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Gypsum

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Materials

Gypsum is part of an evaporite group of minerals that includes chlorides, carbonites, borates, nitrates, and sulfates.[1] A more common name for this mineral compound is calcium sulphate, dihydroxide, or sulphate of lime.[2] It is generally found underground, deposited in sedimentary layers in the sea, lakes, caves, and salt flats close to limestone deposits or other minerals formed as a result of evaporation.

Extraction of gypsum deposits is accomplished through opencast mining or underground mining using the pillar and stall method.[3] Gypsum deposits are mined worldwide but the United States is the leader in gypsum production followed by Canada.

[edit] Process

Gypsum also comes in different forms. A pure, raw form of gypsum is the white crystal alabaster. Another type of unprocessed gypsum that looks like the petals of a flower and is found in the desert is a calcium sulphate nicknamed desert rose.[4] When gypsum is air-heated to a temperature of 200 degrees Celsius,[5] half or more of its original moisture content is removed and the result is a powder called burnt gypsum.[6] When water is added to burnt gypsum, it immediately solidifies. This value-added property of burnt gypsum is marketed as the molding agent Plaster of Paris.[7] Common chalk is also made from burnt gypsum.

A synthetic form of gypsum, called FGD gypsum, is also produced from the flue gas desulphurisation plant (FGD) of the power station industry. FGD gypsum is the end product of a wet purification procedure with natural lime. This process forms FGD gypsum similar to the way natural gypsum is produced, but much faster. One advantage over synthetically produced gypsum is it has a higher purity concentration of 96 percent over natural gypsum that only has an 80 percent purity concentration.[8]

[edit] Uses

As a material, gypsum has many different uses. In home or building construction, gypsum is used in the formation of drywall panels or sheetrock. Gypsum drywall is approximately 90 percent gypsum and 10 percent paper facing and backing. In fact, over 80 percent of all gypsum mined is used to make manufactured products like drywall. As a construction material it is very useful as it can be calcined and then made wet to form a paste that can be instantly molded to any shape upon application. Another unique characteristic of gyspum is that it is fire resistant.[9] Gypsum is also used as mixing agent with cement clinker to make concrete, in agriculture to loosen clay-rich soils, and in fertilizer manufacturing.[10]

[edit] References

  1. Gypsum. Answers.com. 2008-10-07.
  2. What is Gypsum. Wisegeek.com. 2008-10-07.
  3. Fact Sheet. Eurogypsum. 2008-10-07.
  4. What is Gypsum. Wisegeek. 2008-20-07.
  5. What is Drywall. Drywall Recycling. 2008-10-07.
  6. What is Gypsum. Wisegeek. 2008-10-07.
  7. FactSheet. EuroGypsum. 2008-10-07.
  8. FactSheet. Eurogypsum. 2008-10-07.
  9. What is Drywall. Drywall Recycling. 2008-10-07.
  10. Gypsum. Answers.com. 2008-10-07.