Gypsum
Gypsum is a soft sulfate mineral with the chemical formula CaSO4·2H2O, also known as calcium sulfate dihydrate. It is comprised of calcium, sulphur bound to oxygen, and water. Natural gypsum is an abundant mineral in sedimentary rocks that has been mined and used for construction and and as a fertilizer since the time of Ancient Egypt.
More recently the term synthetic gypsum is used to describe gypsum that is manufactured or that forms as a by product of other processes, such as flue gas desulphurisation (FGD) gypsum which forms in coal-fired power stations.
Pure gypsum is typically white, although impurities create a wide range of different colours. Gypsum is moderately water soluble but exhibits retrograde solubility, meaning it becomes less soluble at higher temperatures. It is fire resistant and is effective at preventing the passage of sound.
In terms of production, gypsum rock is mined or quarried and then crushed and ground into a fine powder. A process of calcining heats the powder, driving off most of the chemically-combined water. The two other forms of gypsum are called selenite and satin spar.
This base gypsum is used for a wide variety of applications:
- Plaster, plasterboard, wallboard, and so on.
- Blockwork.
- Mortar.
- Blackboard chalk.
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Please note the requirement for ensuring that gypsum products are correctly disposed of, it should not be mixed with biodegradable waste at a standard landfill site. It is possible to recycle the material.