FGD GYPSUM
FLUE GAS DESULPHURIZATION GYPSUM

Flue Gas Desulfurization (FGD) gypsum is a high-purity, synthetic form of calcium sulfate (CaSO₄·2H₂O) generated as a byproduct during the removal of sulfur dioxide (SO₂) from emissions in coal-fired power plants, where lime or limestone is used to neutralize gases and produce gypsum through oxidation. This material is chemically similar to natural gypsum and typically appears as a white to off-white, odorless fine powder with moderate moisture content. In the cement industry, FGD gypsum plays a critical role as a set retarder, preventing rapid reactions between cement and water that would otherwise cause flash setting; it achieves this by reacting with tricalcium aluminate (C₃A) in clinker to form ettringite, thereby controlling hydration and allowing sufficient time for mixing, transport, and placement. Its use occurs after clinker production, where it is added in controlled proportions (around 3–5%) and ground together with clinker in mills to produce cement. Overall, FGD gypsum enhances workability, ensures consistent setting time, improves long-term strength, and offers sustainability benefits by recycling industrial byproducts and reducing reliance on mined natural gypsum.

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FGD Gypsum in Cement Industry

FGD Gypsum is used as a set retarder in cement.

 

Without Gypsum:

• Cement reacts too fast with water 

• Causes flash setting (instant hardening) 

With Gypsum:

• Controls hydration 

• Gives time for: 

  • Mixing 

  • Transport 

  • Placement 

• Cement contains C₃A (Tricalcium Aluminate) — highly reactive.

• FGD Gypsum reacts with it to form:

• Ettringite (stable compound) 

• This slows down the reaction → controlled setting time