## 1 Introduction  
Coal ash is generated by the combustion of coal in thermoelectric power plants as a waste product. Given the increasing use of mineral coal, there is a need to minimize the impact it causes. The amount of coal ash produced in the world is approximately 500 million tons per year [1]. According to [PERSON] et al. (2015) [1], burning this fuel produces ashes that are classified as slag, bottom ash (heavy), and fly ash (light). Slag and bottom ash are particles of varying dimensions, usually coarse, that accumulate in temporary deposits in companies that burn coal; light ash, or fly ash, is made up of particles smaller than 0.15 nm and is carried away by combustion gases [2]. The largest amount of waste generated from this burning is fly ash (84% of the total coal ash) [1; 3]. The \"ecoba\", European Coal Combustion Products Association [4] classifies fly ash (CF) as a fine-grained powder composed of spherical glassy particles. These ashes mainly contain silicon and aluminum (SiO2 and Al2O3) and are obtained from electrostatic or mechanical precipitates. Approximately 20% of fly ash that is produced on a worldwide scale in the combustion of mineral coal is reused as raw material for cement industries to produce Portland cement. Other applications are in soil improvement, ceramic industries, and the production of catalysts and zeolites [5]. According to [PERSON] et al. (2012) [6], the consumption of mineral coal in Brazil should reach 3.5 or 4 million tons per year; however, the cement industry will not have a significant increase to compensate for this growth. Therefore, processes that can transform these ashes into a material with high added value have become necessary to reduce the accumulation of this material in the environment. The use of fly ash as a precursor to zeolitic materials occurs due to the great similarity in the chemical composition with the volcanic material responsible for the formation of natural zeolites, thus allowing through this residue to synthesize new zeolites as a high-value product and further stimulating its use in this process [5]. Zeolites are crystalline aluminosilicates with wide industrial applications, such as oil refining, the petrochemical industry, and fine chemical production that use zeolite-based catalysts [7]. The actual market for synthetic zeolite materials is approximately US$5.2 billion per year, and it is expected that this value will increase to US$5.9 billion per year by 2023. The most used zeolite types are MFI (ZSM-5), LTA, and FAU (X, Y, and USY). LTA zeolite is the most commercialized in the world both in volume and in value; it is used mainly used as an additive in laundry detergents. The most recent estimate of the size of the zeolite market in the detergent market in 2018 was US$1.4 billion, and that figure is forecast to rise to US$1.8 billion in 2028 [8]. In addition to the use of zeolite LTA for laundry detergents [9], it is also used as a catalyst for the industrial dehydration of ethanol [10], for antimicrobial materials when exchanged with Ag ions [11], and for the separation of gases [12]. LTA zeolites have an Si/Al ratio of 1. It belongs to the cubic system and, when it is completely hydrated and in solid form, has a unit cell parameter equal to 24.60 A. The chemical formula for the unit cell can be expressed as Na\({}_{96}\)Al\({}_{96}\)Si\({}_{96}\)O\({}_{384}\).27H\({}_{2}\)O [7]. The LTA zeolite was the first synthetic zeolite to be commercialized [8]; these materials have been continuously studied. This can be seen in the number of papers that have been published about this zeolite concerning novel synthesis methods, diversification of applications, and upgrading of waste materials containing aluminum and silicon for raw synthesis materials. The synthesis of zeolite LTA can be performed using fly ash as a source of silicon and aluminum [13; 14; 15; 16; 17; 18; 19; 20]. These studies show different methods of synthesis.