Review of Related Literature

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Coal Ash
Coal ash is a collective term for the residues left during the combustion of coal. Depending on the source and makeup of the coal being burned, the composition of the coal ash vary considerably, but all includes substantial amounts of both amorphous and crystalline Silicon dioxide (SiO2) and Calcium oxide (CaO), both being endemic ingredients in many coal-bearing rock strata. Coal ash is made up of two types of combustion by-products: bottom ash and fly ash.

Bottom ash is a coarse, granular, incombustible by-product that is collected from the bottom of the combustion chamber. Bottom ash is coarser portion of the coal ash, with grain sizes spanning from fine sand to fine gravel.

Fly ash, on the other hand, is the finest of coal ash particles. It is called "fly" ash because it is transported from the combustion chamber by exhaust gases. Fly ash is the fine powder formed from the mineral matter in coal, consisting of the noncombustible matter in coal plus a small amount of carbon that remains from incomplete combustion. Fly ash is generally captured by electrostatic precipitators or other particle filtration equipments before the flue gases reach the chimneys.

Flotation is one of the many methods in mineral separation. It could be used for separation of phases for instance to remove solid particles or oil drops from water. More frequently flotation is used for separation of particles having different hydrophobicities. Hydrophobicity is a feature of material characterizing its ability to be wetted with a liquid in the presence of a gas phase. Solids, which can be easily wetted with water, are called hydrophilic while solids with limited affinity for wetting are called hydrophobic. As a result of hydrophobicity, particles adhere to the gas bubble forming a particle-air aggregate which is lighter than water, and travels upwards to the surface of water. The hydrophilic particles do not adhere to...
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