Sulfur

Sulfur is one of the most important elements. It is used to make sulfuric acid, which is the
most abundantly made industrial chemical. The element itself is an essential plant nutrient.
Sulfur (S), is a nonmetallic chemical element belonging to the oxygen group (Group 16 [VIa]
of the periodic table), one of the most reactive element. Sulfur occurs naturally in the
environment and is the thirteenth most abundant element in the earth's crust. Pure sulfur is a
tasteless, odourless, brittle solid that is pale yellow in colour, a poor conductor of electricity,
and insoluble in water. It reacts with all metals except gold and platinum, forming sulfides; it
also forms compounds with several nonmetallic elements. Millions of tons of sulfur are
produced each year, mostly for the manufacture of sulfuric acid, which is widely used in
industry.

Annual production of sulfur

World 70 million tonnes

China 11 million tonnes

U.S. 9 million tonnes

Russia 7 million tonnes

Canada 6 million tonnes

Germany 4 million tonnes

Japan 3 million tonnes

Saudi Arabia 3 million tonnes

Manufacture of sulfur
The vast majority of sulfur is recovered from natural gas and oil, which contain hydrogen
sulfide and a wide variety of organic compounds that contain sulfur (such as CH3SH Methyl
mercaptan, or methanethiol). They have to be removed before the natural gas and oil can be
used as a feedstock for the chemical industry as they poison the catalysts that are used in the
various processes to make chemicals. Equally, they have to be removed if natural gas or oil
are to be used as fuels. Otherwise large amounts of sulfur dioxide, a very dangerous pollutant,
will be released into the atmosphere when the fuels are burnt. The organic sulfur compounds
are converted to hydrogen sulfide by reduction with hydrogen. For example:
Hydrogen sulfide gas is separated from other gases present by dissolving it in an aqueous
solution of an organic base, such as, for example, 2-aminoethanol (monoethanolamine).
Although this is a complex process, the following equation shows the overall reaction:

Figure. Much natural gas and oil contain large quantities of hydrogen sulfide and
organic sulfur compounds which must be removed to produce gas and oil which can be used
as fuels. They are co
nverted into elemental sulfur which is heated so that it becomes molten and then piped into
large moulds where it solidifies. It is stored in the open until it is used to make sulfuric
acid. This photo shows sulfur recovered in the immense Lacq field in southwestern France
where the gas is very 'sour', containing 16% hydrogen sulfide.

Heating the solution of the salt liberates pure hydrogen sulfide and regenerates the
amine. Hydrogen sulfide is then burned with a limited amount of air to give sulfur dioxide,
sulfur and water vapour, and unreacted hydrogen sulfide:

The sulfur is condensed and separated. The remaining gases are passed over a catalyst bed of
alumina to convert more hydrogen sulfide to sulfur:

These two stages are repeated in three separate cycles to achieve over 95% recovery of sulfur.
Sources of Sulfur

Sulfur can be found from the following sources:

(1) Extraction from beneath the earth crust - this is the most important source.

(2) From natural gas - this is the second most important source. The natural gas is found in
southern France, in a place called Lacq.

(3) From other processes - example, as a by-product of the purification of crude coal gas and the
refining of petroleum.

Properties of Sulfur

Sulfur shows the following properties:

Physical Properties

(1). Sulfur is a yellow solid and is insoluble in water but soluble in carbon disulphide and toluene
(methyl benzene).

(2). Sulfur is a non-metal and therefore a poor conductor of heat and electricity.

(3). The boiling point of sulfur is 444oC. When sulfur vapour is condensed, a fine powder, which
forms a floral pattern is obtained - this is called ‘flower of sulfur.

Chemical Properties

(1). Most metals and non-metals combine directly with sulfur.

Example: in the absence of air, sulfur combines directly with most metals to form suphides when
heated

Fe(s) + S(s) → FeS(s)

Zn(s) + S(s) → ZnS(s)

Pb(s) + S(s) → PbS(s)

2Cu(s) + S(s) → Cu2S(s)

Note: the reactive elements, like Na and K may react with sulfur spontaneously (without heating)
(2). Sulfur burns in excess of air with a bright blue flame, to form sulfur(IV) oxide and a little
quantity of sulfur(VI) oxide.

O2(g) + S(s) → SO2(g)

(3). Sulfur combines slowly at high temperature with hydrogen, to form hydrogen sulphide.

H2(g) + S(s) → H2S(g)

(4). Sulfur vapour combines with hot coke to form a liquid - carbon disulphide.

C(s) + S(g) → CS2(l)

(5). Action of oxidizing acids on sulfur

Note:

* With hot concentrated H2SO4, sulfur is oxidized to sulfur (IV) oxide, SO2, while the acid is
reduced to SO2.

2H2SO4(aq) + S(s) → 2H2O(l) + 3SO2(g)

* With hot conc. HNO3 using bromine as catalyst, sulfur is oxidized to tetraoxosulphate(VI)
acid.

6HNO3(aq) + S(s) → H2SO4(aq) + 6NO2(g) + 2H2O(l)

* With dilute acids and with conc. HCl - no reaction with sulfur.

(6). Action of hot concentrated alkalis.

With hot conc. alkalis, sulfur forms a mixture of sulphides and sulphate (IV). Polysulphide and
thiosulphate (VI) are formed in the presence of excess sulfur.

3S + 6OH- → 2S2- + SO32- + 3H2O

With excess sulfur, SO32- + S → S2O32- (thiosulphate (VI))

Uses of sulfur
About 90% of sulfur produced or extracted is used to make sulfur dioxide, which is then
converted to sulfuric acid. The majority of the acid is used in the production of phosphate
fertilizers, a crucial component in the provision of food in the World.
Another important use of elemental sulfur is in fertilizers as a soil nutrient in its own right,
particularly where there is a deficiency of sulfur in the soil.
Sulfur is beginning to be used as a component of infrastructure band structural materials. For
example, adding sulfur pellets to asphalt makes road surfaces more durable and resistant to
damage by cracking when the conditions are very cold. Sulfur concrete is produced by adding
sulfur as concrete is being made. It has a smoother surface, making it easy to paint. It is
strong and is able to withstand acidic and salt waters, making it a possible material for sea
barriers and dams.
The main uses of Sulfur

1. The main use of sulfur is in the preparation of SO2 which is used in the manufacture of
sulfuric acid.

2. Sulfur is used in the manufacture of carbon disulphate, sodium thiosulphate, gun powder,
matches and in fireworks.

3. Sulfur is used on vulcanization of rubber. Natural rubber is soft and sticky. Heating it
with sulfur makes it hard non-sticky and more elastic. This process of heating of natural
rubber with sulfur is known as vulcanization.

4. Sulfur is used as fungicide and insecticide in agriculture and as a disinfectant in

medicines.

5. Sulfur is used in ointments for curing skin diseases.

6. Sulfur is used in beauty parlours to give specific shapes to the hair.

7. Sulfur is also used in many other industries including non-ferrous metals, pigments,
fibers, hydrofluoric acid, carbon disulphide, pharmaceuticals, agricultural pesticides,
personal care products, cosmetics, synthetic rubber vulcanization, water treatment, and
steel pickling

Like nitrogen, phosphorus and potassium, sulfur is one of the essential plant nutrients. It
contributes to an increase in crop yields in three different ways: 1) it provides a direct nutritive
value, 2) it provides indirect nutritive value as soil amendment, especially for calcareous and
saline alkali soils, and 3) it improves the use efficiency of other essential plant nutrients,
particularly nitrogen and phosphorus. In general, sulfur has similar functions in plant growth and
nutrition as nitrogen.