- Sicilian process
- Frasch process.
Sicilian Process
The volcanic regions of Sicily have rocks containing about 25% of sulphur. Special types of kilns with air spaces are made on sloping hillsides. Powdered rocks containing sulphur are piled up on these brick kilns (Fig. 13.19).
Sulphur produced by the Sicilian process is only about 95% pure and thus has to be purified further.
Disadvantages of Sicilian process
1. As the kiln is heated by burning sulphur, about 33% of sulphur is lost.
2. The process is not continuous.3. The process is labor intensive i.e. manual labor is needed to collect and stack powdered sulphur, to rebuild up kilns etc.
4. The sulphur so obtained is of low purity and needs to be further purified.Purification of Sulphur
Impure sulphur is heated in an iron retort. The sulphur vapors formed at 444oC are allowed to escape in a large brick chamber. The vapors condense and form 'flowers of sulphur' on the walls of the chamber. After sometime when the temperature of the chamber rises up to 120oC, these flowers of sulphur melt and collect at the bottom of the chamber. The molten sulphur is poured into cylindrical moulds and allowed to solidify. Sulphur so obtained is called roll sulphur.
Remember :
Flowers of sulphur
When vapors of sulphur are cooled and condensed on the walls of a brick chamber, sulphur is obtained like flowers of sulphur.
Frasch Process
In Louisiana (USA) and Gulf of Mexico large sulphur deposits occur at a depth of about 300-400 metres below the earth's surface. Layers of soft sand, clay and rocks over these sulphur beds make it practically impossible to extract sulphur from the deposits.
Hermen Frasch in 1894 devised a brilliant technique of obtaining sulphur from these deposits. His technique was practical, simple and cost effective. In this process, now called the Frasch process, a system of three concentric pipes is sunk into the earth to reach the sulphur beds (about 300m deep).Outer pipe
In this pipe, superheated water (170oC) is sent down under 10 atm pressure. This melts the sulphur in the beds of the soil.
Inner most pipe
Hot compressed air is simultaneously blown down this pipe, which causes the frothing of sulphur.
Middle pipe
The simultaneous pressure of air in the inner pipe and water of the outermost pipe forces the sulphur froth to rise up while the earthly impurities are left behind (Fig13.21).
Advantages of Frasch Process
1. It is economical since there is no wastage of sulphur.
2. Sulphur of 99.5% purity is obtained. Thus it need not be further purified.3. The process is simple and cost effective.
4. The process is continuous and does not requite rebuilding of structures.