**2.2. Coal ashes**

Coal ashes ares inorganic solid wastes generated after burning coal in power generation processes in power plants worldwide. The formation of ash is achieved by the direct combustion of lignite, which is a solid raw material, consisting of two intimately mixed fractions, an organic (volatile matter more fixed carbon) and a fraction (mineral clay, quartz, pyrite, carbonates, etc.). By the action of heat, generates volatile organic fraction and coke, while the mineral fraction becomes gray with a mineralogy modified in view, the water loss of clays, carbonates and decomposition of sulfide oxidation [3].

The combustion of pulverized coal occurs at high temperatures, between 1200 and 1600º C in an oxidizing gaseous environment and for total or partial melting of matter [4].Three main wastes are generated from coal combustion in power plants, which are:


The fly ashes are usually composed of 30-60% SiO2, 10-20% Al2O3, 5-10% Fe2O3, 5-10% MgO and 2-4% CaO, and other compounds.

In the process of coal combustion, these minerals are partially fused particles form ashes and light in which the crystalline phases such as quartz (SiO2) and mullite (3 Al2O3.2SiO2) remain in the core, while the aluminosilicate (Al2O5 Si) remains the surface [5].

The ash generated from burning coal in power plants in Brazil are comprised 65-80% fly ash and bottom ash of 15-35% [6].

In general, mineral coal ashes are aluminosilicates formed by amorphous and crystalline phases and the pH of ash ranges from 4.5 to 12 depending on the characteristics of the carbon precursor geochemical [7].

From the standpoint of generating electric power, coal ash waste are considered as residues, however, to evaluate its characteristics and possible uses, these can be considered as a resource that can be widely used and exploited [8].

The storage of the dry coal ash has the major advantage that its physicochemical properties of the ash remain unchanged, which constitutes a buffer for further use [9].

Several potential applications of coal ash have been developed or are under development at research centers all over the world. These applications are directed primarily to remove toxic metals present in industrial wastes [10] in the building materials industry [11], and the synthesis of zeolites that have been studied by many researchers [12].

## **2.3. Zeolites**

284 Ion Exchange Technologies

**2.1. Coal** 

production[1].

globe.

waste.

applications.

potential applications [2].

**2.2. Coal ashes** 

**2. Literture review** 

With the progress of humanity and its new challenges, we started to research the various types of energy production coupled with environmental preservation as a tool for sustainable development. Nowadays, the search for new processes using renewable energy sources is increasing, but the non-renewable energy sources occupy yet a large portion of

Although the use of coal represents a small share in electricity generation, its use is extremely important because it's the non-renewable energy resource most abundant of the

The main environmental problems related to use of coal in power generation are: changes in vegetation and geomorphology of mining activities, formation of acidic water in the handling of coal due to the presence of pyrite, a large amount of waste in the process of improvement, gaseous emissions after combustion and the generation of potentially toxic

One way to reduce the environmental impacts of disposal of these wastes in the environment involves the expansion of the potential for their use. An alternative use of these residues is the processing of coal ash in an sorbent low cost. The ashes of coal are composed mainly of silica and alumina, and you can convert them into zeolitic material after hydrothermal treatment in alkaline medium. The zeolitic material is characterized by high cation exchange capacity and good sorption allowing numerous potential

The ashes of coal are composed mainly of silica and alumina, and you can convert them into zeolitic material after hydrothermal treatment in alkaline media. The zeolitic material is characterized by high cation exchange capacity and good sorption allowing numerous

Coal ashes ares inorganic solid wastes generated after burning coal in power generation processes in power plants worldwide. The formation of ash is achieved by the direct combustion of lignite, which is a solid raw material, consisting of two intimately mixed fractions, an organic (volatile matter more fixed carbon) and a fraction (mineral clay, quartz, pyrite, carbonates, etc.). By the action of heat, generates volatile organic fraction and coke, while the mineral fraction becomes gray with a mineralogy modified in view, the water loss

The combustion of pulverized coal occurs at high temperatures, between 1200 and 1600º C in an oxidizing gaseous environment and for total or partial melting of matter [4].Three

of clays, carbonates and decomposition of sulfide oxidation [3].

main wastes are generated from coal combustion in power plants, which are:

Zeolites are hydrated aluminosilicates formed by three-dimensional crystal structures of SiO4 tetrahedra and AlO4, linked together by four oxygen vertices.In this configuration, the negative charges of AlO4 tetrahedra are compensated by interstitial cations (Na+, K+, Ca2+ and Ba2+) and form an open structure with large channels, where water and other molecules can stay and have considerable freedom of movement, permitting ion exchange and reversible hydration [13] .

Zeolites include a wide range of mineral and synthetic products, whose structure has an electrical imbalance, as it has an excess negative charge on each atom of aluminum present.Therefore, atoms of alkali metals and alkaline earth metals cause the balancing of charge, can easily be exchanged for other ions. This transfer of material between the spaces intracristalinos is limited by the pore diameter that ranges from one to another zeolite.

In nature, are usually found in deposits associated with the activation of alkaline volcanic rocks. As naturally occurring normally have a high content of impurities and / or do not possess the properties required for their use, therefore, be synthesized zeolites started [14] .

Zeolites exhibit features as high selectivity, high stability and high exchange capacity, which together with the properties of sorption and catalysis, provide their technological application in various sectors [15] .

One advantage of synthetic zeolites is to provide uniformity in size and shape of the channel, another is its chemical composition pre-defined in relation to the purposes intended. Considering, however, its high cost, synthetic zeolites are reserved for applications that require features more uniform structure and composition, as in the catalysis of hydrocarbons and in the detergent industry. The zeolites type A, X and Y are the predominant for commercial use as ion exchangers and adsorbers [16] .

Among various uses, natural zeolites can be applied to wastewater treatment for removal of toxic metals, in removing odors in the air purification and in the conditioning of soil [17].

The fly ash are sources of aluminum and silicon, which are the main elements in the composition of the zeolites, because of this, the high content of reactive stages of ash and fine particle size thereof, are considered excellent feedstock for the synthesis of zeolites[12] .
