BA). Considering the fact that the major part of the power comes from thermal power plants, a huge amount of coal ashes are generated that cause serious issues for its disposal. Extensive efforts have been made to utilize these ashes for different applications in bulk amount, and building material manufacturing is one of them. Therefore, in this chapter, the characterization and utilization of coal ashes in building material synthesis are discussed with providing a critique on the challenges and future trends of coal ash utilization.
Shaswat Kumar Das, Subhabrata Mishra, Debadutta Das, Syed Mohammed Mustakim, Cyriaque Rodrigue Kaze, Pankaj Kumar Parhi

Chapter 20. Prospective Utilization of Coal Fly Ash for Making Advanced Materials

Coal waste is a fine glass-like solid residue or by-product of the thermal power plant generally collected from the electrostatic precipitator (ESP-2) before flue gas reach out chimneys. As a consequence of time, the overall generation of coal fly ash (CFA) from different domains is being increased worldwide and becomes a very serious environmental issue on its disposal which creates direct effects on soil, air, and water. Though in most of all cases the coal waste (FA) is being used as a land filler for road making, which also causes a substantial threat for the environment owing to bearing toxic metals and other inorganic minerals in it. Therefore, researchers attempted to develop many methodologies for major utilization of these coal wastes after recovering metal values through a suitable leaching processing approach. The CFA resulted from thermal power plant act as the effective product and get attention as the potential raw materials having less harmful, less toxicity afterconverting it to valuable products or substitute raw materials to manufacture valuable products. Presently over 300 Million Tons of FA is being generated worldwide from the thermal plant sectors, but that accounts only about 10–30% of overall FA production is being used worldwide for developing valuable products. Due to the impactful conversion of coal waste to valuable products, environmental pollution is decreasing day-by-day. The various types of useful products from CFA have already been existed in global markets (like Cement, Bricks, and Tiles), and some are under developmental and experimental stages (Matrix membrane, Biodiesel production, lightweight wall element, and lathy tobermorite fiber).
Aritra Kumar Dan, Dipanjan Bhattacharjee, Saikat Ghosh, Saroj Sekhar Behera, Birendra Kumar Bindhani, Debadutta Das, Pankaj Kumar Parhi

Chapter 21. Biochar Production for Green Environment

Several researches of biochar application on improvement of soil quality, soil nutrients and plant growth have been developed in a significant way, in the past few years. Organic matter usually generated from plants and animal wastes called as feedstock has a great capacity to use as an alternative source of energy by following thermochemical conversion technology. Biochar has different physiochemical characteristics which has a good influence on soil agro-ecosystem. Waste management is a huge problem in recent days. To produce biochar from wastes is a great process of utilization of different type of wastes and that follows the environmental sustainability. Biochar is a carbon-rich material which has a good quality to reduce the emission of GHG. The quality of biochar generally dependent on the characteristics of biomass and also the process follows the conversion mechanism. The process parameters are reactor configuration, heating and flow rate, elemental arrangement of biomass, particle size, catalyst, etc. Biochar also has many other characteristics including high C percentage, large surface area, high stability and high porosity, and many research areas developed on this sector of biochar amendment on soil.
Ayantika Banerjee

Chapter 22. Distribution of Rare Earth Elements in Coal and Coal Fly Ash

Rare earth elements are strategic elements, extensively used in hybrid cars, power generators, powerful magnets, electronic gadgets, super alloys, etc., to enhance their performance. They are associated with minerals like bastnasite, monazite, zircon, allanite, xenotime, florencite, and rhabdophane. REEs are present in copious amount than valuable metals like (platinum, gold, and silver) in earth’s crust. China has maximum reserve of REEs in the world and has a greater influence over global market of REEs. China covers more than 90% of global supply therefore has monopoly over REEs trade. These factors led the researcher around the globe to find alternative options for recovery of REEs from secondary sources. Coal fly ash (CFA) is one such resource having 300–500 mg/kg of REEs globally. It is very essential to figure out the distribution of REEs, in coal fly ash in order to develop effective methods to recover REEs. This study is beneficial for enhancing the knowledge about the presence and abundance of REEs in different coals, coal fly ash, and various extraction procedures to recover them from coal fly ash.
Sanjay Agarwal, Vishal Kumar Dubey, Kyung Ho Park, Jin-Young Lee

Chapter 23. Recent Development in Metal Extraction from Coal Fly Ash

Coal fly ash (CFA) represents from 40 to 90% of total coal combustion products (CCPs) generated in thermal power stations (Zierold and Odoh, Reviews on Environmental Health 35:401–418, 2020). As the most abundant fossil fuel, coal still contributes to the production of approximately 36% of the electricity used globally in 2019, despite the current trend in reducing CO2 emission by transition to alternative energy resources (Harris et al. Global aspects on coal combustion products. In: World of Coal Ash Conference, Conference Paper, 2019; IEA, Coal-fired power, 2020). The global coal consumption in 2019 decreased by 1.2% in 2019 with China as the major consumer of 2866 mtce comprising 53.0% of the global share (IEAgency, IEA Energy Atlas. International Energy Agency, 2020). India, USA and Europe follow in the second, third and fourth place with 583, 397 and 253 mtce, respectively.
Hong Vu, Tomáš Frýdl, Tadeáš Bastl, Petr Dvořák, Eva Kristianová, Tomáš Tomáško

Chapter 24. Application of Geochemical Modeling in Rare Earth Elements Leaching of Coal Combustion and Secondary Residues

Geochemical modeling offers the opportunity to predict the extraction behavior of rare earth elements (REEs) from secondary resources, as well as to mechanistically confirm the governing reactions that control leachability and speciation. In this chapter, several studies on the extraction and recovery of REEs from coal combustion residues and mining wastes, where geochemical modeling was utilized, are reviewed. The motivation of each study is discussed and compared, the methodologies utilized in each study are summarized and contrasted, and the main results obtained in these studies are described. Elements of interest for recovery from secondary resources, due to their economic value and relative scarcity, include light (e.g., Nd), middle (e.g., Tb) and heavy (e.g., Er) REEs, in addition to scandium and yttrium. Furthermore, the role that geochemical modeling has to play in environmental studies cannot be overemphasized, and is topic of discussion throughout. Future studies on the geochemical modeling of REEs will likely investigate the leaching kinetics and the long-term stability of REEs in waste storage sites, especially as the capability of geochemical modeling software and the comprehensiveness of thermodynamic databases expand to include the needed tools and data for these types of studies.
Joyce N. Odimba, Rafael M. Santos

Chapter 25. Ionic Liquids for the Recovery of Rare Earth Elements from Coal Combustion Products

Rare earth elements, by virtue of their role in technological advancements, have become critical commodities over the last few decades. The emerging awareness of environmental pollution associated with primary ore mining and the need for processes to preserve these non-renewable minerals, coupled with the attempt to break China’s monopoly of the REEs production and commercialization, has led to research into alternative sources. The crusade for beneficial use of coal combustion products and the proposal that these CCPs are REE-rich sources have therefore received a widespread attention among other alternatives. This chapter seeks to explain the feasibility of the extraction of REEs from CCPs using ionic liquids. The ability to modify ILs to suit the application necessities allows for extraction at better experimental conditions reducing the overall waste generation of the process. Different types of ionic liquids have been studied for rare earth elements recovery and recycling from secondary sources (scraps, electronic waste) using nonfunctional, monofunctional, and bifunctional ionic liquids. However, the recovery of REEs from the by-products of coal combustion has not been studied in depth despite of them being a rich source of these technological key elements.
Isaac Kwabena Danso, Ana Belen Cueva-Sola, Zubair Masaud, Jin-Young Lee, Rajesh Kumar Jyothi


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