Calcium hydroxide (Ca(OH)₂), also known as slaked lime, removes sulfur dioxide (SO₂) through a chemical reaction called wet scrubbing. Here's how it works:

1. Contact: Sulfur dioxide gas is brought into contact with a slurry of calcium hydroxide in water.

2. Reaction: The calcium hydroxide reacts with the sulfur dioxide to form calcium sulfite (CaSO₃) and water:

```

Ca(OH)<sub>2</sub> + SO<sub>2</sub> → CaSO<sub>3</sub> + H<sub>2</sub>O

```

3. Precipitation: The calcium sulfite, being insoluble in water, precipitates out of the solution.

4. Removal: The precipitated calcium sulfite is collected and disposed of, effectively removing the sulfur dioxide from the gas stream.

Benefits of using calcium hydroxide:

* Cost-effective: Calcium hydroxide is a relatively inexpensive reagent.

* Effective: It effectively removes sulfur dioxide from flue gases.

* Environmentally friendly: The byproducts of the reaction, calcium sulfite and water, are relatively harmless.

Limitations:

* Limited Efficiency: Wet scrubbing with calcium hydroxide is not 100% efficient. Some sulfur dioxide may escape the scrubber.

* Byproduct Management: The calcium sulfite needs to be collected and disposed of properly.

* Oxidation: In the presence of oxygen, calcium sulfite can oxidize to calcium sulfate (CaSO₄), which is more difficult to remove.

Applications:

This process is widely used in various industries, including:

* Power plants: To remove sulfur dioxide from flue gases generated by burning fossil fuels.

* Industrial processes: To scrub sulfur dioxide from emissions from various industrial processes.

Note: This process is often referred to as "flue gas desulfurization" (FGD) in the context of power plants. There are other FGD technologies that utilize different reagents and processes, but calcium hydroxide remains a popular and cost-effective option.