What is the end product formed when SO2 is captured in scrubbers using lime or limestone?

• A. Gypsum (calcium sulfate dihydrate).
• B. Calcium carbonate.
• C. Sodium sulfate.
• D. Sulfur trioxide.

Answer: (A)

Wet scrubbing uses a slurry of lime or limestone to remove sulfur dioxide from the gas stream. The SO2 dissolves in the scrubber liquid and, with the calcium from the lime or limestone and some oxygen, is converted into calcium sulfate. This calcium sulfate forms a solid hydrate, known as gypsum (calcium sulfate dihydrate, CaSO4·2H2O), which can be collected.

So the captured end product is gypsum. Using lime or limestone provides the calcium that binds the sulfate, rather than leaving behind calcium carbonate or producing sodium sulfate or sulfur trioxide.