Potassium sulfate (poe-TAS-ee-yum SUL-fate) is also known as potash of sulfur, sulfuric acid dipotassium salt, arcanum duplicatum, and sal polychrestum. It is a colorless or white granular, crystalline, or powdery solid with a bitter, salty taste. It occurs in nature as the mineral arcanite and in the mineral langbeinite (K2Mg2(SO4)3). The compound was known to alchemists as early as the fourteenth century, and was analyzed by a number of early chemists, including Johann Glauber (1604–1670), Robert Boyle (1627–1691), and Otto Tachenius (c. 1620–1690).
Potassium, sulfur, oxygen
Vaporizes at 1689°C (3072°F)
Soluble in water; slightly soluble in glycerol; insoluble in ethyl alcohol, acetone, and most other organic solvents
HOW IT IS MADE
A variety of methods for preparing potassium sulfate is available. In one process, the compound is extracted from the mineral langeinite by crushing and washing the mineral and then separating out the double salt, K2Mg2(SO4)3. The product is then treated with an aqueous solution of potassium chloride (KCl) to separate the two parts of the double salt from each other: K2Mg2(SO4)3 + 4KCl → 3K2SO4 + 2MgCl2. The compound can also be produced synthetically by treating potassium chloride with sulfuric acid (H2SO4): 2KCl + H2SO4 → K2SO4 + 2HCl.
In a variation of this procedure, potassium chloride is treated with the raw materials from which sulfuric acid is made, rather than the acid itself: 4KCl + 2SO2 + 2H2O + O2 → 2K2SO4 + 4HCl.
COMMON USES AND POTENTIAL HAZARDS
Over 90 percent of the potassium sulfate produced in the United States is used as a fertilizer. It provides plants with two essential elements: potassium and sulfur. It finds its greatest use on crops that are sensitive to the chloride ion (Cl-) present in most conventional agricultural fertilizers. Those crops include coffee, tea, tobacco, citrus fruits, grapes, and potatoes. However, its use is somewhat limited because it is twice as expensive as fertilizers that contain potassium chloride.
The second most important use of potassium sulfate is as a supplement for animal feeds, accounting for another 8 percent of the compound produced in the United States. The remaining 1 percent of potassium sulfate goes to the production of gypsum board and gypsum cement, for the synthesis of potassium alum (potassium aluminum sulfate), in the manufacturing of glass and ceramics, for the production of dyes and lubricants, and as a flash suppressant in explosives. A flash suppressent is, as its name suggests, a chemical that reduces the amount of flash produced when an explosive is detonated.
Potassium sulfate, sodium sulfate, and their double salts with calcium and magnesium occur naturally in salt lakes and in volcanic lava. At one time—and on some uncommon occasions today—potassium sulfate was obtained from salt lake sources.
Words to Know
- AQUEOUS SOLUTION
- A solution that consists of some material dissolved in water.
- A chemical reaction in which some desired chemical product is made from simple beginning chemicals, or reactants.
Exposure to moderate amounts of potassium sulfate appears to have no serious effects on human health. Ingestion of large amounts of the compound, can cause severe gastrointestinal irritation that requires medical attention.
FOR FURTHER INFORMATION
"Potassium Sulfate." Hummel Croton, Inc. http://www.hummelcroton.com/msds/k2so4_m.html (accessed on November 3, 2005).
"Potassium Sulfate." International Programme on Chemical Safety. http://www.inchem.org/documents/icsc/icsc/eics1451.htm (accessed on November 3, 2005).
"Potassium Sulfate." J. T. Baker. http://www.jtbaker.com/msds/englishhtml/p6137.htm (accessed on November 3, 2005).