gypsum calcination

Gypsum Calcination: Process and Applications

Gypsum calcination is a thermal treatment process that converts raw gypsum (calcium sulfate dihydrate, CaSO₄·2H₂O) into calcium sulfate hemihydrate (CaSO₄·0.5H₂O) or anhydrite (CaSO₄). This transformation occurs through controlled heating, which removes water molecules from the gypsum structure. The process is critical in producing materials like plaster of Paris, stucco, and other construction products.

Stages of Gypsum Calcination
The calcination process involves three primary stages:

1. Drying: At temperatures around 100–150°C, free moisture is evaporated from the gypsum.
2. Dehydration: Between 150–180°C, gypsum loses its chemically bound water, forming hemihydrate (CaSO₄·0.5H₂O). This is the most common product for plaster applications.
3. Formation of Anhydrite: At higher temperatures (above 200°C), all water is removed, resulting in anhydrous calcium sulfate (CaSO₄), which has different properties and uses.

The exact temperature and duration depend on the desired product and the equipment used, such as rotary kilns, fluidized bed reactors, or kettle calciners.

Applications of Calcined Gypsum
Calcined gypsum is widely used in construction due to its ability to rehydrate and harden when mixed with water. Key applications include:
- Plaster of Paris: Used for molds, casts, and decorative elements due to its quick-setting properties.
- Drywall (Gypsum Board): Hemihydrate gypsum is mixed with additives to create panels for walls and ceilings.
- Cement Additive: Anhydrite or hemihydrate can regulate the setting time of Portland cement.
- Soil Conditioner: In agriculture, calcined gypsum improves soil structure and provides calcium and sulfur nutrients.

Factors Influencing Calcination Quality
Several factors affect the efficiency and output quality of gypsum calcination:
- Particle Size: Finer particles calcine more uniformly but may require careful temperature control to avoid overburning.
- Heating Rate: Slow heating ensures complete dehydration without damaging the crystal structure.
- Residence Time: Prolonged exposure to high temperatures can lead to dead