Cadmium

CADMIUM-I; m.[lat. cadmium from Greek. kadmeia - zinc ore]

1. Chemical element (Cd), a silvery-white soft, malleable metal found in zinc ores (part of many fusible alloys, used in the nuclear industry).

2. Artificial yellow paint in different shades.

◁ Cadmium, th, th. K alloys. K-th yellow(dye).

cadmium

(lat. Cadmium), a chemical element of group II of the periodic system. The name is from the Greek kadméia, zinc ore. Silvery metal with a bluish tint, soft and fusible; density 8.65 g / cm 3, t pl 321.1ºC. It is mined during the processing of lead-zinc and copper ores. Used for cadmium plating, in powerful batteries, nuclear power (control rods of reactors), to obtain pigments. Included in low-melting and other alloys. Cadmium sulfides, selenides and tellurides are semiconductor materials. Many cadmium compounds are poisonous.

CADMIUM

CADMIUM (lat. Cadmium), Cd (read "cadmium"), a chemical element with atomic number 48, atomic mass 112.41.
Natural cadmium consists of eight stable isotopes: 106 Cd (1.22%), 108 Cd (0.88%), 110 Cd (12.39%), 111 Cd (12.75%), 112 Cd (24.07 %), 113 Cd (12.26%), 114 Cd (28.85%) and 116 Cd (12.75%). It is located in the 5th period in group IIB of the periodic system of elements. Configuration of two outer electron layers 4 s 2 p 6 d 10 5s 2 . The oxidation state is +2 (valency II).
The radius of the atom is 0.154 nm, the radius of the Cd 2+ ion is 0.099 nm. Sequential ionization energies - 8.99, 16.90, 37.48 eV. Electronegativity according to Pauling (cm. PAULING Linus) 1,69.
Discovery history
Discovered by German professor F. Stromeyer (cm. STROMEYER Friedrich) in 1817. Magdeburg pharmacists in the study of zinc oxide (cm. ZINC (chemical element)) ZnO was suspected to contain arsenic (cm. ARSENIC). F. Stromeyer isolated a brown-brown oxide from ZnO, reduced it with hydrogen (cm. HYDROGEN) and received a silvery-white metal, which was called cadmium (from the Greek kadmeia - zinc ore).
Being in nature
The content in the earth's crust is 1.35 10 -5% by mass, in the water of the seas and oceans 0.00011 mg / l. Several very rare minerals are known, for example, greenockite GdS, otavite CdCO 3 , monteponite CdO. Cadmium accumulates in polymetallic ores: sphalerite (cm. sphalerite)(0.01-5%), galena (cm. GALENA)(0.02%), chalcopyrite (cm. chalcopyrite)(0.12%), pyrite (cm. PYRITE)(0.02%), fahlore (cm. FAIL ORES) and bed (cm. STANNIN)(up to 0.2%).
Receipt
The main sources of cadmium are intermediate products of zinc production, dust from lead and copper smelters. The raw material is treated with concentrated sulfuric acid and CdSO 4 is obtained in solution. Cd is isolated from a solution using zinc dust:
CdSO 4 + Zn = ZnSO 4 + Cd
The resulting metal is purified by remelting under a layer of alkali to remove impurities of zinc and lead. High purity cadmium is obtained by electrochemical refining with intermediate purification of the electrolyte or by zone melting (cm. ZONE MELTING).
Physical and chemical properties
Cadmium is a silvery white soft metal with a hexagonal lattice ( a = 0,2979, with= 0.5618 nm). Melting point 321.1 ° C, boiling point 766.5 ° C, density 8.65 kg / dm 3. If the cadmium stick is bent, then a faint crack can be heard - these are metal microcrystals rubbing against each other. The standard electrode potential of cadmium is -0.403 V, in a series of standard potentials (cm. STANDARD CAPACITY) it is located before hydrogen (cm. HYDROGEN).
In a dry atmosphere, cadmium is stable; in a humid atmosphere, it gradually becomes covered with a film of CdO oxide. Above the melting point, cadmium burns in air to form brown oxide CdO:
2Cd + O 2 \u003d 2CdO
Vapors of cadmium react with water vapor to form hydrogen:
Cd + H 2 O \u003d CdO + H 2
Compared to its group IIB neighbor, Zn, cadmium reacts more slowly with acids:
Сd + 2HCl \u003d CdCl 2 + H 2
The reaction proceeds most easily with nitric acid:
3Cd + 8HNO 3 \u003d 3Cd (NO 3) 2 + 2NO - + 4H 2 O
Cadmium does not react with alkalis.
In reactions, it can act as a mild reducing agent, for example, in concentrated solutions, it is able to reduce ammonium nitrate to NH 4 NO 2 nitrite:
NH 4 NO 3 + Cd \u003d NH 4 NO 2 + CdO
Cadmium is oxidized with solutions of Cu (II) or Fe (III) salts:
Cd + CuCl 2 \u003d Cu + CdCl 2;
2FeCl 3 + Cd \u003d 2FeCl 2 + CdCl 2
Above its melting point, cadmium reacts with halogens (cm. HALOGENS) with the formation of halides:
Cd + Cl 2 \u003d CdCl 2
With sulfur (cm. SULFUR) and other chalcogens forms chalcogenides:
Cd+S=CdS
Cadmium does not react with hydrogen, nitrogen, carbon, silicon and boron. Cd 3 N 2 nitride and CdH 2 hydride are obtained indirectly.
In aqueous solutions, cadmium ions Cd 2+ form aqua complexes 2+ and 2+ .
Cadmium hydroxide Cd (OH) 2 is obtained by adding alkali to a solution of cadmium salt:
СdSO 4 + 2NaOH \u003d Na 2 SO 4 + Cd (OH) 2 Ї
Cadmium hydroxide practically does not dissolve in alkalis, although the formation of hydroxide complexes 2– was recorded during prolonged boiling in very concentrated solutions of alkalis. Thus, amphoteric (cm. AMPHOTERICITY) the properties of cadmium oxide CdO and hydroxide Cd(OH) 2 are much weaker than those of the corresponding zinc compounds.
Cadmium hydroxide Cd (OH) 2 due to complexation easily dissolves in aqueous solutions of ammonia NH 3:
Cd (OH) 2 + 6NH 3 \u003d (OH) 2
Application
40% of the produced cadmium is used for anti-corrosion coatings on metals. 20% of cadmium is used to make cadmium electrodes used in batteries, normal Weston cells. About 20% of cadmium is used for the production of inorganic colorants, special solders, semiconductor materials and phosphors. 10% cadmium - a component of jewelry and fusible alloys, plastics.
Physiological action
Vapors of cadmium and its compounds are toxic, and cadmium can accumulate in the body. In drinking water MPC for cadmium is 10 mg/m 3 . Symptoms of acute poisoning with cadmium salts are vomiting and convulsions. Soluble cadmium compounds, after being absorbed into the blood, affect the central nervous system, liver and kidneys, and disrupt phosphorus-calcium metabolism. Chronic poisoning leads to anemia and bone destruction.

encyclopedic Dictionary. 2009 .

Synonyms:

See what "cadmium" is in other dictionaries:

- (lat. cadmium). A malleable metal, similar in color to tin. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. Cadmium lat. cadmium, from kadmeia gea, cadmium earth. Metal similar to tin. Explanation of 25,000 foreign ... ... Dictionary of foreign words of the Russian language

CADMIUM- CADMIUM, Cadmium, chem. element, char. Cd, atomic weight 112.41, atomic number 48. It is contained in small quantities in most zinc ores and is obtained as a by-product during zinc mining; can also be obtained ... ... Big Medical Encyclopedia

CADMIUM- see CADMIUM (Cd). It is contained in the branch waters of many industrial enterprises, especially lead-zinc and metalworking plants using electroplating. It is present in phosphate fertilizers. Sulfuric acid dissolves in water, ... ... Fish Diseases: A Handbook

Cadmium- (Cd) silvery white metal. It is used in nuclear power engineering and electroplating, is part of alloys, is used for the preparation of printing plates, solders, welding electrodes, in the production of semiconductors; is a component... Russian encyclopedia of labor protection

- (Cadmium), Cd, chemical element of group II of the periodic system, atomic number 48, atomic mass 112.41; metal, mp 321.1 shC. Cadmium is used to apply anti-corrosion coatings on metals, make electrodes, obtain pigments, ... ... Modern Encyclopedia

- (symbol Cd), a silvery white metal from the second group of the periodic table. First isolated in 1817. Contained in greenockite (in the form of sulfide), but mainly obtained as a by-product from the extraction of zinc and lead. Easily forged… Scientific and technical encyclopedic dictionary

Cd (from Greek kadmeia zinc ore * a. cadmium; n. Kadmium; f. cadmium; i. cadmio), chem. element II group periodic. systems of Mendeleev, at.s. 48, at. m. 112.41. In nature, there are 8 stable isotopes 106Cd (1.225%) 108Cd (0.875%), ... ... Geological Encyclopedia

Husband. metal (one of the chemical principles or indecomposable elements) found in zinc ore. Cadmium, pertaining to cadmium. K admisty, containing cadmium. Dahl's Explanatory Dictionary. IN AND. Dal. 1863 1866 ... Dahl's Explanatory Dictionary

Cadmium- (Cadmium), Cd, chemical element of group II of the periodic system, atomic number 48, atomic mass 112.41; metal, mp 321.1°C. Cadmium is used to apply anti-corrosion coatings on metals, make electrodes, obtain pigments, ... ... Illustrated Encyclopedic Dictionary

CADMIUM- chem. element, symbol Cd (lat. Cadmium), at. n. 48, at. m. 112.41; silvery white shiny soft metal, density 8650 kg/m3, tmelt = 320.9°C. Cadmium is a rare and trace element, poisonous, usually found in ores along with zinc, which ... ... Great Polytechnic Encyclopedia

- (lat. Cadmium) Cd, a chemical element of group II of the periodic system, atomic number 48, atomic mass 112.41. The name is from the Greek kadmeia zinc ore. Silvery metal with a bluish tint, soft and fusible; density 8.65 g/cm³,… … Big Encyclopedic Dictionary

Where does cadmium come from? Cadmium is always found in ores from which zinc, lead are mined, and sometimes in copper ore. Therefore, it inevitably ends up in the waste products of the production of these metals. But they are not thrown away, but they are trying to recycle, because there are many other elements that a person needs. The proportion of cadmium is very high - 0.3–0.5% by weight of zinc concentrate, and 95% is selected from there. Actually, cadmium was discovered in the study of zinc compounds. They tell such a story (see "Chemistry and Life", 1970, No. 9). In 1817, a conflict arose in Magdeburg: the district doctor Rolov ordered all preparations with zinc oxide to be withdrawn from sale, suspecting that there was arsenic in it. Pharmacists swore that there was no arsenic in the preparations, except perhaps iron oxide, which gives the ointment a yellowish color. The arbitrator was Professor Friedrich Stromeyer of the University of Göttingen, who was then Chief Pharmaceutical Inspector. He actually succeeded in isolating a yellowish compound from the preparation. However, it had nothing to do with either arsenic or iron, but turned out to be an oxide of a new element. In the autumn of 1817, in conversations with colleagues, Strohmeyer called it cadmium, which is given the following explanation. The legendary Phoenician prince Cadmus, having come to Boeotia in search of his sister Europe, stolen by Zeus, built the fortress of Cadmeus there. Then the ancient Greek Thebes grew up around it. In ancient times, a specific mixture of zinc compounds was found near this city, called "Cadmeian earth" or cadmea. Stromeyer used this name.

Rolov also soon became convinced that the suspicious impurity was not arsenic, but a compound of a new metal. But his article sent to “ Journal fur der praktischen Heilkunde”, was delayed and came out in April 1818, when among chemists they already knew about the discovery of Stromeyer.

How did the yellow color of the compound affect interest in cadmium? In the most direct way: shortly after the discovery of Stromeyer, a certain Carsten, senior adviser for metallurgy at the plant in Breslau (now Wroclaw), found in the Silesian zinc ore an element that gave a yellow precipitate when passed through a solution of hydrogen sulfide, and called it "melinium" from the Latin word " mellis", which means honey. It was still the same cadmium, and its sulfide became an excellent yellow pigment, first for artists, and then, when the price dropped, in the paint business. Getting cadmium sulfide in different ways, you can make a beautiful paint of different shades - from lemon to orange. Since it is resistant to acids, alkalis and strong heat, cadmium yellow was also suitable for painting ceramics. In addition, when cadmium sulfide is mixed with ultramarine, an excellent green dye is formed - cadmium green. When burning, cadmium gives a blue color, so it was also used in pyrotechnics. Thus, in the 90s of the XX century, 17% of cadmium was used for the preparation of paints for various purposes.

What is the main application of cadmium? Nickel-cadmium batteries: one of the electrodes in them is made of cadmium or its hydroxide, their production consumes more than 60% of all cadmium mined. These batteries are very durable: they can provide several times more discharge-charge cycles than their closest competitors - lead batteries, however, they cost ten times more. And in terms of the ratio of stored electricity to weight, Ni-Cd is twice as superior to Pb, which makes them promising for electric vehicles. The life of modern nickel-cadmium batteries is more than 30 years. They charge quickly and release energy quickly, and due to their low internal resistance, they can provide high current density without heating. Therefore, they are used wherever high current densities are required - in electric cars, trolleybuses, trams, electric trains, screwdrivers, as well as in radio equipment and household appliances. Until recently, they also supplied power to computers and cell phones, but now lithium-ion batteries are taking their place. Nickel-cadmium batteries are also supposed to be used in alternative energy systems, where from time to time it is necessary to pump excess energy somewhere, which then compensates for the lack of production due to bad weather: such batteries can provide reliable storage of up to 6.5 MWh of electricity, which puts them on a par with lead and sodium sulfide.

Among the disadvantages of nickel-cadmium batteries is a large self-discharge and memory effect: if you charge a battery that is not completely discharged, it will accumulate less and less energy each time. It is believed that this effect can be combated if such a battery is very strongly discharged from time to time. But their main drawback is the toxicity of cadmium; because of it, the use of nickel-cadmium batteries, however, as well as cadmium pigments for paints, stabilizers for polymers (10% of metal production), coatings for metals (5%), is constantly decreasing.

What application of cadmium is on the rise? Production of solar panels. Cadmium telluride converts sunlight into electricity quite well, although it is inferior to silicon batteries: the efficiency of modules available on the market is 8–9% and 13–16%, respectively. However, cadmium telluride is deposited as thin films on conductive glass, which requires much less energy and materials than the production of silicon batteries. As a result (" ”, 2012, 16, 5245–5259; doi:10.1016/j.rser.2012.04.034) the energy costs for the production of the battery pay off by generating energy in a year, which is two to three times (as well as carbon dioxide emissions per kilowatt of electricity it produces in Europe) less than that of silicon batteries. In other words, batteries using cadmium compounds are very environmentally friendly. With the growth of efficiency, this difference will increase even more, and there are prospects here, since the record efficiency values ​​for cadmium telluride in 2011 were 15.6 and 13.8% when applying its thin film to glass and flexible polyimide, respectively. Polymer-based batteries weigh hundreds of times less than glass batteries and are easily mounted on curved surfaces, which attract the attention of researchers.

Thin films are not everything. Elements based on quantum dots from chalcogenides - cadmium sulfide, telluride and selenide - are promising representatives of third-generation solar cells, which, according to experts, are finally able to ensure self-sufficiency for this energy source. The dots attract the attention of researchers, because due to the dependence of their properties on size, it is possible to achieve absorption and conversion into electricity of the entire solar spectrum. In addition, in some experiments, chalcogenide quantum dots have shown the ability to obtain several electrons from one photon - the effect of multiple generation of excitons. Obviously, with proper use, it will greatly increase the efficiency of light conversion, and this allows us to count on the convergence of the cost of electricity from the Sun and burning coal.

So far, however, the potential of quantum dots has not been fully disclosed - a record efficiency of 5.42% at the beginning of 2013 was demonstrated by an element based on quantum dots from cadmium sulfide and selenide with manganese additives (“ Renewable and Sustainable Energy Reviews”, 2013, 22, 148–167; doi:10.1016/j.rser.2013.01.030). It is believed that the points themselves are not to blame for this - the optimal material of the electrodes has not yet been selected, which ensures the complete removal of charge carriers from them resulting from the photoreaction. It is possible that cadmium will also be useful in the manufacture of electrodes - experiments with an electrode from cadmium stannate CdSnO 3 for solar cells show good results (“ Solar Energy Materials & Solar Cells”, 2013, 117, 300–305; doi:10.1016/j.solmat.2013.06.009).

What other nanoparticles are made from cadmium compounds? The most diverse: nanorods, nanotubes and even structures similar to sea urchins. It is possible that some of them will find application in the technologies of the future.

Is there cadmium in tin soldiers? It may well be there, because a small addition of cadmium greatly reduces the melting point of other metals and, accordingly, provides a better filling of the mold with a casting alloy. It is not surprising that it is part of the famous Wood's alloy and its varieties. Such alloys are widely used in metallography (they are poured into thin sections, samples for microscopic examination), in precision casting, they serve as investment rods in the manufacture of hollow figures, as well as fusible fuses. Apparently, it was the English engineer Barnaba Wood who was the first to discover the ability of cadmium to lower the melting point of other metals, because the elements that make up the alloy of his name - seven to eight parts of bismuth, four lead and two each of tin and cadmium - have melting points of 271, respectively, 327, 231 and 742°C. And all melt together at 69°C! This result in 1860 was so unexpected that the editorial board of the magazine " The American Journal of Science and Arts” added this postscript to Wood’s article: “We have had time to repeat only a few interesting experiments of Dr. Wood relating to the amazing effect that cadmium has in lowering the melting points of various alloys.” Now the ability of cadmium to reduce the melting point of metals is used by adding it to solders - this is 2% of the world's metal production. Moreover, in solders, not only industrial, but also home-made. Here, for example, on the forum of jewelers, craftsmen give the following recommendations: “Add a little cadmium to gold, its melting point will be lower than that of the metal of the product, and it will be possible to solder the required part. Since cadmium is likely to evaporate during soldering, the sample of the product may not change. Only you need to solder under the draft, so as not to get poisoned.

What is the pathway of cadmium into the body?“Cadmium in children's toys is impossible, it is poisonous,” the reader will say. And he will be right, but only in part, since it is unlikely that cadmium from a tin soldier (any figurine made of silvery heavy metal cast in a small workshop) or from a yellow pattern on a salad bowl can somehow enter the human body. He has completely different paths. There are three of them. Firstly, with cigarette smoke: cadmium is perfectly accumulated in tobacco leaves. Secondly, from the air, especially urban air: it contains a lot of road dust resulting from abrasion of tires and brake pads (and cadmium is part of them); the more you breathe this dust, the higher the content of cadmium in the body. Thus, for traffic controllers it is one and a half times more than for road workers from rural areas (“ Chemosphere”, 2013, 90, 7, 2077–2084). Cadmium is also present in the smoke of thermal stations, if they run on coal, and in the smoke from burning firewood, since trees extract it from the soil. The third source is food, especially the roots, leaves and grains of plants: this is where cadmium accumulates. Studies conducted by scientists from Seattle showed that in young women living in places not polluted with cadmium, smoking is the main source of cadmium, it increases the content of this metal by one and a half times. But among food products, tofu turned out to be a significant source of cadmium - one portion of it per week increases the content of cadmium in the body by 22% (“ Science of the Total Environment”, 2011, 409, 9, 1632–1637). A lot of cadmium is found in mollusks and crustaceans that feed on plankton. New Zealand biologists have found that cadmium in sea water (its concentration in it is 0.11 μg / l) most likely ended up there through the fault of man. Cadmium is contained in phosphate fertilizers, from where, by the way, it mainly enters edible plants. Rains wash fertilizers into rivers, then into the sea. Cadmium travels on the surface of the microparticles. Once in salt water, it is released and ends up in phytoplankton, and with it in oysters. As a result, molluscs grown higher in river mouths, where cadmium has not yet been washed away from microparticles, are relatively pure, and those below contain especially a lot of this metal (“ Science of the Total Environment”, 1996, 181, 1, 31–44). The cadmium content of oysters is 13–26 micrograms per gram of dry weight. For comparison: in sunflower seeds, which are also considered an important source of cadmium, - 0.2–2.5 μg per gram of grains, in tobacco leaves - 0.5–1 μg per gram of dry weight. Because plankton isn't just for oysters, cadmium also ends up in fish caught in dirty seas. And the dirtiest is the Baltic Sea, where many rivers flow from industrial areas and areas with intensive agriculture.

How does anthropogenic cadmium get into the environment? In addition to phosphate fertilizers, road dust and fuel combustion, there are two other ways. The first is non-ferrous metallurgy: with all the efforts aimed at cleaning emissions, a certain amount of it inevitably passes through all filters. The second is landfills and recycling sites, for example, when plastic burns there. However, in a landfill, even without heating, cadmium leaches and enters the soil with water. In general, non-ferrous metallurgy produces 5 thousand tons of cadmium emissions per year, waste incineration - 1.5, and the production of phosphorus fertilizers and wood burning - 0.2 thousand tons each of the more than seven thousand tons that a person dissipates in the environment approximately since the 30s of the XX century. Nature's own possibilities are more modest: 0.52 thousand tons are produced by volcanoes and 0.2 thousand tons - by plant excretions, a total of 0.83 thousand tons (see "Chemistry and Life", 1979, No. 12). In other words, no more than two-thirds of the cadmium extracted from the earth's interior can be turned into metal (and the world output has been fluctuating between 17-20 thousand tons per year for decades), so the prospects for utilization here are very wide. However, there is no incentive, which will be discussed further.

How will new materials containing cadmium behave in a landfill? Differently. A detailed analysis was carried out by Vasily Ftenakos of the Brookhaven National Laboratory (USA), who described in detail the life cycle of a cadmium telluride battery (“ Renewable and Sustainable Energy Reviews”, 2004, 8, 303–334; doi:10.1016/j.rser.2003.12.001). He talks like this. In a solar cell, the cadmium compound is sandwiched between layers of glass or plastic. Therefore, particles containing cadmium can only appear in the environment when the element is destroyed, which happens either in very dusty areas or when it breaks. But even then, as the experiment showed, no rain is able to wash any noticeable amount of cadmium out of the element. The evaporation temperature of CdTe exceeds 1000°C, and CdS, also present in these cells, is 1700°C, so there will be no evaporation during operation.

But what if the element is on the roof of a private house in which there was a fire? In air, cadmium telluride remains stable up to temperatures of 1050°C, which is less heating during a conventional fire. Direct experiments have shown that if the battery is made on a glass substrate, almost all of the cadmium will remain in the molten glass - only 0.6% of its already small amount (after all, this is a thin film) can be released. Some elements, when broken in a landfill, do break down, releasing cadmium, while others, more modern, do not. Legislative regulation can ensure that only harmless elements are thrown away. And it would be better not to throw them away at all, because they contain valuable tellurium.

Unfortunately, Fthenakos does not say anything about polymer-based elements, which are likely to burn out, and no cadmium fusing into glass will occur. But he notes that bans on the use of cadmium can lead to much worse consequences: having lost a sales market, manufacturers of zinc, lead and copper will stop extracting cadmium from waste and they will pollute everything around them much more than landfills (recall a third of cadmium flying into a pipe ). Therefore, the use of cadmium should be expanded with the tightening of measures for the disposal of products.

Separately, there is the issue of devices based on nanodots: when destroyed, these materials will inevitably scatter nanoparticles that can move along the food chain. There is data (“ Journal of Hazardous Materials”, 2011, 192, 15, 192–199; doi:10.1016/j.jhazmat.2011.05.003) that they will by no means remain unchanged: an increase in free cadmium was noted in the liver and kidneys of rats injected with cadmium selenide nanodots into the abdominal cavity. The effect was most pronounced if the nanoparticles were illuminated with ultraviolet light before use (apparently, this will be the case with nanodust under natural conditions). Obviously, the requirements for the disposal of solar cells and other devices based on such nanoparticles should be stricter than when using monolithic products.

Why is cadmium dangerous? The question is much more complicated than it might seem, since cadmium enters the body in microscopic quantities and does not act instantly. Researchers from the University of North Dakota, led by Soisunwan Satarug, write about this in detail (“ ”, 2010, 118, 182–190; doi:10.1289/ehp.0901234). Let's review this review.

It can be considered proven that people living in areas where the soil contains a significant amount of cadmium and food is constantly contaminated with it, there is an increased fragility of the bones. The Japanese called this disease itai-itai: it appeared in the 1940s in Toyama Prefecture, where farmers used water from a zinc mine to irrigate their fields. The content of cadmium in rice was so high that daily intake was 600 micrograms per day, or 4200 micrograms per week, or up to 2 grams per person for a lifetime. It is not difficult to identify a causal relationship here, which cannot be said about the chronic consumption of cadmium in small doses. It all comes down to the percentage risk of getting a particular disease. It is still not completely known what doses of cadmium can be considered harmless. The World Health Organization in 1989 named the maximum allowable intake of cadmium per week as 400–500 micrograms, based on the fact that 2 g in a lifetime is a lot, leads to itai-itai. In 1992, the norm was recalculated, it amounted to 7 micrograms per day per kilogram of weight. It is easy to see that the weekly dose for a person weighing 70 kg is the same - 490 mcg. When calculating, it was assumed that the body absorbs 5% of the cadmium entering it, and 0.005% of the amount of metal that is already in it is excreted in the urine. However, some doctors question this model, pointing out that they have seen cases when the body absorbed even 40% of the cadmium that entered it. Moreover, measurements have shown that consumption as low as 1 microgram per kg per day leads to 2 micrograms of cadmium per gram of creatinine in the urine, and unpleasant effects appear even at much lower levels. (The content of cadmium and other harmful metals in the urine, the concentration of which is low, is usually expressed in micrograms per gram of creatinine - this substance is formed during the work of the muscles and is constantly excreted in the urine. The result presented in such units does not depend on the dilution of the sample. Further, the word " creatinine" will be omitted. It is obvious that measuring cadmium in the urine is much easier than its intake from various sources)

What are these effects? Reading the review, one gets the impression that cadmium causes symptoms of old age. First of all, accumulating in the kidneys, it accelerates the degradation of the renal tubules. According to some data, if 2–4 μg of cadmium is excreted in the urine per day, the probability of kidney degradation is 10%; according to others, when not the daily excretion is measured, but the concentration in the test sample, the cadmium content in the urine of 0.67 μg / g is already dangerous. (If we assume that 1-2 grams of creatinine is excreted in the urine per day, then it turns out that a dangerous daily dose of cadmium excretion is about 1 mcg.) As a result of the degradation of the tubules, the ability of the kidneys to return vitamins, minerals and other useful substances to the body is weakened, for example associated with metallothioneins zinc and copper, calcium, phosphates, glucose, amino acids. A twofold increase in the level of cadmium in the urine increases the content of calcium in it by 2 mg per day. It is not hard to guess that calcium loss increases the risk of osteoporosis. Indeed, in a group of women over 50 with more than 1 µg/g of cadmium in the urine, the risk of osteoporosis is 43% higher than in those who had less than 0.5 µg/g. With a cadmium content between 1 and 2 µg/g, the risk of elevated glucose and the development of type 2 diabetes is 1.48 and 1.24, respectively, compared with those with less than 1 µg/g. A survey of Koreans, a quarter of whom suffered from high blood pressure, showed that the risk of this ailment in people with a high content of cadmium is one and a half times higher than with a low one. The risk of heart attack in women with more than 0.88 mcg/g of cadmium in the urine is 1.8 times higher compared to those with less than 0.43 mcg/g. The probability of death from cancer in men with less than 0.22 and more than 0.48 µg/g of cadmium in the urine differs by 4.3 times. There are suspicions that cadmium reduces fertility in men.

In general, from the data of the work of Dr. Sataruga and colleagues, it follows that it is environmental pollution with cadmium that is to blame for the fact that age-related diseases have become much “younger” over the course of the 20th century.

There are also strange data. Thus, a strong relationship has been observed between the content of cadmium in the urine and the risk of getting high blood pressure in Americans who do not smoke, while such a relationship has not been seen in smokers. Meanwhile, the consumption of cadmium among cigarette lovers is obviously higher, and, in addition, the content of cadmium in the urine of Americans is generally more than three times less than that of the Koreans mentioned above. Smokers with senile retinal degradation had urinary cadmium levels of 1.18 µg/g, almost twice as high as smokers without the disease and healthy non-smokers. However, even those non-smokers who developed the disease had just as little cadmium as healthy people - which means that it is not only about him. Such conflicting data make one ask the question: maybe the increased content of cadmium in the urine reflects not the cause, but the consequence of some systemic processes in the body? After all, cadmium consumption was not measured in most of the studies mentioned in the review, only its output.

How to deal with cadmium in the body? There are few scientific studies on this topic, and the principle is indicated in the same work of researchers from North Dakota. Cadmium is not one of the vital elements, so there are no special mechanisms for its absorption in the body - cadmium uses those that are provided for heavy metals similar to it, which form divalent ions: zinc, iron, manganese and calcium. The lack of any of these elements immediately leads to increased absorption of cadmium. For example, iron deficiency increases cadmium levels in Thai women three to four times. The same was found in a study of Bangladeshi women, but zinc was also in play. It follows from this how important it is to maintain the correct microelement balance in the body.

There are other ideas as well. For example, the Brazilians show that caffeine significantly, more than two times, reduces the content of cadmium both in the blood and in tissues, including genital ones, in experimental rats (“ Reproductive Toxicology”, 2013, 35, 137–143; doi:10.1016/j.reprotox.2012.10.009). According to researchers, caffeine forms complexes with cadmium, preventing its absorption. The conclusion suggests itself: the custom of drinking coffee or tea with a meal, which also contains caffeine, is correct.

Sometimes there is a paradox: food with a high content of cadmium does not affect the body. For example, a 1986 study of oyster drinkers came up with a surprise: at a maximum intake of 72 oysters per week, they ate a whopping 1,750 micrograms of cadmium, but this did not show up in either urine or hair. Where all this cadmium went remains a mystery. There is an assumption that selenium, the content of which in those oysters was high, somehow interfered with the absorption of cadmium, and he apparently came out with other inedible substances through the intestines. However, in 2008, compliance with the general line was restored: among oyster farm workers who ate 18 oysters every week for more than 12 years, the cadmium content in the urine increased 2.5 times compared to the average in the United States - up to 0, 76 mcg/g.

Or maybe it is better to deal with cadmium before it enters the body, for example, make sure that it does not get into the soil and air? It is hardly possible to free phosphate fertilizers from cadmium, it is long and expensive to breed plants with reduced cadmium digestibility, although attempts are being made with respect to tobacco, but it is possible to clean the soil with hyperaccumulator plants - in the case of cadmium, this is black nightshade Solanum nigrum, he is an edible berry of a funnel, a French variety of a shepherd's bag or mustard of a bluish or alpine yarutka ( thlaspi caerulescens) and Chinese stonecrop Sedum alfredii. True, it is not clear what to do with the parts of these plants enriched with cadmium - they are clearly not suitable for compost and ashes obtained in the garden. With the industrial combustion of the so-called solid biofuels - straw, brushwood, etc. - there are opportunities to get rid of harmful metal: it is necessary to separate the high-temperature smoke fractions containing it from the low-temperature ones - then the resulting ash can be safely brought back to the field, restoring its fertility.

But the main thing that should be cleaned is the air. The most radical method was chosen by the American, and now the European Union authorities - an uncompromising fight against tobacco smoking (“ Environmental Health Perspectives”, 2012, 120, 2, 204–209; doi:10.1289/ehp.1104020). The results are clear: the average cadmium content in the urine of Americans has decreased from 0.36 mcg/g in 1988 to 0.26 mcg/g in 2008. Since even for heavy smokers (20 or more packs a year by American standards) it fell from 0.71 to 0.49, and for non-smokers from 0.26 to 0.19, it should be assumed that smoking bans in public places significantly reduced the effects of secondhand smoke. Given the above data on the harmfulness of microdoses of cadmium, such bans seem to be the most easily implemented and very significant contribution to public health. It would also be worthwhile to tighten the requirements for emissions from non-ferrous metallurgy plants, boiler houses and cars, and at the same time make sure that less harmful dust flies from under the wheels “shod” in rubber.

Cadmium- an element of a side subgroup of the second group, the fifth period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 48. It is denoted by the symbol Cd (lat. Cadmium). Soft malleable ductile silver-white transition metal.

The district doctor Rolov was distinguished by a sharp temper. So, in 1817, he ordered that all preparations with zinc oxide produced at Herman's Shenebek factory be withdrawn from sale. By the appearance of the preparations, he suspected that there was arsenic in zinc oxide! (Zinc oxide is still used for skin diseases; ointments, powders, emulsions are made from it.)
To prove his case, the strict auditor dissolved the suspected oxide in acid and passed hydrogen sulfide through this solution: a yellow precipitate fell out. Arsenic sulfides are just yellow!
The owner of the factory began to challenge Rolov's decision. He himself was a chemist and, having personally analyzed product samples, did not find any arsenic in them. He reported the results of the analysis to Rolov, and at the same time to the authorities of the land of Hanover. The authorities, of course, requested samples in order to send them for analysis to one of the reputable chemists. It was decided that the judge in the dispute between Rolov and Herman should be Professor Friedrich Stromeyer, who since 1802 had been the chair of chemistry at the University of Göttingen and the position of inspector general of all Hanoverian pharmacies.
Stromeyer was sent not only oxide, but also other zinc preparations from the Herman factory, including ZnCO3, from which this oxide was obtained. Having calcined zinc carbonate, Strohmeyer obtained oxide, but not white, as it should have been, but yellowish. The owner of the factory explained the coloring with an admixture of iron, but Stromeyer was not satisfied with this explanation. Having bought more zinc preparations, he made a complete analysis of them and without much difficulty isolated the element that caused yellowing. The analysis said that it was not arsenic (as Rolov claimed), but not iron (as Herman claimed).

It was a new, previously unknown metal, chemically very similar to zinc. Only its hydroxide, unlike Zn(OH)2, was not amphoteric, but had pronounced basic properties.

48 element of the periodic table In its free form, the new element was a white metal, soft and not very strong, covered with a brownish oxide film on top. Stromeyer called this metal cadmium, clearly alluding to its "zinc" origin: the Greek word καδμεια has long denoted zinc ores and zinc oxide.

In 1818, Stromeyer published detailed information about the new chemical element, and almost immediately its priority began to be encroached upon. The first to speak was the same Rolov, who previously believed that there was arsenic in the preparations from the German factory. Shortly after Stromeyer, another German chemist, Kersten, discovered a new element in Silesian zinc ore and named it mellin (from the Latin mellinus, "yellow like quince") because of the color of the precipitate formed by the action of hydrogen sulfide. But it was cadmium already discovered by Strohmeyer. Later, two more names were proposed for this element: klaprotium - in honor of the famous chemist Martin Klaproth and junonium - after the asteroid Juno discovered in 1804. But the name given to the element by its discoverer was nevertheless established. True, in Russian chemical literature of the first half of the 19th century. cadmium was often called cadmium.

48 ← Cadmium→ Indium
Atom properties
Name, symbol, number	Cadmium / Cadmium (Cd), 48
Atomic mass (molar mass)	112,411(8) a. e.m. (g/mol)
Electronic configuration
Atom radius
Chemical properties
covalent radius
Ion radius
Electronegativity	1.69 (Pauling scale)
Electrode potential
Oxidation states
Ionization energy (first electron)	867.2 (8.99) kJ/mol (eV)
Thermodynamic properties of a simple substance
Density (at n.a.)
Melting temperature
Boiling temperature
Oud. heat of fusion	6.11 kJ/mol
Oud. heat of evaporation	59.1 kJ/mol
Molar heat capacity	26.0 J/(K mol)
Molar volume	13.1 cm³/mol
The crystal lattice of a simple substance
Lattice structure	hexagonal
Lattice parameters	a=2.979 c=5.618 Å
c/a ratio
Debye temperature
Other characteristics
Thermal conductivity	(300 K) 96.9 W/(m K)

Cadmium is a soft, malleable, but heavy metal of a gray-silver color, a simple element of the periodic table of Mendeleev. Its content in the earth's crust cannot be called high, but cadmium is a trace element: it is found in soil, sea water and even in the air (especially in cities). , as a rule, accompanies zinc minerals, although cadmium minerals also exist. However, most of them have no industrial value. Cadmium does not form separate deposits and is released from waste ores after zinc, lead or copper are smelted from them.

Properties of cadmium

Cadmium is well processed, rolled and polished. In dry air, cadmium reacts with oxygen (burns) only at high temperatures. Reacts with inorganic acids to form salts. Does not react with alkali solutions. In the molten state, it reacts with halogens, sulfur, tellurium, selenium, and oxygen.
- Despite the fact that cadmium is present in trace amounts in all living organisms and participates in their metabolism, its vapors and vapors of its compounds are extremely toxic. For example, a concentration of 2.5 g / cu. m of cadmium oxide in the air kills after 1 minute. It is very dangerous to inhale air containing dust or fumes containing cadmium,
- Cadmium has the ability to accumulate in the human body, in plants, fungi. In addition, cadmium compounds are carcinogens.
- Cadmium is considered one of the most dangerous heavy metals, it is classified as a hazard class 2 substance, just like mercury and arsenic. It negatively affects the enzymatic, hormonal, circulatory and central nervous systems, disrupts calcium-phosphorus metabolism (destroys bones), so when working with it, you must use chemical protection. Cadmium poisoning requires urgent medical attention.

Application

Most of the cadmium mined is used for the production of anti-corrosion coatings. Cadmium coating creates a stronger and more ductile adhesion to the part than all others, so cadmium plating is used to protect against corrosion in particularly difficult conditions, for example, in contact with sea water, to protect electrical contacts.
- It is in great demand in the manufacture of batteries and accumulators.
- Used as a reagent for laboratory research.
- Almost a fifth of the resulting substance goes to the manufacture of pigments - cadmium salts.
- It is used to give alloys the desired properties. Alloys with cadmium are fusible (with lead, tin, bismuth), ductile, and refractory (with nickel, copper, zirconium), wear-resistant. Alloys are used to produce wires for power lines, hard solders for aluminum, bearings for large and powerful engines (ship, aircraft). Low-melting alloys are used for the manufacture of gypsum castings, glass and metal soldering, and in some fire extinguishers.
- A very important area of ​​application is the nuclear industry. Cadmium is used to produce rods to control the rate of an atomic reaction in a reactor, as well as protective screens from neutron radiation.
- Included in semiconductors, film solar cells, phosphors, stabilizers for PVC, dental fillings.
- Alloys with gold are used in jewelry. By varying the ratio of gold and cadmium, alloys of different shades can be obtained, from yellow to greenish.
- Sometimes used in cryotechnics due to high thermal conductivity at very low temperatures.
- Cadmium is able to accumulate in cancer cells, therefore it is used in some methods of anticancer therapy.

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Most of the cadmium produced in the world is used for electroplating and for the preparation of alloys. Cadmium as a protective coating has significant advantages over zinc and nickel, since it is more corrosion resistant in a thin layer; cadmium is tightly bound to the surface of a metal product and does not lag behind it when it is damaged.

Until recently, cadmium coatings had a "disease" that made itself felt from time to time. The fact is that during the electrolytic deposition of cadmium on a steel part, the hydrogen contained in the electrolyte can penetrate into the metal. This very unwanted guest causes a dangerous "disease" in high-strength steels - hydrogen embrittlement, leading to unexpected destruction of the metal under load. It turned out that, on the one hand, cadmium plating reliably protected the part from corrosion, and on the other hand, it created a threat of premature failure of the part. That is why designers were often forced to refuse the "services" of cadmium.

Scientists from the Institute of Physical Chemistry of the USSR Academy of Sciences managed to eliminate this "disease" of cadmium coatings. Titanium is the cure. It turned out that if there is only one titanium atom per thousand of cadmium atoms in the cadmium layer, the steel part is insured against the occurrence of hydrogen embrittlement, since titanium draws all the hydrogen out of the steel during the coating process.

Cadmium is also used by English criminologists: with the help of the thinnest layer of this metal, sprayed onto the surface being examined, it is possible to quickly identify clear fingerprints.

Cadmium is also used in the manufacture of cadmium-nickel batteries. The role of the negative electrode in them is performed by iron grids with spongy cadmium, and the positive plates are coated with nickel oxide; the electrolyte is a solution of caustic potassium. Such current sources are distinguished by high electrical characteristics, high reliability, long service life, and their recharging takes only 15 minutes.

The property of cadmium to absorb neutrons has led to another area of ​​application of cadmium - in nuclear energy.

Just as a car cannot function without brakes, a reactor cannot operate without control rods to increase or decrease the neutron flux.

Each reactor also has a massive emergency rod that comes to work in the event that the control rods for some reason do not cope with the duties assigned to them.

An instructive case arose at a nuclear power plant in California. Due to some structural problems, the emergency rod could not plunge into the boiler in time - the chain reaction became uncontrollable, a serious accident occurred. The reactor with raging neutrons posed a great danger to the surrounding population. I had to urgently evacuate people from the danger zone until the nuclear "fire" went out. Fortunately, there were no casualties, but the losses were very high, and the reactor was out of order for some time.

The main requirement for the material of control and emergency rods is the ability to absorb neutrons, and cadmium is one of the "biggest specialists" in this field. With only one caveat: if we are talking about thermal neutrons, the energy of which is very small (it is measured in hundredths of an electron volt). In the early years of the atomic era, nuclear reactors operated precisely on thermal neutrons, and cadmium has long been considered the "first violin" among the rod materials. Later, however, he had to yield the leading role to boron and its compounds. But for cadmium, atomic physicists find more and more new areas of activity: for example, using a cadmium plate installed in the path of a neutron beam, they study its energy spectrum, determine how homogeneous it is, what is the proportion of thermal neutrons in it.

Of particular interest to scientists was the growth in weightlessness of a CMT crystal, which is a solid solution of cadmium and mercury tellurides. This semiconductor material is indispensable for the manufacture of thermal imaging devices - the most accurate infrared devices used in medicine, geology, astronomy, electronics, radio engineering and many other important areas of science and technology. It is extremely difficult to obtain this compound under terrestrial conditions: due to the large difference in density, its components behave like the heroes of the famous fable by I. A. Krylov - a swan, cancer and pike, and as a result, instead of a homogeneous alloy, a puff "pie" is obtained. For the sake of a tiny MCT crystal, one has to grow a large crystal and cut out the thinnest plate of the boundary layer from it, and everything else goes to waste. It cannot be otherwise: after all, the purity and homogeneity of an MCT crystal are estimated in hundred-millionths of a percent. No wonder that on the world market one gram of these crystals costs "only" eight thousand dollars.

The best yellow paint is a combination of cadmium and sulfur. Large amounts of cadmium are consumed in the manufacture of this paint.

CONCLUSION

In the multifaceted activity of cadmium, there are also negative aspects. A few years ago, one of the US health officials found that there is a direct relationship between mortality from cardiovascular diseases and. cadmium content in the atmosphere. This conclusion was made after a thorough survey of residents of 28 American cities. In four of them - Chicago, New York, Philadelphia and Indianapolis - the content of cadmium in the air was significantly higher than in other cities; the proportion of deaths due to heart disease was also higher.

While physicians and biologists determine whether cadmium is harmful and look for ways to reduce its content in the environment, representatives of technology are taking every measure to increase its production. If during the entire second half of the last century only 160 tons of cadmium were mined, then at the end of the 20s of our century its annual production in the capitalist countries was already about 700 tons, and in the 50s it reached 7000 tons (after all, it was during this cadmium gained the status of a strategic material intended for the manufacture of nuclear reactor rods). And in the 21st century, the use of cadmium will only increase, thanks to its irreplaceable properties.

REFERENCES

1) Dzliev I.I. Metallurgy of cadmium. Moscow: Metallurgizdat, 1962.

2) Krestovnikov A.N. Cadmium. Moscow: Tsvetmetizdat, 1956.

3) Krestovnikov A.N. Karetnikova V.P. Rare metals. Moscow: Tsvetmetizdat, 1966.

4) Lebedev B.N. Kuznetsova V.A. Nonferrous metals. Moscow: Nauka, 1976.

5) Lyubchenko V.A. Nonferrous metals. Moscow: Nauka, 1963.

6) Maksimova G.V. Cadmium // Journal of Inorganic Chemistry, No. 3, 1959, P-98.

7) Plaksin I.N. Yukhtanov D.M. Hydrometallurgy. Moscow: Metallurgizdat, 1949.

8) Peisakhov I.L. Nonferrous metals. Moscow: Nauka, 1950.

9) Glider V.I. Cadmium as a corrosion preventive. Moscow: Tsvetmetizdat, 1952.