Preparation

Sulfur

1. The Frasch method (from the minerals of free sulfur) is based on the sulfur fusibleness and its relatively low specific density. Overheated water steam (at 170⁰) and compressed air is pumped on pipes under earth (see figure below). Molten sulfur forms foam and is darted out on a surface. So elemental sulfur is obtained with a purity up to 99.5%, which is suitable for the direct use.

The Frasch process of sulfur production

2. Klaus method (from industrial and natural gases which contain H₂S and SO₂):

SO₂ + 2H₂S = 2H₂O + 3S (a catalytic action have traces of water)

3. Decomposition of pyrite:

FeS₂ FeS + S (without access of air)

(reaction of selfoxidation-selfreduction, or disproportionation):

Industrial uses of sulfur

Selenium, Tellurium, Polonium

In industry. Se and Te can be isolated from wastes of copper, iron, and lead processing where selenium and tellurium are by-products:

- SеO₂ and ТеO₂ having special applications are formed next to SO₂ at FeS₂ oxidising annealing. They are separated, concentrated, and then reduced by SO₂ in concentrated HCl to elemental chalcogens:

EO₂ + SO₂ + H₂O = E + 2H₂SO₄.

Sеlenium is separated at first and Tе can be isolated after the strong dilution of a solution (the content of tellurides in sulfide ores is considerably lower than selenides).

- at electrorefining of metallurgical copper from anode slime(mud) in considerable amounts.

content of the method: metallurgical copper is used as a soluble anode, copper of high purity (99.9% Cu) is formed during the cathode process on a cathode. Se and Te pass to anode slime that is accumulated on the bottom of electrolysis bath and serve as a raw material for production of elemental chalcogens Se and Te (oxidation of raw material to ЕO₂ and its subsequent reduction by SO₂).

Polonium (²¹⁰Ро) is produced (in kilogram amounts) in atomic reactors at bombardment of bismuth (²⁰⁹Ві) by neutrons:

²⁰⁹Ві (n, ) ²¹⁰Ві ²¹⁰Po

and also from wastes of uranium ores processing.

Chemical properties

Elemental sulfur

Sulfur is an active non-metal. It is able to oxidize alkaline metals and mercury at heating – in these reaction forms simple and polysulfides:

Fe + S = FeS; G⁰_f = -100,8 kJ/mol

Hg + S = HgS; G⁰_f = -51,4 kJ/mol

H₂Se + S = Se + H₂S

In comparison with oxygen sulfur is a weaker oxidant, therefore oxygen oxidizes it easily:

S + О₂ = SО₂; G⁰_f = -300 kJ/mol

Sulfur is oxidized by halogens, and also by acids-oxidants (H₂SO_4(conc.), HNO₃ and etc.:

2HNO₃ + S = H₂SO₄ + 2NO

2H₂SO₄ + S = 3SO₂ + 2H₂O

In hot solutions of alkalis it disproportionates:

3S⁰ + 6NaOH = 2Na₂S^-2 + Na₂SO₃⁺⁴ + 3H₂O

Chemical properties of sulfur is useful to present by a chart:

Chemical PROPERTIES

Elemental selenium, tellurium, and polonium

From the chemical point of view Se and Te are analogues of sulfur. Se is a typical non-metal. Contribution of metallicity in Te is larger, that is why, for example, halides ТеX₂ and ТеX₄ display salt-like behaviour.

Possible oxidation states (between -2 and +6) signify their ability to be oxidants and reductants. For instance, the disproportionation reaction in hot alkaline solutions:

Se + 6KOH K₂ Se⁺⁴O₃ + 2K₂Se ^-2 + H₂O

In the series O—S—Se—Te—Po (R_a and metallic properties grow) reducing agent strength grows and oxidizing ability decreases.

Reducing properties. Те is able to reduce water to free hydrogen:

Те + 2Н₂О = ТеО₂ + 2Н₂

Such process is impossible in case of sеlenium and sulfur. Unlike them Ро reacts with dilute acids as an ordinary metal:

Ро + 2HCl = PoCl₂ + H₂

All these elements are oxidized concentrated HNO₃

S + 6HNO₃ = H₂S⁺⁶O₄ + 6NO₂ + 2H₂O

Se + 4HNO₃ = H₂Se⁺⁴O₃ + 4NO₂ + H₂O

Te + 4HNO₃ = Te⁺⁴O₂ + 4NO₂ + 2H₂O (TeO₂ is low solubley)

Ро + 8HNO₃ = Ро⁺⁴(NO₃)₄ + 4NO₂ + 4H₂O (behaves as a metal)

At heating Se, Те, and Ро oxidize О₂ and Hal₂ easily enough, forming the appropriate compounds (+4):

Ро + О₂ = РоО₂

Oxidizing properties. Their weakening in the series O—S—Se—Te—Po proves the change of Gibbs energy, for example:

Н₂ + Е = Н₂Е

	Н2О(g)	Н2S(g)	Н2Se(g)	Н2Te(g)
Gf, kJ/mol	-229	-34	+20	+85

(that is why Sе + Н₂ reacts partially when heated, and Te + Н₂ have no reaction).

They also have oxidising properties in reactions with metals:

Fe + Se = FeSe