Page 16 - Curriculum Visions Dynamic Book

Extracting sulphur
For centuries it was commonplace to collect sulphur by lowering people down the inside of volcanoes in baskets so they could scrape the sulphur off the walls of the vents. Needless to say, this was not a very popular occupation.
The main technique used to recover sulphur from buried deposits of native sulphur, such as those associated with salt domes (see pages 8 and 9), relies on the fact that sulphur has a low melting point, while at the same time being insoluble
in water.
Superheated water (raised to a temperature of about 165°C) is pumped underground through a pipe. Inside this pipe are two smaller pipes. Compressed air is pumped down the central pipe, and
a frothy mixture of liquid sulphur, water and air is pushed up through the remaining pipe. This system is called the Frasch process, named for its inventor Herman Frasch, an American chemist who invented the process in 1891.
Most sulphur mined by the Frasch process is transported as liquid in insulated railway wagons and ships and taken to sulphuric acid plants.
Sulphur from pyrites
In the past, many sulphide-rich ores have been roasted, not to recover the metals, but to produce compounds of sulphur. The roasting of pyrite produces sulphur dioxide gas, which can then be converted to sulphuric acid (see page 26).
Sulphur from fossil fuels
Although natural gas has a lower sulphur content than the other fossil fuels, it is still important to recover the sulphur to prevent pollution.
The sulphur is obtained by reacting hydrogen sulphide contained in
the natural gas with oxygen. This produces sulphur dioxide gas, which can then be made into sulphuric acid by reacting the sulphur dioxide with oxygen and water.
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