Potassium sulfate is a non-flammable white crystalline salt which is soluble
in water. The chemical is commonly used in fertilizers, providing both potassium
and sulfur. History
Potassium sulfate has been known since early in the 14th century, and it was
studied by Glauber, Boyle and Tachenius. In the 17th century, it was named
arcanuni or sal duplicatum, as it was a combination of an acid salt with an
alkaline salt. It was also known as vitriolic tartar and Glaser's salt or
sal polychrestum Glaseri after the pharmaceutical chemist Christopher
Glaser who prepared it and used medicinally.
Natural resources The mineral form of potassium sulfate,
arcanite, is relatively rare. Natural resources of potassium sulfate are
minerals abundant in the Stassfurt salt. These are cocrystallizations of
potassium sulfate and sulfates of magnesium calcium and sodium.
The minerals are: Kainite, MgSO4·KCl·H2O
Schönite, K2SO4·MgSO4·6H2O Leonite, K2SO4·MgSO4·4H2O
Langbeinite, K2Mg2(SO4)3 Glaserite, K3Na(SO4)2
Polyhalite, K2SO4·MgSO4·2CaSO4·2H2O From some of the minerals like kainite,
the potassium sulfate can be separated, because the corresponding salt is less
soluble in water. Kieserite, MgSO4·H2O, can be combined
with a solution of potassium chloride to produce potassium sulfate.
Manufacture The process for manufacturing potassium
sulfate is similar to that used for the manufacture of sodium sulfate.
Potassium sulfate can be synthesised by reaction of potassium chloride with
sulfuric acid according to the Leblanc process. Potassium sulfate is produced
according to the following reaction: 2 KCl + H2SO4 → 2 HCl + K2SO4
The Hargreaves process uses sulfur dioxide, oxygen and water and potassium
chloride as the starting materials to produce potassium sulfate. Hydrochloric
acid evaporates off. SO2 is produced through the burning of sulfur.
Properties The anhydrous crystals form a double
six-sided pyramid, but are in fact classified as rhombic. They are
transparent, very hard and have a bitter, salty taste. The salt is soluble
in water, but insoluble in solutions of potassium hydroxide, or in absolute
ethanol. It melts at 1,067 °C. Uses
The principal use of potassium sulfate is as a fertilizer. K2SO4 does not
contain chloride, which can be harmful to some crops. Potassium sulfate is
preferred for these crops, which include tobacco and some fruits and vegetables.
Crops that are less sensitive may still require potassium sulfate for optimal
growth if the soil accumulates chloride from irrigation water.
The crude salt is also used occasionally in the manufacture of glass. Potassium
sulfate is also used as a flash reducer in artillery propellant charges. It
reduces muzzle flash, flareback and blast overpressure.
Sometimes used as an alternative blast media similar to soda in soda blasting
as it is harder and similarly water-soluble.
Potassium hydrogen sulfate Potassium hydrogen sulfate or bisulfate,
KHSO4, is readily produced by mixing K2SO4 with an equivalent number of moles
of sulfuric acid. It forms rhombic pyramids, which melt at 197 °C. It
dissolves in three parts of water at 0 °C. The solution behaves much as if its
two congeners, K2SO4 and H2SO4, were present side by side of each other
uncombined; an excess of ethanol the precipitates normal sulfate with excess
acid remaining. The behavior of the fused dry salt is
similar when heated to several hundred degrees; it acts on silicates,
titanates, etc., the same way as sulfuric acid that is heated beyond its
natural boiling point does. Hence it is frequently used in analytical chemistry
as a disintegrating agent. For information about other salts that
contain sulfate, see sulfate. See also
Arcanum duplicatum, the term for this substance in alchemy
References External links
mindat.org: Arcanite webmineral: Arcanite