Sulfur is an element of paradoxes. It is vital to plant and animal life, but it can be a major source of air pollution. Sulfur is an essential raw material for the chemical industry, but it can cause waster disposal problems for that industry. It is an energy source but also a contaminant of other energy sources. Sulfur (sometimes spelled sulphur) is also a paradox biologically. Sulfur-containing amino acids are essential to life, but sulfur dioxide (SO2) can cause damage to crops and forests and hydrogen sulfide (H2S) is a deadly poison.
Sulfur is the 18th most-abundant element of earth, just behind chlorine. In the crust of the earth, it occurs as the familiar yellow element in volcanic rocks, subterranean salt domes, and sedimentary evaporite basins, and as sulfur compounds (metal sulfides and sulfates) in many ores. "Sour" natural gas contains hydrogen sulfide, and petroleum and coal contain organic sulfur compounds. The oceans contain 0.08 percent sulfur, mostly as sulfates; plants and animals contain sulfur in a variety of forms.
Sulfur is also a versatile element, as shown by its physical and chemical properties. It can assume any of five stages of valency (-2,+2,+3,+4,+6). In some sulfur compounds, sulfur atoms in different parts of the molecule have different valencies. Some sulfur compounds are strong reducing agents; others are powerful oxidizers.
Sulfur Production - From Mined to Recovered
Sulfur was first classified as an element in 1777 by Antoine Lavoisier, though it had been known and produced since antiquity. The Greeks, Egyptians, and Chinese produced it thousands of years ago from volcanic deposits; however, the first large-scale commercial production began in Sicily in the 15th century and by the mid-18th century, sulfur had become the main industry of that country.
At first, the production process was primitive. The mined ore was piled up, covered with earth, and ignited. The heat of the burning sulfur melted the remainder of the sulfur, which flowed out of the bottom of the pile. Only about half of the sulfur in the ore was recovered; much of the rest escaped to the atmosphere as sulfur dioxide. (This was before the days of environmental concern.) Toward the end of the 19th century, furnaces with improved heat recovery rates eventually reached 80 percent.
During the 19th century, demand for sulfur increased rapidly because the industrial revolution needed sulfuric acid. Sicily, as the main source, increased its price with the demand. Sulfur consumers looked for alternative, cheaper sources, and the European pyrite industry was born. Deposits of iron pyrite (iron sulfide, FeS2), plentiful in many countries, could be roasted to give sulfur dioxide, that could be converted to sulfuric acid. Pyrite has remained the alternative to sulfur as the raw material for sulfuric acid manufacture to this day, although its relative importance has declined markedly over the last 20 years.
Sulfur production entered a new era in 1894, when Herman Frasch, in Louisiana, succeeded in mining underground salt dome deposits of sulfur by pumping in superheated water and pumping out the molten sulfur. The process, which bears his name, has produced more that 300 million tons of sulfur from deposits in Texas, Louisiana, Mexico,
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