Introduction
Flue gas desulphurization gypsum (FGD gypsum) is a perfect example of industrial ecology, turning a waste product from air pollution control into a valuable, sustainable material. This synthetic gypsum is produced when sulfur dioxide (SO2) is removed from the exhaust gases of coal-fired power plants. This article explores the production process and the remarkable journey of FGD gypsum from waste to resource.

The Production of FGD Gypsum
The process begins with flue gas desulfurization (FGD), a technology used to reduce SO2 emissions from power plants. There are two main processes:

• Wet FGD: This is the most common method. The flue gas is scrubbed with a limestone slurry. The SO2 reacts with the calcium carbonate in the limestone to form calcium sulfite (CaSO3). This is then oxidized with air to form calcium sulfate dihydrate (CaSO4·2H2O), which is desulfurization gypsum. The resulting gypsum slurry is dewatered and processed.

• Dry FGD: A dry sorbent (like lime) is injected into the flue gas. The resulting byproduct is a dry mixture of fly ash and gypsum, which has different properties.

Key Properties of FGD Gypsum
FGD gypsum is chemically identical to natural gypsum but often has distinct advantages:

• High Purity: It can be produced with a higher and more consistent purity (over 90-95%) than many natural gypsum deposits .

• Constant Quality: The controlled industrial process results in a consistent chemical and physical product.

• Fine Particle Size: It is typically a fine powder, which is ideal for certain applications.

From Byproduct to Building Material
The journey from a power plant to a construction site involves:

1. Processing: The raw FGD gypsum is dried and may be ground to meet specific size requirements.

2. Calcination: For wallboard production, the gypsum is heated (calcined) to remove water and form stucco (calcium sulfate hemihydrate), which sets when water is added.

3. Application: The processed gypsum is then used in wallboard, cement, or other products.

Conclusion
Flue gas desulphurization gypsum is a cornerstone of the circular economy. Its transformation from an industrial waste into a high-quality, sustainable material is a success story in environmental stewardship. For more on this process, explore the desulphurization gypsum market report.

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