It occurs naturally as the mineralsylvite, which is named after the salt's historical designations sal degistivum Sylvii and sal febrifugum Sylvii,[14] and in combination with sodium chloride as sylvinite.[15]
Uses
Fertilizer
Potassium chloride, compacted, fertilizer grade
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.[16][17] 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.[18][19][20][21] The vast majority of potash fertilizer worldwide is sold as muriate of potash.[22][23] The dominance of muriate of potash in the fertilizer market is due to its high potassium content (approximately 60% K 2O equivalent) and relative affordability compared to other potassium sources like sulfate of potash (potassium sulfate).[21][24] 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.[25][26] 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 (0.014oz) per liter of water.[27][28]
Potassium chloride (KCl) is used to represent intracellular and/or extracellular fluid in biophysical experiments with model cell membranes. A higher concentration of potassium chloride is used as both an osmotic gradient and an ionic current for the same electrophysiological experiments.[35][36][37][38][39]
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.[40] Complaints of bitterness or a chemical or metallic taste are also reported with potassium chloride used in food.[41]
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.[42][43][44]
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.
Potassium chloride is also an optical crystal with a wide transmission range: from 210nm to 20μm. 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 infraredoptics, they have been mostly replaced by much tougher crystals such as zinc selenide.
The typical amounts of potassium chloride found in the diet appear to be generally safe.[49] In larger quantities, however, potassium chloride is toxic. The LD50 of orally ingested potassium chloride is approximately 2.5g/kg, or 190 grams (6.7oz) for a body mass of 75 kilograms (165lb). In comparison, the LD50 of sodium chloride (table salt) is 3.75g/kg.
Intravenously, the LD50 of potassium chloride is far smaller, at about 57.2mg/kg to 66.7mg/kg; this is found by dividing the lethal concentration of positive potassium ions (about 30 to 35mg/kg)[50] by the proportion by mass of potassium ions in potassium chloride (about 0.52445mg K+/mg KCl).[51]
Solutions of KCl are common standards, for example for calibration of the electrical conductivity of (ionic) solutions, since KCl solutions are stable, allowing for reproducible measurements. In aqueous solution, it is essentially fully ionized into solvated K+ and Cl− ions.
Redox and the conversion to potassium metal
Although potassium is more electropositive than sodium, KCl can be reduced to the metal by reaction with metallic sodium at 850°C because the more volatile potassium can be removed by distillation (see Le Chatelier's principle):
KCl(l) + Na(l) ⇌ NaCl(l) + K(g)
This method is the main method for producing metallic potassium. Electrolysis (used for sodium) fails because of the high solubility of potassium in molten KCl.[15]
Other potassium chloride stoichiometries
Potassium chlorides with formulas other than KCl have been predicted to become stable under pressures of 20 GPa or more.[53] Among these, two phases of KCl3 were synthesized and characterized. At 20-40 GPa, a trigonal structure containing K+ and Cl3− is obtained; above 40 GPa this gives way to a phase isostructural with the intermetallic compound Cr3Si.
Physical properties
Under ambient conditions, the crystal structure of potassium chloride is like that of NaCl. It adopts a face-centered cubic structure known as the B1 phase with a lattice constant of roughly 6.3 Å. Crystals cleave easily in three directions. Other polymorphic and hydrated phases are adopted at high pressures.[54]
Some other properties are
Transmission range: 210nm to 20μm
Transmittivity = 92% at 450nm and rises linearly to 94% at 16μm
Refractive index = 1.456 at 10μm
Reflection loss = 6.8% at 10μm (two surfaces)
dN/dT (expansion coefficient)= −33.2×10−6/°C
dL/dT (refractive index gradient)= 40×10−6/°C
Thermal conductivity = 0.036 W/(cm·K)
Damage threshold (Newman and Novak): 4 GW/cm2 or 2 J/cm2 (0.5 or 1 ns pulse rate); 4.2 J/cm2 (1.7 ns pulse rate Kovalev and Faizullov)
Most potassium chloride is produced as agricultural and industrial-grade potash in Saskatchewan, Canada, Russia, and Belarus. Saskatchewan alone accounted for over 25% of the world's potash production in 2017.[56]
Laboratory methods
Potassium chloride is inexpensively available and is rarely prepared intentionally in the laboratory. It can be generated by treating potassium hydroxide (or other potassium bases) with hydrochloric acid:
KOH + HCl → KCl + H2O
This conversion is an acid-base neutralization reaction. The resulting salt can then be purified by recrystallization. Another method would be to allow potassium to burn in the presence of chlorine gas, also a very exothermic reaction:
↑Rayner-Canham G, Overton T (22 December 2013). Descriptive inorganic chemistry (Sixthed.). New York, NY: W. H. Freeman. ISBN978-1-4641-2557-7. OCLC882867766.
↑Havlin, John L.; Tisdale, Samuel L.; Nelson, Werner L.; Beaton, James D. (2016). Soil Fertility and Fertilizers: An Introduction to Nutrient Management. Pearson. ISBN978-93-325-7034-4.
↑Mineral Commodity Summaries: Potash(PDF). United States Geological Survey (USGS). U.S. Department of the Interior. Archived(PDF) from the original on 2024-11-12. Retrieved 2024-11-24.
12World Health Organization (2019). World Health Organization model list of essential medicines: 21st list 2019. Geneva: World Health Organization. hdl:10665/325771. WHO/MVP/EMP/IAU/2019.06. License: CC BY-NC-SA 3.0 IGO.
↑Lorient D, Linden G (1999). New ingredients in food processing: biochemistry and agriculture. Boca Raton: CRC Press. p.357. ISBN978-1-85573-443-2. ... in dietary food containing potassium chloride, thaumatin added in the ratio of 1 ppm considerably reduces the sensation of bitterness. ...
↑Sinopoli DA, Lawless HT (September 2012). "Taste properties of potassium chloride alone and in mixtures with sodium chloride using a check-all-that-apply method". Journal of Food Science. 77 (9): S319–S322. doi:10.1111/j.1750-3841.2012.02862.x. PMID22901084.
↑Bhatkhande CY, Joglekar VD (1977-01-01). "Fatal poisoning by potassium in human and rabbit". Forensic Science. 9 (1): 33–36. doi:10.1016/0300-9432(77)90062-0. PMID838413.
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