Sulphur occurs in nature in free and combined states. In the free state, it mainly occurs near volcanic regions of the earth. Free sulphur is usually found under the earth’s surface at about 700 – 900 feet below. Sulphur in the combined state is found in nature as: Next paragraph, I will describe the Extraction of sulphur, uses of sulphur, and the key properties of sulphur.
| Iron Pyrites | FeS2 |
| Galena | Cu2S . FeS2 |
| Cinnabar | PbS |
| Orpiment | HgS |
| Gypsum | As2S3 |
| Gypsum | (CaSO4 . 2H2O) |
Extraction Of Sulphur.
Sulphur is being extracted by different methods which depend upon the source. The following methods are more common:
Frasch Method.
This process is used for getting sulphur from the underground. A hole is drilled through which four concentric pipes are passed up to the sulphur-bearing bed. The innermost pipe is used to compress air and the pipe next to it is used to pass steam which melts the sulphur under the earth. Molten sulphur and its emulsion with water flow out of the third pipe (from inside). The outermost pipe allows the unused steam to be removed.
The emulsified sulphur is transferred to large settling tanks where it solidifies on cooling. This process gives about 99% pure sulphur which can directly be used without further purification.
Sicilian Process.
in Sicily, sulphur is found mixed with gypsum and quartz. The lumps of ore in the form of heap are heated in closed chamber. Sulphur melts and is collected from the base of the chamber.
The sulphur thus obtained is further refined in closed iron retorts and sulphur vapours are collected in large chambers to get flowers of sulphur. This is melted to get roll sulphur or brimstone.
From Sulphides and Sulphide Ores.
The sulphide ores are usually treated to extract metals, and SO2 is obtained as a result of roasting during this process. Sometimes it becomes necessary to reduce SO2 to free sulphur.
SO2 + C → S + CO2
The Overall process staring From CaS is:
CaS + H2O + CO2 → CaCO3 + H2S
2H2S + O2 → 2S + 2H2O
From Coal Gas.
Coal gas contains H2S which is removed by passing the gas over heated Fe2O3 to get Fe2S3, and FeS. The mixture is known as spent oxide. When Fe2S3 and FeS mixture is allowed to remain in contact with water and air to undergo weathering, sulphur is deposited.
Fe2O3 + 3H2S → Fe2S3 + 3H2O
2Fe2S3 + 3O2 + 2H2O → 2Fe2O3 + 2H2O + 6S
By Bacterial Action
Certain bacteria have the remarkable ability to convert sulphates into free sulphur. Artificially prepared strains of bacteria have been used to prepare sulphur from calcium sulphate.
Uses Of Sulphur.
- It is used in the manufacture of an important industrial acid, H2SO4
- S and SO2 are used for industrial bleaching purpose.
- S is used, for the production of CS2 which is an industrial solvent.
- Raw rubber is cured or vulcanized by sulphur in order to get elasticity.
- Gunpowder and explosive have sulphur as an essential ingredient.
- Matches industry utilizes sulphur as an essential item.
- For the preparation of ultramarine (a blue dye) sulphur is largely used.
Properties of Sulphur.
Elementary sulphur is a non-metallic stable solid and quite reactive. Many metals undergo ready reaction with metals. Thus, rubbing mercury with sulphur would give HgS.
Elementary sulphur is both oxidizing and reducing agent. Sulphur contains 3s2 3p4 valence electrons and would take up 2 electrons to get 3s2 3p6 (next inert gas configuration) electrons and hence would act as an oxidizing agent and the S is reduced to S2-. The oxidation of S involves loss of electrons and is oxidized to +4 and +6 oxidation states whereby acting as a reducing agent.
The following are the typical reactions of sulphur:
1.Reaction with H2.
Sulphur combines directly with H2 to gives H2s.
H2 + S → H2S
The amount of H2s formed increase with temperature.
2. Reaction With non-metals.
Sulphur reacts directly with other non-metals, i.e., C, Cl2 etc.
C + 2S → CS2
3. Reaction with metals.
Sulphur reacts with metal such as Zn, Al and Fe on heating to give sulphides.
Zn + S → ZnS
Fe + S → FeS
It represents the oxidizing action of S.
Structure of Sulphur.
The two hydrogen atoms are covalently bonded to sulphur atom with H – S – H bond angle of 92°.
