Usually, the date of discovery of phosphorus is considered to be 1669, but there are some indications that it was known earlier. Gefer, for example, reports that in an alchemical manuscript from a collection stored in the Paris Library, it is said that around the 12th century. a certain Alkhid Bekhil obtained a substance by distillation of urine with clay and lime, which he called "escarbucle". Perhaps this was phosphorus, which is the great secret of the alchemists. In any case, it is known that in search of the philosopher's stone, alchemists subjected to distillation and other operations all kinds of materials, including urine, feces, bones, etc.
Since ancient times, phosphors have been called substances that can glow in the dark. In the 17th century Bolognese phosphorus was known - a stone found in the mountains near Bologna; after burning on coals, the stone acquired the ability to glow. It also describes "Baldwin's phosphorus", prepared by the volost foreman Alduin from a calcined mixture of chalk and nitric acid. The glow of such substances caused extreme surprise and was considered a miracle.
In 1669, the Hamburg amateur alchemist Brand, a bankrupt merchant who dreamed of improving his affairs with the help of alchemy, processed a wide variety of products. Assuming that physiological products might contain the "primordial matter" thought to be the basis of the Philosopher's Stone, Brand became interested in human urine.
Oh, how he was carried away by the idea, what efforts he made to implement it! Believing that the products of the vital activity of a person, the “king of nature”, can contain the so-called primary energy, the tireless experimenter began distilling human urine, one might say, on an industrial scale: in the soldiers’ barracks, he collected a whole ton of it in total! And he evaporated to a syrupy state (not in one go, of course!), And after distillation, he again distilled the resulting “urine oil” and calcined it for a long time. As a result, white dust appeared in the retort, which settled to the bottom and glowed, which is why it was called “cold fire” (kaltes Feuer) by Brand. Brand's contemporaries called this substance phosphorus because of its ability to glow in the dark (another Greek jwsjoroV).
In 1682, Brand published the results of his research, and he is now rightly considered the discoverer of element No. 15. Phosphorus was the first element whose discovery was documented, and its discoverer is known.
Interest in the new substance was enormous, and Brand took advantage of this - he demonstrated phosphorus only for money or exchanged small amounts of it for gold. Despite numerous efforts, the Hamburg merchant could not fulfill his cherished dream - to obtain gold from lead using "cold fire", and therefore he soon sold the recipe for obtaining a new substance to a certain Kraft from Dresden for two hundred thalers. The new owner managed to make a much larger fortune on phosphorus - with "cold fire" he traveled all over Europe and demonstrated it to scientists, high-ranking and even royal people, for example, Robert Boyle, Gottfried Leibniz, Charles II. Although the method of preparing phosphorus was kept in the strictest confidence, in 1682 Robert Boyle managed to obtain it, but he also disclosed his method only at a closed meeting of the Royal Society of London. Boyle's method was made public after his death, in 1692.
In the spring of 1676, Kraft arranged a session of experiments with phosphorus at the court of Elector Friedrich Wilhelm of Brandenburg. At 9 pm on April 24, all the candles in the room were extinguished, and Kraft showed those present experiments with "eternal fire", without revealing, however, the method by which this magical substance was prepared.
In the spring of the following year, Kraft came to the court of Duke Johann Friedrich in Hannover3, where at that time the German philosopher and mathematician G.W. Leibniz (1646-1716) served as a librarian. Kraft also arranged a session of experiments with phosphorus here, showing, in particular, two flasks that glowed like fireflies. Leibniz, like Kunkel, was extremely interested in the new substance. At the first session, he asked Kraft if a large piece of this substance would not be able to light up the whole room. Kraft agreed that it was quite possible, but would be impractical, since the process of preparing the substance is very complicated.
Who had this? I had.
Leibniz's attempts to persuade Kraft to sell the secret to the duke failed. Then Leibniz went to Hamburg to Brand himself. Here he managed to conclude a contract between Duke Johann Friedrich and Brand, according to which the former was obliged to pay Brand 60 thalers for revealing the secret. From that time on, Leibniz entered into regular correspondence with Brand.
At about the same time, I.I. Becher (1635-1682) arrived in Hamburg with the aim of luring Brand to the Duke of Mecklenburg. However, Brand was again intercepted by Leibniz and taken to Hanover to Duke Johann Friedrich. Leibniz was fully convinced that Brand was very close to discovering the "philosopher's stone", and therefore advised the duke not to let him go until he had completed this task. Brand, however, stayed in Hanover for five weeks, prepared fresh supplies of phosphorus outside the city, showed, according to the contract, the secret of production and left.
Then Brand prepared a significant amount of phosphorus for the physicist Christian Huygens, who studied the nature of light, and sent a supply of phosphorus to Paris.
Brand, however, was very dissatisfied with the price Leibniz and Duke Johann Friedrich gave him for revealing the secret of phosphorus production. He sent an angry letter to Leibniz, complaining that the amount received was not enough even to support his family in Hamburg and pay travel expenses. Similar letters were sent to Leibniz and Brand's wife, Margarita.
Brand was also dissatisfied with Kraft, to whom he expressed resentment in letters, reproaching him for having resold the secret for 1000 thalers to England. Kraft forwarded this letter to Leibniz, who advised Duke Johann Friedrich not to irritate Brand, to pay him more generously for revealing the secret, fearing that the author of the discovery, in the form of an act of revenge, would share the recipe for making phosphorus with someone else. Leibniz sent a reassuring letter to Brand himself.
Apparently, Brand received a reward, tk. in 1679 he again came to Hanover and worked there for two months, receiving a weekly salary of 10 thalers with additional payment for the table and travel expenses. Correspondence between Leibniz and Brand, judging by the letters kept in the Hanover Library, continued until 1684.
Let us now return to Kunkel. According to Leibniz, Kunkel learned through Kraft the recipe for making phosphorus and set to work. But his first experiments were unsuccessful. He wrote letter after letter to Brand, complaining that he had been sent a recipe that was very incomprehensible to another person. In a letter written in 1676 from Wittenberg, where Kunkel was then living, he asked Brand about the details of the process.
In the end, Kunkel achieved success in his experiments, somewhat modifying Brand's method. By adding a little sand to dry urine before distilling it, he received phosphorus and ... made a claim to the independence of the discovery. In the same year, in July, Kunkel told about his successes to his friend, Professor of Wittenberg University Kaspar Kirchmeyer, who published a work on this issue under the title "Permanent night lamp, sometimes sparkling, which was long sought, now found." In this article, Kirchmeyer speaks of phosphorus as a long-known luminous stone, but does not use the term "phosphorus" itself, obviously not yet accustomed to that time.
In England, independently of Brand, Kunkel and Kirchmeyer in 1680, phosphorus was obtained by R. Boyle (1627-1691). Boyle knew about phosphorus from the same Kraft. As early as May 1677, phosphorus was demonstrated at the Royal Society of London. In the summer of the same year, Kraft himself came with phosphorus to England. Boyle, according to his own account, visited Kraft and saw phosphorus in his solid and liquid form. In gratitude for the warm welcome, Kraft, saying goodbye to Boyle, hinted to him that the main substance of his phosphorus was something inherent in the human body. Obviously, this hint was enough to give an impetus to Boyle's work. After Kraft's departure, he began to test blood, bones, hair, urine, and in 1680 his efforts to obtain a luminous element were crowned with success.
Boyle began to exploit his discovery in the company of an assistant, the German Gaukwitz. After Boyle's death in 1691, Gaukwitz launched the production of phosphorus, improving it on a commercial scale. By selling phosphorus at three pounds sterling an ounce and supplying the scientific institutions and individual scientists of Europe with it, Gaukwitz amassed a huge fortune. To establish commercial connections, he traveled to Holland, France, Italy and Germany. In London itself, Gaukwitz founded a pharmaceutical company that became famous during his lifetime. It is curious that, despite all his experiments with phosphorus, sometimes very dangerous, Gaukwitz lived to be 80 years old, outliving his three sons and all the people who participated in the work related to the early history of phosphorus.
Since the discovery of phosphorus by Kunkel and Boyle, it has rapidly fallen in price as a result of the competition of inventors. In the end, the heirs of the inventors began to acquaint everyone with the secret of its production for 10 thalers, all the while lowering the price. In 1743, A.S. Marggraf found an even better way to produce phosphorus from urine and immediately published it, because. fishing is no longer profitable.
Currently, phosphorus is not produced anywhere by the Brand-Kunkel-Boyle method, since it is completely unprofitable. For the sake of historical interest, we will nevertheless give a description of their method.
Rotting urine is evaporated to a syrupy state. The resulting thick mass is mixed with three times the amount of white sand, placed in a retort equipped with a receiver, and heated for 8 hours on an even fire until the volatile substances are removed, after which the heating is increased. The receiver is filled with white vapor, which then turns into bluish solid and luminous phosphorus.
Phosphorus got its name due to the property to glow in the dark (from Greek - luminiferous). Among some Russian chemists there was a desire to give the element a purely Russian name: "gem", "lighter", but these names did not take root.
Lavoisier, as a result of a detailed study of the combustion of phosphorus, was the first to recognize it as a chemical element.
The presence of phosphorus in the urine gave chemists a reason to look for it in other parts of the body of animals. In 1715, phosphorus was found in the brain. The significant presence of phosphorus in it served as the basis for the assertion that "without phosphorus there is no thought." In 1769, Yu.G. Gan found phosphorus in the bones, and two years later, K.V. Scheele proved that the bones consist mainly of calcium phosphate, and proposed a method for obtaining phosphorus from the ash remaining after bones were burned. Finally, in 1788, M.G. Klaproth and J.L. Proust showed that calcium phosphate is an extremely widespread mineral in nature.
The allotropic modification of phosphorus - red phosphorus - was discovered in 1847 by A. Schretter. In a work entitled "A New Allotropic State of Phosphorus", Schretter writes that sunlight changes white phosphorus to red, and factors such as dampness, atmospheric air, have no effect. Schretter separated the red phosphorus by treatment with carbon disulfide. He also prepared red phosphorus by heating white phosphorus to a temperature of about 250 ° C in an inert gas. At the same time, it was found that a further increase in temperature again leads to the formation of a white modification.
It is very interesting that Schroetter was the first to predict the use of red phosphorus in the match industry. At the World Exhibition in Paris in 1855, red phosphorus, already obtained by the factory, was demonstrated.
The Russian scientist A.A. Musin-Pushkin in 1797 received a new modification of phosphorus - violet phosphorus. This discovery is erroneously attributed to I.V. Gittorf, who, having almost completely repeated the Musin-Pushkin method, received violet phosphorus only in 1853.
In 1934, Professor P.W. Bridgman, subjecting white phosphorus to a pressure of up to 1100 atm, turned it into black and thus obtained a new allotropic modification of the element. Along with the color, the physical and Chemical properties phosphorus: white phosphorus, for example, ignites spontaneously in air, and black, like red, does not have this property.
sources
H 3 PO 4 - strong acid, K 1 7.1 10 -3 (pK a 2.12), K 2 6.2 10 -8 (pK a 7.20), K 3 5.0 10 -13 (pK a 12.32); the values of K 1 and K 2 depend on the t-ry. Dissociation in the first stage is exothermic, in the second and third - endothermic. The phase diagram of the H 3 PO 4 - H 2 O system is shown in fig. 2. The maximum of the crystallization curve is at t-re 302.4 K and the content of H 3 PO 4 91.6% (solid phase - hemihydrate). In table. St. Islands solutions of phosphoric acid are given.
CHARACTERISTICS OF H 3 PO 4 AQUEOUS SOLUTIONS
|
T. shutter, 0 C |
T. b., 0 C |
kJ/(kg K) |
Pa s (25 0 C) |
Oud. electric conductivity, S/m (25 0 C) |
|||||
|
H3PO4 |
P2O5 |
||||||||
|
5 |
3,62 |
0,8 |
100,10 |
4,0737 |
0,0010 |
10,0 |
3129,1 |
||
|
10 |
7,24 |
2,10 |
100,20 |
3,9314 |
0,0011 |
18,5 |
3087,7 |
||
|
20 |
14,49 |
6,00 |
100,80 |
3,6467 |
0,0016 |
18,3 |
2986,4 |
||
|
30 |
21,73 |
11,80 |
101,80 |
3,3411 |
0,0023 |
14,3 |
2835,7 |
||
|
40 |
28,96 |
21,90 |
103,90 |
3,0271 |
0,0035 |
11,0 |
2553,1 |
||
|
50 |
36,22 |
41,90 |
104,00 |
2,7465 |
0,0051 |
8,0 |
2223,8 |
||
|
60 |
43,47 |
76,9 |
114,90 |
2,4995 |
0,0092 |
7,2 |
1737,1 |
||
|
70 |
50,72 |
43,00 |
127,10 |
2,3278 |
0,0154 |
6,3 |
1122,6 |
||
|
75 |
54,32 |
17,55 |
135,00 |
2,2692 |
0,0200 |
5,8 |
805,2 |
||
F osphoric acid under normal conditions is inactive and reacts only with carbonates, hydroxides and certain metals. In this case, one-, two- and three-substituted phosphates are formed (see Inorganic phosphates). When loading above 80 0 C reacts even with inactive oxides, silica and silicates. At elevated temperatures phosphoric acid is a weak oxidizing agent for metals. When acting on a metal a surface solution of phosphoric acid with additions of Zn or Mn forms a protective film (phosphating). Phosphoric acid at heating. loses water with the formation of successively pyro- and metaphosphoric acids:
Phospholeum (liquid phosphoric anhydride, superphosphoric acid) includes to-you containing from 72.4 to 88.6% P 2 O 5, and is an equilibrium system consisting of ortho-, pyro-, Tripoli-, tetrapoly- and other phosphoric to-t (see Condensed phosphates). When diluted with superphosphorus water, it stands out. amount of heat, and polyphosphoric to-you quickly turn into orthophosphoric.
From other phosphoric to-t H 3 PO 4 can be distinguished by p-tion with AgNO 3 - a yellow precipitate Ag 3 PO 4 falls. The remaining phosphoric acids form white precipitates.
Receipt. Phosphoric acid in the lab. conditions, it is easy to obtain by oxidation of phosphorus with a 32% solution of nitric acid:
In the industry, phosphoric acid is obtained by thermal and extraction methods.
Thermal method (allows you to produce the most pure phosphoric acid) includes DOS. stages: combustion (oxidation) of elemental phosphorus in excess air, hydration and absorption of the resulting P 4 O 10 (see Phosphorus oxides), condensation of phosphoric acid and trapping of fog from the gas phase. There are two ways to obtain P 4 O 10: the oxidation of P vapor (rarely used in the industry) and the oxidation of liquid P in the form of drops or films. The degree of oxidation P in prom. conditions is determined by t-swarm in the oxidation zone, diffusion of components, and other factors. The second stage of obtaining thermal. phosphoric acid - hydration P 4 O 10 - is carried out by absorption to-that (water) or mutual mod. vapor P 4 O 10 with water vapor. Hydration (P 4 O 10 + 6H 2 O4H 3 PO 4) proceeds through the stages of formation of polyphosphoric acids. The composition and concentration of the resulting products depend on the temperature and partial pressure of water vapor.
All stages of the process can be. combined in one apparatus, except for catching fog, a cut is always produced in a separate apparatus. In the industry, schemes of two or three mains are usually used. devices. Depending on the principle of gas cooling, there are three ways to produce thermal. phosphoric acid: evaporative, circulation-evaporative, heat exchange-evaporative. Evaporate systems based on the removal of heat during the evaporation of water or dil. phosphoric acid, max. simple in hardware design. However, due to the relatively large volume of exhaust gases, the use of such systems is advisable only in installations of small unit capacity.
Circulating-evaporate. systems allow to combine in one apparatus the stages of burning P, cooling the gas phase of the circulating to-one and hydration P 4 O 10 . The disadvantage of the circuit is the need to cool large volumes of k-you. Heat exchange-evaporate. systems combine two methods of heat removal: through the wall of the combustion and cooling towers, as well as by evaporating water from the gas phase; a significant advantage of the system is the absence of circulation circuits to-you with pumping and refrigeration equipment.
On the fatherlands. enterprises operate technology. schemes with circulation-evaporate. cooling method (two-tower system). Distinguish. features of the scheme: the presence of additionalnit. gas cooling towers , use of efficient plate heat exchangers in circulation circuits ; high performance application. nozzles for burning P, providing a uniform fine atomization of the jet of liquid P and its complete combustion without the formation of lower oxides.
Technol. Figure 1 shows a diagram of a plant with a capacity of 60,000 tons per year of 100% H 3 PO 4 . 3. Molten yellow phosphorus is atomized with heated air at a pressure of up to 700 kPa through a nozzle in a combustion tower irrigated by a circulating filter. Heated in the tower to-that is cooled by circulating water in plate heat exchangers. Productive to-ta, containing 73-75% H 3 PO 4 is discharged from the circulation circuit to the warehouse. In addition, the cooling of gases from the combustion tower and absorption to-you are carried out in the cooling tower (hydration), which reduces the afterbirth, the temperature load on the electrostatic precipitator and contributes to effective gas purification. Heat removal in the hydration tower is carried out by circulating 50% H 3 PO 4 cooled in plate heat exchangers. Gases from the hydration tower after being cleaned from H 3 PO 4 mist in a plate electrostatic precipitator are released into the atmosphere. For 1 ton of 100% H 3 PO 4, 320 kg of P is consumed.
Rice. 3. Circulation double-tower scheme for the production of thermal. H 3 PO 4: 1 - sour water collector; 2 - storage of phosphorus; 3.9 - circulation collectors; 4.10 - submersible pumps; 5.11 - plate heat exchangers; 6 - combustion tower; 7 - phosphorus nozzle; 8 - hydration tower; 12 - electrostatic precipitator; 13 - fan.
A more economical extraction method for obtaining phosphoric acid is based on the decomposition of nature. phosphates to-tami (mainly sulfuric, to a lesser extent nitric and slightly hydrochloric). Phosphoric acid solutions obtained by decomposition of nitric acid are processed into complex fertilizers, by decomposition of hydrochloric acid - into precipitate.
Sulfuric acid decomposition of phosphate raw materials [in the CIS countries Ch. arr. Khibiny apatite concentrate (see Apatite) and Karatau phosphorites] - main. method for obtaining extraction phosphoric acid, used for the production of conc. phosphate and complex fertilizers. The essence of the method is the extraction (extraction) of P 4 O 10 (usually f-lu P 2 O 5 is used) in the form of H 3 PO 4 . According to this method, phosphates are treated with H 2 SO 4 followed by filtration of the resulting pulp to separate phosphoric acid from the Ca sulfate precipitate. Part of the selected core. the filtrate, as well as the entire filtrate obtained by washing the precipitate on the filter, is returned to the extraction process (dilution solution) to ensure sufficient mobility of the pulp during its mixing and transportation. Mass ratio between liquid and solid phases from 1.7:1 to 3.0:1.
Natural phosphates decompose according to the scheme:
Accompanying impurities are also decomposed to-tami: calcite, dolomite, siderite, nepheline, glauconite, kaolin and other minerals. This leads to an increase in the consumption of used to-you, and also reduces the extraction of P 2 O 5 in the target product due to the formation of insoluble iron phosphates FeH 3 (PO 4) 2 2.5H 2 O at P 2 O 5 concentrations above 40% (content P 4 O 10 is usually given in terms of P 2 O 5) and FePO 4 · 2H 2 O - at lower concentrations. I single outCO 2, which is released during the decomposition of carbonates, forms stable foam in extractors; p-rime phosphates of Mg, Fe and Al reduce the activity of phosphoric acid, and also reduce the content of assimilable forms of P 2 O 5 in fertilizers during the last. processing of phosphoric acid.
Taking into account the influence of impurities, the requirements for phosphate raw materials are determined, according to Crimea prir. phosphates with a high content Comm. Fe, Al, Mg, carbonates and org. in-in unsuitable for the production of phosphoric acid.
Depending on the temperature and concentration of phosphoric acid in the CaSO 4 -H 3 PO 4 -H 2 O system, Ca sulfate precipitates as dihydrate (gypsum), hemihydrate or anhydrite. In real conditions, the precipitate is contaminated with P 2 O 5 impurities in the form of undecomposed nature. phosphates, underwashed H 3 PO 4 , co-crystallized phosphates decomp. metals, etc., so the resulting Ca sulfates called. resp. phosphogypsum, phosphohemihydrate and phospho-anhydrite. Depending on the type of precipitated sulfate, there are three direct methods for the production of extraction phosphoric acid: dihydrate, hemihydrate (hemihydrate) and anhydrite, as well as combined: hemihydrate-dihydrate and dihydrate-hemihydrate.
In the CIS, naib. the dihydrate method has been worked out in the industry, to-ry it is distinguished by a high yield of P 2 O 5 (93-96.5%) in the production to-that; however relatively lowWhat concentration of phosphoric acid requires its last. evaporation. Main process steps: extraction with ext. or int. circulation and vacuum or air cooling of the extraction pulp, ripening of the pulp after the extractor, separation of phosphoric acid on bulk vacuum filters. The efficiency of the process is determined in the main.
Orthophosphoric (sometimes the name phosphoric) acid is an acid of inorganic origin, of medium power. It is a simple chemical formula and is denoted as H3PO4.
Under typical storage conditions and optimum storage temperatures, it appears as neat, colorless, hygroscopic crystals. In cases where the temperature warms up to +42 to +213 degrees Celsius, the mentioned substance is converted into pyrophosphoric acid with a similar chemical formula - H4P2O7.
Phosphoric acid is most often referred to as an approximately 85% water-based solution, which has no aroma and is characterized by a moderately thick syrup-like appearance. In addition to water, the mentioned acid is also perfectly soluble in alcohol and other popular solvents.
How is phosphoric acid obtained?
In order to get the mentioned chemical compound, you do not need to have a lot of money or time. Like citric acid, orthophosphoric acid is now in great demand and is produced in huge quantities. To date, experts know three correct methods for the extraction of phosphoric acid:
1. Hydrolysis of phosphorus pentachloride;
2. Obtaining from phosphate (extraction method);
3. By mixing phosphorus(V) oxide with ordinary water, obtained by burning phosphorus in oxygen (thermal method).
Since the reaction with water is very active, phosphorus (V) oxide is treated with a concentrated solution of phosphoric acid heated to 200 degrees Celsius.
A small amount of the substance can be easily obtained in the laboratory by the oxidation of phosphorus. But for the production of such a compound on a serious, industrial scale, one cannot do without an extraction and thermal method.
Orthophosphoric acid in different areas of human life: where it is used
The scope of phosphoric acid today is very interesting and diverse. Thus, the mentioned chemical substance is indispensable in various industries, among which is food.
Orthophosphoric acid has barely pronounced acidic properties, easily reacts with salts of weak acids, all kinds of metals, basic oxides, bases, ammonia. Affordable price has made phosphoric acid in demand in completely different areas.
Agriculture and farming
The compound is a very common additive for the manufacture of popular phosphate or combined fertilizers: ammonium, calcium, sodium, manganese salts. According to statistics, about 90% of phosphorus-containing ore is used for the production of fertilizers. Phosphorus is important for plants in the formation of seeds and fruits. At the same time, the United States of America, Russia and Morocco are considered to be the producing countries of such fertilizers, and almost all countries of Africa, Asia and the European Union are considered to be the consuming countries.
On farms, veterinarians often advise feeding animals with a solution of phosphoric acid in order to prevent the formation of kidney and gallstones, and increase the level of stomach acid.
food industry
Of particular interest is the use of chemical elements, including phosphoric acid in the food industry. So, in this area, phosphoric acid acts as an acidity regulator and is indicated by the marking E338. It is an excellent antioxidant, retains color and extends the shelf life of various drinks and foods.
In particular, the E338 additive is often added to such products that are in demand among the population: various sausages, processed cheeses, baking powder, bakery and confectionery products, milk and baby food, sweetened carbonated drinks, and so on.
The most popular drink containing phosphoric acid is Coca-Cola. As you know, such a drink can even clean metal surfaces from rust. At the same time, the concentration of acid in this drink is not so high as to seriously harm the human stomach when consumed in small quantities.
Production of household chemicals and building materials
Thanks to the active use of phosphoric acid and its availability, manufacturers are launching fire-resistant paints and varnishes on the building materials market, including: varnish, enamel, impregnation, wood boards and other materials for construction and repair. Phosphoric acid is also indispensable for the production of matches.
Orthophosphoric acid solutions are actively used by craftsmen at woodworking farms. Due to the impregnation of wood with this substance, the wood becomes fire resistant.
Phosphoric acid salts perfectly soften chlorinated water; they are contained in many household chemicals. For example, these are washing powders and gels, dishwashing liquids, liquids for removing rust and grease on surfaces, and so on.
Molecular biology
It is used by specialists for various experiments and studies.
The medicine
Interestingly, in medicine, phosphoric acid is a component of activated carbon. Also for many years it has been actively used in dentistry - for fillings. In small quantities, this compound is present in toothpastes and tooth whiteners.
Few people realize that phosphoric acid is also an element of wicking for the manufacture of waterproof and windproof outerwear, in particular, ski suits.
Is phosphoric acid harmful to humans?
Remember that everything is good in moderation. Orthophosphoric acid is considered a relatively safe chemical compound, subject to the norms of its consumption. Excess consumption of phosphoric acid along with food can lead to feeling unwell, aversion to food, weight loss, brittle bones. Therefore, it is better to avoid excessive consumption of foods with food additive E338.
If acid in the form of a concentrated solution gets on the skin and mucous membranes of a person, burns are possible. Also, some dentists have noticed that phosphoric acid damages the top layer of tooth enamel when used frequently for dental treatment.
In contact with
Raw materials for the production of phosphoric acid
More than 120 minerals are known in nature. The most common and industrially important minerals of the apatite group are fluorapatite Ca 10 F 2 (PO 4) 6, hydroxideapatite Ca 10 (PO 4) 6 (OH) 2, chlorapatite.
Phosphates of the apatite group include minerals with the general formula Ca 10 R 2 (PO 4) 6, where R is F, Cl, OH.
Some part of Ca in apatites is replaced by Sr, Ba, Mg, Mn, Fe and trivalent rare earth elements in combination with alkali metals.
The thickness of the seams reaches 200 m. The minerals included in the ore differ in their physicochemical and flotation properties, which makes it possible to enrich the resulting concentrate with a target product content of 92-93% during flotation.
Pure calcium fluorapatite contains: 42.22% P 2 O 5 ; 55.6% CaO, 3.76% - F.
By origin, phosphates are igneous and sedimentary. Igneous, or proper apatite rocks were formed either by direct solidification of molten magma, or in separate veins in the process of crystallization of magmatic melt (hematite veins), or by separation from hot aqueous solutions (hydrothermal formations), or by the interaction of magma with limestone (contact).
Apatite rocks have a granular macrocrystalline structure and are characterized by the absence of polydispersity and microporosity.
Sedimentary phosphates - phosphorites. They were formed as a result of weathering of rocks, interaction with other rocks - and their deposition both in a scattered state and with the formation of large accumulations.
Phosphorite ores differ from apatite ones in the high dispersion of the phosphate minerals contained in them and in their close intergrowth with accompanying minerals (impurities). Phosphorites dissolve faster in acids than apatites.
The best raw material for extracting phosphoric acid is an apatite concentrate containing 2% R2O3 or 5% of the total P 2 O 5 content. It contains almost no carbonates. As a result, the smallest (compared to other types of raw materials) amount of sulfuric acid is spent on its decomposition.
During the extraction of phosphoric acid from Karatau phosphorites containing a significant amount of carbonates, ferruginous and clay substances, not only the consumption of sulfuric acid increases, due to the need for decomposition of carbonates, but also phosphoric acid is of poorer quality. It contains sulfates and phosphates of magnesium, iron and aluminum, which causes the neutralization of a significant part (up to half) of phosphoric acid. In addition, P 2 O 5 can be extracted from such raw materials by 3-6% less than from apatite concentrate. This is mainly due to the deterioration of the conditions for filtering and washing phosphogypsum, which is released from the solution in the form of small crystals, penetrated by impurities of fine clay particles.
Other types of phosphorites are sandy (Aktobe, Shchigrovsky), clayey-glauconite (Vyatka, Ryazan-Egorievsk) even after enrichment achieved modern methods, are not currently used for the production of phosphoric acid. They can be used in mixture with apatite concentrate. The amount of added apatite should provide such a ratio of R2O3: P2O5, which allows the process to be carried out with minimal losses.
Thermal method for the production of phosphoric acid
The thermal method consists in high-temperature reduction of phosphates and sublimation in electric furnaces of elemental phosphorus in the presence of carbon and silica
Ca 3 (RO 4) 2 + 5C + 2SiO 2 = P 2 + 5CO + Ca 3 Si 2 O 7 - 1460 kJ / mol.
The resulting phosphorus is oxidized to phosphoric anhydride, and then the latter is hydrated with water; resulting in the formation of phosphoric acid
2P2 + 5O2 = 2P2O5; P2O5 + 3H2O = 2H3RO4.
According to the principle of gas cooling, the processes of obtaining phosphates based on elemental phosphorus can be classified into systems with a change in the state of aggregation of the refrigerant and systems without changing the state of aggregation of the refrigerant. The refrigerants are always water or phosphoric acid.
The main advantage of the thermal method, in comparison with the extraction method, is the possibility of processing any type of raw material, including low-quality phosphorites, and obtaining a high purity acid.
Extraction method for obtaining phosphoric acid
The acid method is based on the displacement of phosphoric acid from phosphates by strong acids. The method of sulfuric acid extraction has found the greatest distribution in practice.
The process proceeds according to the following summary equation:
Ca 5 F (PO 4) 3 + 5H 2 SO 4 \u003d 5CaSO 4 (tv) + 3H 3 RO 4 + HF.
Depending on the process temperature and P2O5 concentration in the solution, calcium sulfate (phosphogypsum) is released in the form of CaSO4 2H2O (dehydrate mode), CaSO4 0.5H2O (hemihydrate mode) and CaSO4 (anhydride mode). The first two modes have found industrial distribution.
The resulting hydrogen fluoride interacts with H2SiO3
4HF + H 2 SiO 3 \u003d SiF 4 + 3H 2 O.
In this case, SiF4 is partially released into the gas phase, and partially remains in the EPA solution in the form of H2SiF6.
Typically, the resulting extraction acid is contaminated with raw material impurities and has a low concentration (25-32% P 2 O 5), so it must be evaporated to a higher concentration.
The main advantages of the extraction process are its simplicity and the possibility of producing cheaper H 3 PO 4 . The disadvantage is that the resulting EPA is contaminated with an admixture of sesquioxides (Al2O3, Fe2O3), fluorine compounds and CaSO 4 .
Production of phosphoric acid by dihydrate and hemihydrate methods
There are various ways to obtain phosphoric acid of different concentrations with the release of calcium sulfate dihydrate. The most convenient classification and evaluation different ways depending on the concentration of the resulting acid, since it is the main indicator of product quality and one of the main technological parameters that determine all others - temperature, the duration of the interaction of the reagents, the shape and filtering properties of the precipitated calcium sulfate crystals, etc.
Currently, the dihydrate method produces H 3 RO 4 with a content of 20-25% P 2 O 5 (usually from low-grade raw materials - poor phosphorites) and 30-32% P 2 O 5 (from high-quality raw materials - apatite concentrate)
Upon receipt of an acid containing 30-32% P 2 O 5 hemihydrate-dehydrate method, the process is carried out in two stages. The first stage - the decomposition of phosphate - is carried out under such conditions that calcium sulfate is released in the form of a relatively stable hemihydrate, which does not become hydrated during the extraction to gypsum. In the second stage, the separated hemihydrate, which is not separated from the liquid phase, is recrystallized in the reaction pulp into a dihydrate in the presence of gypsum seed crystals with the release of large, well-formed and rapidly filtering crystals.
The advantages of this method are the maximum (up to 98.5%) extraction of phosphoric acid from the raw material into the solution with a minimum consumption of sulfuric acid and the production of high quality gypsum containing no more than 0.3% of the total P 2 O 5 (instead of the usual 0.5-1 .5%) and 0.02-0.08% water-soluble P 2 O 5 . This is due to the prevention of replacement by sulfate ions in the crystal lattice of the precipitate and the release of HPO4- ions, which were retained (adsorbed on the surface of the initially precipitated particles of the solid phase, since the hemihydrate previously passed into the liquid phase.
In contrast to the currently used dihydrate method, the hemihydrate method can teach an acid containing 45-50% P 2 O 5 . This makes it possible to increase the capacity of existing workshops by 1.5 - 1.8 times and somewhat reduce the amount of waste - sulfate residue.
For the production of concentrated phosphorus and complex fertilizers, phosphoric acid containing 37-55% P2O5 or more is required, and for the production of ammonium polyphosphates and concentrated liquid fertilizers, acid containing 72-83% P2O5 is required. Therefore, in many cases, the extraction phosphoric acid is subjected to concentration by evaporation.
At the stage of experimental development is the production of phosphoric acid containing up to 55% P 2 O 5 by the anhydrite method (without evaporation). The easiest way to get an acid containing 53-55% P 2 O 5 because the process is reduced only to the evaporation of water and is not accompanied by dehydration of phosphoric acid and the formation of phosphorus anhydrite is not in the ortho form. However, this process is also complicated by severe corrosion of the equipment and the release of impurities contained in the acid.
Hot phosphoric acid has a strong corrosive effect on most known metals, alloys and silicate-ceramic materials. The precipitates released during the evaporation process can clog the equipment, resulting in a sharp decrease in its productivity. This makes it difficult to use typical and widely used evaporators for phosphoric acid evaporation. Acid containing 53 - 55% P2O5 can be obtained from relatively little contaminated phosphates - apatite concentrate or enriched high-grade phosphorites
Production of phosphoric acid by other methods
Of interest in industry is the method of obtaining H3PO4, based on the oxidation of phosphorus with steam on a copper-zirconium catalyst, the optimal process conditions are: t = 973°C, the ratio of steam and phosphorus is 20:1
P 4 + 16H 2 O \u003d 4H 3 RO 4 + 10H 2 + 1306.28 kJ.
In the laboratory, H3PO4 is obtained
3P + 5HNO 3 + 2H 2 O \u003d 3H 3 RO 4 + 5NO
The extraction of phosphoric acid from phosphates with sulfuric acid has significant disadvantages: a large consumption of sulfuric acid (2.5–3.1 tons of monohydrate per 1 ton of P2O5) and the need to process or store a significant amount of waste - phosphogypsum (4.5–6.0 tons per 1 ton of P2O5 in terms of dry matter), the processing of which into sulfuric acid is associated with the release of significant quantities of cement or lime at the same time, which are not always widely sold. Therefore, the possibilities of extracting phosphoric acid with other inorganic acids - nitric, hydrochloric, fluoric and fluorosilicic acids are continuously being sought.
The main difficulty in the decomposition of phosphate by nitric or hydrochloric acid is the separation of phosphoric acid from the highly soluble calcium nitrate and chloride. When using fluorosilicic or hydrofluoric acids, a precipitate is formed, which is easily separated by filtration. However, in this case, acid regeneration requires the use of high temperatures, but it is possible to carry out the process without additional reagents - acids, using fluorine contained in the raw material.
Getting phosphates
The content of various anionic forms in the solution depends on the pH of the solution. All alkali metal and ammonium phosphates are highly soluble in water. For other metals, only dihydrogen phosphates are soluble. Solutions of medium phosphates of alkali metals due to hydrolysis have a strongly alkaline reaction. (0.1 M Na3PO4 solution has a pH of 12.7). Under these conditions, in the presence of medium alkali metal phosphates as a reagent, it is not possible to obtain medium phosphates of other metals - either basic salts or hydroxides and oxides precipitate from solutions:
4Na 3 PO 4 + 5CaCl 2 + H 2 O \u003d Ca 5 (PO 4) 3 OH + 10NaCl + Na 2 HPO 4
2AgNO 3 + 2Na 3 PO 4 + H 2 O \u003d Ag 2 O + 2Na 2 HPO 4 + 2NaNO 3
Therefore, to obtain medium salts of phosphoric acid, it is necessary to reduce the pH. This is achieved by using a solution of sodium hydrogen phosphate in the presence of ammonia:
2Na 2 HPO 4 + CaCl 2 + 2 NH 3 = Ca 3 (PO 4) 2 + 2 NH 4 Cl + 4NaCl
Phosphates (both medium and acidic) can also be obtained by exchange reactions, where there are a lot of different variations of reagents:
1. Direct interaction of metal with phosphoric acid:
2H3PO4+3Ca= Ca3(PO4)2+ 3H2
2. Reaction between basic oxide and phosphoric acid:
2H 3 PO 4 + 3CaO \u003d Ca 3 (PO 4) 2 + 3H 2 O
3. Exchange reaction between salts, one of which necessarily contains a phosphate or dihydrophosphate anion:
2Na 3 PO 4 + 3CaCl 2 = Ca 3 (PO 4) 2 + 6NaCl.
4. Exchange reaction of phosphoric acid and hydroxide:
2H 3 PO 4 + 3Ca(OH) 2 \u003d CaHPO 4 2H 2 O
2H 3 PO 4 + 3NaOH \u003d Na 3 PO 4 + 3H 2 O
5. Phosphate and hydroxide exchange reaction:
2Na 3 PO 4 + 3Ca(OH) 2 = Ca 3 (PO 4) 2 + 3 NaOH
6. Interaction of dihydrophosphates or hydrophosphates with alkali:
It is possible to obtain phosphate directly from the simple substance of phosphorus. White phosphorus is dissolved in an alkaline solution of hydrogen peroxide:
P 4 + 10H 2 O 2 + 12NaOH \u003d 4Na 3 PO 4 + 16H 2 O
The main method for controlling the purity of the obtained water-insoluble phosphate is its abundant washing with water while filtering the precipitate. With respect to water-soluble ammonium and alkali metal phosphates, accurate and non-disposable crystallization is necessary to control purity, as well as pre-filtration of the solution from possible insoluble impurities.
All of the above methods for the synthesis of phosphates are applicable both in laboratory conditions and in industry.