Extracting and Processing Natural Gypsum
Sourcing and Processing FGD Gypsum
Manufacturing Eco-efficiently

Extracting and Processing Natural Gypsum

Gypsum/Anhydrite are produced from open-cast mines or underground mines using pillar and stall mining methods that give extraction rates of up to 75%.

Gypsum is normally only screened to remove ‘fines’ (mainly mudstones), then crushed and finely ground. Gypsum/Anhydrite for cement manufacture is supplied in crushed form for further fine grinding with cement clinker.

When Gypsum (CaSO4,2H2O) is ground to a powder and heated at 150° to 165° C, three-quarters of its combined water is removed producing hemi-hydrate plaster (CaSO4,1/2H2O), commonly known as the ‘Plaster of Paris’. When this powder is mixed with water the resulting paste sets hard as the water recombines to produce Gypsum again. This process can be repeated almost indefinitely, with important implications for recycling.

Sourcing and Processing FGD Gypsum

The Gypsum Industry is working towards building value for society by offering safe, economic and recyclable products for the home owner using substitutes to natural Gypsum whenever possible, in order to reduce the pressure on natural resources.

FGD Gypsum

An intelligent alternative is Gypsum that comes from the flue gas desulphurisation plant (FGD) of the power station industry. This FGD Gypsum is the end product of a wet purification procedure with natural lime, that essentially forms according to the same laws as natural Gypsum–but in a speeded-up process taking only a few hours.

FGD Gypsum is an important supplement to the supply of natural Gypsum.

This synthetic Gypsum has a higher purity (Gypsum content of 96%) than most natural Gypsum (80%). This means that lower quality Gypsum can be blended with high purity Desulphogypsum, allowing material that would not have been mined in the past to be classified as exploitable reserves.

Processing FGD Gypsum

The desulphurisation process takes place in scrubbing towers in which the flue gases are brought into contact with an aqueous suspension containing powdered limestone or slaked quicklime as its alkaline component. The SO2 is washed out by the water, oxidised to Sulphates SO3 in the aqueous solution and precipitated with Calcium from the limestone/quicklime into Dihydrous Calcium Sulphate (CaSO4,2H2O), Gypsum. The Gypsum crystals are separated out of the suspension as a moist, fine crystalline powder with the aid of centrifuges or filters.

FGD Gypsum: Quality Criteria and Analysis Methods-en-de-fr.pdf

Gypsum products and solutions used every day are designed to:

• Be manufactured using by-products and recycled materials
• Be manufactured with low energy intensity; 
• Be manufactured with low emissions. The main emission of the production process is steam;
• Use little packaging;
• Be recycled at the end of their life cycle;
• Promote indoor air quality;
• Be sound insulation efficient;
• Be impact and fire resistant;
• Be energy-efficient in its use – thereby playing an important role in the reduction of carbon emissions in the built environment;
• Extend the lifetime of a building thus enhancing overall sustainabilit

Conclusion: Speed and ease of assembly and finishing mean that constructing with gypsum products is economical and fast.  The magic properties of gypsum, and the products’ eternal recyclability, improve the overall eco-efficiency and sustainability of buildings