Coal Ash

Coal Ash Coal ash is the mineral matter present in the coal. It is a waste which is left after coal is combusted (burned). It is the particulate material which remains after coal is burned. It includes fly ash (fine powdery particles which are carried up the smoke stack and captured by pollution control devices) as well as coarser materials which fall to the bottom of the furnace. It has different physical and chemical properties depending on the geochemical properties of the coal being used and how that coal is burned. Coal ash is also referred to as coal combustion residuals. It has very little organic fraction. Chemical constituents of coal ash may include nitrogen (N2), sulphur (S), unburned carbon (C), heavy metals, radioactive elements, and polycyclic aromatic hydrocarbons (PAHs). Coal ash also contains coarse particles and fine particles which can be inhaled and may contribute to public health and environmental problems. Coal ash contains many toxic contaminants. When coal ash spills, leaks or leaches into nearby ground water or waterways, the toxins contained within pose serious health risks to nearby communities. Depending on where the coal was mined, coal ash typically contains heavy metals including arsenic, lead, mercury, cadmium, chromium and selenium, as well as aluminum, antimony, barium, beryllium, boron, chlorine, cobalt, manganese, molybdenum, nickel, thallium, vanadium, and zinc. If eaten, drunk or inhaled, these toxicants can cause cancer and nervous system impacts such as cognitive deficits, developmental delays and behavioral problems. They can also cause heart damage, lung disease, respiratory distress, kidney disease, reproductive problems, gastrointestinal illness, birth defects, and impaired bone growth in children. A large amount of coal ash is disposed in dry landfills, frequently at the power plant where the coal was burned. Coal can also be mixed with...

Fly ash

                       Fly ash Fly ash is a product of combustion of coal. It is normally produced while burning coal in a boiler of a power plant and is generally captured before the flue gas goes to the chimney. The other ash from the boiler is bottom ash which is removed from the bottom of coal fired boiler. Depending upon the type of the coal used, the composition of the fly ash vary widely  but all the types of fly ash include silicon dioxide (SiO2) (both amorphous and crystalline) and calcium oxide (CaO). Fly ash is a fine glass like powder. The particle size of the ash is in microns. The composition of fly ash in case of bituminous coals is as follows: SiO2 – 20%- 60% Al2O3 – 7% – 35% Fe2O3 – 12% – 40% CaO – 2% – 12% LOI – 0%- 12% Fly ash contains environmental toxins in significant amounts. These toxins include arsenic (45 ppm); barium (805 ppm); beryllium (5 ppm); boron (310 ppm); cadmium (3 ppm); chromium (135 ppm); chromium VI (90 ppm); cobalt (35 ppm); copper (110 ppm); fluorine (30 ppm); lead (55 ppm); manganese (250 ppm); nickel (75 ppm); selenium (8 ppm); strontium (775 ppm); thallium (10 ppm); vanadium (250 ppm) and zinc (180 ppm). The use of fly ash as an engineering material is due to its pozzolanic nature, spherical shape, and relative uniformity. The following are the various uses of fly ash: Portland cement and and in materials for grout Embankments and structural fill Waste stabilization and solidification Raw feed for cement clinkers Mine reclamation Stabilization of soft soils Sub base for road Aggregates Flowable fill Mineral filler in asphaltic concrete Roofing tiles Filler in wood and plastic products Fly ash is used as a...