**1. Introduction**

The electricity production from coal-fired power plants currently accounts for 37% of all electricity produced worldwide. This percentage is substantially more significant in developing nations that are rapidly urbanizing. A poll estimates that more than 62% of the total electrical energy consumed in 2020 was produced by coal-fired power plants, which have long held the primary position in China's power supply.

In India, coal is also the primary source of electricity production due to its accessibility and affordable price [1]. However, the pulverized coal's impurities will produce a significant quantity of coal combustion leftovers, typically making up 30–50% of the powdered coal burned. The precise residue composition depends on the type of coal used ([2], p. 942). In addition, fly ash is the component with the most significant volume fraction of all the solid residues [3].

According to Huang's review, the total amount of coal ash produced worldwide is estimated to be around 600 million tons, with fly ash making up roughly 500 million tons, 75–80% of the total ([4], p. 1). Nevertheless, coal ash production is predicted to reach 1000 million tons in 2031 [1]. The lack of knowledge about fly ash has created a void regarding the best way to utilize this priceless resource.

Fly ash used to be disposed of on the surface as a terrible waste that took up much space and polluted the ecosystem around it. Researchers have undertaken extensive research on fly ash's physical, chemical, and practical applications since realizing its potential value for use. As a result, fly ash has been systematically categorized according to its performance and quality. Fly ash was partially recycled and used in various valuable uses, such as asphalt concrete, ground improvement, agricultural sector, roller compacted concrete, brick, road, and mining, based on all the extensive studies undertaken by engineers and academics [1].

However, different countries have varied percentages of recycled fly ash (**Figures 1** and **2**). There is a noticeable difference between the generation and use of fly ash in some countries. For example, the output of fly ash in Russia alone is no less than 25 million tons per year, whereas the utilization of fly ash is not higher than 7–8%. Although the overall recycling rate of fly ash in China reached about 78% in 2020 (**Figure 3**), only 2% of the fly ash was used in the mining industry (**Figure 2**). The main applications of fly ash in the mining industry are generally in two ways, one is to use its small particle characteristics as fine particles to adjust the gradation of the filling material and increase the compactness of the filling material [5], and the other is to use its pozzolanic properties to replace cement as a cementitious material [6] to enhance the compressive strength of the filling body. However, the operational complexity and higher capital cost of the backfill mining method compared to traditional mining methods has made it not widely accepted by mining companies at present, which has directly led to the use of fly ash in mining remaining at a low level. It is likely that as the potential of fly ash for carbon sequestration is progressively exploited, the proportion of its use in functional infill mining will explode [7].

**Figure 1.** *Top countries with best utilization of fly ash.*

**Figure 2.** *Fly ash application and percentage in China, 2019.*

**Figure 3.** *Demonstration of the generation and the utilization of fly ash in China.*

Those pioneers who have explored the application of fly ash for decades have nearly achieved 100% beneficially re-use ([8], p. 107). Therefore, identifying the area where fly ash can be increased and increasing application techniques with considerable practical significance can be identified. For example, in China and other comparable regions, using fly ash in the mining industry can enhance the utilization rate of fly ash as it is too low.

The present chapter contributes a state-of-the-art review on using fly ash in mining practices. In addition, it also discusses the significant performance of fly ash to facilitate better application and specifically expounds on its utilization in the mining sector, which still has a great deal of potential.
