Applications, Science, and Sustainability of Coal Ash .
20161220&ensp·&enspThe coal is burned in this bubbling, liquidlike (or "fluidized") mixture. Rather than released as emissions, sulfur from combustion gases combines with the limestone to form a solid compound recovered with the ash. Fly ash — The finely divided particles of ash suspended in gases resulting from the combustion of fuel. Electrostatic201867&ensp·&enspa solid byproduct called coal ash . A number of different substances fall under the label "coal ash": fly ash, bottom ash, boiler slag, and flue gas desulfurization gypsum, among others Once the coal ash is collected, it is often impounded and stored in a storage pond or in a landfill or can be used for various industrial purposes .