The English name for the element potassium comes from the word “potash” (early method of extracting various potassium salts; placing in a pot the ash of burnt wood or tea leaves, adding water, heating and evaporating the solution) with the symbol ‘K’ (from Latin word kalium, which itself comes from root word alkali, which in turns comes from the Arabic word “plant ashes”). In the periodic table, it is classified as one of the alkali metal with atomic number 19, all of which have a single valence electron in the outer valence shell, that is easily removed to create an ion with positive charge-a cation. In nature, it occurs only in ionic salts. Potassium in its element form reacts vigorously with water and burns with a lilac-coloured flame.
Potassium is a soft solid with a low melting point and can be easily cut with a knife. When cut with a knife, in starting, it is silvery in appearance but after exposure to air, it immediately begins to tarnish towards grey. In a flame test, potassium and its compounds emit a lilac colour.
Potassium reacts with oxygen to form potassium peroxide. It reacts with water to form potassium hydroxide and this reaction can be violently exothermic since the coproduced hydrogen gas can ignite. Due to this, potassium and the liquid sodium-potassium (NaK) alloy are potent desiccants (which means a hygroscopic substance that is used to sustain a state of dryness in its vicinity); although, they are no longer used as such.
The potassium-oxygen compounds (such as potassium oxide, potassium peroxide, potassium superoxide) reacts with water to form potassium hydroxide. Potassium hydroxide (KOH) is a strong base. It has a hydrophilic character. Anhydrous KOH is rarely found. KOH readily reacts with carbon dioxide to form potassium carbonate and in principle, it could be used to remove traces of the gas from the air. Potassium hydroxide reacts with fats to produce soaps. In general, potassium compounds are ionic and due to its high hydration energy of the K+ ion, have excellent water solubility. Organopotassium compounds illustrate nonionic compounds of potassium. They have a highly polar covalent character. Potassium also intercalates (reversible insertion of a molecule into materials) into graphite to give a variety of compounds.
There are 26 known isotopes of potassium but only three occurs naturally. The two stable forms Potassium-39, Potassium-41, and a very long-lived radioisotope Potassium-40. Potassium-40 is the largest source of natural radioactivity in healthy animals and humans. In a human body of 70 kg mass, about 4,400 nuclei of Potassium-40 decay per second. The decay of Potassium-40 to Argon-40 is used in potassium-argon dating of rocks. Minerals are dated by measurement of the concentration of potassium and the amount of radiogenic Argon-40 that has accumulated. In the studies of weathering (breaking down of rocks), Potassium-40 has been extensively used. All other potassium isotopes have half-lives under a day, most under a minute. As potassium is a macronutrient required for life, various potassium isotopes have been used for nutrient cycling (nature’s recycling system.)
Potash consists of various mined and manufactured salts that contain potassium in water (soluble form). It is produced worldwide in amounts exceeding 90 million tonnes per year. The single greatest industrial use of elemental potassium in the world is, in various kinds of fertiliser-potash. The commercial plant deposits come from evaporite deposits and are often buried deep below the earth’s surface. Potash ores are typically rich in potassium chloride (KCl), sodium chloride (NaCl) and other salts and clays, and are typically obtained by conventional shaft mining with the extracted ore ground into a powder. Other methods include dissolution mining and evaporation methods from brines.
Potash in fertilizers
Potassium is the third major plant and crop nutrient after nitrogen and phosphorous. It has been used since ancient times as a soil fertilizer. Elemental potassium does not occur in nature because it reacts violently with water. Potash is important for agriculture because it improves water retention, yield, nutrient value, taste, colour, texture and disease resistance of food crops. It has wide application to fruit and vegetables, rice, wheat and other grains, sugar, corn, soybeans, palm oil and cotton, all of which benefit from the nutrient’s quality-enhancing properties. The world’s largest consumers of potash are China, the United States, Brazil, and India. Brazil imports 90% of the potash it needs. Potash consumption for fertilizers is expected to increase to about 37.8 million tonnes by 2022.
Other Uses of Potash
Potassium chloride is important in many industries, where it is used in metal electroplating, aluminium recycling (where scrap aluminium is reused in products after its initial production), snow and ice melting, in medicine as a treatment of hypokalemia (low level of potassium in blood serum), and water softening (removal of calcium, magnesium and certain other metal cations in hard water.) Potassium hydroxide is used for industrial water treatment. Potassium carbonate is used to produce cement, fire extinguishers, food products, textiles. It is also used in brewing beer, pharmaceutical preparations, and as a catalyst for synthetic rubber manufacturing. Also combined with silica sand to produce potassium silicate, sometimes known as water glass, for use in paints and arc welding electrodes.
Potassium in biology
The human body has about as much potassium as sulfur and chlorine, and only calcium and phosphorus are more abundant. Potassium ions are present in a wide variety of proteins and enzymes. Potassium levels influence multiple physiological processes, including; hormone secretion and action, glucose and insulin metabolism.
Potassium is present in all fruits, vegetables, meat and fish. Foods with high potassium concentrations include yam, parsley, dried apricots, milk, chocolate, all nuts (especially almonds and pistachios), potatoes, bamboo shoots, bananas, avocados, coconut water, soybeans, and bran (hard outer layer of cereal grain.)
Diets low in potassium can lead to hypertension and hypokalemia.
Potassium, in the form of potassium chloride, is used to treat and prevent low blood potassium. Low blood potassium may occur due to vomiting, diarrhoea, or certain medications. It is given by slow injection into a vein or by mouth.
Rochelle salt (potassium sodium tartrate) is a main component of some varieties of baking powder. It is also used in the silvering of mirrors. Potassium bisulfite (KHSO3) is used as a food preservative, for example, in wine and beer-making. It is also used to bleach textiles and straw and in the tanning of leathers.
- Potassium chromate (K2CrO4) is widely used in the manufacturing of various items of our daily use. These include inks, dyes, safety matches, fireworks etc. It is also needed in the tanning of leathering.
- Potassium cyanide is capable of dissolving precious metals like gold and silver. It has a major application in gold mining.
- Potassium forms an alloy with sodium (NaK), which is liquid at room temperature. This alloy is used as a desiccant to produce various dry solvents. It is also used as a medium for heat transfer in several industries.
- Potassium hydroxide (KOH) has strong basic properties; therefore, it is used for the neutralisation of acids and thus controlling pH value. It is used in saponification of fatty and oily substances and used in different hydrolysis reactions.