Sulfur

Sulfur: the essentials

 Brief description: the spelling of sulphur is "sulfur" in the USA and now that IUPAC has decided it has jurisdiction over the British English language (as distinct from American English) as well as nomenclature, so we in the UK are expected to use the f word.

Sulphur is found in meteorites, volcanoes, hot springs, and as galena, gypsum, Epsom salts, and barite. It is recovered commercially from "salt domes" along the Gulf Coast of the USA.

Jupiter's moon Io owes its colours to various forms of sulphur. A dark area near the crater Aristarchus on the moon may be a sulphur deposit.

Sulphur is a pale yellow, odourless, brittle solid, which is insoluble in water but soluble in carbon disulphide. Sulphur is essential to life. It is a minor constituent of fats, body fluids, and skeletal minerals.

Carbon disulphide, hydrogen sulphide, and sulphur dioxide should be handled extremely carefully. Hydrogen sulphide in very small concentrations can be metabolized, but in higher concentrations it can cause death quickly by respiratory paralysis. It is insidious in that it quickly deadens the sense of smell. Sulphur dioxide is a dangerous component in atmospheric air pollution and is one of the factors responsible for acid rain.

Table: basic information about and classifications of sulfur.

Name: Sulfur Symbol: S Atomic number: 16 Atomic weight: 32.065 (5) [see notes g r] Standard state: solid at 298 K CAS Registry ID: 7704-34-9

Group in periodic table: 16 Group name: Chalcogen Period in periodic table: 3 Block in periodic table: p-block Colour: lemon yellow Classification: Non-metallic

The picture above shows the result from burning a mixture of zinc metal powder and sulphur.

Isolation

Isolation: it is not normally necessary to make sulphur in the laboratory as it is so readily available. It is found as the native element in nature and extracted by the Frasch process. This is an interesting process since it means that sulphur can be extracted from underground without mining it. In the Frasch process underground deposits of sulphur are forced to the surface using superheated water and steam (160°C, 16 atmospheres, to melt the sulphur) and compressed air (25 atmospheres). This gives molten sulphur which is allowed to cool in large basins. Purity can reach 99.5%.

The process in energy intensive. Commercial success for this operation depends upon suitable geological conditions as well as access to cheap water and energy.

Hydrogen sulphide, H₂S, is an important impurrity in natural gas which must be removed before the gas is used. This is done by an absorption and regeneration process to concentrate the H₂S, followed by a catalytic oxidation (Claus process) using porous catalysts such as Al₂O₃ or Fe₂O₃.

8H₂S + 4O₂ → S₈ + 8H₂O

Over the years the Claus process has been improved and a modified process can yield 98% recovery.

In the laboratory, sulphur can be purified by recrystallisation from solutions in carbon disulphide, CS₂. However the resulting crystals are contaminated with solvent, H₂S, and SO₂. One good way to purify sulphur is to use a quartz heater (700°C) immersed in liquid sulphur. Carbon impurities decompose to form volatile materials of solid carbon, which coat the heater. After a week or so, finishing with a distillation under vacuum, the result is sulphur with a carbon content of about 0.0009%.

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Sulfur	Soufre
Schwefel	Zwavel
Solfo	Azufre
Svavel	Enxofre