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In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid, phosphoric acid .
The phosphate or orthophosphate ion is derived from phosphoric acid by the removal of three . Removal of one proton gives the dihydrogen phosphate ion while removal of two protons gives the hydrogen phosphate ion . These names are also used for salts of those anions, such as ammonium dihydrogen phosphate and trisodium phosphate.
Phosphoric acid
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Dihydrogen
phosphate
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Hydrogen
phosphate
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Phosphate or orthophosphate
In organic chemistry, phosphate or orthophosphate is an organophosphate, an ester of orthophosphoric acid of the form where one or more hydrogen atoms are replaced by organic compound groups. An example is trimethyl phosphate, . The term also refers to the trivalent functional group in such esters. Phosphates may contain sulfur in place of one or more oxygen atoms ( and organothiophosphates).
Orthophosphates are especially important among the various phosphates because of their key roles in biochemistry, biogeochemistry, and ecology, and their economic importance for agriculture and industry. The addition and removal of phosphate groups (phosphorylation and dephosphorylation) are key steps in cell metabolism.
Orthophosphate can condense to form .
Many phosphates are solubility in water at standard temperature and pressure. The sodium, potassium, rubidium, caesium, and ammonium phosphates are all water-soluble. Most other phosphates are only slightly soluble or are insoluble in water. As a rule, the hydrogen and dihydrogen phosphates are slightly more soluble than the corresponding phosphates.
| p Ka1 = 2.14 | ||
| p Ka2 = 7.20 | ||
| p Ka3 = 12.37 |
The p K a values are the pH values where the concentration of each species is equal to that of its . At pH 1 or lower, the phosphoric acid is practically undissociated. Around pH 4.7 (mid-way between the first two p K a values) the dihydrogen phosphate ion, , is practically the only species present. Around pH 9.8 (mid-way between the second and third p K a values) the monohydrogen phosphate ion, , is the only species present. At pH 13 or higher, the acid is completely dissociated as the phosphate ion, .
This means that salts of the mono- and di-phosphate ions can be selectively crystallised from aqueous solution by setting the pH value to either 4.7 or 9.8.
In effect, , and behave as separate because the successive p K a differ by more than 4.
Phosphate can form many ions such as pyrophosphate, , and triphosphate, . The various metaphosphate ions (which are usually long linear polymers) have an empirical formula of and are found in many compounds.
Inorganic phosphate is generally denoted Pi and at physiological (Homeostasis) pH primarily consists of a mixture of and ions. At a neutral pH, as in the cytosol (pH = 7.0), the concentrations of the orthophosphoric acid and its three anions have the ratios
Thus, only the and ions are present in significant amounts in the cytosol (62% , 38% ). In extracellular fluid (pH = 7.4), this proportion is inverted (61% , 39% ).
Inorganic phosphate can also be present as pyrophosphate anions , which give orthophosphate by hydrolysis:
Organic phosphates are commonly found in the form of esters as (e.g. AMP, ADP, and ATP) and in DNA and RNA. Free orthophosphate anions can be released by the hydrolysis of the phosphoanhydride bonds in ATP or ADP. These phosphorylation and dephosphorylation reactions are the immediate storage and source of energy for many metabolism processes. ATP and ADP are often referred to as high-energy phosphates, as are the in muscle tissue. Similar reactions exist for the other nucleoside diphosphates and triphosphates.
Phosphates induce vascular calcification, and a high concentration of phosphates in blood was found to be a predictor of cardiovascular events.
The largest global producer and exporter of phosphates is Morocco. Within North America, the largest deposits lie in the Bone Valley region of central Florida, the Soda Springs region of southeastern Idaho, and the coast of North Carolina. Smaller deposits are located in Montana, Tennessee, Georgia, and South Carolina. The small island nation of Nauru and its neighbor Banaba Island, which used to have massive phosphate deposits of the best quality, have been mined excessively. Rock phosphate can also be found in Egypt, Israel, Palestine, Western Sahara, Navassa Island, Tunisia, Togo, and Jordan, countries that have large phosphate-mining industries.
Phosphorite mines are primarily found in:
In 2007, at the current rate of consumption, the supply of phosphorus was estimated to run out in 345 years. However, some scientists thought that a "peak phosphorus" would occur in 30 years and Dana Cordell from Institute for Sustainable Futures said that at "current rates, reserves will be depleted in the next 50 to 100 years". Reserves refer to the amount assumed recoverable at current market prices. In 2012 the USGS estimated world reserves at 71 billion tons, while 0.19 billion tons were mined globally in 2011.U.S. Geological Survey Phosphate Rock Phosphorus comprises 0.1% by mass of the average rockU.S. Geological Survey (while, for perspective, its typical concentration in vegetation is 0.03% to 0.2%), and consequently there are quadrillions of tons of phosphorus in Earth's 3×1019-ton crust,American Geophysical Union, Fall Meeting 2007, abstract #V33A-1161. Mass and Composition of the Continental Crust albeit at predominantly lower concentration than the deposits counted as reserves, which are inventoried and cheaper to extract. If it is assumed that the phosphate minerals in phosphate rock are mainly hydroxyapatite and fluoroapatite, phosphate minerals contain roughly 18.5% phosphorus by weight. If phosphate rock contains around 20% of these minerals, the average phosphate rock has roughly 3.7% phosphorus by weight.
Some phosphate rock deposits, such as Mulberry in Florida, are notable for their inclusion of significant quantities of radioactive uranium isotopes. This is a concern because radioactivity can be released into surface waters from application of the resulting phosphate fertilizer.
In December 2012, Cominco Resources announced an updated JORC compliant resource of their Hinda project in Congo-Brazzaville of 531 million tons, making it the largest measured and indicated phosphate deposit in the world.
Around 2018, Norway discovered phosphate deposits almost equal to those in the rest of Earth combined.
In July 2022 China announced quotas on phosphate exportation.
The largest importers in millions of metric tons of phosphate are Brazil 3.2, India 2.9 and the USA 1.6.
| + Production and global reserves of natural phosphate by country in 2019 (USGS, 2021) ! Country !! Production (millions kg) !! Share of global production (%) !! Reserves (millions kg) |
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Calcium hydroxyapatite and calcite precipitates can be found around bacteria in alluvial topsoil. As clay minerals promote biomineralization, the presence of bacteria and clay minerals resulted in calcium hydroxyapatite and calcite precipitates.
Phosphate deposits can contain significant amounts of naturally occurring heavy metals. Mining operations processing phosphate rock can leave tailings piles containing elevated levels of cadmium, lead, nickel, copper, chromium, and uranium. Unless carefully managed, these waste products can leach heavy metals into groundwater or nearby estuaries. Uptake of these substances by plants and marine life can lead to concentration of toxic heavy metals in food products.
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