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The Frasch process is a method to extract sulfur from underground deposits. Most of the world's sulfur was obtained this way until the late 20th century, when sulfur recovered from petroleum sources (recovered sulfur) became more commonplace. As of 2002, all Frasch sulfur mines of note have ceased operation worldwide.
Holes are drilled down through the overlying rock into the sulfur deposits. A series of concentric perforated pipes are then inserted into the drill hole. The outer pipes contain superheated steam (usually about 160 °C) which is pumped down into the deposit.
Since the melting point of sulfur is so low (115.21 °C, just a little over the boiling point of water), it readily liquefies. As the sulfur becomes molten, it is removed by pumping air down the central pipe. When the molten sulfur reaches the surface, it is pumped onto wooden blocks where the sulfur again solidifies.
The Frasch process is able to produce sulfur of very high purity, often above 99.5%.
In 1867, miners discovered sulfur in the caprock of a salt dome in Calcasieu Parish, Louisiana, but it was beneath quicksand, which prevented mining. In 1894 the German-born American chemist, Herman Frasch, devised his Frasch method of sulfur removal using pipes to bypass the quicksand. The process proved successful, on December 24, 1894, when the first molten sulfur was brought to the surface. However, the high cost of fuel needed to heat the water made the process uneconomic until the 1901 discovery of the Spindletop oil field in Texas provided cheap fuel oil to the region. The Frasch process began economic production at Sulfur Mine, Louisiana in 1903.
When Frasch's patent expired, the process was widely applied to similar salt-dome sulfur deposits along the US Gulf Coast. The second Frasch-process mine opened in 1912 in Brazoria County, Texas. The US Gulf Coast came to dominate world sulfur production in the early and middle 20th century. However, starting in the 1970s, byproduct sulfur recovery from oil and natural gas lowered the price of sulfur and drove many Frasch-process mines out of business. The last US Frasch sulfur mine closed in 2000.
- ↑ D'Arcy Shock (1992) "Frasch sulfur mining," in SME Mining Engineering Handbook, Society for Mining Metallurgy and Exploaration, p.1512, accessed 20 February 2009.
- ↑ Handbook of Texas Online: Sulfur industry, accessed 20 February 2009.
- ↑ Joyce A. Ober (2002) Materials Flow of Sulfur, US Geological Survey, Open-File Report 02-298, p.12, PDF file, retrieved 20 February 2009.
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- History of Sulphur (Sulphur, Louisiana)
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