Extraction

  Traditionally, sulfur has been produced using the Frasch process, in which superheated water (440K under pressure) is used to melt the sulfur, and compressed air then forces it to the surface. For environmental reasons, the Frasch process is in decline and many operations have been closed.  Canada and the US are the largest producers of sulfur in the world, and Figure 15.2 shows the dramatic changes in methods of sulfur production in the US over the period from 1970 to 2001. The trend is being followed worldwide, and sulfur recovery from crude petroleum refining and natural gas production is now of greatest importance. In natural gas, the source of sulfur is H₂S which occurs in concentrations of up to 30%. Sulfur is recovered by reaction below.   An alternative source of sulfur is as a by-product from the manufacture of sulfuric acid.

  Commercial sources of Se and Te are flue dusts deposited during the refining of, for example, copper sulfide ores and from anode residues from the electrolytic refining of copper.