Sulfur

Sulfur makes up only 0.05% of the Earth's crust, but it is easy to get because it occurs uncombined as the element, S₈ (eight sulfur atoms tied together into each molecule of the element and joined in a ring).

Sulfur occurs in huge, deep underground deposits of almost-pure element, notably along the Gulf coast of the United States and in Poland and Sicily. However, miners do not have to go underground to get it. They make the sulfur come to them by a clever arrangement of three pipes within pipes, drilled down into the sulfur bed. This arrangement is called the Frasch Process. Superheated steam is shot down through the outermost pipe to melt the sulfur. (The steam has to be superheated because sulfur doesn't melt until 239°F [115°C], which is hotter than "regular" steam.) Then, compressed air is shot down the innermost pipe, which forces the liquid sulfur up and out the middle pipe.

Sulfur is also widely distributed in the form of minerals and ores. Many of these are in the form of sulfates, including gypsum (calcium sulfate, CaSO₄ • 2H₂O), barite (barium sulfate, BaSO₄) and Epsom salts (magnesium sulfate, MgSO₄ • 7H₂O). Others are metal sulfides, including iron pyrites (iron sulfide, FeS₂), galena (lead sulfide, PbS), cinnabar (mercuric sulfide, HgS), stibnite (antimony sulfide, Sb₂S₃) and zinc blende (zinc sulfide, ZnS). The sulfur is recovered from these metal ores by roasting them—heating them strongly in air, which converts the sulfur to sulfur dioxide. For example,

Then the sulfur dioxide can go directly into the manufacture sulfuric acid, which is where more than 90% of the world's mined sulfur winds up.