The name is derived from the english word potash. The chemical symbol K comes from kalium, the Mediaeval Latin for potash, which may have derived from the arabic word qali, meaning alkali. Potassium is a soft, silvery-white metal, member of the alkali group of the periodic chart. Potassium is silvery when first cut but it oxidizes rapidly in air and tarnishes within minutes, so it is generally stored under oil or grease. It is light enough to float into water with which it reacts instantly to release hydrogen, which burns with a lilac flame.

The chemistry of potassium is almost etirely that of the potassium ion, K⁺.

Applications

Most potassium (95 %) goes into fertilizers and the rest goes mainly into making potassium hydroxide (KOH), by the electrolysis of potassium chloride solution, and then converting this to potassium carbonate (K₂CO₃). Potassium carbonate goes into glass manufacture, expecially the glass used to make televisions, while potassium hydroxide is used to make liquid soaps and detergents. A little potassium chloride goes into pharmaceuticals, medical drips and saline injections.
Other potassium salts are used in baking, photography and tanning leather, and to make iodize salts. In all cases it is the negative anion, not the potassium, which is the key to their use.

Potassium in the environment

Most potassium occurs in the Earth's crust as minerals, such as feldspars and clays. Potassium is leached from these by weathering, which explains why there is quite a lot of this element in the sea (0.75 g/liter).
Minerals mined for their potassium are pinkish and sylvite, carnallite and alunite. The main mining area used to be Germany, which had a monopoly of potassium before the first World War. Today most potassium minerals come from Canada, USA and Chile. The world production of potassim ores is about 50 million tonnes, and reserves are vast (more than 10 billion tonnes).
Potassium is a key plant element. Although it is soluble in water, little is lost from undisturbed soils because as it is released from dead plants and animal excrements, it quickly become strongly bound to clay particles, and it is retained ready to be reabsorbed by the roots of other plants.

Health effects of potassium 

Potassium can be found in vegetables, fruit, potatoes, meat, bread, milk and nuts. It plays an important role in the physical fluid system of humans and it assists nerve functions. Potassium, as the ion K+, concentrate inside cells, and 95% of the body's potassium is so located. When our kidneys are somehow malfunctioning an accumulation of potassium will consist. This can lead to disturbing heartbeats.

Potassium can effect you when breathed in. Inhalation of dust or mists can irritate the eyes, nose, throat, lungs with sneezing, coughing and sore throat. Higher exposures may cause a build up of fluid in the lungs, this can cause death. Skin and eye contact can cause severe burns leading to permanent damage.

Environmental effects of potassium  

Together with nitrogen and phosphorous, potassium is one of the essential macrominerals for plant survival.  Its presence is of great importance for soil health, plant growth and animal nutrition. Its primary function in the plant is its role in the maintenance of osmotic pressure and cell size, thereby influencing photosynthesis and energy production as well as stomatal opening and carbon dioxide supply, plant turgor and translocation of nutrients. As such, the element is required in relatively large proportions by the growing plant. 

The consequences of low potassium levels are apparent in a variety of symptoms: restricted growth, reduced flowering, lower yields and lower quality produce. 

High water soluble levels of potassium cause damage to germinating seedlings, inhibits the uptake of other minerals and reduces the quality of the crop.

Potassium in Water

Seawater contains about 400 ppm potassium. It tends to settle, and consequently ends up in sediment mostly. Rivers generally contains about 2-3 ppm potassium. This difference is mainly caused by a large potassium concentration in oceanic basalts. Calcium rich granite contains up to 2.5% potassium. In water this element is mainly present as K⁺ (aq) ions.
⁴⁰K is a naturally abundant radioactive potassium isotope. Seawater contains a natural concentration of about 4.5 . 10^-5 g/L.

In what way and in what form does potassium react with water?

Potassium reacts rapidly and intensely with water, forming a colourless basic potassium hydroxide solution and hydrogen gas, according to the following reaction mechanism:

2K (s) + 2H₂O (l) -> 2KOH (aq) + H₂ (g)

This is an exothermal reaction and potassium is heated to such an extend that it burns a purple flame. Additionally, hydrogen released during the reaction strongly reacts with oxygen and ignites. Potassium reacts with water more slowly than does rubidium, which is placed under potassium in the periodic chart. It reacts with water more rapidly than does sodium, which is placed higher in the periodic chart.

Solubility of potassium and potassium compounds

Potassium is non-water soluble, but it does react with water as was explained earlier. Potassium compounds may be water soluble. Examples are potassium dichromate with a water solubility of 115 g/L, potassium permanganate with a water solubility of 76 g/L, potassium iodide with a water solubility of 92 g/L, and potassium iodide, of which even up to 1480 g may be dissolved in one litre of water.

Why is potassium present in water?

Potassium occurs in various minerals, from which it may be dissolved through weathering processes. Examples are feldspars (orthoclase and microcline), which are however not very significant for potassium compounds production, and chlorine minerals carnalite and sylvite, which are most favourable for production purposes. Some clay minerals contain potassium. It ends up in seawater through natural processes, where it mainly settles in sediments.
Elementary potassium is extracted from potassium chloride, but does not serve many purposes because of its extensive reactive power. It is applied in alloys and in organic synthesis.
A number of potassium compounds, mainly potassium nitrate, are popular synthetic fertilizers.95% of commercially applied potassium is added to synthetic fertilizers. Potassium salts and mixtures of magnesium and calcium compounds are also applied regularly. Regeneration releases wastewater that is hazardous when discharged on surface water, and that is difficult to purify.
Potassium is applied in glass production to make it stronger and solid. This glass is mainly applied in television screens. Other potassium compounds are applied in fluid soap production, added to medicines or infusions, or applied in photography or tanning. In most cases potassium is not the active ingredient, but rather the adjacent anion. This also applies to potassium chlorate application in matches and fireworks, and for potassium nitrate in powder. Potassium alums are bases for paper glue and are applied as a filler of synthetic rubber.
Potassium compounds are the most reactive basic chemical compounds, which for example applies to potassium hydroxides and nitrates. Potassium hydroxide forms caustic potash and is applied in detergents, softeners, green soap, de-sulphurization of oil and carbon dioxide absorbers.
Other examples of potassium compound application include potassium iodide for waste sample oxidative capacity measurements, potassium dichromate for organic matter oxidative capacity measurements in soil science and biological wastewater treatment, and potassium dicyano aureate, which is an extremely toxic water soluble gold compound that is applied for technical gilding. Potassium compounds may end up in wastewater through urine. An unusual application is increasing the amount of rain in dry regions by potassium chloride. It is released just below the clouds from planes, rises up and doubles the amount of moist in clouds, causing it to start raining harder.
As potassium release from landfills for domestic waste is usually exceptionally high, this compound may be applied as an indicator for other toxic compounds in groundwater.

What are the environmental effects of potassium in water?

Potassium is an dietary requirement for nearly any organism but a number of bacteria, because it plays an important role in nerve functions.
Potassium plays a central role in plant growth, and it often limits it. Potassium from dead plant and animal material is often bound to clay minerals in soils, before it dissolves in water. Consequently, it is readily taken up by plants again. Ploughing may disturb this natural process. Consequently, potassium fertilizer are often added to agricultural soils. Plants contain about 2% potassium (dry mass) on average, but values may vary from 0.1-6.8%. Mosquito larvae contain between 0.5 and 0.6% potassium, and beetles contain between 0.6 and 0.9% potassium (dry mass). Potassium salts may kill plant cells because of high osmotic activity.
Potassium is weakly hazardous in water, but it does spread pretty rapidly, because of its relatively high mobility and low transformation potential. Potassium toxicity is usually caused by other components in a compound, for example cyanide in potassium cyanide.
The LD₅₀ value for rats is 5 mg/kg. For potassium bromate this is 321 mg/kg, and for potassium fluoride this is 245 mg/kg. Examples of LD₅₀ values for water organisms include 132 mg/L for fish and 1.16 mg/L for daphnia.
One of three naturally occurring potassium isotopes is ⁴⁰K, which is radioactive. It is suspected this compound causes plant an animal gene modifications. However, it does not have a radio toxicity class, because of its natural origin. There is a total of twelve instable potassium isotopes.

What are the health effects of potassium in water?

Potassium is a dietary requirement for us, and we take up about 1-6 g per day at a requirement of 2-3.5 g per day. The total potassium amount in the human body lies somewhere between 110 and 140 g and mainly depends upon muscle mass. The muscles contain most potassium after red blood cells and brain tissue.
Whereas its opponent sodium is present in intracellular fluids, potassium is mainly present within cells. It preserves osmotic pressure. The relation of potassium in cells to potassium in plasma is 27:1, and is regulated by means of sodium-potassium pumps.
Vital functions of potassium include its role in nerve stimulus, muscle contractions, blood pressure regulation and protein dissolution. It protects the heart and arteries, and may even prevent cardiovascular disease. The relation of sodium to potassium used to be 1:16, and is now about 3:1, which mainly prevents high sodium uptake.
Potassium shortages are relatively rare, but may lead to depression, muscle weakness, heart rhythm disorder and confusion. Potassium loss may be a consequence of chronic diarrhoea or kidney disease, because the physical potassium balance is regulated by the kidneys. When kidneys operate insufficiently, potassium intake must be limited to prevent greater losses.
Skin contact with potassium metals results in caustic potash corrosion. This is more hazardous than acid corrosion, because it continues unlimitedly. Caustic potash drops are very damaging to the eyes.
The intake of a number of potassium compounds may be particularly harmful. At high doses potassium chloride interferes with nerve impulses, which interrupts with virtually all bodily functions and mainly affects heart functioning. Potassium alum may cause stomach complaints and nausea at concentrations as low as 2 g, and may be corrosive and even lethal in higher concentrations. Potassium carbonate is lethal to adults at doses above 15 g. The same goes for potassium tartrate at 1 g, and for potassium cyanide at only 50 mg. Potassium dichromate is lethal at between 6 and 8 g, and 30 g of potassium nitrate causes severe intoxication, which may result in death. Because of its strongly corrosive mechanism potassium hydroxide concentrations between 10 and 12 ml in a 15% caustic may be lethal. Potassium permanganate is applied in bleaches and disinfection, and is lethal at between 5 and 8 g.

Which water purification technologies can be applied to remove potassium from water?

Potassium may be removed from water by means of reverse osmosis.
Potassium is applied in water purification. For example, potassium permanganate is applicable for oxidation of waterborne compounds, such as for iron or manganese removal, and disinfection. This is however not generally recommended. Potassium permanganate application makes it possible to determine the oxidative capacity of organic matter in water. Generally this exceeds BOD. Potassium dichromate is applied for COD determination.