Frasch process

The Frasch process is a method to extract sulfur from underground deposits. Most of the world's sulfur is obtained this way.

Holes are drilled down through the overlying rock into the sulfur deposits. A special series of pipes are then inserted into the drill hole. The pipes are arranged in a circular pattern. The outer pipes will 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%.

History
In 1867, miners discovered sulfur hidden under quicksand in Louisiana and Texas. The German born American chemist, Herman Frasch, devised a new method of sulfur removal which was used to mine the sulfur using pipes to avoid the quicksand. The process proved successful, on December 24, 1894, when the first molten sulfur was brought to the surface. The process is still used all over the world.