Potassium sulfate (US) or potassium sulphate (UK), also called sulphate of potash (SOP), arcanite, or archaically potash of sulfur, is the
inorganic compound with formula K
2SO
4, a white water-
soluble
In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solubi ...
solid. It is commonly used in
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
s, providing both
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosph ...
and
sulfur.
History
Potassium sulfate (K
2SO
4) has been known since early in the 14th century. It was studied by
Glauber,
Boyle
Boyle is an English, Irish and Scottish surname of Gaelic, Anglo-Saxon or Norman origin. In the northwest of Ireland it is one of the most common family names. Notable people with the surname include:
Disambiguation
*Adam Boyle (disambiguation), ...
, and
Tachenius. In the 17th century, it was named ''arcanuni'' or ''sal duplicatum'', as it was a combination of an
acid salt Acid salts are a class of salts that produce an acidic solution after being dissolved in a solvent. Its formation as a substance has a greater electrical conductivity than that of the pure solvent. An acidic solution formed by acid salt is made dur ...
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
Christopher Glaser (1615 – between 1670 and 1678), a pharmaceutical chemist of the 17th century.
Life
He was born in Basel. He became demonstrator of chemistry, as successor of Lefebvre, at the Jardin du Roi in Paris, and apothecary to Louis ...
who prepared it and used medicinally.
Known as ''arcanum duplicatum'' ("double secret") or ''panacea duplicata'' in pre-modern
medicine
Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pr ...
, it was prepared from the residue (''
caput mortuum
''Caput mortuum'' (plural ''capita mortua'') is a Latin term whose literal meaning is "dead head" or "worthless remains", used in alchemy.
''Caput mortuum'' (alternately called '' nigredo'') signified a useless substance left over from a chemi ...
'') left over from the production of
aqua fortis
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
(nitric acid, HNO
3) from
nitre
Niter or nitre is the mineral form of potassium nitrate, KNO3. It is a soft, white, highly soluble mineral found primarily in arid climates or cave deposits.
Historically, the term ''niter'' was not well differentiated from natron, both of w ...
(potassium nitrate, KNO
3) and
oil of vitriol
Sulfuric acid ( American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
(sulphuric acid, H
2SO
4) via
Glauber's process:
:2 KNO
3 + H
2SO
4 → 2 HNO
3 + K
2SO
4
The residue was dissolved in hot water, filtered, and evaporated to a cuticle. It was then left to crystallise. It was used as a
diuretic
A diuretic () is any substance that promotes diuresis, the increased production of urine. This includes forced diuresis. A diuretic tablet is sometimes colloquially called a water tablet. There are several categories of diuretics. All diuretics i ...
and
sudorific
Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals.
Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distribu ...
.
According to Chambers's ''
Cyclopedia'', the recipe was purchased for five hundred
thalers by
Charles Frederick, Duke of Holstein-Gottorp
Charles Frederick, Duke of Schleswig-Holstein-Gottorp () (30 April 1700 – 18 June 1739) was a Prince of Sweden and Duke of Schleswig-Holstein-Gottorp and an important member of European royalty. His dynasty, the Dukes of Schleswig-Holstein-Gott ...
. Schroder, the duke's physician, wrote wonders of its great uses in
hypochondriac
Hypochondriasis or hypochondria is a condition in which a person is excessively and unduly worried about having a serious illness. An old concept, the meaning of hypochondria has repeatedly changed. It has been claimed that this debilitating cond ...
al cases, continued and intermitting
fever
Fever, also referred to as pyrexia, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using val ...
s, stone,
scurvy
Scurvy is a disease resulting from a lack of vitamin C (ascorbic acid). Early symptoms of deficiency include weakness, feeling tired and sore arms and legs. Without treatment, decreased red blood cells, gum disease, changes to hair, and bleeding ...
, and more.
Natural resources
The mineral form of potassium sulfate,
arcanite, is relatively rare. Natural resources of potassium sulfate are
minerals
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed ...
abundant in the
Stassfurt salt. These are cocrystallizations of potassium sulfate and sulfates of
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
,
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
, and
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
.
Relevant minerals are:
*
Kainite
Kainite ( or ) (KMg(SO4)Cl·3H2O) is an evaporite mineral in the class of "Sulfates (selenates, etc.) with additional anions, with H2O" according to the Nickel–Strunz classification. It is a hydrated potassium-magnesium sulfate-chloride, natura ...
, KMg(SO
4)·Cl·3H
2O
*
Schönite
Picromerite (synonyms: schoenite, schönite) is a mineral from the class of hydrous sulfates lacking additional anions, and containing medium to large cations according to the Nickel–Strunz classification.
Etymology
The name comes from the Gr ...
(now known as picromerite), K
2SO
4·MgSO
4·6H
2O
*
Leonite
Leonite is a hydrated double sulfate of magnesium and potassium. It has the formula K2SO4·MgSO4·4H2O. The mineral was named after Leo Strippelmann, who was director of the salt works at Westeregeln in Germany. The mineral is part of the blodit ...
, K
2SO
4·MgSO
4·4H
2O
*
Langbeinite
Langbeinite is a potassium magnesium sulfate mineral with the chemical formula K2Mg2(SO4)3. Langbeinite crystallizes in the isometric-tetartoidal (cubic) system as transparent colorless or white with pale tints of yellow to green and violet cry ...
, K
2Mg
2(SO
4)
3
*
Aphthitalite
Aphthitalite is a potassium sulfate mineral with the chemical formula: (K,Na)3Na(SO4)2.
It was first described in 1835 for an occurrence on Mount Vesuvius, Italy. The name is from the Greek άφθητος, "unalterable", and άλας, "salt", fo ...
(previously known as glaserite), K
3Na(SO
4)
2
*
Polyhalite
Polyhalite is an evaporite mineral, a hydrated sulfate of potassium, calcium and magnesium with formula: . Polyhalite crystallizes in the triclinic system, although crystals are very rare. The normal habit is massive to fibrous. It is typically c ...
, K
2SO
4·MgSO
4·2CaSO
4·2H
2O
The potassium sulfate can be separated from some of these minerals, like kainite, because the corresponding salt is less soluble in water.
Kieserite
Kieserite, or magnesium sulfate monohydrate, is a hydrous magnesium sulfate mineral with formula (MgSO4·H2O).
It has a vitreous luster and it is colorless, grayish-white or yellowish. Its hardness is 3.5 and crystallizes in the monoclinic cry ...
, MgSO
4·H
2O, can be combined with a solution of
potassium chloride to produce potassium sulfate.
Production
Approximately 1.5 million tons were produced in 1985, typically by the reaction of
potassium chloride with
sulfuric acid, analogous to the
Mannheim process for producing sodium sulfate.
The process involves intermediate formation of
potassium bisulfate
Potassium bisulfate/ Potassium Sulphate is an inorganic compound with the chemical formula KHSO4 and is the potassium acid salt of sulfuric acid. It is a white, water-soluble solid.
Preparation
More than 1 million tons were produced in 1985 a ...
, an exothermic reaction that occurs at room temperature:
:KCl + H
2SO
4 → HCl + KHSO
4
The second step of the process is endothermic, requiring energy input:
:KCl + KHSO
4 → HCl + K
2SO
4
Structure and properties
Two crystalline forms are known. Orthorhombic β-K
2SO
4 is the common form, but it converts to α-K
2SO
4 above 583 °C.
[ These structures are complex, although the sulfate adopts the typical tetrahedral geometry.
File:Structure of K2SO4, K2CrO4 and some related compounds.tif, Structure of β-K2SO4.
File:TopView10cnK.tif, Coordination sphere of one of two types of K+ site.
File:SO4sphere.tif, SO4 environment in β-K2SO4.
It does not form a hydrate, unlike sodium sulfate. The salt crystallizes as double six-sided pyramids, 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
Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash.
Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...
( sp. gr. 1.35), or in absolute ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
.
Uses
The dominant use of potassium sulfate is as a fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
. 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
Artillery is a class of heavy military ranged weapons that launch munitions far beyond the range and power of infantry firearms. Early artillery development focused on the ability to breach defensive walls and fortifications during siege ...
propellant charges. It reduces muzzle flash
Muzzle flash is the light — both visible and infrared — created by a muzzle blast, which is caused by the sudden release and expansion of high-temperature, high-pressure gases from the muzzle of a firearm during shooting. Both the blast ...
, flareback and blast overpressure.
It is sometimes used as an alternative blast media similar to soda
Soda or SODA may refer to:
Chemistry
* Some chemical compounds containing sodium
** Sodium carbonate, washing soda or soda ash
** Sodium bicarbonate, baking soda
** Sodium hydroxide, caustic soda
** Sodium oxide, an alkali metal oxide
* Sod ...
in soda blasting
Soda blasting is a mild form of abrasive blasting in which sodium bicarbonate particles are blasted against a surface using compressed air. It has a much milder abrasive effect than sandblasting. An early use was in the conservation-restoration ...
as it is harder and similarly water-soluble.
Potassium sulfate can also be used in pyrotechnics in combination with potassium nitrate
Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and nitr ...
to generate a purple flame.
A 5% solution of potassium sulfate was used in the beginning of the 20th century as a topical mosquito repellent.
Reactions
Acidification
Potassium hydrogen sulfate
Potassium bisulfate/ Potassium Sulphate is an inorganic compound with the chemical formula KHSO4 and is the potassium acid salt of sulfuric acid. It is a white, water-soluble solid.
Preparation
More than 1 million tons were produced in 1985 as t ...
(also known as potassium bisulfate), KHSO4, is readily produced by reacting K2SO4 with sulfuric acid. It forms rhombic pyramids, which melt at . It dissolves in three parts of water at . 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 little bisulfate) with excess acid remaining.
The behavior of the fused dry salt is similar when heated to several hundred degrees; it acts on silicates, titanate In chemistry, titanate usually refers to inorganic compounds composed of titanium oxides.
Together with niobate, titanate salts form the Perovskite group.
In some cases, the term is used more generally for any titanium-containing anion, e.g. i ...
s, 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
The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
.
References
External links
mindat.org: Arcanite
webmineral: Arcanite
{{Authority control
Potassium compounds
Sulfates
Inorganic fertilizers
E-number additives