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Review

Status of Coal-Based Thermal Power Plants, Coal Fly Ash Production, Utilization in India and Their Emerging Applications

by
Virendra Kumar Yadav
1,
Amel Gacem
2,
Nisha Choudhary
3,
Ashita Rai
4,
Pankaj Kumar
5,
Krishna Kumar Yadav
6,*,
Mohamed Abbas
7,8,
Nidhal Ben Khedher
9,10,
Nasser S. Awwad
11,
Debabrata Barik
12 and
Saiful Islam
13
1
Department of Biosciences, School of Liberal Arts & Sciences, Mody University of Science and Technology, Lakshmangarh, Sikar 332311, Rajasthan, India
2
Department of Physics, Faculty of Sciences, University 20 Août 1955, Skikda 21000, Algeria
3
Department of Environmental Sciences, P P Savani University, Surat 394125, Gujarat, India
4
School of Environment and Sustainable Development, Central University of Gujarat, Gandhinagar 382030, Gujarat, India
5
Department of Environmental Science, Parul Institute of Applied Sciences, Parul University, Vadodara 391760, Gujarat, India
6
Faculty of Science and Technology, Madhyanchal Professional University, Ratibad, Bhopal 462044, Madhya Pradesh, India
7
Electrical Engineering Department, College of Engineering, King Khalid University, Abha 61421, Saudi Arabia
8
Electronics and Communications Department, College of Engineering, Delta University for Science and Technology, Gamasa 35712, Egypt
9
Department of Mechanical Engineering, College of Engineering, University of Ha’il, Ha’il 81451, Saudi Arabia
10
Laboratory of Thermal and Energy Systems Studies, National School of Engineering of Monastir, University of Monastir, Monastir 5000, Tunisia
11
Department of Chemistry, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia
12
Department of Mechanical Engineering, Karpagam Academy of Higher Education, Coimbatore 641021, Tamil Nadu, India
13
Civil Engineering Department, College of Engineering, King Khalid University, Abha 61421, Saudi Arabia
 
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Author to whom correspondence should be addressed.
Minerals 2022, 12(12), 1503; https://doi.org/10.3390/min12121503
Submission received: 14 October 2022 / Revised: 2 November 2022 / Accepted: 22 November 2022 / Published: 25 November 2022
(This article belongs to the Special Issue Fly Ashes: Characterization, Processing and Utilization)
Browse Figures
Figure 1
<p>Coal fly ash production and utilization in the last seven years starting from 2015 to 2021.</p> "> Figure 2
<p>Utilization of CFA in civil engineering works.</p> "> Figure 3
<p>CFA properties for road construction.</p> ">
Versions Notes

Abstract

:
Both fossil and renewable fuel sources are used widely to produce electricity around the globe. The dependency on fossil fuels for energy leads to the depletion of reserves and various forms of pollution. Coal fly ash (CFA) is one of the most burning issues in the whole world due to its large amount of production in thermal power plants. Every year a million tons (MTs) of CFA are generated globally of which almost half is utilized in various forms, while the remaining half remains unused, leading to various types of pollution. Hence, there is an immediate requirement for CFA management approaches for the efficient and sustainable use of fly ash. In the present review, the authors emphasize the status of energy and its supply and demand. A detailed description of coal fly ash-based thermal power plants, fly ash production, and utilization is provided. Moreover, the current and emerging applications of CFA are also provided.

1. Introduction

Energy, being one of the fundamental requisites across the globe, is essential to all significant activities such as industry, transportation, and other related fields. There was a time when energy was required only in a few sectors but, today, we cannot think of any field without energy. This energy is fulfilled by various sources like coal, nuclear, hydro, wind, and solar [1]. Historically, several economies relied heavily on energy derived from fossil fuels, but significant numbers of industrialized nations embrace cleaner energy instead. However, for a growing nation like India, wherein coal is still the primary source of energy, it will always be a major accomplishment. This is a result of India’s substantial coal reserves, which impose on it a dependency on coal-fired thermal power plants (CF-TPPs) [2,3,4,5].
A nation’s economic development is critically correlated with its energy usage. The national per capita income has a direct correlation with the energy demand [6]. The necessity to address the increased energy demand is due to the growing demand for energy brought on by globalization. The efficient conversion of resources into energy perhaps relies on technical prowess plus resource availability. Fossil fuels, among which coal makes up a substantial proportion, are still the major source of energy [5]. Gradually, around the whole globe, the demand for energy is increasing in the sectors like agriculture, defense, transport, etc. In addition to this, an extra burden has been put on energy due to rapid industrialization, urbanization, and the explosion of the human population [7]. In comparison to 2020, the demand for energy has increased in 2021, as in 2020, there was a decline of 4.1% due to COVID-19. As per the International Energy Agency (IEA, 2021), there was an increase in power generation in 2021 around the globe, it increased by 9% to 10,350 TWh in 2021. India is a developing country; energy plays a vital role, as its economy is predicted to develop by 8%–10% per year.
To meet the increasing demand for energy by the increasing population, India mainly relies on coal-based TPPs. These TPPs utilize pulverized coal and generate fly ash as a byproduct during the generation of electricity. Even in 2022, almost 50% of CFA is left unused and disposed of in the fly ash dumping sites leading to various types of pollution and environmental threats. Hence, there is a requirement for an effective fly ash management approach. There is a requirement for an updated study, suggesting the effective CFA utilization in some emerging areas like composite development, metallurgy, defense, and wastewater, etc.
After searching coal fly ash on Science Direct, we have found 10,709 articles from the year 2018 to 2022 (July) out of which 1749 (in 2018), 2019 (1826), and 2020 (2125), 2022 (2341). Hence, after analysis, it was found that every year, the number of articles increases rapidly on this material. By the half year 2022 alone, there are about 2341 articles, and there is the possibility that by the end of 2022, it will be at the highest figure. Out of the total value, 7904 were research articles while others were book chapters or review articles. This clearly indicates that coal fly ash is the most burning issue in the scientific community. From these statistics, one can conclude that coal fly ash is one of the hottest topics and issues around the whole globe. This could be due to their hazardous nature or their significance as a value-added material with the advancement of time [8,9].
The current review work emphasizes the demand and supply of energy in India and around the globe. It also focuses on total power generation by the world and India and their sources. Moreover, it focuses on the major sources of fuel as energy in India and the whole globe. The availability of coal reserves in various developed and developing countries including India. The report also highlights the state of thermal power plants (TPPs) using coal as a fuel currently, as well as the scenario with TPPs using coal in India. A year-by-year pattern in the generation and use of coal fly ash (CFA) in India is also the subject of this study. Finally, this study also emphasizes the current and future possible applications of CFA.

2. Coal as a Source of Energy in India

The largest known source of energy for the generation of electricity worldwide is coal, and its proportion is increasing. Coal-fired power plants produce more than 42% of the world’s electricity [10]. The world’s largest reserves of all types of coal are believed to be over 990 BTs, which is plenty for 150 years as the per current usage. Coal is by far the most prevalent and accessible fossil fuel worldwide (BGR, 2009) [6]. According to the access to coal, the Indian coal sector decided to set two objectives for the fiscal year (FY) 2021, the first of which was 1.5 BTs of income and the other was to double its output in order to fulfil the growing demand. Indian power sectors would naturally need to concentrate on having a positive influence in the near future in order to reach the FY 2021 goal. The growth of India’s coal use has been supported by its investment in new CB-TPP capacity.

3. Status of Thermal Power Plants in India

As of now, India has over 197 coal/lignite-based thermal power plants (CB-TPPs), that generate 133 MTs of CFA (half yearly) [MT] (2021–2022). These plants generate (70–75% of the country’s electricity. According to official statistics from the half-year period of 2021–2022 (half yearly), no new TPPs will be commissioned for the purpose of generating energy beyond 2027. Approximately 50,025 MW of coal-based thermal power (CB-TPP) facilities are now planned for construction in India (Coal projects 2010); (NEP 2021). This information is encouraging because it suggests that India would become a stronger superpower in terms of economics and energy. Hence, a reliable source of coal that can be supplied to CB-TPPs is required for the uninterrupted and reliable energy generation by TPPs.
By 2031–2032, the CFA generation figure could surpass 1000 MT. Despite ongoing study and improvement around CFA consumption, a significant portion, about 50% of CFA, remains underutilized each year. All three types of pollution—land, water, and air—are caused by the ongoing disposal of leftover CFA. An extensive analysis of government data on CB-TPPs revealed a yearly increase that has been happening over time, making the problem untenable. The commissioning of super TPPs will not only have a positive impact but rather the pollution generated in all forms will be a major concern for the government as well as locals.

4. Basic Structural and Chemical Properties of CFA

Coal is basically an organic sediment which contains several elements like H, S, N, C, and O along with a broad range of trace metal concentrations [11]. The amount of carbon in coal’s constitution determines its qualitative value [12]. Coal might incorporate one or more dangerous elements, such as Arsenic, Beryllium, Boron, Cadmium, Chromium, Cobalt, Lead, Manganese, Mercury, Molybdenum, Selenium, Strontium, Thallium, and Vanadium, in either significant or minute concentrations, based on the origin [13,14,15,16,17,18]. The ignition of pulverized coal in the TPPS results in the production of CFA, a finer powdery material that resembles glass [17]. Its size is approximately in microns ranging between 0.01 to 100, and its surface is glassy heterogeneous [19,20]. CFA also contains a number of the elements found in coal, including silica, alumina, and iron, which are significant oxides, as well as minor oxides of Na, Mg, Ca, P, K, and Ti [21]. The type of coal used in TPPs to produce electricity affects CFA’s Al, Si, and calcium content. The classification is essentially centered on the total amount of calcium, silicon, and aluminum oxides; if this amount surpasses 70%, it is class F fly ash, which is made from top varieties of coal, while if it is less than 70% and contains calcium greater than 5%, it is class C fly ash. Poorer varieties of fossil fuels like peat and sub-bituminous coal are the sources of class C fly ash. One of the most notable characteristics of CFA is size-based because CFA particles have a large surface-area-to-volume ratio (SVR). Heavy metals and other elements may accumulate on their surface readily when particle size decreases [22,23].

5. CFA Production and Utilization in India

Annual coal production was roughly 40 MTs during 1993–1994, whereas CFA utilization was only 3% or 1 MT. Conversely, CFA usage significantly climbed from 6.64 MTs in 1996–1997 to 107.77 MTs or 60.97% during 2015–2016. One may anticipate a brighter future for thermal power stations based on total coal consumption, CFA generation, and CFA utilization by looking at these figures. Without question, one may presume a prosperous India, dominating globally relative to its stronger economy. Although coal burning provides energy, environmental pollution is a detrimental component of the process. A significant number of techniques have been developed for their effective handling and disposal. Nonetheless, the management of the CFA will continue to be a significant matter of debate. Considering the advancements in CFA-based techniques and products, CFA has been upgraded from hazardous waste to a “useful and saleable asset” [24]. Coal-fired TPPs were built in India by state-owned companies, private businesses, central agencies like the national thermal power corporation (NTPC), and others.
For electricity generation, India has a substantial coal reserve and coal-based TPPs. Different federal agencies monitor the TPP’s operation, installation, life cycle, carbon dioxide emission, CFA generation, and utilization on a regular basis. The Central Electrical Authority of India (CEA) gathers relevant information from all thermal power facilities and releases half-yearly and annual reports in the month of June and December, respectively. Therefore, according to CEA reports spanning from 2010–2011 to 2021–2022, the following data have been acquired, which are listed in Table 1.
From the data in Table 1, it can be inferred that CFA generation and utilization have increased steadily from 1996-1997 to 2021–2022 (CEA, 2022). It is indeed suspected that the increasing production of CFA is attributable to the addition of new super TPPs. Whilst increased use of CFA could be attributed to rigorous government directives, regulations, awareness, legislation, and technological advancements. The instruments aid in the assessment of CFA’s comprehensive characteristics, which may also play a significant role in CFA’s enhanced usage rates. The use of CFA has grown rapidly from 1996–1997 to 2021–2022, as shown in Table 1. Only 9.63% of CFA were used in 1996–1997, following which there was a gradual increase in the use of the different forms. Whereas the CFA utilization percentage grew to 81.65 (half yearly) per cent in 2021–2022. India’s CFA usage is projected to improve in the coming time, depending on such figures. Considering the developments in technology, governmental initiatives, regulations, and public awareness, there will be no serious pollution in the form of hazardous waste in the foreseeable future. The government estimates that between 2020 to 2025, roughly 240 and 300 MTs of CFA will be generated [25].
Roughly 226 MTs of CFA were produced using coal and lignite supplies during the 2020 fiscal year, amongst which 83% was used in India’s coal and lignite TPPs. The detailed analysis of CFA utilization rates revealed an increasing trajectory from 2015 to 2021 (The first half fiscal year). Figure 1 shows CFA production and utilization in the last seven years in India (2015–2021). The fly ash utilization and generation for the year 2021 are shown for the first half year only. Table 2 shows Indian TPPs with less than 50% CFA utilization during the year 2020–2021.

6. Current and Possible Future Applications of CFA

CFA could be used in huge quantities in two areas: ash dyke construction and low-lying region filling [26,27,28]. In several affluent countries, CFA has been utilized successfully as a structural filler [27]. However, in India, this type of large-scale ash reuse is yet to be realized. Since the majority of India’s TPPs are situated in regions wherein natural resources are limited or costly; therefore, the availability of CFA is almost certain to include a cost-effective substitute for natural soil [29]. CFA released by electricity generating facilities should indeed be appropriately treated, according to the regulation encouraging ash management. CFA gets recycled into material for the preparation of cement and concrete to the tune of 40%, with the remaining designated for landfills (CEA reports 2022) [30]. The challenge of the increasing demand for CFA in the field of cement and concrete engineering necessitates the development of a novel recycling methodology that makes use of a significant volume of CFA. CFA has indeed been utilized as a Portland cement replacement material in concrete [31,32,33,34], structural infill, agricultural fertilizers, and soil conditioners owing to its core components, as it is comparable to those seen underneath. There are two categories of CFA usage based on conventional and new utilization methods and techniques: simple and advanced forms. Mining, highways, soil stabilization, barrier materials, and other basic types are employed in a simple form, whereas advanced types use cenospheres, metal recovery [35], carbon products, adsorbents [36,37], zeolites [38], and glass [39]. Furthermore, CFA applications can be categorized as high, medium, or low technology. The extraction of valuable minerals and fillers for polymer and matrix composites through CFA is considered a high-tech application. CFA is used as a medium technology in the preparation of mixed cement [39], lightweight aggregates, and bricks, among several other things. Besides, CFA can be used for land reclamation in low-tech applications.
CFA is most often used in civil engineering [40], mining [41], and agriculture [42]. The applications of CFA for road construction, brick manufacturing, tiles manufacturing, kitchen panels [43], road embankments, concrete, cement, landfills, and land reclamation fall under civil engineering. The application of CFA as a herbicide, biofertilizer, insecticide, pesticide, or micronutrient falls under the category of agriculture [44]. Figure 2 depicts most of the primary locations in which CFA might be useful in civil engineering. CFA is a nutrient-rich resource containing secondary elements (Ca, Mg, and S) and micronutrients (Zn, Fe, Cu, Mn). CFA also has a higher water-retention capacity which facilitates freshwater conservation and sodic soil restoration, besides its applicability as an insecticide and pesticide carrier. It also finds application in the mining industry viz. neutralizing acid mine drainage, soil reclamation, stabilizing abandoned mines, and filling their void [45]. As shown below, it is also employed in the extraction of metals and minerals, as well as value-added goods, fillers, and wasteland rehabilitation.

6.1. CFA in Civil Engineering, Cement, Tiles, Pavement Blocks and Bricks

CFA can be used as a feedstock in the civil engineering field to produce cement, bricks, flexible pavements, concrete, lightweight aggregates, and embankment. Alternative applications for CFA in the construction industry include landfill, road stabilization, controlled low-strength fills asphaltic mineral fillers, lightweight bricks, and building components [46,47,48].
CFA can be used in a variety of CFA-based cement since it has pozzolanic properties, Pozzolans are a larger class of siliceous and aluminous substances when properly fragmented, interact with calcium hydroxide, and bond with it in the vicinity of water in room temperature to produce cementitious substances. Furthermore, the CFA content is nearly identical to cement with high Al, Si, and Fe components. CFA is primarily deficient in Cao, which functions as a binder and must be applied to CFA before it can be used as cement. However, mixing CFA with cement has specific limits, such as that it can only be used up to a certain percentage, or else it will damage the concrete elements. CFA can be used to compensate for up to 66% of the cement in dam construction. In the vicinity of moisture, CFA reacts with free lime, calcium hydroxide, and atmospheric CO2 and causes the concrete to crumble. The use of CFA in R.C.C. reduces the cost of cement while also improving its performance and durability. CFA can also be used to improve the performance of concrete made using Portland cement. Calcium oxide is used to make Portland cement, and part of it is liberated in a free state during the hydration process. The use of CFA in cement concrete reduces carbon dioxide emissions to the amount that is present in the cement.
Presently, all civil or building products, such as bricks, tiles, cement blocks, and so on use CFA in varying proportions, which contributes to saving the rich top layer of soil indirectly. CFA-amended building materials can be just as good as clay-based materials. It offers a lot of potential for CFA use, specifically for thermal power stations close to load centers. It can be manufactured and used in two different ways: ready-mixed concrete and pre-cast CFA concrete. Superior quality control, reduced waste, labor, and management are all advantages of ready-mixed concrete, which are typically related to precast CFA concrete generated on-site. Precast construction modules made of CFA might include solid and hollow core slabs, door and window frames, and more. In the fabrication of flooring and roofing components such as cored units, channel units, and cellular units, it can be utilized as an insubstantial cement replacement [48,49,50,51,52,53,54]. The Bandra-Sea link in Mumbai, for instance, is made up of precast CFA concrete units.
CFA could be used to make bricks by combining them with clay in definite amounts. This is feasible because CFA and clay have chemical compositions that are quite similar. Furthermore, the unburned carbon in the CFA will be used as fuel during the kiln fire of the bricks, resulting in a reduction in overall fuel consumption. CFA can be used to replace roughly 0.25 to 0.80% of clay in the brickmaking process. Recently, a technology for employing CFA to build bricks was developed by the Central Fuel Research Institute (CFRI), a pioneer in the domain, at Dhanbad. CFA-based bricks provide a variety of benefits over conventional burnt clay bricks, including the use of unburned carbon residue as a fuel source for burning and a 20%–30% reduction in energy consumption while using 25 to 40% CFA.
These items are long-lasting, cost-effective, quick and simple to put together, self-interlocking, and aesthetically pleasing. These types of blocks are an alternative to typical blocks made of cement. Such methods are more eco-friendly. Unglazed tiles to be used on pathways can be made with CFA. CFA concentration in such tiles might be up to 35%, resulting in less water absorption and fire shrink, as well as less energy use [55]. Sokololar and Vodovac (2011) reported the development of dry-pressed ceramic tiles based on the CFA clay body. Further, the investigators observed the effect of fluidized CFA on the features of the developed tiles. In India, CSIR, central glass and ceramics research institute CGCRI, Ahmedabad, is the company behind these items [55].

6.2. Sintered CFA Products

Sintering is a process that involves heating items to a higher temperature in a muffle furnace or a kiln. Sintering turns CFA into a lightweight material, allowing it to be used in construction projects. It aids in the decrease in CFA volume when disposed of. The bulk density of sintered CFA lightweight aggregate varies between 640 kg/m3 and 750 kg/m3. Developing structurally and inexpensive lightweight concrete building components that can be utilized as load-bearing and non-load-bearing sections can be done using sintered CFA aggregate [56]. It has a higher demand and potential in areas where CFA is readily accessible and stone aggregates are expensive [57,58].

6.3. CFA-Based Polymers

For doors and panels, CFA-based polymer materials are the best option. The use of CFA for such applications reduces the amount of wood used, hence saving trees and forests. As a result of the employment of CFA, such approaches are more economical and place less of a burden on the timber industry. CFA-based polymer goods comprising the CFA matrix and jute fabric strengthening have already been produced. By putting jute fabric through a polymer CFA matrix and curing it, it can be laminated. The number of layers in the laminates is raised to achieve the appropriate width. Door shutters, partition panels, wall paneling, and ceiling and flooring tiles are examples of such products. The developed polymer goods offer various advantages over wood-based products, including being nearly 5–7 times stronger, fire and weather-tolerant, and also termite and fungus-resistant [59,60]. Furthermore, they are corrosion-resistant and less expensive than wood. In India, the Regional Research Laboratory (RRL) Bhopal collaborated with the Building Materials and Technology Promotion Council (B.M.T.P.C) and TIFAC to produce such a remarkable product. Currently, a pilot factory in Pondicherry is producing CFA-based panels that have been cleared by the CPWD and recognized by IIT Delhi.

6.4. CFA for Geopolymers

The term “geopolymers,” typically refers to nonmetallic inorganic compounds featuring amorphous or quasi-crystalline structures that are also charge-balanced by employing alkali metal ions with an activator [61]. CFA can be used to make geopolymers, which are similar to cement. The geopolymer technology is a promising alternative to using CFA that has a low environmental impact on CFA that has low environmental importance. CFA production using Alkali-activated geopolymerization might proceed at moderate temperatures and has been recognized as a clean technique as it generates very little carbon dioxide compared to cement production [62]. By using geopolymerization, the traces of dangerous metallic elements that come from CFA or other sources can be acquired and remedied [63]. The geopolymerization reaction depends critically on the Si/Al ratios, type and volume of alkali solution, temperature, curing conditions, as well as additives. Mechanical qualities of the CFA-based geopolymers, which include compressive strength, flex and split tensile, plus longevity characteristics namely resistance against chloride, sulfate, acids, heating, freezing-thawing, and efflorescence, seem to be the most arduous to transcend [64]. The properties of CFA-based geopolymers have been influenced by chemical components, complex formation, and permeability. By fine-tuning the Si/Al ratios, alkali treatments, and curing conditions, as well as adding slag, fibers, rice husk, etc., the products’ mechanical characteristics and durability can be increased [65]. A geopolymer based on CFA is anticipated to be used as a new type of green cement that could also be utilized to absorb and immobilize hazardous or radioactive elements [66]. These geological polymer materials were altered utilizing the central composite response surface technique in a work by Ding, et al., 2020. Four factors, including Na2SiO3 concentration, curing time (ct) at 120 and 250 °C, and CFA to slag ratios, have been discovered to affect the bending strength of the material based on the results of the Plackett–Burman study and the steepest ascent test, i.e., 2.2.5 h (ct at 120 °C) and 2.32 h. Despite being substantial pollution, CFA from coal-fired power stations can be utilized in agriculture as a soil-improving agent to boost plant biomass and output. The effect of CFA treatment on plant biomass and the accumulation of beneficial and detrimental components in plants, however, are unknown [67]. A thorough meta-analysis based on 88 publications was performed by Yu, et al., (2019) to assess the effects on plant biomass and 21 element levels in plants as a result of CFA treatment. These included macronutrients (N, P, K, Ca, and S), micronutrients (B, Co, Cu, Fe, Mn, Mo, Ni, and Zn), and metal(loid)s (B, Co, Cu, Fe, Mn, Mo, Ni, and Zn) (Al, As, Cd, Cr, Pb, and Se). CFA utilization resulted in a 15.2% reduction in plant biomass. On the other hand, at lower treatment rates (less than 25% of soil mass), plant biomass was increased by 11.6 to 29.2%, while at higher application rates, it decreased by 45.8%. (i.e., 50%–100%). Despite its growing efficiency, the use of CFA caused a considerable decrease in subsurface biomass. Following the administration of CFA, the levels of the majority of elements in plants were increased in the following order: metal(loids) > micronutrients > macronutrients. The proportions of components increased as the rate of CFA administration did as well. According to the observations, CFA must be applied at a rate of less than 25% in order to increase plant biomass and output whilst minimizing metalloid accumulation [68,69].
At 250 °C, 19.52% (Na2SiO3 concentration) and 8.21% (fly ash to slag ratios) were the ideal values for the chosen variables. The modified specimen’s determined bend strength was 37.28 MPa. While trona-syn, which is produced when too much alkali is added, has been determined to be detrimental to the material’s bend strength, the innovative formation of needle-like ferrierite-Na observed in X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) investigations may improve the materials’ bending strength.
Under exceptional circumstances, geopolymers can also be utilized in place of regular Portland cement. Geopolymer has the ability to integrate pollutants and by-products, which is useful for the environment. Due to this reason, CFA has gained popularity for the formation of geopolymers. The investigators’ intention would be to see how temperature exposure (up to 1000 °C) influences the microstructure and mechanical characteristics of geopolymer mortars [70]. Four different permutations have been tested using CFA as the main precursor and four separate concentrations of slag substitute (0, 10, 30, and 50 wt. %). Damage evolution and identification tests were evaluated using ultrasonic pulse velocity, scanning electron microscopy (SEM), mercury intrusion porosimetry, thermal stress measurements, differential thermal analysis, and thermogravimetry. The study’s aim was to build a high thermal stability mortar that could withstand high temperatures. Whilst adding slag to CFA geopolymer mortar improves mechanical qualities (compressive strength exceeding 100 MPa), the mortar lacking slag functioned well at higher temperatures. Engineered mortars exhibited a 30% increase in strength and a twofold rise in tensile strength when heated to 200 °C. Additionally, at 1000 °C, developed formulations showed compressive strength recovery of up to 90%, demonstrating the CFA geopolymer’s capacity as a high-temperature application product [71]. There are several pieces of literary work where CFA geopolymer has been used for the remediation of pollutants like heavy metals from wastewater [72].

6.5. CFA for Zeolite Synthesis

In 1985, Heller and Wirsching became the first to create zeolite using CFA as a raw material. Since the discovery, innumerable articles on various zeolite synthesis processes and settings have been published. According to Langauer et al., 2021, and several other investigators, the synthesis of zeolite from CFA is a complex physicochemical process [73]. The hydrothermal method and alkaline fusion followed by hydrothermal crystallization are probably the most popular synthesis procedures [74]. To produce zeolite with different structures, the hydrothermal method uses an array of activating solution/fly ash ratios, temperature, pressure, and reaction time [75,76]. Similar to the previous methods, this one also calls for integrating an alkali solution (usually NaOH or KOH) with ash in its vitreous state (which is high in Si and Al).
In contrast to landfilling waste, processing CFA to make zeolite results in higher-value products. The hydrothermal synthesis of zeolite from CFA in alkaline media, on the other hand, can result in the accumulation of dangerous heavy metals, which would potentially harm the environment [76]. There is nothing in the way of in-depth research on the topic of the transportation of heavy metals in CFA-derived zeolites. During the synthesis of high-quality type, A zeolites (471 m2/g surface area), Feng et al., (2018) examined the mobility and transit of heavy metals from CFA to finished zeolites and wastewater. With the least amount of secondary solid waste, high conversions of main elements (98.2% aluminum and 96.5% silicon) were accomplished. The effluent was found to include large amounts of arsenic, selenium, and metalloid elements with significant amphoteric tendencies, such as molybdenum. Only about 20% of the heavy elements with poor amphoteric properties, such as copper, chromium, and lead, transferred to the CFA effluent, while the majority, primarily all cadmium, iron, and nickel, were incorporated into the zeolites that were developed. Zeolites were determined safe to use because no significant leaching was observed at different pH levels despite the presence of heavy metal components in them. Additionally, it has been demonstrated that these zeolites are efficient at removing trace cesium and strontium cations from wastewater [77].
CFA contents are essentially identical to those seen in naturally occurring zeolites. The key distinction between CFA and zeolites is that CFA contains lesser Na. CFA may serve as natural zeolites if adequate Na content is introduced or managed. CFA’s Si/Al ratio typically ranges from 1 to 1.5, putting it in the low or intermediate silica-containing zeolites category. Zeolites have been used to purify wastewater, remove heavy metals, and remove dyes, among other things [38]. Treatment with strong alkali hydroxides at various temperatures, concentrations of hydroxides, and time results in the production of zeolites. Natural zeolites have limited pore diameters and channels, whereas CFA-based synthetic zeolites have a multitude of pore shapes and are potentially and likely economically effective sorbent minerals for trapping diverse pollutants from air and water [38].
In a recent attempt, Yadav et al., in 2021, synthesized micron-sized zeolites whose sizes varied from 60 to 120 nm in width and 80 to 700 nm in length. The shape of the zeolite varied from spherical to needle and rod-shaped. Further, it was used for the removal of heavy metals from fly ash aqueous solutions, which proved to be an economical and efficient adsorbent for wastewater treatment [76]. The utilization of CFA in such a way is also a unique way of developing value-added materials from CFA.

6.6. Roads and Embankments

Road and flyover embankments are another sector with the potential to use considerable amounts of CFA. The most common application of CFA is in the construction of civil works such as roads, embankments, and flyovers, as well as the rising of ash dikes [78]. CFA is being employed in building roads and embankments, that offer numerous advantages over conventional techniques, along with the preservation of soil surface and the establishment of low-lying areas. It minimizes the expenditures of excavation of soil from one place for subsequent development and restoration of low-lying regions. CFA can be used in road construction for a variety of reasons, including:
  • Sub-base or base stabilization and construction
  • pavement’s topmost strata
  • and for the purpose of filling.
The CFA-modified concrete (10%–20% by weight) is economical and enhances the rigid pavement’s performance [26]. Recently, CFA has been used to build embankments and roadways in a number of locations, including Okhla, Hanuman Setu, Delhi’s second Nizamuddin Bridge, and various roads in Raichur, Calcutta, and Dadri. In Delhi, DMRC has recently employed CFA for railway embankments and land fillings in Shastri Park, which has used approximately 950 K cubic meters of CFA to fill up lands. In order to use CFA for road construction, it must have several properties, which are shown in Figure 3.

6.7. Paints and Enamels

The major constituents of CFA are cenospheres, which make them ideal for use in paints and enamels [79,80]. Cenospheres are solid-filled CFA particles with a spherical shape that form after coal combustion in TPPs [79,80]. CFA cenospheres in paints and enamels are up to 30%–40% and 18%–22%, respectively. Cenospheres are rich in Ca, Si, and Al and are renowned for their high mechanical strength-to-density ratios, thermal shock resistance, insulating refractory, and durability [79]. Aside from that, they have better extending qualities (less oil absorption). Paints and enamels are both corrosion- and abrasion-resistant, as well as long-lasting [81].

6.8. CFA in Metallurgy

CFA is a rich source of numerous elements and minerals. It mainly consists of ferrous, alumina, and silica along with rutile and CaO. Till now throughout the world, more than 100 elements have been identified from CFA. Some parts of the world have reported Ag, Au, and many other precious metals which could vary based on the mining area around the coal used for combustion in the TPPs. If these minerals can be extracted, then it would reduce pollution as well as act as resource material. The CFA contains about 20%–25% alumina, 40%–60% of silica and 5%–15% ferrous. The ferrous fractions can be extracted by the magnetic extraction method. There are several investigators who have reported the extraction of ferrous fractions from CFA and used them directly for several applications. For instance, Yadav et al., 2020, reported the extraction of ferrospheres from class F CFA, and secondly synthesized iron oxide nanoparticles by chemical and physical routes with high purity (86%–94%) [82]. Yadav et al., 2021, also extracted ferrospheres from CFA and performed a surface modification of ferrospheres with acid to make them efficient adsorbents for dye removal from wastewater [18]. Besides this, Sahoo et al., 2016 [83], Goodarzi and Senei, 2009, Valentim et al., 2016, Anshits et al., 2018 [84], and several others have reported the extraction of ferrous fractions from CFA.
It can be used for the recovery of alumina and silica through chemical approaches and microbial approaches. To date, several investigators have reported the recovery of alumina from CFA, from various techniques like hydrothermal, NaOH roasting, calcination, and sintering, etc. The purity of the recovered alumina has reached up to 99%. Kumar et al., 2020 [85], Kamarudin et al., 2009 [86], and many more achieved the same with certain modifications to the method.
CFA has the highest amount of silica which is extractable in the form of silicates by treatment with strong hydroxides followed by treatment with dilute acids to obtain silica gel by the sol-gel method. Yadav et al., 2019 and 2020, synthesized amorphous silica nanoparticles from CFA and fly ash tiles, respectively [87,88].
Fong et al., 2007, reported the recovery of Gallium and vanadium from CFA in significant yield [89]. CPRI Bangaluru in India recently developed a method for extracting alumina from CFA. One ton of CFA may produce 150 kg of alumina and 1250 kg of Pozzolanic cement when combined with 400 kg of additional materials, including lime and gypsum. This is an abundant raw material for extraordinarily high-quality bricks. There are some circumstances where considerable amounts of other metals, such as zinc and selenium, can be eliminated.
Yadav and Fulekar, 2019, reported the utilization of CFA for the extraction of silica, iron oxides, and zeolites. The investigators extracted silicate and synthesized silica nanoparticles by using Bacillus cereus bacteria and Fusarium oxysporum fungi. In addition, SiNPs were also synthesized by chemical method. The purity of the synthesized silica nanoparticles [90] was 88%–96% [91]. The synthesized iron oxide nanoparticles were mainly magnetite, maghemite, and hematite by chemical approaches whose purity was 85%–92% [92].

6.9. Mining: As Fillers and Land Reclamation

CFA is generally used as a filling material in mine areas. All the major coal sites in a country like India are currently filled with CFA which is cheaper in cost and an easily available material which reduces the burden on the soil and the sand to fill the mined areas. Previously soil and sand were used for the filling of open mine areas created after the extraction of coals and minerals. A few of the application domains of CFA in such areas include mine void filling (underground), rehabilitation of unoccupied surface coal mines, neutralization of acid mine drainage, stabilization of abandoned mines, haul road repair and maintenance in opencast coal mines, oil, and grease traps in workshops in which heavy earth moving machinery is maintained, repair and maintenance of coal handling plant sedimentation ponds exist, and there is surface–mine spoil reclamation [93,94].
The overall applications of CFA in the mine include the stowing of underground mines with CFA (instead of sand); stowing of underground mines with CFA (instead of sand); and stowing of underground mines with CFA instead of sand. It is critical since sand has become a scarce commodity in many areas. Stowing with CFA reduces the amount of water required by 50% and the amount of energy required for water recirculation by 50%. CFA fills the hollow all the way to the roof since it flows quickly and does not form a cone-shaped mound as sand does. CFA is a suitable material for backfilling open-cast mines on its own [95].

6.10. CFA in Agriculture

CFA can be used as manure in agricultural areas because it contains several micronutrients such as B, Mo, Cu, Co, Ni, Zn, S, Mn, Mg, Ca, and Fe. It is also employed as a herbicide or pesticide, to keep the pH of agricultural soils stable, and also to improve soil quality.
(a)
CFA as herbicide
The smallest proportion of the ash is also used as a herbicide or pesticide carrier, exhibiting positive outcomes. Insects, pests, and other plant-eating insects can be dehydrolyzed by CFA’s alkali hydroxides. The splinter components of CFA do appear to be capable of hurting the mouth cavity and mandible of the gnawing organisms, strangling them to death whenever sprinkled on the surfaces of the leaves and stems and ingested by pests and flies. The splinters harm the digestive system and kill the insect when consumed. As a result, alkali-rich CFA can be used as a herbicide following proper categorization. With a full grasp of the many properties of CFA and appropriate adjustments. The impact of accumulation in the open fields of coal-based thermal power stations can be lessened by the widespread use of CFA in agricultural activities. CFA is also piled up in shallow and swampy places. Mosquitoes, flies, and insects would be kept at bay if these alkali activators were used [96]. Additionally, CFA has been suggested for use as a pesticide carrier, and an adjuvant in insecticide formulation [96,97].
  • (b) CFA as fertilizer
CFA helps plants absorb necessary nutrients and minerals (Ca, Mg, Fe, Zn, Mo, S, and Se) which functions as a growth promoter [98]. It can act as a soil modification, improving moisture retention and fertility. It is treated with soil to improve the water retention capacity and to modify the pH. It can be used as a gypsum substitute (up to 66%) for the reclamation of saline-alkali soils and the in agriculture/forestry recovery of degraded, eroded, waste/low-lying areas.
Recently Santi et al., 2021, have used CFA as a silica biofertilizer. Here, the investigators pretreated the CFA with the alkali, i.e., NaOH. The investigators observed the dissolution of silica with various organic acids and with citric acid treatment [99].
Su et al., 2021, developed a modified CFA by sintering and alkali treatment in order to use it as a slow-release microbial fertilizer for restoring the mine areas. Here, the CFA was used as an effective carrier matrix, which was obtained after hydrothermal alkali treatment sintering [100].
  • (c) CFA as soil stabilizers
Soil stabilization is the process of changing the properties of soils in order to improve their engineering performance. The temporary increase in subgrade stability to expedite construction is known as soil property modification. CFA has been effectively employed in a number of projects to improve soil strength and properties, particularly compressive and shearing strength. On-site soil characteristics, delayed duration, water content at compression, and the CFA additive proportion, all determine the compressive strength of CFA-treated soil [101]. Soil modification also aids in the reduction of water content. Density, water content, plasticity, and strength are the most adjusted characteristics.

6.11. CFA for Wastewater Treatment

A sustainable civilization needs clean drinking water that is separate from wastewater discharges. Awareness of recycling CFA waste has increased in response to low-cost treatment methods. CFA may effectively cleanse domestic wastewater by utilizing straightforward procedures and inexpensive adsorbents. CFA is a cost-effective, environmentally responsible, and efficient way to treat wastewater [102]. The UC in CFA, as indicated, helps with the adsorption of organic contaminants from effluent, including phenols, dyes, toxic metals, herbicides, petroleum components, and other pollutants [103]. Substantial health risks are posed by toxic heavy metals in wastewater. Among many other removal techniques, the method of using CFA for the remediation of heavy metals has proven to be affordable, dependable, and effective. CFA generates an alkaline pH of 10 to 13 when it is dissolved in water. CFA becomes negatively charged at high pH levels, enabling electrostatic adsorption to precipitate heavy metal ions from water. CFA can be converted or altered into new compounds for the adsorption of heavy metal ions. Class F fly ash is highly suited to be transformed into various substrates having strong adsorption because of its high Al2O3 and SiO2 concentration. Class F fly ash underwent hydrothermal treatment to chemically convert it into a substrate with a highly polar surface, displaying a complex adsorption process from a pollutant system containing various cations (cadmium, lead, and zinc combined).
The adsorption potential of CFA can be increased by converting it into synthetic zeolites using metallic elements, metal oxides, and hydroxides [104]. Synthetic zeolites made from CFA contain a negative-charged zeolite component and a positive-charged non-zeolite fraction [73]. Heavy metal contaminants including anionic and cationic heavy metals are removed by these fractions. Anionic toxins are removed from water by the non-zeolite part, and cationic pollutants are removed by the zeolite fraction [105]. Ion exchange capacity, crystallinity, and thermal stability are a few of the physical and chemical properties of zeolite [106]. Using synthetic zeolite, zeolite NaeP1, zeolite X, and zeolite material developed through hydrothermal modification, metal ions were removed from the studies [107]. CFA-based membrane filters are another fascinating way to use CFA in wastewater treatment [108]. Because of their high chemical, thermal, and structural strength, robust design, low energy consumption, environmentally friendly status, prolonged operation with good selectivity, removal rate, and potential for membrane regeneration by backflushing, ceramic, inorganic, and porous membranes they have drawn a lot of interest [109]. The ceramic membrane’s key drawbacks are a lack of raw materials like ZrO2, SiO2, Al2O3, TiO2, and other oxides, as well as a high price that limits its use with respect to the polymeric membrane. Due to the high SiO2 and Al2O3 content of CFA, much attention has been put into developing microporous inorganic membrane filters for handling massive amounts of effluent [110].
Further, CFA has been shown to be effective at removing a number of effluents [111]. CFA is an excellent material for water treatment because of its chemical and pozzolanic capabilities [112]. The effluent contains a variety of chemicals including pesticides, phenols, substituted phenols, methylene blue (MB), methyl orange (MO), dyes, heavy metal ions including Hg, Cu, Cr, As, and Pb, and many other organic and inorganic ions like fluoride and phosphate. These contaminants can be eliminated using a CFA adsorption technique. In the study, various adsorption isotherms and kinetics for the removal of different effluents are investigated. The goal of the research is to investigate the photocatalytic activity of CFA and modified CFA along with various methods for using CFA and modified fly ash for treating wastewater. Finally, the uses of CFA for water remediation research in the future have been investigated.
In a most recent study, Yadav et al., 2021, reported the recovery of ferrous particles from class F fly ash by using the wet slurry method. Further, the extracted ferrous particles were treated with mild acids to create pores on their surface which were confirmed by sophisticated instruments. The adsorbent was magnetic in nature and even in a small amount showed that the removal of Azure A dye from the aqueous solution was much more efficient. Since the magnetic fractions could be collected after the experiment and could be reused for the next cycle, the adsorption process was much more economical for the removal of dye [109].

6.12. Carbon and Carbon-Based Products Recovery

Carbon in the form of soots, unburned carbons, fullerenes, carbon nanotubes, hydrocarbons, polyaromatic hydrocarbons, and many other forms can be recovered from CFA. It can be processed and used as fillers in tires or in the development of carbon-based composite materials where the impurity is not an issue.
There are several reports in the literature, where CFA which is generally rich in carbon fractions was used for the recovery of unburned carbons (UC), soots, polyaromatic hydrocarbons, and carbon nanotubes. The reported literature reveals that these carbon-rich fractions of CFA could be collected in either wet or dry form. Generally, the wet form is preferred where CFA is mixed with water and slurry is prepared. The slurry is mixed with frother, pine oil, retarder, kerosene oil, etc., as per the process designed. The slurry is subjected to aeration, where the UCs become attached to the oil parts and float at the top of the slurry, which could be recovered, dried, and used further. There are several reports which show that the collected UCs were used again as fuel in the furnace, which further reduced the cost of fuel in running the TPPs. Furthermore, investigators have also reported the extraction of metallofullerenes, fullerenes, bulk onions, and synthesized carbon nanotubes under optimized conditions. Recently, Alam et al., 2021, summarized the various carbon-based products recovered from the CFA in the recent few years [113].

6.13. Coal Fly Ash for Air Quality Management

CFA is generally regarded as a polluting material that poses a risk to the environment, but various research investigations reveal that it could be utilized to remove dangerous gaseous contaminants from the air, such as sulfur and nitrogen oxides, and mercury, etc. CFA has all of the physical and chemical properties that make it a suitable adsorbent material, including porosity, surface area, bulk density, water-holding capacity, small particle size, and other physical and chemical properties. In addition, CFA contains unburned carbon particles that may operate as a precursor to activated carbon, resulting in CFA having a greater surface area and adsorption capacity [114]. As a result, CFA can be used to replace a variety of materials and resources now employed in air quality management.

6.14. Application in Making Membrane Filters for Cleaner Biodiesel Production

Glycerol in biodiesel can be a fatal source of engine failure, thus many organizations are concerned about eliminating it to produce cleaner biodiesel. The performance of ceramic membranes in separation processes is being evaluated using tubular membranes made of CFA. The use of CFA in membrane manufacturing is a significant step toward repurposing hazardous waste as a valuable resource that will help to create a cleaner and safer environment for future generations. Since binders are crucial in the manufacturing of ceramic membranes, different concentrations of the sodium salt of carboxymethyl cellulose (Na-CMC) binder (2–3.5 wt. %) have been employed to produce optimal membrane properties. The ideal binder amount was chosen for further usage because the constructed membranes had a wide range of parameters (mechanical strength 12.60–20.28 MPa, average pore diameter 0.133–0.190 m, porosity 40.17%–41.65%). Membranes constructed with a 2-wt. % Na-CMC solution (membrane M2) exhibited good mechanical and chemical durability (6.56 ± 1.67% weight loss in acid; 2.77 ± 0.67% weight loss in base) with a median pore size of 0.133 µ. Membrane M2 was used to extract glycerol from the biodiesel emulsion. The membrane was reported to recover glycerol from a synthetic biodiesel solution efficiently, and the resulting filtrate met ASTM D6751 and EN14214 criteria for free glycerol concentration in biodiesel.

6.15. Application in Flue Gases Purification

Flue gases, also known as exhaust gases, are particularly detrimental to the environment and are released by automobiles, factories, and TPPs. They include pollutants such as sulfur oxides and nitrogen oxides. Calcium-gypsum desulfurization and ammonia-catalytic denitrification are two current flue gas treatment technologies. These methods, despite being efficient and reliable, are not economically feasible due to their high operating costs. Sulfur removal from flue gases, for example, is done using dry, semi-dry, and wet procedures, with wet desulfurization being the most successful. However, this procedure consumes a large amount of water, which has a significant treatment cost [115]. The most frequent application of activated carbon was for the scale-up-expensive oxidation of reduced sulfur oxides. CFA might be a more advantageous substitute for activated carbon as a cheap adsorbent material. Therefore, the capability of CFA to desulfurize flue gases has been investigated. CFA has been used in several investigations and trials to remove SO and NO from flue gases. AlShawabkeh et al., 1995, produced reactive sulfur dioxide adsorbent material by processing CFA with Ca(OH)2 and used them for desulfurization [116]. The investigators observed that the reaction between sulfur dioxide and the CFA-Ca(OH)2 adsorbent was a first-order reaction. The simultaneous elimination of sulphur oxides and nitrogen oxides in the presence of CFA has been studied. Sulfur and nitrogen oxide removal efficacies were shown to be enhanced by CFA. The addition of CFA to the flue gases of TPPs, which hold a small amount of moisture, indicated improved NO removal. Table 3 lists several experiments in which modified CFA was utilized as an adsorbent to remove sulfur oxides.
Another dangerous pollution from power plants is mercury. Precombustion, combustion, and flue gas control are all options for controlling it, and the devices employed are electrostatic precipitators and bag filters. These devices are efficient at eliminating oxidized mercury from flue gases, but they are ineffective against mercury in its elemental form. Activated carbon has also been used to remove mercury from flue emissions, although it is a costly process when employed on a large scale. Unburned carbon from CFA is a cost-effective alternative to activated carbon that removes mercury from gas phases significantly [115]. The separation of these unburned carbon particles from CFA already has been accomplished using a low-cost approach [117,118].
Table
Table 3. Utilization of CFA for purification of flue gas/capture of gases.
Table 3. Utilization of CFA for purification of flue gas/capture of gases.
AdsorbentConstituentsReference
(CaO)x(SiO2)
Hydrated calcium silicates		CFA,
Calcium hydroxide		[116,119,120]
CFA,
Calcium oxide,
Calcium sulfate		[121]
CFA/CaCO3CFA,
Calcium carbonate
Calcium hydroxide		[121]
CFA,
Calcium hydroxide
Calcium sulfate		[121]
LILACCFA,
Calcium carbonate,
Calcium sulfate dihydrate		[122]
CFA,
Calcium hydroxide
Calcium sulfate dihydrate		[122]
Potassium based CFA[123]
CFA-zeolite[124]
CO2 contributes to global warming and climate change as a greenhouse gas. CO2 reduction strategies include chemical absorption, solid adsorption, and membrane separation. Among these, solid adsorption, in which chemical doping is employed to generate CO2 adsorbent materials, is an effective approach. After CO2 capture, a sorbent must be discharged to a CO2 reservoir to be reused. As a result, the whole cost, including operation and transportation costs, is extremely high. CFA has been used to extract CO2 in many experiments [124]. CO2 adsorption on CFA is accomplished through two methods: adsorption and carbonation. The contact between CO2 and the OH group in CFA causes adsorption, while the reaction between CO2 and metal oxide causes carbonation. Both processes can be reversed. CFA that has been CO2-loaded can also be employed as a mineral admixture in concrete [122].

7. Conclusions

Energy is one of the basic requirements for the whole world and is continually increasing with the increase in industrialization and population. There are several sources of energy production, but coal is the most preferred one due to its availability. Much of the energy is generated from coal-based thermal power plants. Fly ash is one of the major byproducts produced by these thermal power plants, which is one of the major global concerns. The utilization rate of fly ash is still lower than the production rate in most countries. With the advancement of technology, the fly ash utilization rate has increased drastically in some developing countries. Fly ash has entered the field of metallurgy, adsorbents, environmental cleanup, civil engineering, polymers, nanocomposites, and paint enamels, etc. This has been achieved with the advancement in this field along with time. In future, fly ash must be classified as a useable material instead of a hazardous pollutant.

Author Contributions

Conceptualization, S.I., D.B., P.K., K.K.Y. and M.A.; data curation, D.B. and A.G.; methodology, N.C. and D.B.; validation, S.I., M.A. and N.C., formal analysis, A.G. and N.S.A.; resources, M.A., A.G. and N.B.K.; writing—original draft preparation, V.K.Y., A.R. and P.K.; writing—review and editing, A.G., M.A., S.I., P.K., V.K.Y., K.K.Y., N.B.K., N.C., D.B. and A.R., supervision, V.K.Y., N.S.A. and A.R., project administration, N.B.K. and V.K.Y., funding acquisition, N.S.A. and K.K.Y., investigation, N.S.A. and K.K.Y.; software’s, A.R., P.K. and N.B.K.; visualization, S.I. and N.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Not applicable.

Acknowledgments

The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University (KKU) for funding this work through the Research Group Program Under the Grant Number: (R.G.P.1/256/43). The authors acknowledge the Mody University of Science and Technology for providing infrastructural facilities for conducting this research.

Conflicts of Interest

The authors declare no conflict of interest.

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Minerals 12 01503 g001 550
Figure 1. Coal fly ash production and utilization in the last seven years starting from 2015 to 2021.
Figure 1. Coal fly ash production and utilization in the last seven years starting from 2015 to 2021.
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Figure 2. Utilization of CFA in civil engineering works.
Figure 2. Utilization of CFA in civil engineering works.
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Figure 3. CFA properties for road construction.
Figure 3. CFA properties for road construction.
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Table
Table 1. Progressive CFA production and utilization during the period from 1996–1997 to 2020–2022 (CEA reports December 2021/July 2022).
Table 1. Progressive CFA production and utilization during the period from 1996–1997 to 2020–2022 (CEA reports December 2021/July 2022).
S. NoYearCFA Production (Million Tonnes)CFA Utilization
(Million Tonnes)		Percentage
(%)
1 1996–199768.886.649.63
2 1997–199878.068.4310.80
3 1998–199978.999.2211.68
4 1999–200074.038.9112.03
5 2000–200186.2913.5415.70
6 2001–200282.8115.5718.80
7 2002–200391.6520.7922.68
8 2003–200496.2828.2929.39
9 2004–200598.5737.4938.04
10 2005–200698.9745.2245.69
11 2006–2007108.1555.0150.86
12 2007–2008116.9461.9853.00
13 2008–2009116.6966.6457.11
14 2009–2010123.5477.3362.60
15 2010–2011131.0973.1355.79
16 2011–2012145.4185.0558.48
17 2012–2013163.56100.3761.37
18 2013–2014172.8799.6257.63
19 2014–2015184.14102.5455.69
20 2015–2016176.74107.7760.97
21 2016–2017169.25107.163.28
22 2017–2018196.44131.8767.28
23 2018–2019217.04168.467.13
24 2019–2020226.14189.0177.59
25 2020–2021232.56214.9183.28
26 2021–2022270.82259.8692.41
27 2022–2023---
Table
Table 2. Thermal Power stations with less than 50% CFA utilization during the first half of 2020–2021.
Table 2. Thermal Power stations with less than 50% CFA utilization during the first half of 2020–2021.
Sr. No.Name of Thermal Power Station and Power Utility SourceInstalled Capacity (Megawatts)Fly Ash Generation and Utilization (Tonnes)% Fly Ash Utilization
1Nabinagar-BRBCL, Bhartiya Rail Bijlee Company Ltd., Bihar10000.4870, 0.141629.07
2Korba (East), CSPGCL (Chhattisgarh)4400.2898, 0.060120.73
3Dr Shyama Prasad Mukherjee TPS, CSPGCL (Chhattisgarh)5000.5427, 0.096624.95
4Korba (West), CSPGCL (Chhattisgarh)13401.4838, 0.370117.80
5Raghunathpur, Damodar Valley Corporation (West Bengal)12000.6277, 0.082213.20
6O.P. Jindal Super (Stage-I), Jindal Power Limited (Chhattisgarh)10000.4670, 0.108023.13
7O.P. Jindal Super (Stage-II), Jindal Power Limited (Chhattisgarh)24001.3145, 0.313723.86
8Amarkantak, LANCO, LANCO Amarkantak Power Limited (Chhattisgarh)6000.5939, 0.173729.25
9Anpara-C, LANCO Anpara Power Limited, Uttar Pradesh12000.8992, 0.157517.51
10Meja, Meja Urja Nigam Private Limited, Uttar Pradesh6600.3310, 0.055716.84
11Shree Singaji, MPPGCL, Madhya Pradesh12000.5294, 0.201638.07
12Chandrapur Super, MSPGCL (Madhya Pradesh)29202.3519, 0.345714.70
13Durgapur Captive, NSPCL (West Bengal)1200.0899, 0.040545.05
14Singrauli, NTPC Limited (Uttar Pradesh)20001.3956, 0.317122.72
15Korba-NTPC, NTPC Limited (Chhattisgarh)26002.4220, 1.207649.86
16Vindhyachal, NTPC Limited (Madhya Pradesh)47604.7415, 1.230825.96
17Gadarwara, NTPC Limited (Madhya Pradesh)8000.2351, 0.00291.25
18Sipat, NTPC Limited (Chhattisgarh)29802.7597, 0.852730.90
19Darlipali, NTPC Limited (Odisha)8000.5694, 0.00320.56
20Lara Super, NTPC Limited (Chhattisgarh)8000.4671, 0.03667.84
21Barauni, BSPGCL (JV) (Bihar)2200.2031, 0.066932.95
22IB Valley, OPGCL (Odisha)17401.5895, 0.334821.07
23Chhabra Super Critical, RRUNL (Rajasthan)13200.7249, 0.328545.32
24Yeramarus, Raichur Power Corporation Limited (Karnataka)16000.1615, 0.029618.33
25RINL Cative, Visakhapatnam, Rashtriya Ispat Nigam Limited (Andhra Pradesh)3150.3329, 0.02968.88
26Sasan UMPP, Reliance Power Limited (Madhya Pradesh)39602.5915, 0.11174.31
27Talwandi SABO Power Limited, Talwandi SABO Power Limited (Punjab)19800.9600, 0.230023.96
28Kothagudem-V, TSGENCO (Telangana)5000.4692, 0.133628.48
29Kothagudem-VII, TSGENCO (Telangana)8000.3935, 0.101225.73
30Anpara ‘A’ and ‘B’, UPRVUNL, Uttar Pradesh26301.7330, 0.401723.18
31OBRA, UPRVUNL (Uttar Pradesh)10000.6853, 0.03715.41
32BANDEL, WBPDCL (West Bengal)3350.1307, 0.053941.20
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Yadav, V.K.; Gacem, A.; Choudhary, N.; Rai, A.; Kumar, P.; Yadav, K.K.; Abbas, M.; Khedher, N.B.; Awwad, N.S.; Barik, D.; et al. Status of Coal-Based Thermal Power Plants, Coal Fly Ash Production, Utilization in India and Their Emerging Applications. Minerals 2022, 12, 1503. https://doi.org/10.3390/min12121503

AMA Style

Yadav VK, Gacem A, Choudhary N, Rai A, Kumar P, Yadav KK, Abbas M, Khedher NB, Awwad NS, Barik D, et al. Status of Coal-Based Thermal Power Plants, Coal Fly Ash Production, Utilization in India and Their Emerging Applications. Minerals. 2022; 12(12):1503. https://doi.org/10.3390/min12121503

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Yadav, Virendra Kumar, Amel Gacem, Nisha Choudhary, Ashita Rai, Pankaj Kumar, Krishna Kumar Yadav, Mohamed Abbas, Nidhal Ben Khedher, Nasser S. Awwad, Debabrata Barik, and et al. 2022. "Status of Coal-Based Thermal Power Plants, Coal Fly Ash Production, Utilization in India and Their Emerging Applications" Minerals 12, no. 12: 1503. https://doi.org/10.3390/min12121503

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