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UPSC Prelims 2020 · Environment · Pollution Files
Consider the following statements: Which of the statements given above is/are correct?
- Coal ash contains arsenic, lead, and mercury.
- Coal-fired power plants release sulphur dioxide and oxides of nitrogen into the environment.
- High ash content is observed in Indian coal.
- (a) 1 only
- (b) 2 and 3 only
- (c) 3 only
- (d) 1, 2 and 3
Show the answer and explanation
Answer: (d) 1, 2 and 3
All three are true.
Statement by statement
1. ✓ CORRECT Fly ash contains arsenic, lead and mercury.
2. ✓ CORRECT Coal plants emit SO₂ and NOₓ.
3. ✓ CORRECT Indian coal has high ash content (30–45%).
The idea
Coal is not pure carbon. Whatever does not burn is left as ash, and the trace metals in the coal are concentrated in it. Indian coal has a lot of ash (30–45%) but little sulphur. So India’s special coal problem is ash, while sulphur is the bigger problem with many imported coals.
Coal burns in the boiler → Fine fly ash rises with the smoke; coarse ash falls to the bottom → Fly ash is caught by electrostatic precipitators → Stored as slurry in ash ponds → Arsenic, lead and mercury can leach into water
Also know
Fly ash is useful: bricks, Portland pozzolana cement, road embankments, filling of old mines. Government rules require power plants to use all of their ash. Ash-pond breaches have polluted rivers and fields in the Singrauli region.
🔒 Indian coal: high ash, low sulphur. Fly ash → bricks, cement.