Potassium chloride (KCl, or potassium salt) is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a salt-like taste. Potassium chloride can be obtained from ancient dried lake deposits. KCl is used as a salt substitute for table salt (NaCl), as a fertilizer, as a medication, in scientific applications, in domestic water softeners (as a substitute for sodium chloride salt), as a feedstock, and in food processing, where it may be known as E number additive E508. It occurs naturally as the mineral sylvite, which is named after the salt's historical designations sal degistivum Sylvii and sal febrifugum Sylvii, and in combination with sodium chloride as sylvinite.
Uses
Fertilizer The majority of the potassium chloride produced is used for making fertilizer, called potash, since the growth of many plants is limited by potassium availability. The term "potash" refers to various mined and manufactured salts that contain potassium in water-soluble form. Potassium chloride sold as fertilizer is known as "muriate of potash"—it is the common name for potassium chloride (KCl) used in agriculture. The vast majority of potash fertilizer worldwide is sold as muriate of potash. The dominance of muriate of potash in the fertilizer market is due to its high potassium content (approximately 60% K2O equivalent) and relative affordability compared to other potassium sources like sulfate of potash (potassium sulfate). Potassium is one of the three primary macronutrients essential for plant growth, alongside nitrogen and phosphorus. Potassium is required for plant physiological processes including enzyme activation, photosynthesis, protein synthesis, and water regulation. For watering plants, a moderate concentration of potassium chloride (KCl) is used to avoid potential toxicity: 6 mM (millimolar) is generally effective and safe for most plants, which is approximately 0.4 grams (0.014 oz) per liter of water.
Medical use
Potassium is vital in the human body, and potassium chloride by mouth is the standard means to treat low blood potassium, although it can also be given intravenously. It is on the World Health Organization's List of Essential Medicines. It is also an ingredient in Oral Rehydration Therapy (ORT)/solution (ORS) to reduce hypokalemia caused by diarrhoea, which is also on the WHO's List of Essential Medicines. Potassium chloride contains 52% of elemental potassium by mass. Overdose causes hyperkalemia which can disrupt cell signaling to the extent that the heart will stop, reversibly in the case of some open heart surgeries.
Culinary use Potassium chloride can be used as a salt substitute for food, but because not everyone likes its flavor, it is often mixed with ordinary table salt (sodium chloride) to improve the taste, to form low sodium salt. The addition of 1 ppm of thaumatin considerably reduces this bitterness. Complaints of bitterness or a chemical or metallic taste are also reported with potassium chloride used in food. The World Health Organization guideline Use of lower-sodium salt substitutes strongly recommends reducing sodium intake to less than 2 g/day and conditionally recommends replacing regular table salt with lower-sodium salt substitutes that contain potassium. This recommendation is intended for adults (not pregnant women or children) in general populations, excluding individuals with kidney impairments or with other circumstances or conditions that might compromise potassium excretion.
Industrial In 2005, an estimated 5% of potassium chloride was used as a chemical feedstock. It is used for the manufacture of potassium hydroxide and chlorine.
Niche and archaic
Potassium chloride is also used in specialized medicinal and scientific applications. It is used as a supplement in animal feed to boost the potassium level in the feed. As an added benefit, it is known to increase milk production. It is sometimes used in solution as a completion fluid in petroleum and natural gas operations, as well as being an alternative to sodium chloride in household water softener units. Because natural potassium contains a tiny amount of the isotope potassium-40, potassium chloride is used as a beta radiation source to calibrate radiation monitoring equipment. It also emits a relatively low level of 511 keV gamma rays from positron annihilation, which can be used to calibrate medical scanners. Potassium chloride is used in some de-icing products designed to be safer for pets and plants, though these are inferior in melting quality to calcium chloride. It is also used in various brands of bottled water. Potassium chloride was once used as a fire extinguishing agent, and in portable and wheeled fire extinguishers. Known as Super-K dry chemical, it was more effective than sodium bicarbonate-based dry chemicals and was compatible with protein foam. This agent fell out of favor with the introduction of potassium bicarbonate (Purple-K) dry chemical in the late 1960s, which was much less corrosive, as well as more effective. It is rated for B and C fires. Along with sodium chloride and lithium chloride, potassium chloride is used as a flux for the gas welding of aluminium. Potassium chloride is also an optical crystal with a wide transmission range: from 210 nm to 20 μm. While cheap, KCl crystals are hygroscopic. This limits its application to protected environments or short-term uses such as prototyping. Exposed to free air, KCl optics will "rot". Whereas KCl components were formerly used for infrared optics, they have been mostly replaced by much tougher crystals such as zinc selenide. Potassium chloride is used as a scotophor with designation P10 in dark-trace CRTs, e.g. in the Skiatron.
Toxicity The typical amounts of potassium chloride found in the diet appear to be generally safe. In larger quantities, however, potassium chloride is toxic. The LD50 of orally ingested potassium chloride is approximately 2.5 g/kg, or 190 grams (6.7 oz) for a body mass of 75 kilograms (165 lb). In comparison, the LD50 of sodium chloride (table salt) is 3.75 g/kg. Intravenously, the LD50 of potassium chloride is far smaller, at about 57.2 mg/kg to 66.7 mg/kg; this is found by dividing the lethal concentration of positive potassium ions (about 30 to 35 mg/kg) by the proportion by mass of potassium ions in potassium chloride (about 0.52445 mg K+/mg KCl).
Chemical properties
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