Ash is produced whenever combustion of solid material takes place. 

• Fly ash is one such residue which rises with the gases into the atmosphere.  
• Fly ash is a very fine powder and tends to travel far in the air. The ash which does not rise is termed as bottom ash. 

• Nearly 73% of India’s total installed power generation capacity is thermal, of which 90% is coal-based generation, with diesel, wind, gas, and steam making up the rest. 

Composition: 

• Aluminum silicate (in large amounts) 
• Silicon dioxide (SiO2) and 
• Calcium oxide (CaO). 

Fly ash particles are oxide rich and consist of silica, alumina, oxides of iron, calcium, and magnesium and toxic heavy metals like lead, arsenic, cobalt, and copper. 

Source: Shankar