UPSC Prelims 2015 Question:

With reference to 'fly ash' produced by the power plants using coal as fuel, which of the following statements is/are correct?

1. Fly ash can be used in the production of bricks for building construction. 
2. Fly ash can be used as a replacement for some of the Portland cement contents of concrete. 
3. Fly ash is made up of silicon dioxide and calcium oxide only, and does not contain any toxic elements.
   
   

Select the correct answer using the codes given below.

Explanation:

• Fly ash is a fine powder that is a byproduct of burning pulverized coal in electric generation power plants. This residue is created when the mineral impurities in the coal fuse together as they come out of the combustion chamber, then cool down and harden.
  
  
• Fly ash is a pozzolan, a substance containing aluminous and siliceous material that forms cement in the presence of water. When mixed with lime and water, fly ash forms a compound similar to Portland cement. This makes fly ash suitable as a prime material in blended cement, mosaic tiles, bricks and hollow blocks, among other building materials. So, statements 1 and 2 are correct.
  
  

• Fly ash consists primarily of oxides of silicon, aluminum iron and calcium. Magnesium, potassium, sodium, titanium, and sulfur are also present to a lesser degree. Fly ash is considered as an environmental hazard worldwid. Fly ash produced during the combustion of coal contains several toxic heavy metals like lead (Pb), nickel (Ni), zinc (Zn), manganese (Mn). So, statement 3 is not correct.
  
  

Therefore, option (1) is the correct answer.

Subject: Environment | Pollution