Flue gas desulphurisation gypsum (FGD)
Flue Gas Desulphurisation (FGD) gypsum is a type of synthetic gypsum that can be used to supplement the supply of natural gypsum, it can be 96% pure which is higher than most natural gypsums at 80%, so can be used in gypsum blends.
It is a by-product of a wet purification procedure with natural lime, formed in scrubbing towers of power plants. It forms in the same process as natural gypsum only one that is extremely accelerated down to a few hours. The SO2 is washed out by water, oxidised to sulphates SO3 in an aqueous solution, calcium from quicklime precipitates into a purer form (than natural) of gypsum, dihydrous calcium sulphate (CaSO4,2H2O).
It is the most common process to create synthetic gypsum and an important supplement to natural gypsum, although it is a by product is is also reliant on the firing of coal powered energy centres. Other synthetic gypsums are phosphogypsum, titanogypsum, citrogypsum, fluoroanhydrite, as well as other processes.
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