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, 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 allocated 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.
Metaphosphoric acid- monobasic acid, the simplest formula of which is HPO 3 ; the actual composition of its molecules is expressed by the formula (HPO 3) n, where n \u003d 3.4.5, etc. In its pure form, it is a vitreous mass, easily soluble in water.
Obtained by the interaction of phosphorus (V) oxide with water:
Physicochemical characteristics
Metaphosphoric acid is a white glassy substance, highly soluble in water and, by attaching it, gradually turns into orthophosphoric acid:
A very toxic substance.
H 3 PO 4
Orthophosphoric acid (phosphoric acid)- inorganic acid of medium strength, with the chemical formula H 3 PO 4 , which under standard conditions is a colorless hygroscopic crystals.
At temperatures above 213 ° C, it turns into pyrophosphoric acid H 4 P 2 O 7. Very well soluble in water. Orthophosphoric (or simply phosphoric) acid is usually called an 85% aqueous solution (colorless, odorless syrupy liquid). Soluble also in ethanol and other solvents.
Phosphoric acid is obtained from phosphate:
Can be obtained by hydrolysis of phosphorus pentachloride:
Or by interaction with water of phosphorus (V) oxide, obtained by burning phosphorus in oxygen:
The reaction with water is very violent, so phosphorus(V) oxide is treated with a concentrated solution of phosphoric acid heated to 200 ° C.
Molten phosphoric acid and its concentrated solutions have a high viscosity, which is due to the formation of intermolecular hydrogen bonds.
H 3 PO 4 is a tribasic acid of medium strength. When interacting with a very strong acid, for example, with perchloric HClO 4, phosphoric acid shows signs of amphoterism - phosphoryl salts are formed, for example [P (OH) 4 ]ClO 4 .
A distinctive reaction of phosphoric acid from other phosphoric acids is the reaction with silver nitrate - a yellow precipitate is formed:
A qualitative reaction to the PO 4 3− ion is the formation of a bright yellow precipitate of ammonium molybdenum phosphate:
Salts of phosphoric acid are called phosphates. Phosphoric acid forms one-, two- and three-substituted salts.
(sodium dihydrogen phosphate)
(sodium hydrogen phosphate)
(sodium phosphate)
Dihydrophosphates (monosubstituted phosphates) are acidic, hydrophosphates (disubstituted phosphates) are slightly alkaline, medium (trisubstituted phosphates, or simply phosphates) are alkaline.
Dihydrophosphates are usually highly soluble in water, almost all hydrophosphates and phosphates are slightly soluble. The calcination of salts leads to the following transformations:
Phosphates do not decompose when calcined, with the exception of ammonium phosphate (NH 4) 3 PO 4 .
Organic phosphates play a very important role in biological processes. Phosphates of sugars are involved in photosynthesis. Nucleic acids also contain a phosphoric acid residue.
Application:
It is used in soldering as a flux (on oxidized copper, on ferrous metal, on stainless steel), for research in the field of molecular biology. It is also used for removing rust from metal surfaces. Forms a protective film on the treated surface, preventing further corrosion. It is also used as a part of freons, in industrial freezers as a binder.
As part of hydraulic fluids NGZH-5U and its foreign analogues.
Phosphoric acid is registered as a food additive E338. It is used as an acidity regulator in carbonated drinks.
In animal husbandry (in particular, when growing minks), a solution of orthophosphoric acid is used to drink to prevent an increased pH of the stomach and urolithiasis.
Orthophosphoric acid is used for etching (removing the smeared layer) of enamel and dentin before filling teeth. When using adhesive materials of the 2nd and 3rd generation, etching of the tooth enamel with acid is required, followed by rinsing and drying. In addition to additional time costs for carrying out these stages, they carry the risk of various errors and complications.
When applying phosphoric acid, it is difficult to control the degree and depth of demineralization of dentin and enamel. This leads to the fact that the applied adhesive does not completely (over the entire depth) fill the open dentinal tubules, and this, in turn, does not ensure the formation of a full-fledged hybrid layer.
In addition, it is not always possible to completely remove phosphoric acid after it has been applied to dentin. It depends on how the phosphoric acid is thickened. Residues of phosphoric acid degrade the strength of the bonding, and also lead to the formation of the so-called "acid mine".
With the advent of adhesive materials, the 4th and 5th generations began to use the technique of total etching (dentin - enamel). In 6th and 7th generation adhesive systems, there is no separate acid etching step. So the adhesives are self-etching. Although some manufacturers still recommend short-term etching of the enamel to enhance adhesion even when using self-etching adhesives.
H 4 P 2 O 7
Diphosphoric acid- an inorganic compound, a tetrabasic oxygen-containing acid with the formula H 4 P 2 O 7 , colorless crystals, soluble in water, forms crystalline hydrates.
Receipt:
Dissolution of phosphorus oxide in water:
Heating phosphoric acid:
The reaction of phosphoric acid with phosphorus oxide:
Physical properties:
Diphosphoric acid is a white amorphous or crystalline substance, very hygroscopic. It exists in two crystalline modifications with melting points of 54.3 and 71.5°C; the mixture melts at 61°C.
It dissolves well in water, ethanol, ether.
It is a tetrabasic acid with dissociation constants p K 1 = 1, p K 2 = 2, p K 3 = 6.6, p K 4 = 9.6.
Forms crystalline hydrates of the form H 4 P 2 O 7 n H 2 O, where n = 1, 5 and 6
Chemical properties:
When heated in a vacuum, it decomposes:
When boiling aqueous solutions, it turns into phosphoric acid:
Reacts with alkalis to form normal or acidic salts:
Enters into exchange reactions.
Phosphoric acid is obtained from phosphate:
Can be obtained by hydrolysis of phosphorus pentachloride:
Or by interaction with water of phosphorus (V) oxide, obtained by burning phosphorus in oxygen:
The reaction with water is very violent, so phosphorus(V) oxide is treated with a concentrated solution of phosphoric acid heated to 200 ° C.
Molten phosphoric acid and its concentrated solutions have a high viscosity, which is due to the formation of intermolecular hydrogen bonds.
Orthophosphoric acid in aqueous solutions much weaker than sulfuric and nitric acids. It is a tribasic acid. The electrolytic dissociation of the acid, like other polybasic acids, is carried out in steps:
H3PO4 H+ + H2RO4- (Stage I)
H2PO4- H+ + HPO42- (stage II)
HPO42- H+ + RO43- (III stage)
H3PO4 3H+ + PO43- (Total reduction)
General characteristics of p-elements of the VIA subgroup. The structure of atoms. Features of the structure of the oxygen atom. Distribution and forms of finding in nature. Valence and oxidation states in compounds. Receipt. Hydrides of H2E composition. The structure of molecules. Thermal stability. Physical and chemical properties. Getting. Reducing and acidic properties.
The elements of group VI of the main subgroup include: oxygen, sulfur, selenium, tellurium and polonium (radioactive). The table below summarizes the data on the electronic structure of the atoms of these elements and the melting and boiling points (oC)
2s22p4 3s23p4 4s24p4 5s25p4
218.8 119.3 217 449.8
183 444.6 685 990
General characteristics. The oxygen subgroup includes five elements: oxygen, sulfur, selenium, tellurium and polonium (a radioactive metal). These are p-elements of group VI periodic system of D.I. Mendeleev. They have a group name - chalcogens, which means "forming ores."
Chalcogen atoms have the same structure of the external energy level - ns 2 np 4. This explains the similarity of their chemical properties. All chalcogens in compounds with hydrogen and metals exhibit an oxidation state of -2, and in compounds with oxygen and other active non-metals, usually +4 and +6. For oxygen, as well as for fluorine, an oxidation state equal to the group number is not typical. It exhibits an oxidation state of usually -2 and in combination with fluorine +2. Such values of oxidation states follow from the electronic structure of chalcogens.
At the oxygen atom the 2p sublevel has two unpaired electrons. Its electrons cannot be separated, since there is no d-sublevel at the outer (second) level, i.e., there are no free orbitals. Therefore, the valency of oxygen is always equal to two, and the oxidation state is -2 and +2 (for example, in H 2 O and OF 2). The valency and oxidation states of the sulfur atom in the unexcited state are the same. Upon transition to an excited state (which occurs when energy is supplied, for example, when heated), the 3p- and then 3s-electrons are first separated from the sulfur atom (shown by arrows). The number of unpaired electrons, and, consequently, the valency in the first case is four (for example, in SO 2), and in the second - six (for example, in SO 3). Obviously, even valencies 2, 4, 6 are characteristic of sulfur analogues - selenium, tellurium and polonium, and their oxidation states can be equal to -2, +2, +4 and +6.
Hydrogen compounds of elements of the oxygen subgroup correspond to the formula H 2 R (R is the symbol of the element): H 2 O, H 2 S, H 2 Se, H 2 Te. They are called hydrogen chalcides. When dissolved in water, acids are formed. The strength of these acids increases with an increase in the atomic number of the element, which is explained by a decrease in the binding energy in the series of H 2 R compounds. Water, dissociating into H + and OH - ions, is an amphoteric electrolyte.
Phosphorus, production and use (technical). The starting material for the factory production of F. is the average calcium phosphate salt Ca 3 (PO 4) 2, which is widely distributed in nature. At phosphorus plants, it is usually converted into an acid salt Ca (H 2 PO 4) 2, which is then mixed with coal and calcined; while Ca (H 2 RO 4) 2 first releases water and passes into the metaphosphoric salt: Ca (H 2 PO 4) 2 \u003d Ca (PO 3) 2 + 2H 2 O, and the latter is already reduced by coal: 3Ca (RO 3) 2 + 10C \u003d P 4 + Ca 3 (RO 4) 2 + 10CO. Such a preliminary conversion of the average phosphorus-calcium salt into an acid one is based on the fact that the average salt itself is much more difficult to reduce with coal. As can be seen from the above decomposition equation, in this way at most 2/3 of the total available F. can be isolated, and 1/3 of it remains in the waste. To eliminate this drawback, at the suggestion of Wöhler, silica is also introduced into the reaction: 2Ca(PO 3) 2 + 2SiO 2 + 10C = P 4 + 2CaSiO 3 + 10CO, but then the operation requires such a high temperature, which can be economically obtained only in electric furnaces, which in recent times are more and more gaining a place in technology. The use of electricity for the production of F. is of great importance in the sense that it made it possible to use for reduction not the acid salt Ca (H 2 PO 4) 2, but directly the average phosphorus-calcium salt Ca 3 (RO 4) 2; Thus, in addition to the completeness of the isolation of phosphorus, the use of electric furnaces eliminates the complex operation of converting Ca 3 (PO 4) 3 into Ca (H 2 PO 4) 2, which takes up a lot of space in the usual equipment of phosphorus plants. In this article, we will first consider the commonly practiced methods of fabricating F., and then we will indicate those methods that are based on the use of electricity. Of all the materials from which acid phosphorus-calcium salt can be prepared (see Phosphorus fertilizers), bones are preferred at phosphorus plants. The denser the bone, the next, it is richer in phosphate salts, the more it is valued; e.g. horse, bull and sheep bones are in great demand. As a rule, they do not undergo any preliminary operations (for example, to extract fat, etc.), but are directly fired until they completely turn into ash. The burning of bones is often carried out in such furnaces, which make it possible to carry out the operation continuously, and the entire combustion process is carried out at the expense of the organic substances contained in the bones. During firing, measures are taken to ensure that unburned, odorous gases are not released into the surrounding atmosphere. According to Fleck, quite practical is the arrangement shown in FIG. one. A shaft furnace loaded with bones through a hole closed by a lid a. To start the stove, holes are used b, through which firewood is introduced and set on fire. These openings have shutters, which make it possible to regulate the amount of air entering the furnace, and in addition, already completely burned material is raked out of the furnace through them. The gases formed during combustion rise to the top of the furnace with and here they pass over the firebox d, where they burn out in full and then over the boar AT out into the exhaust duct WITH. Over the hog AT there is a row of evaporating vats with solutions assigned for thickening. According to Fleck, for 100 parts of fresh bones taken, 55 parts of completely burned (white) ash are obtained, which contains 80-84% calcium phosphate, 2-3% magnesium phosphate, 10-14% calcium carbonate and calcium fluoride. Burnt bones are ground and treated with sulfuric acid to convert the average phosphorus-calcium salt into acidic; in this case, gypsum CaSO 4 is also obtained according to the equation: Ca s (PO 4) 2 + 2H 2 SO 4 \u003d Ca (H 2 PO 4) + 2CaSO 4. Since the resulting Ca (H 2 PO 4) 2 is soluble in water, and gypsum is poorly soluble, they can be easily separated. The operation is carried out in large wooden vats (up to 1.3 m in diameter), lined with lead and equipped with a stirrer. For 100 hours of bone ash, according to various sources, from 66 to 90 hours of strong sulfuric acid is taken. Having loaded ash (up to 140 kg) into the vat, so much boiling water is poured here so that it covers the ash, and then sulfuric acid is gradually added with constant stirring. At the same time, the mass foams strongly from the decomposition of calcium carbonate. Decomposition ends in two days with stirring; water is then added to the vat and left to stand still for 12 hours. The settled liquid is drained by a siphon into lead frying pans for evaporation; the undissolved mass is washed several times with water to possibly completely extract the acid phosphorus-calcium salt, and the washing water is added to the first solution, excluding the last water, which is intended to wet a new portion of bone ash, which is decomposed with sulfuric acid. In order to use as little water as possible for such washing (since it then has to be evaporated), washing is carried out in special filtering apparatus; of these, the simplest are wooden boxes lined with lead inside with a perforated bottom, on which sand is placed, first coarse, and then finer and finer, as well as straw and coarse linen. Such boxes are sometimes placed one above the other in a terrace-like manner, which makes it possible to carry out methodical leaching of the washed mass. To evaporate a solution of an acidic phosphorus-calcium salt, either the lost heat of bone-burning and other furnaces, or steam, is used, and the liquid is constantly mixed. This is done for the reason that when the solution thickens, gypsum, which is in the solution in a small amount, is released, which, when the liquid is in a calm state, gives a strong bark on the walls of the pan, which does not conduct heat well; this does not happen when mixing. The thickening of the solution is continued until ud. the weight will not reach 1.4-1.5 (which corresponds to the content of 62% P 2 O 5). Gypsum is separated by filtration, and about 25% of coarse coke or charcoal powder is added to the solution. The mixture is dried in an iron kettle (according to Fleck, so that about 5.5% water remains) and then subjected to calcination in retorts. Retorts are made of refractory clay and are pear-shaped or cylindrical in shape and are designed to load 6-15 kg of the mixture. Depending on the productivity of the plant, the type of fuel, etc. , the design of furnaces for heating retorts is quite diverse. Usually the retorts are located in the furnace not alone, but in groups, sometimes in several rows, one above the other. In FIG. 2 shows a cross section of one of these furnaces. It is arranged for 36 retorts and has a length of 6.6-7 m, a width of 1.32 m and a height of 1.61 m; she has two fireboxes, which are separated from one another by a low (0.286 meter above the firebox) wall e running along the entire furnace. Firebox grate a(0.55 m long) has grates only in its front part, but throughout the rest of its length it is made of bricks. The retorts lie horizontally on either side of the longitudinal wall e leaning on her with his back. Flue gases, embracing the retorts, exit into the burs d(height 0.175 m and 0.695 m wide) through the holes in the roof and sent to the chimney g; at the same time, behind the oven, they pass under the pans, where the solutions of phosphorus-calcium salt are evaporated. The neck of each retort exits the furnace to the outside (through a wall that is dismountable for each pair of retorts) and is connected to a receiver for condensing ph.; the latter consists of two clay glazed caps with tubes, with the help of which they are connected to each other and to the neck of the retort. Each cap has a height of 0.18 m, dia. 0.154 m and stands on a round base 0.01 m high. and 0.24 m dia., filled with water. In FIG. 3 shows an oven for cylindrical retorts; she also has 2 fireboxes. The retorts lie on one and the other side of the middle wall With three rows, with the lower row resting with its back on the wall itself, while the upper rows are supported by spacers x. Flue gases rise to the roof n and through holes l go to the hog AT and then into the pipe Ζ
. throat r each three retorts are connected to one common receiver op(separately Fig. 4 for two retorts) made of enameled iron. It consists of a vertical pipe about with side pipes, which include tips mounted on the throat of the retorts, and from the cylindrical part pp divided into three sections. Pairs F. by pipe about they enter the upper compartment filled with water, where for the most part they thicken, and the F. is collected under water. Uncondensed vapors and gases, as shown in FIG. arrow, go to the middle compartment, also filled with water, and then through the tube located here in the middle they pass into the lower compartment (with water) and go out, catching fire. F. is collected under water in all three compartments. There are other kinds of devices, like furnaces, and retorts and receivers. The operation itself is carried out as follows: the retorts are loaded and smeared into the furnace; their throats are inserted into receivers and smeared with clay or other putty so that there are no cracks through which fumes would escape; then they begin to gradually heat up the furnace (with rapid heating, the retorts may crack). The temperature gradually rises, and F. begins to distil; together with it, unpleasantly smelling and unhealthy gases (hydrogen phosphorous, carbon monoxide, etc.) are released from the receivers; therefore, receivers try to isolate and ventilate the rooms where they are located. During the distillation of F., it is observed that there is no blockage in the receivers, and they are cleaned from time to time with an iron rod. After a day, the race is greatly weakened, which is noticed by the flame of gases coming out of the receivers; after 1 1/2 - 2 days it completely stops, and then the heat in the oven is gradually reduced. When the furnace has cooled down, the receivers are separated from the retorts and attached to them is the end of the throat of the retort, where the f. is usually located; the wall of the furnace is dismantled, the retort is taken out and usually thrown aside, after making sure that there is no undecomposed mixture in it. In their place, new loaded retorts are pressed into the furnace. F. is selected from receivers and fragments of retorts under water with the help of special spatulas. Raw F. has a reddish or brownish appearance; according to Fleck, it turns out 15.4%, counting for bone ash. In addition to the admixture of red F., it contains various compounds of F. with carbon, silicon, etc. To purify raw F., it is filtered at some plants and distilled at others. For filtering, F. is placed in a suede bag, which is placed in water heated to 50-60 °; melted F. is squeezed out of the bag with a special press. In French factories, molten F. is mixed with coal powder and placed in an iron cylinder with a partition made of porous clay; letting steam into the cylinder at a known pressure, they push the filter through the pores of the partition, and most of the impurities remain with the coal and, thus, do not contaminate the porous plate; the remaining coal is mixed with a new portion of F. F. distillation is carried out in cast-iron retorts, which are placed in two or three in one furnace (Fig. 5). F. is melted in a copper cauldron under water and mixed with sand (1/8 of its weight). When the mass hardens upon cooling, it is loaded into retorts, which are first turned over so that, if possible, all the water is glass, and then placed in the oven. The throat of the retort is immersed 1.5-2 cm into a tub of water, where there is a lead cup with an iron handle to collect the distilled F. 5-6 kilos of raw F is loaded into the retort. Heating is carried out slowly and intensifying evenly; they try to remove the water as completely as possible before the start of the race, since it serves as a material for the formation of hydrogen phosphide, which is constantly emitted from the retort. When the distillation is over, the furnace is cooled, the retorts are pulled out and cleaned. The first collected portions of F. resemble bleached wax in color, the next have a yellowish-red appearance, and the last consist of red F. The more carefully the race is carried out, the more white F. is obtained and the greater its yield in general. Loss during distillation reaches 10-15%. Clear F. and by the chemical way. For this purpose, according to Readman, it is melted in a lead vessel under water with steam; draining the water as much as possible, add 4% dichromium potassium salt, mix well for 1/2 hour and then add the same amount of sulfuric acid; the lower oxides of F. are oxidized, and it becomes completely white. If oxidation does not help, F. is subjected to distillation. Purified F. turns out 8-11% for taken bone ash. F. usually goes on sale in the form of sticks. To mold it in France proceed as follows. F. is melted under water; then the worker takes a glass tube with an iron tip, equipped with a tap, and, having immersed it in F., sucks it up with his mouth to the tap, which then closes; the tap serves to prevent the molten F. from getting into the mouth. A worker has up to 20 such tubes. The tubes are cooled, and F. is pushed out of them through the opening of the tap with an iron rod. One worker can prepare in this way up to 100 kg of F. In English factories, this operation is carried out in a way that is safer for the workers. The molding apparatus consists of a rectangular copper box placed in an iron cauldron filled with water; it contains F., which melts when water is heated in a cauldron. Two horizontal brass tubes are inserted into the bottom of the box, polished inside. These tubes, having passed the walls of the boiler, enter with their end (up to 3 cm) into a long (2-3 meters) box, through which a current of cold water passes. F. freezes in the tube, but remains rather soft and viscous. Before starting work, a bent end of an iron wire is inserted into these tubes, which envelops the frozen F. By pulling on the wire, you can gradually pull out such a long stick of F. from the tube as far as the size of the box allows (up to 2-3 meters). When it is no longer possible to pull it out further, the F. is cut off almost at the very brass tube, however, a small piece of it is left, for which they continue to pull the new F. stick; the work thus goes on uninterruptedly. It can be stopped at night and then continued in the same order. Sometimes F. is made in the form of tiles or circles, which are often made up of separate pieces. F. packaging requires many precautions, in the absence of which it can ignite during transportation and storage. F. sticks are placed in tin cans weighing 2.5-3 kilograms, filled with water and carefully sealed so that the water cannot be sucked in anywhere, as they are convinced by holding the can for some time on white pass paper. When transporting a large consignment of F., for example. up to 300 kilos, the corresponding number of tins is placed in a wooden box lined with tin; they are then filled with water. Sometimes tins with F. are transported in small wine barrels; at the same time they are filled with water containing some alcohol to prevent the water from freezing in winter. The barrels are pitched, wrapped in hay and lined with canvas. From friend. methods of production F. can point to the method proposed by Fleck, who had in mind to use the organic constituents of the bones for the preparation of glue. Fresh bones are crushed to pieces the size of a nut and kept for some time in warm water at 50-60 ° to separate the fat; then they are placed in baskets and immersed in hydrochloric acid. beats in. 1.05 for a week until they become slightly transparent and flexible; then they are placed in hydrochloric acid. beats in. 1.02 until they are completely soft. The residue that does not dissolve in the acid is processed into glue; the solution is evaporated in clay cups, taking advantage of the lost heat of retort furnaces, until the acid calcium phosphate begins to crystallize; then the liquid is cooled in wooden vats, the released salt is separated from the mother liquor, squeezed out, dried at 100 ° and mixed with coal powder. From the mother liquor, first, with further evaporation, an impure acidic phosphorus-calcium salt is separated, and then, by adding lime, the remaining phosphoric acid is isolated from it in the form of an average calcium salt. In the future, it is again processed into an acid salt together with the rest of the retorts. A significant amount of evaporation, which is introduced with this method, generally pays little for the device of gluing production, and it could not supplant the old method of producing F. with the help of sulfuric acid. This last method also has many disadvantages. First of all, with it it is required to have a sulfuric acid plant nearby so as not to overpay a lot for its transportation; then it is necessary to have a workshop for the production of retorts, which do not last long and yield up to 1/2-1 kg F.; a significant inconvenience is the storage of acidic liquids, evaporation and filtration of solutions, removal of gypsum, etc. Ridlin proposed to conduct extraction of F. in an electric furnace. The starting material is natural phosphate; it is ground, mixed with sand and coal, and quenched with electric current. F. disappears as it forms and is collected in a special receiver; the remainder gives liquid slag, which flows out of the furnace, and in its place comes a new portion of the mixture of phosphorite with coal and sand, etc. Production goes on continuously. The furnace serving for this purpose at one English factory (in Wednesfield "e) has the following device (Fig. 6). F. - shaft furnace, on top of which there is a funnel for loading material a with dampers BUT and screw AT to feed it into the oven. Electric current is introduced into the furnace using carbon electrodes WITH", reinforced in metal sleeves With. Thin electrodes are used to start the formation of a voltaic arc. C2(carbon or metal) that either lie next to the electrodes WITH", or go through them. The resulting vapors and gases exit into the hole g, and the slag flows into h. Holes are used to monitor the progress of the operation. x; through them, the electrodes are sprinkled with coal powder in order to more or less protect them from burning out. According to Colardo, take a mixture of 310 hours of average phosphorus-calcium salt, 260 hours of lime and 160 hours of coal (all in powder) and calcined in an electric furnace. Subject to this proportion of the reactants, a mixture of calcium carbonate (carbide) and calcium phosphorous is obtained; only an insignificant part of F. is released in vapors together with carbon monoxide. In order not to thicken the phosphorus from here, the vapors are passed through hot lime, which absorbs the phosphorus. The resulting mixture of carbide with calcium phosphorous is decomposed by water, and acetylene and hydrogen phosphide are obtained. These gases are first passed through a heated retort or a carbon tube filled with coal, where hydrogen phosphide is decomposed into F. and hydrogen, then they pass through a series of washing apparatuses in which F. settles and acetylene is separated from hydrogen (by absorption, for example, with acetone). Hydrogen is used for heating. There is a rather complicated Billaudot patent, where F. and carbide are simultaneously obtained. The main idea of the patent is the construction of special condensers for F. vapors, where condensation occurs without F. contact in a heated state with water, as is usually practiced, which makes it possible to avoid F. losses (from its interaction with water) and eliminates the need for further purification. F. (by filtration, etc.) Simultaneously with F., calcium carbide is also obtained. Diehl (Dill) proposed to decompose a mixture of phosphoric acid with coal powder by current. To a concentrated solution of phosphoric acid beats. weight 50-60 ° add 1/4 - 1/5 by weight of coal and this mixture is loaded into a clay cylinder through a special funnel. The cylinder stands on a support made of a conductor of electricity, through which positive electricity enters the carbon electrode. The other electrode enters the cylinder through the plug at the top; it can be raised and lowered by means of a screw device. F.'s couples leave through an outlet tube in the condenser; operate with a current of 80-150 amperes with a voltage of 120 volts. When most of the F. has been released, the current is interrupted for a while, a new portion of the mixture is loaded, and then work is continued again. From other methods of obtaining F., we point out the proposal of Frank and Rossel to carry out the reduction of acid. f-no-calc. aluminum salts in the presence of silica: 3Ca(PO 3) 2 + 10Al + 3SiO 2 = 6P + 5Al 2 O 3 + 3CaSiO 3. At the suggestion of Shearer and Clapp, natural aluminum phosphate Al 2 O 3 P 2 O 5 is taken, mixed with common salt and coal, and calcined in a stream of hydrogen chloride HCl; in this case, a double salt of aluminum chloride with sodium chloride Al 2 Cl 6 4NaCl is formed and F., carbon monoxide CO and hydrogen are released. The reaction can be represented by the following equation: Al 2 O 3 P 2 O 5 + 4NaCl + 6HCl + 8C \u003d Al 2 Cl 6 NaCl + 8CO + 3Η 2 + 2P. The materials taken must be well ground. Ignition is first carried out for about 10 hours at a dark red heat until carbon monoxide and hydrogen cease to be released, then the temperature is raised to white heat, and only then does F begin to be distilled off. The race lasts up to 30 hours, depending on the amount of F. Alfred Kraus suggested calcining a mixture of phosphates with iron ores, for example. hematite, and thus prepare iron phosphorous; the latter is then alloyed with pyrite; F. at the same time evaporates and thickens, and iron sulfide remains. It is left to mature in the open air and gradually oxidizes into iron sulfate, etc. White F. usually contains an admixture of arsenic (0.5-3.5 °); sulfur, carbon, calcium, etc. are found in it. To obtain in large sizes red phosphorus is often used by the method proposed back in 1845 by Schrötter. In the oven F(Fig. 7) two boilers are placed one inside the other, the gap between which is filled with an alloy of tin and lead N(in equal amounts). On the inner boiler M there is a lid G bolted HH to the edges of the outer boiler. in the boiler M there is sand B, in which the third portable boiler is placed With with glass or porcelain receiver R. In the lid of it E iron or copper curved tube ends J that goes through the lid G and with its other end is immersed in water or mercury in a vessel k; she has a faucet x. under the pipe J there is an alcohol lamp to warm it up in case of blockage F. Lid E held in place by a spring S, which, with a sudden high pressure inside the boiler With is supplied and the lid can be lifted. The operation of turning white F. into red is very simple with this apparatus. Dry pieces of F. are placed in a cauldron With put the lid back in place Ε
and G and start heating up gradually. Air from the boiler With out through the tube J. The temperature is raised to 260 ° (it is determined by a thermometer lowered into the molten metal N), and keep it for several days (up to 10), after which the oven is cooled by closing the tap beforehand x, and break out the resulting red F. Schrötter's apparatus was subjected to numerous modifications. Coignet at Lyons performs the same operation in one iron pot. Red F. obtained by the described method usually contains traces of white F. In one sample of raw red F. Fresenius and Luk (Luck) found white F. 0.56%, phosphorous acid. 1.302%, phosphoric acid. 0.880%, water and other impurities 4.622% and red F. 92.63%. Various means are used to remove white F.. Raw red F. is treated with carbon disulfide, which dissolves white F. without touching the red. F. is isolated from this solution by distillation of carbon disulfide, which is then used again. Phosphate is sometimes forced to slowly oxidize in air to phosphoric and phosphorous acid, and then it is washed with water. At the suggestion of Nickles, F. is stirred up in a solution of calcium chloride beats. weight 1.95; white F., being lighter, floats to the surface, and red collects at the bottom. It is then washed with water and dried. The main mass of F. mined in the technique is used for the production of matches; a certain amount of it goes to obtain phosphoric anhydride, for the preparation of explosives, etc. S. Vukolov. Δ. Phosphorus(medical) - Of the two modifications of F. red, or amorphous, insoluble in tissue fluids and physiologically therefore completely indifferent, even when used in large doses; yellow-white crystalline, or official, F. dissolves, although in very small quantities, in water, alcohol, fats and bile and has pronounced toxic properties. In 100 parts of warm water, 0.00027 F is dissolved; solubility in intestinal fats and bile is 0.01-0.026 per 100. The effect of official F. on the body seems to be completely different, depending mainly on the size of the dose and the duration of use. With the introduction of very small doses for a long time, F. exhibits an irritating effect almost exclusively on bone-forming substances, and this irritation does not lead to the degeneration of the affected tissues, but to their proliferation. Wegner, giving for weeks to young growing animals such small amounts of F., which are unable to cause disorders of the general condition, found in the blood of the experimented extremely remarkable changes. It turned out that in all those places where, under normal conditions, wide-looped spongy bone substance with a rich content of red brain tissue develops from cartilage, under the influence of F., a completely uniform dense and strong tissue is obtained, in its appearance, microscopic structure and chemical composition (according to the ratio of organic to inorganic substances, in terms of the content of phosphate salts) is no different from the compact bone tissue of the cortical layer of tubular bones. The spongy bone substance formed earlier, before feeding F., remains at the same time completely unchanged. The bone tissue that forms from the side of the periosteum, that is, that which causes the growth of the bone in thickness, undergoes a similar process of thickening, although less pronounced. However, if small amounts of F. are administered to the animal for too long, then the spongy substance remaining unchanged is first absorbed, and subsequently the artificially formed bone substance is subjected to the same process of rarefaction, with the formation of red brain tissue in both cases. Such are the phenomena upon repeated administration of very small doses of phosphorus. Observations by various investigators further established that if phosphorus is administered in moderate but gradually increasing doses, or if phosphorus vapors are frequently inhaled, as is the case in match factories, then as a result very pronounced inflammatory changes in the bones, leading to their necrosis. Observed among workers in match factories, the so-called. phosphorous necrosis of the jaws usually comes from carious teeth or ulcerated gums (see. ). The data obtained by Wegner, confirmed by other researchers, served as the starting point for the therapeutic use of very small doses of F. in certain pathological conditions of the skeletal system, especially with a delay or insufficient development of the bone skeleton in childhood (with rickets), with osteomalacia, with insufficient ossification of calluses, after fractures; Adults are given 0.0003 grams to 0.001 grams per dose 1-3 times a day (the largest dose per day is 0.005 grams), children are not more than 0.0005 grams per day. If the indicated cautious doses are exceeded, then poisoning, the reason for it is rarely imprudence, mostly an attempted suicide. For the latter purpose, they usually use the heads of phosphorus matches, less often - phosphorus paste, which is used to kill rats (a mixture of F. with ordinary dough, with the addition of fat). In the 50-70s. of the last century, when Swedish matches prepared with the help of harmless red F. were not yet in use, F. poisoning, especially in Germany and France, was a fairly common occurrence. In France in 1851-71. among 793 poisonings, 267 (38%) fall on F poisoning. Large whole pieces of F. can, without dissolving, pass through the intestines without much harm. Attacks of poisoning are detected already a few hours after the introduction of the poison, expressed in a feeling of thirst, in severe pain in the stomach, in vomiting with a garlic smell and masses glowing in the dark. With relatively small doses of F., the matter is limited to this, especially if most of the poison was excreted by vomiting or artificial pumping out of the contents of the stomach. In more serious cases, the described local phenomena first subside for 3-4 days, but after this seeming lull, the poisoning unfolds into a severe picture of a general eating disorder. Gastrointestinal disorders resume, the liver enlarges, the skin and sclera take on a yellowish color, the general condition worsens, cardiac activity is more and more upset, the patient complains of muscle pain and general weakness, simultaneously from all mucous membranes, from the nose, intestines, uterus appear bleeding; artificially induced and menstrual bleeding are very profuse and usually do not stop. The amount of urine excreted gradually decreases, bile pigment, bile acids, protein open in it, and in the last days of the disease, the renal epithelium, blood and fatty cylinders. The excretion of nitrogen in the urine increases very significantly, often three times against the norm, the urea content, on the contrary, decreases very sharply, in severe cases meat-lactic acid, peptone, often leucine and tyrosine are found in the urine. Consciousness for the most part remains until the very end, in other cases - one or two days before death, brain disorders, drowsiness, delirium, and convulsive phenomena occur. Death usually occurs 7-8 days after poisoning. With the introduction of poison in a very large dose, the patient can die in a few hours from heart paralysis. However, cases of recovery are known, which lasted 4-6 weeks and was accompanied by increased urine output. Post-mortem anatomical diagnosis characterized by 1) numerous hemorrhages in the skin, subcutaneous and intermuscular tissue, mucous membranes, peritoneum, pleura and 2) fatty degeneration of the liver, kidneys, heart, pancreas, glands of the mucous membranes of the stomach (gastroadenitis) and intestines, skeletal muscles and walls vessels. The essence of pathological changes in acute F. poisoning lies in a deep metabolic disorder, which is based on a decrease in oxidative processes in the body and increased protein breakdown. According to Bauer, under the influence of F., the release of carbonic acid decreases by 47%, and the absorption of oxygen by 45%. Due to insufficient oxidation, protein substances do not turn into ordinary end products, but form intermediate substances, from which diffusible substances (lactic acid, peptone, etc.) are excreted in the urine, while colloidal substances, like fats, are deposited in the tissues. The jaundice is due to the pressure exerted by enlarged fatty liver cells on the bile ducts. The cause of bleeding lies in the fatty degeneration of the walls of all, even the smallest, vessels and in the inherent very low coagulability of the blood that came out of the vessels during F. poisoning. Treatment of acute poisoning F. Perhaps early mechanical removal of the poison by means of a gastric pump or emetic. The best emetic is copper sulphate, which acts simultaneously as an antidote. It is given in 0.2 gr. every 5 minutes until vomiting occurs, and then continue to give after 1/4 hour, 0.05 g each, as an antidote. Copper covers the particles of F. with a layer of poorly soluble and therefore inactive phosphorous copper. In view of the slow absorption of F. from the intestines, one can also count on laxatives; it is necessary, however, to carefully avoid oily laxatives, as well as the introduction of any fatty (milk, eggs) or alcohol-containing substances. An excellent antidote is also crude, oxygen-containing turpentine oil (1.0-2.0 g every 1/4 - 1/2 hour, only 5-10 g). If the poison has already managed to be absorbed and collapse begins, then in the foreground, agents that stimulate the activity of the heart will appear. At the forensic opening F. suspicious masses (contents of the stomach, intestines, food products, drinks, etc.) are distilled, according to Mitcherlich, in a dark room after their preliminary acidification with diluted sulfuric acid. In the case of F.'s presence, a characteristic glow is noticed at the cooled end of the vapor tube. 1 milligram is enough to show the reaction. F. in 200,000 parts of liquid. A negative result, however, does not speak against the presence of F., since the presence in the test mass of many substances, such as turpentine oil, chloroform, ether, benzene, chlorine, sulfurous acid, hydrogen sulfide, and essential oils, prevents luminescence. According to Dussard, the masses to be tested are heated in an apparatus similar to Marchev's, with pure zinc and sulfuric acid; Hydrogen phosphorus, which is released from the gas outlet tube during the presence of F., burns with a beautiful emerald green color when ignited. The flame is viewed in a dark room against a white porcelain plate. This very sensitive reaction is partly modified, partly masked when some organic volatile substances (hydrogen sulfide, alcohol of wine, ether) are present in the test mass, and therefore, according to Blondlot, it is advisable to pass the gas released during this method first through a solution of caustic alkali, and then through a solution silver nitrate and the resulting substance (silver phosphite) is decomposed again with zinc and sulfuric acid. Wed Wegner, "Der Einfluss des Phosphors auf den Organismus" ("Arch. für Pathol. Anatomie und caet.", 1872 v. 55, p. 11); Kassowitz, "Die normale Ossification und die Erkrankungen des Knochensystems bei Rachitis und hereditärer Syphilis" (1882); H. Korsakov, "On the pathogenesis of the English disease" (dissertation, 1883); Mandelstam, "Doctor" (1889, Nos. 5, 7, 9, 10 and 11); Shabanova, "Doctor" (1889, nos. 16-19); Busch, "Sitzungsber. der Niederrheins. Geschichte für Natur und Heilkunde" (1881); Voit, "Zeitschrift für Biologie" (1880, vol. XVI, p. 55); "Eulenhurg" s Real-Encyclop. "(1888, vol. XV, pp. 549 and 554); "Maschk" s "Handbuch" (1888, vol. II, pp. 176-228); Bauer, "Der Stoffamsatz bei der Phosphorvergiftung" ("Zeits. für Biologie", 1871, vol. VII, p. 63); Bamberger, "Zur Theorie und Behandlung der acuten Phosphorverg." ("Wirzburg. medicin. Zeitung" (1867); Gager, "Manual to pharmaceutical and medical-surgical practice "(1893). See also guides on pharmacology (Binz, Rossbach and Notnagel, etc.) and toxicology (Kobert, Hoffmann, etc.). M. B. Kotsyn. Phosphorus in living organisms is part of three organic substances that have a very important physiological significance: lecithin, nuclein and glycerol-phosphorus. sour In addition, phosphoric acid is found in the body in combination with sodium, potassium, lime and magnesia. The predominance of phosphates in the blood is one of the characteristic features of carnivores, while in the blood of herbivores carbonic compounds predominate, and, like potassium salts, phosphoric acid is found mainly in the blood globules, in muscles and in the brain. Finally, the same phosphoric acid in combination with lime makes up the largest part of the inorganic substances that make up bones and teeth. Phosphates are found in all body fluids; but they are especially rich in urine, with which they are excreted from the body, at least in carnivores and in animals with a mixed diet. Herbivores, on the other hand, excrete phosphates mainly together with intestinal eruptions. In the human nervous system is about 12 gr. phosphoric acid, in the muscular system 130 gr., in the bones of the skeleton 1400 gr. - F. is excreted from the body in the form of phosphates, which are formed from the decomposition of lecithin, nuclein and glycerol of phosphoric acid and the oxidation of phosphorus-containing products of this splitting. A person excretes daily from 2.50 to 3.50 grams. phosphoric acid. Most of the F. is excreted from the body in the form of an acidic potassium phosphate salt, which gives the urine of carnivores and animals with a mixed diet an acidic reaction; in addition, thanks to the same acid salt, the phosphates of the earths in the urine are in a dissolved state. F. urine refers to the total nitrogen of the urine approximately as 1 to 6 or 7; but this relation, of course, varies according to the nature of the food. Judging by the fact that F. is a part of such important compounds as lecithin and nuclein and, in addition to the fact that it is an integral part of organs and mainly of the nervous system, muscles and gonads, its importance for life should be very outstanding. F. and is listed among the biogenic elements. The formation of acid phosphates from neutral ones is explained by the many effects on these latter organic acids formed during the activity of organs. encyclopedic Dictionary
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Phosphoric acid H 3 PO 4 is the most important intermediate product in the production of concentrated phosphorus fertilizers. In addition, phosphoric acid is used in the production of various technical salts, a variety of organophosphorus products, including insecticides, semiconductors, activated carbon, ion-exchange resins, to create protective coatings on metals. Purified (food) H 3 PO 4 is used in the food industry, for the preparation of feed concentrates, pharmaceuticals. Phosphoric acid is obtained from complex, multicomponent raw materials, during the processing of which numerous and diverse wastes are formed.
Phosphoric acid is formed directly when the ore is dissolved, i.e. direct extraction, extraction of phosphorus compounds. Hence the name of the product - extractive phosphoric acid. Thermal phosphoric acid is obtained from poorer ores. The process is based on the reduction of phosphorus from natural phosphates with coke at high temperatures and the further production of H 3 PO 4 and from phosphorus.
Oxygen acids of phosphorus, which are products of hydration of phosphoric anhydride. A distinction is made between orthophosphoric acid (usually called phosphoric acid) and condensed F. to. The most studied and important is orthophosphoric acid H 3 PO 4 , which is formed when P 4 O 10 is dissolved (or P 2 O 5) in water.
Forms three series of salts - phosphates. When acid solutions are heated, it dehydrates with the formation of condensed phosphoric acids.
In industry, phosphoric acid is obtained by extraction (sulphuric acid) or thermal methods.
The thermal method is based on the combustion of phosphorus to phosphoric anhydride P 4 + 5O2 P 4 O 10 and hydration of the latter.
Industrial orthophosphoric acid is the most important intermediate for the production of phosphate and complex fertilizers and industrial phosphates, it is also widely used for metal phosphating, as a catalyst in organic synthesis. Food grade phosphoric acid is used to make soft drinks, medicines, dental cements, etc.
The technological process for the production of phosphoric acid by the electrothermal method can be built according to two options:
- --according to a single-stage scheme, without preliminary condensation of phosphorus vapors, with direct combustion of the phosphorus-containing gas leaving the reduction stage (Fig. 1);
- --according to a two-stage scheme, with preliminary condensation of phosphorus vapor and its subsequent processing into phosphoric acid (Fig. 2.):
Rice. one
Rice. 2
During the oxidation of phosphorus and the hydration of phosphorus (V) oxide, a large amount of heat is released, which must be removed from the system in order to maintain the optimal thermal regime of the process.
The most common are circulating-evaporative schemes in which gases are cooled due to heat exchange with circulating phosphoric acid and as a result of water evaporation from it. A similar technological scheme of the installation with a capacity of 60 thousand tons per year of 100% acid or 2.5 t/h for combusted phosphorus is shown in fig. 3.
Rice. 3 Technological scheme for the production of thermal phosphoric acid by a two-stage method: 1 - electric furnace, 2 - charge hopper, 3 - gas separator, 4, 14 - electrostatic precipitators, 5 - hot condenser, 6 - cold condenser, 7, 8 - liquid phosphorus collector, 9 - liquid sump phosphorus, 10 - combustion tower, 11, 13 - refrigerators, 12 - hydration tower, 15 - phosphoric acid collector
A three-phase electric furnace RKZ-72 F (ore-thermal, round, closed, with a capacity of 72 MB. A, phosphoric) with self-sintering anodes 1 is fed from hopper 2 with a charge consisting of phosphate, silicon oxide (quartzite) and coke. The gas leaving the furnace, containing 6-10% phosphorus, passes through the gas cutter 3 into the electrostatic precipitator 4, where dust is removed from it. The purified gas is sent to condensers - washers - hot 5 and cold 6, cooled by water sprayed into them, which circulates in a closed circuit. The condensed liquid phosphorus is collected in collectors 7 and 8, from where it enters the sump 9.
The degree of condensation of phosphorus from the gas reaches 0.995. The gas leaving the condensers, containing up to 85% vol. carbon monoxide is used as fuel or burned. The slag accumulated in the lower part of the kiln 1 is continuously pumped out and used in the production of cement and other building materials. From the sump 9, the molten phosphorus is fed into the combustion tower 10, where it is sprayed by nozzles in a stream of air. Circulating phosphoric acid is supplied to the cooling tower, pre-cooled in the refrigerator 11, part of it in the form of 75% phosphoric acid is removed as production and goes to the warehouse. For replenishment, the required amount of water is introduced into the system. From the combustion tower, gas at a temperature of 100°C enters the hydration-cooling tower 12, irrigated with phosphoric acid, where the hydration process ends. Due to irrigation, the temperature of phosphoric acid at the outlet is reduced to 40 - 45°C. The acid circulating in the hydration tower is cooled in the refrigerator 13. From the hydration tower 12, the gas is sent to the electrostatic precipitator 14. The phosphoric acid condensed in it from the mist enters the collector 15, and the exhaust gases are emitted into the atmosphere.
The main apparatuses in the production of thermal phosphoric acid are the combustion (combustion) tower and the hydration tower.
The combustion tower is hollow, conical in shape, about 4 m in diameter and about 14 m high. The tower lid is cooled with water and has a nozzle for spraying phosphorus. The hydration tower is made in the form of a cylinder with a height of 15 m and a diameter of 3 m and contains a nozzle of Raschig rings and three tiers of nozzles for spraying acid.
The technological scheme of the installation with a capacity of 60 thousand tons per year of 100% H3PO4 is shown in fig. 4. Molten yellow phosphorus is atomized with heated air at a pressure of up to 700 kPa through a nozzle in a combustion tower sprayed with circulating acid. The acid heated in the tower is cooled by circulating water in plate heat exchangers. Production acid containing 73-75% H3PO4 is discharged from the circulation circuit to the storage. In addition, the cooling of gases from the combustion tower and the absorption of acid 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% H3PO4 cooled in plate heat exchangers. Gases from the hydration tower after being cleaned from H3PO4 mist in a plate electrostatic precipitator are released into the atmosphere. For 1 ton of 100% H3PO4, 320 kg of P is consumed.
Rice. 4 Circulation two-tower scheme for the production of thermodynamically H3PO4, where 1 is the 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
Accompanying impurities are also decomposed by acids: calcite, dolomite, siderite, nepheline, glauconite, kaolin, and other minerals. This leads to an increase in the consumption of the acid used, and also reduces the extraction of P2O5 into the target product due to the formation of insoluble iron phosphates FeH3(PO4)2* 2.5H2O at P2O5 concentrations above 40% (P4O10 content is usually given in terms of P2O5) and FePO4* 2H2O - at lower concentrations. The CO2 released during the decomposition of carbonates forms a stable foam in the extractors; soluble phosphates of Mg, Fe and Al reduce the activity of phosphoric acid, and also reduce the content of assimilable forms of P2O5 in fertilizers during subsequent processing of phosphoric acid.
Taking into account the influence of impurities, the requirements for phosphate raw materials are determined, according to which natural phosphates with a high content of Fe, Al, Mg compounds, carbonates and organic substances are unsuitable for the production of phosphoric acid
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