Tribasic phosphoric acid forms three types of salts with calcium. These are calcium hydrogen phosphate CaHPO4, calcium dihydrogen phosphate Ca (H2PO4) 2 and calcium phosphate or phosphate, the formula of which is: Ca3 (PO4) 2. This salt is an inorganic substance, under standard conditions it is in the solid state, and it passes into the liquid state (melts) at a temperature of more than 1200 C. The density is 2.81 g / cm³, the molar mass is 310.2 g / mol. Calcium phosphate is poorly soluble in water: at 20 C its mass fraction does not exceed 0.0025%. Unlike most other compounds, its solubility decreases with increasing temperature. Thus, in heating systems, this salt is able to form deposits.
Calcium phosphate is a white crystalline substance that is part of the minerals apatite (belongs to the class of phosphates containing up to 56% CaO and about 41% P2O5), phosphorite (a fibrous or dense aggregate of apatite containing over 18% P2O5) and hydroxylapatites (the main component of the bone tissue of humans and animals). The provenance of some deposits from excrement or corpses of animals. Other deposits (for example, in the ancient seas) were formed as a result of the activity of “phosphorobacteria”. But in some places the deposits of this mineral are of purely mineral origin. All of them are widespread in nature and are used in the national economy.
Apatite serves as a raw material for the production of phosphorus, phosphorus fertilizers and phosphoric acid, and is also used in non-ferrous and ferrous metallurgy, in the production of glass and ceramics. Natural minerals phosphorites are rocks of various origin, but often sedimentary, they are used for further enrichment and in the production of phosphate fertilizers. Reserves of phosphorites and apatites are of great importance for agriculture, as they are used not only to obtain fertilizers, but also as a source of calcium for feeding birds or cattle: feed calcium phosphate is produced according to GOST 23999-80.
A mineral of inorganic origin - apatite - is used in more than twenty production processes. It is used in the manufacture of abrasives, glass and ceramics, as well as for the production of phosphoric acid and free phosphorus. The process proceeds according to the scheme: 3SiO2 + Ca3 (PO4) 2 + 5C → 3CaSiO3 + 5CO + 2P. This substance is also in demand in the food industry: it is produced in the form of food additives E341 according to GOST R 53945-2010, which, along with 1- and 2-substituted salts of phosphoric acid, includes calcium phosphate. The receipt of this product implies stringent requirements for the feedstock. In the production of food additives, orthophosphoric acid of grade A is used according to GOST 10678-76, calcium hydroxide according to GOST 9262-77 and chemically precipitated chalk according to GOST 8253-79.
A mineral containing calcium phosphate plays an important role in the human body. Hydroxylapatite can be represented by the formula 3Ca3 (PO4) 3 • Ca (OH) 2. It is the main component and building material of human bones. This mineral is part of tooth enamel in the form of fluorapatite. The daily requirement for phosphorus is great and lies in the range from 800 to 1500 mg. The liver is responsible for the metabolism of phosphorus compounds in the human body, and hormones and vitamin D regulate this process. Various diseases of bones and teeth develop with a lack of phosphorus in the body. Calcium phosphate comes with food, strengthens teeth and bones, and in combination with other minerals it supports the cardiovascular system, prevents colon cancer, regulates nerve function, participates in the construction of collagen, and helps lower cholesterol. Phosphates are excreted in feces, and about 4 g of phosphoric acid salts are excreted daily in urine.
The main sources of calcium phosphate for humans are cow's milk and dairy products, cereals, fortified juices, cheese, goat's milk, salmon, sardines and anchovies. Being poorly soluble in water, calcium phosphate is in high concentration in milk, because it exists in the colloidal system in the form of micelles - particles consisting of a very small insoluble core, which is surrounded by solvent molecules and adsorbed ions. It is a part of milk casein, more precisely, calcium caseinate, which refers to phosphoproteins, as it contains a phosphate group. However, experts recommend avoiding excess calcium phosphate, especially in the form of fortified foods and supplements, if a person has one of the following diseases: parathyroid glands, kidney stones, or during ongoing treatment, including tetracycline antibiotics.