Which sorbent is commonly used in flue gas desulfurization scrubbers to remove SO2?

• A. Activated carbon.
• B. Sodium hydroxide.
• C. Lime or limestone.
• D. Water.

Answer: (B)

Desulfurization in flue gas uses a basic substance that chemically reacts with sulfur dioxide to capture it as a solid. Lime or limestone slurry is the go-to choice because it readily reacts with SO2 to form calcium sulfite, which can be further converted to calcium sulfate (gypsum). This solid byproduct can be collected and even sold, making the process cost-effective for large-scale emissions control. Activated carbon targets other pollutants such as mercury or organic compounds, not SO2. Water by itself won’t remove SO2, since it doesn’t provide the necessary chemical reaction to neutralize the acidic gas. Sodium hydroxide can absorb SO2 in some systems, but it’s typically more expensive for large plants, so lime/limestone is the common, economical option.