Cadmium crystal lattice. Cadmium: facts and facts

Cadmium is an element of the secondary subgroup of the second group, the fifth period of the periodic table of chemical elements of D.I. Mendeleev, with atomic number 48. It is designated by the symbol Cd (lat. Cadmium). A soft, malleable, malleable transition metal with a silvery-white color.

History of the discovery of cadmium

The district doctor Rolov had a tough temperament. Thus, in 1817, he ordered the withdrawal from sale of all preparations containing zinc oxide produced at Herman’s Schenebec factory. Based on the appearance of the preparations, he suspected that the zinc oxide contained arsenic! (Zinc oxide is still used for skin diseases; ointments, powders, and emulsions are made from it.)

To prove he was right, a strict auditor dissolved the suspected oxide in acid and passed hydrogen sulfide through this solution: a yellow precipitate formed. 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 state of Hanover. The authorities, naturally, requested samples to be sent for analysis to one of the reputable chemists. It was decided that the judge in the dispute between Rolov and Hermann should be Professor Friedrich Strohmeyer, who since 1802 had occupied the department of chemistry at the University of Göttingen and the position of inspector general of all Hanoverian pharmacies.

Strohmeyer was sent not only zinc oxide, but also other zinc preparations from Herman's factory, including ZnCO 3, from which this oxide was obtained. Having calcined zinc carbonate, Strohmeyer obtained an oxide, but not white, as it should have been, but yellowish. The factory owner explained the coloring as an iron impurity, but Strohmeyer was not satisfied with this explanation. Having purchased more zinc preparations, he carried out a complete analysis of them and, without much difficulty, isolated the element that caused the yellowing. The analysis said that it was not arsenic (as Rolov claimed), but also not iron (as Herman claimed).

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

In its free form, the new element was a white metal, soft and not very strong, covered on top with a brownish film of oxide. Strohmeier called this metal cadmium, clearly hinting at its “zinc” origin: the Greek word καδμεια has long been used to designate zinc ores and zinc oxide.

In 1818, Strohmeyer published detailed information about the new chemical element, and almost immediately his priority began to be encroached upon. The first to speak was the same Rolov, who previously believed that the drugs from Herman’s factory contained arsenic. Soon after Strohmeyer, another German chemist, Kersten, found a new element in Silesian zinc ore and named it mellin (from the Latin mellinus - “yellow like a quince”) because of the color of the precipitate formed by the action of hydrogen sulfide. But this was cadmium already discovered by Strohmeier. 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 nevertheless became established. True, in Russian chemical literature of the first half of the 19th century. cadmium was often called cadmium.

The average cadmium content in the earth's crust is 130 mg/t. Cadmium is a rare, trace element: it is found as an isomorphic impurity in many minerals and always in zinc minerals. Only 6 cadmium minerals are known. Very rare cadmium minerals are greenockite CdS (77.8% Cd), howliite (the same), otavite CdCO 3, montemponite CdO (87.5% Cd), cadmoselite CdSe (47% Cd), xanthochroite CdS (H 2 O) x (77.2% Cd). The bulk of cadmium is dispersed in a large number of minerals (more than 50), mainly in sulfides of zinc, lead, copper, iron, manganese and mercury.

Although independent cadmium minerals are known - greenockite(CdS), will respond(CdCO 3), monteponite(CdO) and selenide(CdSe), they do not form their own deposits, but are present as impurities in zinc, lead, copper and polymetallic ores, which are the main source of industrial production of cadmium. The maximum concentration is observed in zinc minerals and primarily in sphalerite (up to 5%). In most cases, the cadmium content in sphalerite does not exceed 0.4 – 0.6%. In other sulfides, for example, in stanina, the cadmium content is 0.003 - 0.2%, in galena 0.005 - 0.02%, in chalcopyrite 0.006 - 0.12%; Cadmium is usually not extracted from these sulfides.
Cadmium, by the way, is present in certain quantities in the air. According to foreign data, the cadmium content in the air is 0.1-5.0 ng/m3 in rural areas (1 ng or 1 nanogram = 10 -9 grams), 2 - 15 ng/m3 - in cities and from 15 to 150 ng/m3 - in industrial areas. This is due, in particular, to the fact that many coals contain cadmium as an impurity and, when burned at thermal power plants, it enters the atmosphere. In this case, a significant part of it settles on the soil. Also, the use of mineral fertilizers contributes to an increase in the cadmium content in the soil, because Almost all of them contain minor cadmium impurities.
Cadmium can accumulate in plants (mostly in mushrooms) and living organisms (especially in aquatic organisms) and can be “supplied” to humans further along the food chain. There is a lot of cadmium in cigarette smoke.

Under natural conditions, cadmium enters groundwater as a result of the leaching of non-ferrous metal ores, as well as as a result of the decomposition of aquatic plants and organisms capable of accumulating it. In recent decades, the anthropogenic factor of cadmium pollution of natural waters has become prevalent. Cadmium is present in water in dissolved form (cadmium sulfate, chloride, cadmium nitrate) and in suspended form as part of organo-mineral complexes. The cadmium content in water is significantly influenced by the pH of the environment (in an alkaline environment, cadmium precipitates in the form of hydroxide), as well as sorption processes.

The only mineral that is of interest in obtaining cadmium is greenockite, the so-called “cadmium blende”. It is mined together with fireite during the development of zinc ores. During refining, cadmium is concentrated in the by-products of the process, from which it is then recovered. Currently, over 10³ tons of cadmium are produced per year.

When processing polymetallic ores, it, an analogue of zinc, invariably ends up mainly in zinc concentrate. And cadmium is reduced even more easily than zinc, and has a lower boiling point (767 and 906°C, respectively). Therefore, at temperatures around 800°C it is not difficult to separate zinc and cadmium.

Silver-white soft metal with a hexagonal lattice. If you bend a cadmium rod, you can hear a faint crackling sound - this is metal microcrystals rubbing against each other (a tin rod also cracks).

Cadmium is soft, malleable, and easy to machine. This also facilitated and accelerated his path to nuclear technology. The high selectivity of cadmium and its sensitivity specifically to thermal neutrons were also beneficial to physicists. And in terms of the main operating characteristic - the thermal neutron capture cross section - cadmium occupies one of the first places among all elements of the periodic table - 2400 barn. (Recall that the capture cross section is the ability to “absorb” neutrons, measured in conventional units of barns.)

Natural cadmium consists of eight isotopes (with mass numbers 106, 108, 110, 111, 112, 113, 114 and 116), and the capture cross section is a characteristic in which the isotopes of one element can differ greatly. In the natural mixture of cadmium isotopes, the main “neutron absorber” is an isotope with mass number 113. Its individual capture cross section is huge - 25 thousand barns!

By adding a neutron, cadmium-113 turns into the most common (28.86% of the natural mixture) isotope of element No. 48 - cadmium-114. The share of cadmium-113 itself is only 12.26%. Unfortunately, separating eight isotopes of cadmium is much more difficult than separating two isotopes of boron.

The crystal lattice of Cadmium is hexagonal, a = 2.97311 Å, c = 5.60694 Å (at 25 °C); atomic radius 1.56 Å, ionic radius of Cd 2+ 1.03 Å. Density 8.65 g/cm 3 (20 °C), melting point 320.9 °C, boiling point 767 °C, coefficient of thermal expansion 29.8·10 -6 (at 25 °C); thermal conductivity (at 0°C) 97.55 W/(m K) or 0.233 cal/(cm sec °C); specific heat capacity (at 25 °C) 225.02 J/(kg K) or 0.055 cal/(g °C); electrical resistivity (at 20 °C) 7.4·10 -8 ohm·m (7.4·10 -6 ohm·cm); temperature coefficient of electrical resistance 4.3·10 -3 (0-100° C). Tensile strength 64 MN/m2 (6.4 kgf/mm2), relative elongation 20%, Brinell hardness 160 MN/m2 (16 kgf/mm2).

Cadmium is located in the same group of the periodic table with zinc and mercury, occupying an intermediate place between them, therefore some of the chemical properties of these elements are similar. Thus, sulfides and oxides of these elements are practically insoluble in water. Cadmium does not interact with carbon, which means that cadmium does not form carbides.

In accordance with the external electronic configuration of the 4d 10 5s 2 atom, the valence of Cadmium in compounds is 2. In air, Cadmium fades, becoming covered with a thin film of CdO oxide, which protects the metal from further oxidation. When strongly heated in air, Cadmium burns into CdO oxide - a crystalline powder from light brown to dark brown in color, density 8.15 g/cm 3 ; at 700°C CdO sublimes without melting. Cadmium combines directly with halogens; these compounds are colorless; CdCl 2 , CdBr 2 and CdI 2 are very easily soluble in water (about 1 part anhydrous salt in 1 part water at 20 ° C), CdF 2 is less soluble (1 part in 25 parts water). With sulfur, Cadmium forms lemon-yellow to orange-red sulfide CdS, insoluble in water and dilute acids. Cadmium easily dissolves in nitric acid with the release of nitrogen oxides and the formation of nitrate, which gives the hydrate Cd(NOa) 2 4H 2 O. From hydrochloric and dilute sulfuric acids, Cadmium slowly releases hydrogen, and when the solutions are evaporated, chloride hydrates 2CdCl 2 crystallize from them. 5H 2 O and sulfate 3CdSO 4 ·8H 2 O. Solutions of Cadmium salts have an acidic reaction due to hydrolysis; caustic alkalis precipitate from them white hydroxide Cd(OH) 2, insoluble in excess of the reagent; however, by the action of concentrated alkali solutions on Cd(OH) 2, hydroxocadmiates, for example Na 2, were obtained. The Cd 2+ cation easily forms complex ions with ammonia 2+ and with cyanide 2- and 4-. Numerous basic, double and complex salts of Cadmium are known. Cadmium compounds are poisonous; Inhalation of its oxide vapors is especially dangerous.

Cadmium gained popularity in the 40s of the 20th century. It was at this time that cadmium turned into a strategic material - control and emergency rods of nuclear reactors began to be made from it.

At first, cadmium turned out to be the main “rod” material, primarily because it absorbs thermal neutrons well. All reactors at the beginning of the “atomic age” (and the first of them was built by Enrico Fermi in 1942) operated on thermal neutrons. Only many years later it became clear that fast neutron reactors are more promising both for energy and for producing nuclear fuel - plutonium-239. But cadmium is powerless against fast neutrons; it does not stop them.

However, the role of cadmium in reactor construction should not be exaggerated, because the physical and chemical properties of this metal (strength, hardness, heat resistance - its melting point is only 321°C) leave much to be desired. Cadmium was the first core material. Then boron and its compounds began to take center stage. But cadmium is easier to obtain in large quantities.

The production of alloys consumes approximately a tenth of the world's cadmium production. Cadmium alloys are used mainly as antifriction materials and solders. The well-known alloy of composition 99% Cd and 1% Ni is used for the manufacture of bearings operating in automobile, aircraft and marine engines at high temperatures. Since cadmium is not sufficiently resistant to acids, including organic acids contained in lubricants, cadmium-based bearing alloys are sometimes coated with indium.

Alloying copper with small additions of cadmium makes it possible to make more wear-resistant wires on electric transport lines. Copper with the addition of cadmium is almost no different in electrical conductivity from pure copper, but it is noticeably superior in strength and hardness.

An alloy of cadmium with gold has a greenish color. An alloy of cadmium with tungsten, rhenium and 0.15% uranium 235 - sky blue in color - was obtained by Spanish scientists in 1998.

Everyone knows galvanized sheet metal, but not everyone knows that to protect iron from corrosion, not only galvanizing is used, but also cadmium plating. Cadmium coating is now applied only electrolytically; cyanide baths are most often used in industrial conditions. Previously, cadmium was used to immerse iron and other metals in molten cadmium.

Despite the similar properties of cadmium and zinc, cadmium coating has several advantages: it is more resistant to corrosion, and it is easier to make it even and smooth. In addition, cadmium, unlike zinc, is stable in an alkaline environment. Cadmium-plated sheet metal is used quite widely; its access is restricted only to the production of food containers, because cadmium is toxic. Cadmium coatings have another interesting feature: in the atmosphere of rural areas they have significantly greater corrosion resistance than in the atmosphere of industrial areas. Such a coating fails especially quickly if the content of sulfur dioxide or sulfuric anhydrides in the air is high.

The most important area of ​​application of cadmium is the production of chemical power sources. Cadmium electrodes are used in batteries and accumulators. The negative plates of nickel-cadmium batteries are made of iron meshes with cadmium sponge as the active agent. The positive plates are coated with nickel hydroxide. The electrolyte is a solution of potassium hydroxide. Compact batteries for guided missiles are also made on the basis of cadmium and nickel, only in this case, not iron, but nickel meshes are installed as the base.

Nickel-cadmium alkaline batteries are more reliable than lead acid batteries. These current sources are distinguished by high electrical characteristics, stable operation, and long service life. They can be charged in just one hour. However, nickel-cadmium batteries cannot be recharged without being completely discharged first (in this regard they are inferior to metal hydride batteries).

About 20% of cadmium is used for the manufacture of cadmium electrodes used in batteries (nickel-cadmium and silver-cadmium), normal Weston cells, and reserve batteries (lead-cadmium cell, mercury-cadmium cell, etc.

About 20% of cadmium is used for the production of inorganic dyes (sulfides and selenides, mixed salts, for example, cadmium sulfide - cadmium citric).

• Cadmium is sometimes used in experimental medicine.

Cadmium is used in homeopathic medicine.

• In recent years, cadmium has begun to be used in the creation of new antitumor nanomedicines. In Russia, in the early 1950s, the first successful experiments were carried out related to the development of antitumor drugs based on cadmium compounds.

• Cadmium sulfide is used for the production of film solar cells with an efficiency of about 10-16%, and also as a very good thermoelectric material.

• Used as a component of semiconductor materials and phosphors.

• The thermal conductivity of a metal near absolute zero is the highest among all metals, which is why cadmium is sometimes used for cryogenic technology.

The effect of cadmium on the human body

Cadmium is one of the most toxic heavy metals and therefore the Russian SanPiN classifies it as hazard class 2.

Cadmium compounds are poisonous. A particularly dangerous case is the inhalation of vapors of its oxide (CdO). Cadmium is a cumulative poison (can accumulate in the body). In drinking water, the maximum permissible concentration for cadmium is 0.001 mg/dm³

Soluble cadmium compounds, after absorption into the blood, affect the central nervous system, liver and kidneys, and disrupt phosphorus-calcium metabolism. Chronic poisoning leads to anemia and bone destruction.

Cadmium is normally present in small quantities in the body of a healthy person. Cadmium easily accumulates in rapidly multiplying cells (for example, in tumor or reproductive cells). It binds to the cytoplasmic and nuclear material of cells and damages them. It changes the activity of many hormones and enzymes. This is due to its ability to bind sulfhydryl (-SH) groups.

In 1968, an article appeared in a well-known magazine called “Cadmium and the Heart.” It said that Dr. Carroll, a US public health official, had discovered a relationship between cadmium levels in the atmosphere and the incidence of deaths from cardiovascular diseases. If, say, in city A the content of cadmium in the air is higher than in city B, then the heart patients of city A die earlier than if they lived in city B. Carroll made this conclusion after analyzing data for 28 cities.

According to USEPA, WHO and Health Canada, the total daily intake of cadmium into the human body from all sources is 10-50 mcg. The main and most “stable” source is food - on average from 10 to 30-40 mcg of cadmium per day. Vegetables, fruits, animal meat, and fish usually contain 10-20 mcg of cadmium per kilogram of weight. However, there are no rules without exceptions. Cereal crops grown on cadmium-contaminated soil or irrigated with cadmium-containing water may contain increased amounts of cadmium (more than 25 μg/kg).

Smokers receive a significant "increase" in cadmium. One cigarette contains 1 mcg (and sometimes more - up to 2 mcg) of cadmium. So consider this: a person who smokes a pack of cigarettes a day exposes his body to additional exposure to at least 20 mcg of cadmium, which, for reference, is not retained even by a carbon filter.
It should also be noted that cadmium is more easily absorbed by the body through the lungs - up to 10-20%. Those. from one pack of cigarettes 2 - 4 mcg of cadmium will be absorbed. When administered through the gastrointestinal tract, the percentage of digestibility is only 4-7% (0.2 - 5 mcg of cadmium per day in absolute figures). Thus, a smoker increases the “load” of cadmium on his body by at least 1.5-2 times, which is fraught with adverse health consequences.

World cadmium market

About 20 thousand tons of cadmium are produced annually. The volume of its production is largely related to the scale of zinc production.

About 82% of the world's supply of refined cadmium comes from nickel-cadmium power supplies, but after restrictions on their production in Europe one third of cadmium consumption will be affected. As a result of increased zinc production in Europe and decreased cadmium use, there may be "free" cadmium available, most often in the form of solid waste, but production of nickel-cadmium batteries is growing in Asia, production is moving to Asia and, as a result, demand for cadmium is growing in Asian region. For now, this will keep global cadmium consumption at the current level. In 2007, cadmium prices, starting at $4.18/kg, rose to $13/kg, but by the end of the year they amounted to $7/kg.

In 2010, South Korean Young Poong Corp. increased cadmium production by 75%, to 1,400 tons per year, and plans to launch new capacities soon, a company official said.

Most of the cadmium produced in the world is used for electrical coatings 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 leave it when it is damaged.

Until recently, cadmium coatings had a “sickness” that made itself felt from time to time. The fact is that when cadmium is electrolytically applied to a steel part, the hydrogen contained in the electrolyte can penetrate into the metal. This very unwelcome guest causes a dangerous “disease” in high-strength steels - hydrogen embrittlement, which leads 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, it created the threat of premature failure of the part. That is why designers were often forced to refuse the “services” of cadmium.

Scientists at the Institute of Physical Chemistry of the USSR Academy of Sciences managed to eliminate this “disease” of cadmium coatings. Titanium acted as a medicine. It turned out that if there is only one titanium atom per thousand of its atoms in the cadmium layer, the steel part is protected from 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 a thin 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 potassium hydroxide. 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 operate without brakes, a reactor cannot operate without control rods that increase or decrease the neutron flux.

Each reactor is also equipped with a massive emergency rod, which comes into action if the control rods for some reason fail to cope with their duties.

An instructive case arose at a nuclear power plant in California. Due to some design problems, the emergency rod could not be immersed in the boiler in a timely manner - the chain reaction became uncontrollable, and a serious accident occurred. A reactor with raging neutrons posed a huge danger to the surrounding population. We had to urgently evacuate people from the danger zone before the nuclear “fire” went out. Fortunately, there were no casualties, but the losses were very large, 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 low (it is measured in hundredths of an electron volt). In the first years of the atomic era, nuclear reactors operated precisely on thermal neutrons, and cadmium was for a long time considered the “first violin” among rod materials. Later, however, he had to give up the leading role to boron and its compounds. But for cadmium, nuclear physicists are finding 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 MRT crystal, which is a solid solution of cadmium and mercury tellurides. This semiconductor material is indispensable for the manufacture of thermal imagers - highly accurate infrared devices used in medicine, geology, astronomy, electronics, radio engineering and many other important fields of science and technology. It is extremely difficult to obtain this compound under terrestrial conditions: its components, due to the large difference in density, behave like the heroes of the famous fable by I. A. Krylov - a swan, a crayfish and a pike, and as a result, instead of a homogeneous alloy, a layered “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 a MCT crystal is estimated in hundred millionths of a percent. It is 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 quantities of cadmium are used to make this paint.

CONCLUSION

The multifaceted activities of cadmium also have negative sides. Several years ago, one of the US health officials found that there is a direct link 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 here.

While doctors and biologists are determining whether cadmium is harmful and looking for ways to reduce its content in the environment, technology representatives are taking all measures 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 capitalist countries was already approximately 700 tons, and in the 50s it reached 7000 tons (after all, it was during this period that Since then, cadmium has acquired 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, due to its irreplaceable properties.

REFERENCES

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

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

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

4) Lebedev B.N. Kuznetsova V.A. Non-ferrous metals. M.: Nauka, 1976.

5) Lyubchenko V.A. Non-ferrous metals. M.: Nauka, 1963.

6) Maksimova G.V. Cadmium // Journal of inorganic chemistry, No. 3, 1959, S-98.

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

8) Peysakhov I.L. Non-ferrous metals. M.: Nauka, 1950.

9) Glider V.I. Cadmium as a corrosion preventative. M.: Tsvetmetizdat, 1952.

The content of the article

CADMIUM(Cadmium) Cd is a chemical element of Group II of the Periodic Table. Atomic number 48, relative 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 (7.58%). Oxidation state +2, rarely +1.

Cadmium was discovered in 1817 by the German chemist Friedrich Stromeyer Friedrich (1776–1835).

When checking zinc oxide produced by one of the Schenebec factories, a suspicion arose that it contained an admixture of arsenic. When the drug was dissolved in acid and hydrogen sulfide was passed through the solution, a yellow precipitate similar to arsenic sulfides formed, but a more thorough check showed that this element was not present. For the final conclusion, a sample of suspicious zinc oxide and other zinc preparations (including zinc carbonate) from the same factory were sent to Friedrich Strohmeyer, who from 1802 held the chair of chemistry at the University of Göttingen and the position of inspector general of Hanoverian pharmacies.

Having calcined zinc carbonate, Strohmeyer obtained an oxide, but not white, as it should have been, but yellowish. He assumed that the color was caused by an admixture of iron, but it turned out that there was no iron. Strohmeyer completely analyzed zinc preparations and found that the yellow color appeared due to a new element. It was named after the zinc ore in which it was found: the Greek word kadmeia, "cadmium earth" is the ancient name for smithsonite ZnCO 3 . This word, according to legend, comes from the name of the Phoenician Cadmus, who allegedly was the first to find zinc stone and notice its ability to give copper (when smelted from ore) a golden color. The same name was given to the hero of ancient Greek mythology: according to one legend, Cadmus defeated the Dragon in a difficult duel and on his lands built the fortress of Cadmea, around which the seven-gate city of Thebes then grew.

Prevalence of cadmium in nature and its industrial extraction.

The cadmium content in the earth's crust is 1.6·10–5%. It is close in abundance to antimony (2·10–5%) and twice as common as mercury (8·10–6%). Cadmium is characterized by migration in hot underground waters along with zinc and other chemical elements prone to the formation of natural sulfides. It concentrates in hydrothermal sediments. Volcanic rocks contain up to 0.2 mg of cadmium per kg; among sedimentary rocks, clays are the richest in cadmium - up to 0.3 mg/kg, and to a lesser extent - limestones and sandstones (about 0.03 mg/kg). The average cadmium content in soil is 0.06 mg/kg.

Cadmium has its own minerals - greenockite CdS, otavite CdCO 3, monteponite CdO. However, they do not form their own deposits. The only industrially significant source of cadmium is zinc ores, where it is found in concentrations of 0.01–5%. Cadmium also accumulates in galena (up to 0.02%), chalcopyrite (up to 0.12%), pyrite (up to 0.02%), stannite (up to 0.2%). The total world resources of cadmium are estimated at 20 million tons, industrial ones - at 600 thousand tons.

Characteristics of a simple substance and industrial production of metallic cadmium.

Cadmium is a silvery solid with a bluish sheen on a fresh surface, a soft, malleable, malleable metal, easily rolled into sheets, and easy to polish. Like tin, cadmium sticks make a cracking sound when bent. It melts at 321.1° C, boils at 766.5° C, density is 8.65 g/cm 3, which allows it to be classified as a heavy metal.

Cadmium is stable in dry air. In humid air it quickly fades, and when heated it easily interacts with oxygen, sulfur, phosphorus and halogens. Cadmium does not react with hydrogen, nitrogen, carbon, silicon and boron.

Cadmium vapor interacts with water vapor to release hydrogen. Acids dissolve cadmium to form salts of this metal. Cadmium reduces ammonium nitrate in concentrated solutions to ammonium nitrite. It is oxidized in aqueous solution by cations of certain metals, such as copper(II) and iron(III). Unlike zinc, cadmium does not interact with alkali solutions.

The main sources of cadmium are intermediate products of zinc production. Metal precipitates obtained after purification of zinc sulfate solutions by the action of zinc dust contain 2–12% cadmium. The fractions formed during the distillation production of zinc contain 0.7–1.1% cadmium, and the fractions obtained during the rectification purification of zinc contain up to 40% cadmium. Cadmium is also extracted from dust from lead and copper smelters (it can contain up to 5% and 0.5% cadmium, respectively). The dust is usually treated with concentrated sulfuric acid and then the cadmium sulfate is leached with water.

Cadmium sponge is precipitated from solutions of cadmium sulfate by the action of zinc dust, then it is dissolved in sulfuric acid and the solution is purified from impurities by the action of zinc oxide or sodium carbonate, as well as by ion exchange methods. Metal cadmium is isolated by electrolysis on aluminum cathodes or by reduction with zinc.

To remove zinc and lead, cadmium metal is melted under a layer of alkali. The melt is treated with aluminum to remove nickel and ammonium chloride to remove thallium. Using additional purification methods, it is possible to obtain cadmium with an impurity content of 10–5% by weight.

About 20 thousand tons of cadmium are produced annually. The volume of its production is largely related to the scale of zinc production.

The most important area of ​​application of cadmium is the production of chemical power sources. Cadmium electrodes are used in batteries and accumulators. The negative plates of nickel-cadmium batteries are made of iron meshes with cadmium sponge as the active agent. The positive plates are coated with nickel hydroxide. The electrolyte is a solution of potassium hydroxide. Compact batteries for guided missiles are also made on the basis of cadmium and nickel, only in this case, not iron, but nickel meshes are installed as the base.

The processes occurring in a nickel-cadmium alkaline battery can be described by the overall equation:

Cd + 2NiO(OH) + 2H 2 O Cd(OH) 2 + 2Ni(OH) 2

Nickel-cadmium alkaline batteries are more reliable than lead acid batteries. These current sources are distinguished by high electrical characteristics, stable operation, and long service life. They can be charged in just one hour. However, nickel-cadmium batteries cannot be recharged without being completely discharged first (in this regard they are inferior to metal hydride batteries).

Cadmium is widely used to apply anti-corrosion coatings to metals, especially when they come into contact with seawater. The most important parts of ships, aircraft, as well as various products intended for operation in tropical climates are cadmium-plated. Previously, iron and other metals were cadmium-coated by immersing products in molten cadmium; now the cadmium coating is applied electrolytically.

Cadmium coatings have some advantages over zinc coatings: they are more resistant to corrosion and are easier to make even and smooth. The high ductility of such coatings ensures the tightness of threaded connections. In addition, cadmium, unlike zinc, is stable in an alkaline environment.

However, cadmium plating has its own problems. When cadmium is electrolytically applied to a steel part, the hydrogen contained in the electrolyte can penetrate into the metal. It causes so-called hydrogen embrittlement in high-strength steels, leading to unexpected failure of the metal under load. To prevent this phenomenon, a titanium additive is introduced into cadmium coatings.

In addition, cadmium is toxic. Therefore, although cadmium tin is used quite widely, it is prohibited to use it for the manufacture of kitchen utensils and food containers.

About a tenth of the world's cadmium production is spent on the production of alloys. Cadmium alloys are used mainly as antifriction materials and solders. The alloy, containing 99% cadmium and 1% nickel, is used for the manufacture of bearings operating in automobile, aircraft and marine engines at high temperatures. Since cadmium is not sufficiently resistant to acids, including organic acids contained in lubricants, cadmium-based bearing alloys are sometimes coated with indium.

Alloying copper with small additions of cadmium makes it possible to make wires on electric transport lines more wear-resistant. Copper with the addition of cadmium is almost no different in electrical conductivity from pure copper, but is noticeably superior in strength and hardness.

Cadmium is included in Wood's metal, a low-melting alloy containing 50% bismuth, 25% lead, 12.5% ​​tin, 12.5% ​​cadmium. Wood's alloy can be melted in boiling water. It is curious that the first letters of the components of Wood's alloy form the abbreviation VOSK. It was invented in 1860 by the not very famous English engineer B. Wood. This invention is often mistakenly attributed to his namesake - the famous American physicist Robert Williams Wood, who was born only eight years later. Low-melting cadmium alloys are used as material for producing thin and complex castings, in automatic fire protection systems, for soldering glass to metal.Solders containing cadmium are quite resistant to temperature fluctuations.

A sharp rise in demand for cadmium began in the 1940s and was associated with the use of cadmium in the nuclear industry - it was discovered that it absorbs neutrons and control and emergency rods of nuclear reactors began to be made from it. The ability of cadmium to absorb neutrons of strictly defined energies is used in the study of the energy spectra of neutron beams.

Cadmium compounds.

Cadmium forms binary compounds, salts and numerous complex, including organometallic, compounds. In solutions, the molecules of many salts, in particular halides, are associated. The solutions have a slightly acidic environment due to hydrolysis. When exposed to alkali solutions, starting from pH 7–8, basic salts precipitate.

Cadmium oxide CdO is obtained by reacting simple substances or by calcining cadmium hydroxide or carbonate. Depending on the "thermal history" it can be greenish-yellow, brown, red or almost black. This is partly due to particle size, but is largely a result of lattice defects. Above 900° C, cadmium oxide is volatile, and at 1570° C it completely sublimes. It has semiconductor properties.

Cadmium oxide is easily soluble in acids and poorly soluble in alkalis, easily reduced by hydrogen (at 900° C), carbon monoxide (above 350° C), and carbon (above 500° C).

Cadmium oxide is used as an electrode material. It is included in lubricating oils and batches for producing special glasses. Cadmium oxide catalyzes a number of hydrogenation and dehydrogenation reactions.

Cadmium hydroxide Cd(OH) 2 precipitates as a white precipitate from aqueous solutions of cadmium(II) salts when alkali is added. When exposed to very concentrated alkali solutions, it turns into hydroxocadmates, such as Na 2. Cadmium hydroxide reacts with ammonia to form soluble complexes:

Cd(OH) 2 + 6NH 3 H 2 O = (OH) 2 + 6H 2 O

In addition, cadmium hydroxide goes into solution under the influence of cyanides of alkali elements. Above 170°C it decomposes to cadmium oxide. The interaction of cadmium hydroxide with hydrogen peroxide in an aqueous solution leads to the formation of peroxides of various compositions.

Cadmium hydroxide is used to obtain other cadmium compounds, and also as an analytical reagent. It is part of cadmium electrodes in current sources. In addition, cadmium hydroxide is used in decorative glasses and enamels.

Cadmium fluoride CdF 2 is slightly soluble in water (4.06% by weight at 20° C), insoluble in ethanol. It can be obtained by the action of fluorine on a metal or hydrogen fluoride on cadmium carbonate.

Cadmium fluoride is used as an optical material. It is a component of some glasses and phosphors, as well as solid electrolytes in chemical current sources.

Cadmium chloride CdCl 2 is highly soluble in water (53.2% by weight at 20° C). Its covalent nature determines its relatively low melting point (568.5° C), as well as its solubility in ethanol (1.5% at 25° C).

Cadmium chloride is obtained by reacting cadmium with concentrated hydrochloric acid or chlorinating the metal at 500° C.

Cadmium chloride is a component of electrolytes in cadmium galvanic cells and sorbents in gas chromatography. It is part of some solutions in photography, catalysts in organic synthesis, and fluxes for growing semiconductor crystals. It is used as a mordant in dyeing and printing fabrics. Organocadmium compounds are obtained from cadmium chloride.

Cadmium bromide CdBr 2 forms scaly crystals with a pearlescent luster. It is very hygroscopic, highly soluble in water (52.9% by weight at 25°C), methanol (13.9% by weight at 20°C), ethanol (23.3% by weight at 20°C).

Cadmium bromide is obtained by bromination of the metal or by the action of hydrogen bromide on cadmium carbonate.

Cadmium bromide serves as a catalyst in organic synthesis, is a stabilizer of photographic emulsions and a component of vibrating compositions in photography.

Cadmium iodide CdI 2 forms shiny leaf-shaped crystals, they have a layered (two-dimensional) crystal structure. Up to 200 polytypes of cadmium iodide are known, differing in the sequence of layers with hexagonal and cubic close packing.

Unlike other halogens, cadmium iodide is not hygroscopic. It is highly soluble in water (46.4% by weight at 25°C). Cadmium iodide is obtained by iodizing the metal by heating or in the presence of water, as well as by the action of hydrogen iodide on cadmium carbonate or oxide.

Cadmium iodide serves as a catalyst in organic synthesis. It is a component of pyrotechnic compositions and lubricants.

Cadmium sulfide CdS was probably the first compound of this element that the industry became interested in. It forms lemon-yellow to orange-red crystals. Cadmium sulfide has semiconducting properties.

This compound is practically insoluble in water. It is also resistant to alkali solutions and most acids.

Cadmium sulfide is obtained by the interaction of cadmium and sulfur vapors, precipitation from solutions under the influence of hydrogen sulfide or sodium sulfide, and reactions between cadmium and organosulfur compounds.

Cadmium sulfide is an important mineral dye, formerly called cadmium yellow.

In the painting business, cadmium yellow subsequently began to be used more widely. In particular, passenger cars were painted with it because, among other advantages, this paint resisted locomotive smoke well. Cadmium sulfide was also used as a coloring agent in textile and soap production. Corresponding colloidal dispersions were used to obtain colored transparent glasses.

In recent years, pure cadmium sulfide has been replaced by cheaper pigments - cadmopon and zinc-cadmium lithopone. Cadmopon is a mixture of cadmium sulfide and barium sulfate. It is obtained by mixing two soluble salts - cadmium sulfate and barium sulfide. As a result, a precipitate is formed containing two insoluble salts:

CdSO 4 + BaS = CdSI + BaSO 4 Ї

Zinc-cadmium lithopone also contains zinc sulfide. When making this dye, three salts precipitate simultaneously. Lithopone is cream or ivory in color.

With the addition of cadmium selenide, zinc sulfide, mercury sulfide and other compounds, cadmium sulfide produces thermally stable pigments with bright colors ranging from pale yellow to dark red.

Cadmium sulfide gives the flame a blue color. This property is used in pyrotechnics.

In addition, cadmium sulfide is used as an active medium in semiconductor lasers. It can be used as a material for the manufacture of photocells, solar cells, photodiodes, LEDs, and phosphors.

Cadmium selenide CdSe forms dark red crystals. It is insoluble in water and decomposes with hydrochloric, nitric and sulfuric acids. Cadmium selenide is obtained by fusing simple substances or from gaseous cadmium and selenium, as well as by precipitation from a solution of cadmium sulfate under the action of hydrogen selenide, the reaction of cadmium sulfide with selenous acid, and the interaction between cadmium and organoselenium compounds.

Cadmium selenide is a phosphor. It serves as an active medium in semiconductor lasers and is a material for the manufacture of photoresistors, photodiodes, and solar cells.

Cadmium selenide is a pigment for enamels, glazes and artistic paints. Ruby glass is colored with cadmium selenide. It was this, and not chromium oxide, as in the ruby ​​itself, that made the stars of the Moscow Kremlin ruby ​​red.

Cadmium telluride CdTe can range in color from dark gray to dark brown. It is not soluble in water, but is decomposed by concentrated acids. It is produced by the interaction of liquid or gaseous cadmium and tellurium.

Cadmium telluride, which has semiconductor properties, is used as a detector of X-rays and gamma radiation, and mercury-cadmium telluride has found wide application (especially for military purposes) in IR detectors for thermal imaging.

When stoichiometry is violated or impurities are introduced (for example, copper and chlorine atoms), cadmium telluride acquires photosensitive properties. It is used in electrophotography.

Organocadmium compounds CdR 2 and CdRX (R = CH 3, C 2 H 5, C 6 H 5 and other hydrocarbon radicals, X - halogens, OR, SR, etc.) are usually obtained from the corresponding Grignard reagents. They are less thermally stable than their zinc counterparts, but are generally less reactive (usually non-flammable in air). Their most important application is the production of ketones from acid chlorides.

Biological role of cadmium.

Cadmium is found in the organisms of almost all animals (in terrestrial animals it is about 0.5 mg per 1 kg of mass, and in marine animals it is from 0.15 to 3 mg/kg). At the same time, it is considered one of the most toxic heavy metals.

Cadmium is concentrated in the body mainly in the kidneys and liver, while the cadmium content in the body increases with old age. It accumulates in the form of complexes with proteins that participate in enzymatic processes. Entering the body from the outside, cadmium has an inhibitory effect on a number of enzymes, destroying them. Its action is based on binding the –SH group of cysteine ​​residues in proteins and inhibiting SH enzymes. It may also inhibit the action of zinc-containing enzymes by displacing zinc. Due to the proximity of the ionic radii of calcium and cadmium, it can replace calcium in bone tissue.

People are poisoned by cadmium by drinking water contaminated with cadmium-containing waste, as well as vegetables and grains growing on lands located near oil refineries and metallurgical plants. Mushrooms have a special ability to accumulate cadmium. According to some reports, the cadmium content in mushrooms can reach units, tens, and even 100 or more milligrams per kg of their own weight. Cadmium compounds are among the harmful substances found in tobacco smoke (one cigarette contains 1–2 mcg of cadmium).

A classic example of chronic cadmium poisoning is a disease first described in Japan in the 1950s and called “itai-itai.” The disease was accompanied by severe pain in the lumbar region and muscle pain. Characteristic signs of irreversible kidney damage also appeared. Hundreds of itai-itai deaths have been recorded. The disease became widespread due to the high environmental pollution in Japan at that time and the specific diet of the Japanese - mainly rice and seafood (they are capable of accumulating cadmium in high concentrations). Studies have shown that those with "Itai-Itai" consumed up to 600 mcg of cadmium per day. Subsequently, as a result of environmental protection measures, the frequency and severity of syndromes like “Itai-Itai” decreased markedly.

In the USA, a relationship was found between cadmium levels in the atmosphere and the incidence of deaths from cardiovascular diseases.

It is believed that about 1 mcg of cadmium per 1 kg of body weight can enter the human body per day without harm to health. Drinking water should not contain more than 0.01 mg/l of cadmium. The antidote for cadmium poisoning is selenium, but consuming foods rich in this element leads to a decrease in sulfur content in the body, in which case cadmium again becomes dangerous.

Elena Savinkina

Where do you get cadmium from? Cadmium is always contained in the ores from which zinc and lead are extracted, and sometimes in copper ore. Therefore, it inevitably ends up in the production waste of these metals. But they are not thrown away, but are tried to be recycled, since there are many other elements that people need. The share of cadmium is very large - 0.3–0.5% of the weight of the zinc concentrate, and 95% of it is taken from there. Actually, cadmium was discovered while studying zinc compounds. They tell the following 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 they contained arsenic. Pharmacists swore that there was no arsenic in the preparations, except perhaps iron oxide, which gives the ointment a yellowish color. The arbiter was Professor Friedrich Strohmeyer from the University of Göttingen, who was at that time the chief pharmaceutical inspector. He actually managed to isolate a yellowish compound from the drug. However, it had nothing to do with either arsenic or iron, but turned out to be the oxide of a new element. In the fall of 1817, in conversations with colleagues, Strohmeyer called it cadmium, for which the following explanation is given. The legendary Phoenician prince Cadmus, having come to Boeotia in search of his sister Europa, stolen by Zeus, built the Cadme fortress there. Ancient Greek Thebes later grew around it. In ancient times, a specific mixture of zinc compounds was found near this city, called “Cadmean earth” or cadmium. Strohmeyer 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 published in April 1818, when chemists already knew about Strohmeyer’s discovery.

How did the yellow color of the compound affect interest in cadmium? In the most direct way: soon after Strohmeyer's discovery, a certain Karsten, senior advisor for metallurgy at the Breslau (now Wroclaw) plant, found in Silesian zinc ore an element that gave a yellow precipitate when hydrogen sulfide was passed through its solution, 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, for painting. By obtaining cadmium sulfide in different ways, you can make beautiful paint in different shades - from lemon to orange. Since it is resistant to acids, alkalis and strong heat, cadmium yellow is also suitable for painting ceramics. In addition, when cadmium sulfide is mixed with ultramarine, an excellent green paint is formed - cadmium green. When burned, cadmium produces a blue color, so it was also used in pyrotechnics. Thus, in the 90s of the 20th century, 17% of cadmium was used to prepare 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 mined cadmium. 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 high as Pb, which makes them promising for electric vehicles. The lifespan of modern nickel-cadmium batteries is more than 30 years. They charge quickly and quickly release energy, and due to their low internal resistance they can provide a high current density without heating up. 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 energy to computers and cell phones, but now their place is taken by lithium-ion. Nickel-cadmium batteries are also supposed to be used in alternative energy systems, where from time to time it is necessary to pump in 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 are high self-discharge and memory effect: if you charge a battery that is not completely discharged, it will accumulate less and less energy each time. There is an opinion 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, as well as cadmium pigments for paints, stabilizers for polymers (10% of metal production), and coatings for metals (5%), is constantly decreasing.

Which cadmium application 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 in the form of 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 battery production are recouped by energy production within a year, which is two to three times (as well as carbon dioxide emissions per kilowatt of electricity produced by it in Europe) less than that of silicon batteries In other words, batteries using cadmium compounds are very environmentally friendly. With increasing efficiency, this difference will increase even more, and there are prospects here, since the record efficiency values ​​for cadmium telluride were 15.6 and 13.8% in 2011 when applying its thin film to glass and flexible polyimide, respectively. Polymer-based batteries weigh hundreds of times less than glass ones and are easily mounted on curved surfaces, which is what attracts the attention of researchers.

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

So far, however, the potential of quantum dots has not been fully revealed - a record efficiency of 5.42% at the beginning of 2013 was demonstrated by an element based on quantum dots made of 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 electrode material has not yet been selected to ensure complete removal of the charge carriers resulting from the photoreaction from them. It is possible that cadmium will also be useful in the manufacture of electrodes; experiments with an electrode made 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 like sea urchins. It is possible that some of them will find application in future technologies.

Is there cadmium in tin soldiers? It may well end up there, because a small addition of cadmium greatly reduces the melting point of other metals and, accordingly, ensures better filling of the mold with the casting alloy. It is not surprising that it is part of the famous Wood 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 lost-melt 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 reduce the melting point of other metals, because the elements that make up the alloy named after him - seven to eight parts of bismuth, four of lead and two each of tin and cadmium - have a melting point of 271, respectively. 327, 231 and 742°C. And all together melt at 69°C! This result was so unexpected in 1860 that the editorial board of the journal “ The American Journal of Science and Arts” added the following note to Wood’s article: “We have had time to repeat only a few of the interesting experiments of Dr. Wood relating to the amazing effect that cadmium has in lowering the melting points of various alloys.” Nowadays, cadmium’s ability to reduce the melting point of metals is used by adding it to solders - this accounts for 2% of global metal production. Moreover, the solders are not only industrial, but also homemade. For example, on the jewelers’ forum, 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. You just have to solder under pressure so as not to get poisoned.”

What is the route of cadmium into the body?“Cadmium in children’s toys is impossible, it’s poisonous,” the reader will say. And he will be right, but only partly, since it is unlikely that cadmium from a tin soldier (any figure 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 ways. There are three of them. Firstly, with cigarette smoke: cadmium accumulates well in tobacco leaves. Secondly, from the air, especially urban air: it contains a lot of road dust resulting from the abrasion of tires and brake pads (and cadmium is part of their composition); The more you breathe this dust, the higher the cadmium content in the body. Thus, among traffic controllers it is one and a half times more than among road workers from rural areas (“ Chemosphere”, 2013, 90, 7, 2077–2084). Cadmium is also present in the smoke of thermal power plants, if they operate on coal, and in the smoke from burning wood, since trees extract it from the soil. The third source is food, especially roots, leaves and grains of plants: this is where cadmium accumulates. Research conducted by scientists from Seattle showed that among young women living in areas not contaminated 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 bean curd turned out to be a significant source of cadmium - one serving of it per week increases the cadmium content 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 due to human fault. Cadmium is contained in phosphorus fertilizers, from where it, by the way, mainly ends up in edible plants. Rains wash fertilizers into rivers and then into the sea. Cadmium travels on the surface of microparticles. Once in salt water, it is released and ends up in phytoplankton, and with it in oysters. As a result, mollusks that are grown higher up in river mouths, where cadmium has not yet been washed away from microparticles, are relatively pure, and those that are lower contain especially a lot of this metal (“ Science of the Total Environment”, 1996, 181, 1, 31–44). The cadmium content in oysters is 13–26 micrograms per gram of dry weight. For comparison: in sunflower seeds, which are also considered an important source of cadmium, there is 0.2–2.5 mcg per gram of grains, in tobacco leaves - 0.5–1 mcg per gram of dry weight. Since not only oysters feed on plankton, cadmium also ends up in fish caught in dirty seas. And the dirtiest is the Baltic Sea, into which many rivers flow from industrial areas and areas with intensive agriculture.

How does anthropogenic cadmium enter the environment? Besides 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, some of it inevitably passes through all the filters. The second is landfills and waste 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 burning - 1.5, and the production of phosphate fertilizers and wood burning - 0.2 thousand tons each of the more than seven thousand tons that humans disseminate into the environment approximately since the 30s of the XX century. Nature’s own capabilities are more modest: 0.52 thousand tons are provided 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 cadmium extracted from the earth’s bowels can be converted into metal (and global production has fluctuated between 17 and 20 thousand tons per year for decades now), so the prospects for utilization here are very broad. 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 Fthenakos from 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 reasons like this. In a solar cell, the cadmium compound is located between layers of glass or plastic. Therefore, particles containing cadmium can appear in the environment only when the element is destroyed, which happens either in a very dusty area or during a breakdown. But even then, as the experiment showed, no rain is able to wash out any noticeable amount of cadmium from the element. The evaporation temperature of CdTe exceeds 1000°C, and CdS, also present in these elements, is 1700°C, so there will be no evaporation during operation.

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 than the heating during a normal fire. Direct experiments have proven 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, it is a thin film) can be released. Some elements, when broken down in a landfill, actually break down, releasing cadmium, while others, more modern ones, 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 says nothing about polymer-based elements, which will most likely burn out and no cadmium will fuse into the glass. But he notes that bans on the use of cadmium can lead to much worse consequences: having lost the sales market, manufacturers of zinc, lead and copper will stop extracting cadmium from waste and they will begin to pollute everything around much more than landfills (remember a third of the cadmium that flies into the chimney ). Therefore, the use of cadmium must be expanded while measures for the disposal of products are tightened.

There is a separate question about devices based on nanodots: when destroyed, these materials will inevitably disperse nanoparticles that can move through the food chain. There is data (“ Journal of Hazardous Materials”, 2011, 192, 15, 192–199; doi:10.1016/j.jhazmat.2011.05.003), that at the same time they will not remain unchanged: in the liver and kidneys of rats to which cadmium selenide nanodots were injected into the abdominal cavity, an increase in free cadmium was noted. 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 must 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 Soysunwan Satarug, write about this in detail (“ ”, 2010, 118, 182–190; doi:10.1289/ehp.0901234). Let's retell 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 have increased bone fragility. The Japanese called this disease itai-itai: it appeared in the 40s in Toyama Prefecture, where farmers used water from a zinc mine to irrigate their fields. The cadmium content in rice was so high that daily intake was 600 mcg per day, or 4,200 mcg per week, or up to 2 grams per person over a lifetime. It is not difficult to identify a cause-and-effect relationship here, which cannot be said about chronic consumption of cadmium in small doses. It all comes down to the percentage of risk of getting a particular disease. It is still completely unknown what doses of cadmium can be considered harmless. The World Health Organization in 1989 gave a maximum tolerable intake of cadmium per week: 400–500 mcg, on the basis that 2 g over a lifetime is a lot, leading to itai-itai. In 1992, the norm was recalculated, it was 7 mcg 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 that enters it, and 0.005% of the amount of metal that is already in it comes out with urine. However, some doctors question this model, pointing out that they have encountered cases where the body absorbed 40% of the cadmium that entered it. Moreover, measurements have shown that consumption of as little as 1 mcg per kg per day results in 2 mcg 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 urine, the concentration of which is low, is usually expressed in micrograms per gram of creatinine - this substance is formed during muscle activity and is constantly excreted in the urine. The result presented in such units does not depend on the dilution of the sample. The following is the word “ creatinine" we will omit. Obviously, measuring cadmium in urine is much easier than its intake into the body from different sources)

What are these effects? When 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 mcg of cadmium is excreted in the urine per day, the probability of kidney degradation is 10%; according to others, when they measure not the daily excretion, but the concentration in the test sample, a cadmium content in urine of 0.67 mcg/g is already dangerous. (If we assume that 1–2 grams of creatinine are excreted in the urine per day, then it turns out that the dangerous daily dose of cadmium excretion is about 1 mcg.) As a result of tubular degradation, the ability of the kidneys to return vitamins, minerals and other useful substances to the body is weakened, for example zinc and copper associated with metallothioneins, calcium, phosphates, glucose, amino acids. A twofold increase in the level of cadmium in the urine increases the calcium content in it by 2 mg per day. It is not difficult to guess that calcium loss increases the risk of osteoporosis. Indeed, in the group of women over 50 years of age with more than 1 mcg/g of cadmium in their urine, the risk of osteoporosis was 43% higher than in those who had less than 0.5 mcg/g. With cadmium levels between 1 and 2 μg/g, the risk of elevated glucose levels 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 high cadmium levels is one and a half times higher than those with low levels. The risk of heart attack in women with more than 0.88 mcg/g of cadmium in their urine is 1.8 times higher compared to those with less than 0.43 mcg/g. The likelihood of dying 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 work of Dr. Sataruga and his 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” throughout the 20th century.

There are also strange data. Thus, there was a strong association between urinary cadmium levels and the risk of high blood pressure in Americans who do not smoke, while no such association was observed among smokers. Meanwhile, among cigarette lovers, cadmium consumption is obviously higher, and, in addition, the cadmium content in the urine of Americans is generally more than three times less than that of the Koreans mentioned above. In smokers with age-related retinal degradation, the level of cadmium in the urine was 1.18 μg/g - almost twice as high as in smokers without this disease and healthy non-smokers. However, those non-smokers who developed the disease had just as little cadmium as healthy people - which means it’s not just that. Such contradictory data raise 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? In the end, most of the studies mentioned in the review did not measure cadmium consumption, only its output.

How to deal with cadmium in the body? There is little scientific research on this topic, and the principle is indicated in the same work by researchers from North Dakota. Cadmium is not one of the vital elements, so the body does not have any special mechanisms for its absorption - cadmium uses those provided for similar heavy metals that form divalent ions: zinc, iron, manganese and calcium. A deficiency of any of these elements immediately leads to increased absorption of cadmium. Thus, iron deficiency increases the cadmium content in Thai women by three to four times. A study of Bangladeshi women found the same thing, but zinc was also at play. From this it follows how important it is to maintain the correct microelement balance in the body.

There are other ideas. For example, Brazilians show that caffeine significantly, more than two times, reduces the cadmium content in the blood and tissues, including reproductive tissues, 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 washing down your meal with coffee or tea, which also contains caffeine, is correct.

Sometimes a paradox arises: food high in cadmium has no effect on the body. Thus, a study of oyster eaters conducted in 1986 led to a surprise: at a maximum consumption of 72 oysters per week, they ate a monstrous 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 was high in those oysters, somehow interfered with the absorption of cadmium, and it 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 their urine increased by 2.5 times compared to the average in the United States - to 0. 76 µg/g.

Or maybe it is better to deal with cadmium before it enters the body, for example, to ensure that it does not get into the soil and air? It is hardly possible to free phosphorus fertilizers from cadmium; growing plants with reduced cadmium digestibility is time-consuming and expensive, although attempts are being made with regard to tobacco, but it is possible to cleanse the soil with hyperaccumulator plants - in the case of cadmium, this is black nightshade Solanum nigrum, also known as the edible blackberry berry, a French variety similar to a shepherd's purse or mustard, the glaucous berry or the alpine berry ( Thlaspi caerulescens) and Chinese sedum Sedum alfredii. True, it is unclear where to put the cadmium-enriched parts of these plants - they are clearly not suitable for compost and ash obtained from the garden plot. During the industrial combustion of so-called solid biofuels - straw, brushwood, etc. - there are opportunities to get rid of harmful metals: it is necessary to separate the high-temperature fractions of the smoke 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 to clean is the air. The most radical method has been chosen by the American and now the European Union authorities - an irreconcilable 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 decreased from 0.36 µg/g in 1988 to 0.26 µg/g in 2008. Since even among heavy smokers (and by American standards this is 20 or more packs per year) it fell from 0.71 to 0.49, and among non-smokers - from 0.26 to 0.19, it should be assumed that smoking bans in public places significantly reduced the effects of secondhand tobacco smoke consumption. 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 worth tightening the requirements for emissions from non-ferrous metallurgy factories, boiler houses and cars, and at the same time making sure that less harmful dust flies from under tire-shod wheels.

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 low-melting alloys, used in the nuclear industry).

2. Artificial yellow paint in different shades.

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

(lat. Cadmium), chemical element of group II of the periodic table. The name comes 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 by processing lead-zinc and copper ores. Used for cadmium plating, in high-power batteries, nuclear power (control rods for reactors), and for producing pigments. It is part of low-melting and other alloys. Cadmium sulfides, selenides and tellurides are semiconductor materials. Many cadmium compounds are poisonous.

CADMIUM (lat. Cadmium), Cd (read “cadmium”), 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%). Located in period 5 in group IIB of the periodic table of elements. Configuration of two outer electronic layers 4 s 2 p 6 d 10 5s 2 . Oxidation state +2 (valence II).
The radius of the atom is 0.154 nm, the radius of the Cd 2+ ion is 0.099 nm. Energies of sequential ionization - 8.99, 16.90, 37.48 eV. Electronegativity according to Pauling (cm. PAULING Linus) 1,69.
History of discovery
Discovered by German professor F. Strohmeier (cm. STROHMEYER Friedrich) in 1817. Pharmacists of Magdeburg while studying zinc oxide (cm. ZINC (chemical element)) ZnO was suspected of containing arsenic (cm. ARSENIC). F. Strohmeier isolated a brown-brown oxide from ZnO and reduced it with hydrogen (cm. HYDROGEN) and obtained 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%), faded ores (cm. BLACK ORES) and stannina (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 solution using zinc dust:
CdSO 4 + Zn = ZnSO 4 + Cd
The resulting metal is cleaned by melting 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 smelting method (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/dm3. If you bend a cadmium rod, you can hear a faint crackling sound - this is metal microcrystals rubbing against each other. Standard electrode potential of cadmium is -0.403 V, in the range of standard potentials (cm. STANDARD POTENTIAL) it is located before hydrogen (cm. HYDROGEN).
In a dry atmosphere, cadmium is stable, but in a humid atmosphere it is gradually covered with a film of CdO oxide. Above the melting point, cadmium burns in air to form brown oxide CdO:
2Сd + O 2 = 2CdO
Cadmium vapor reacts with water vapor to form hydrogen:
Cd + H 2 O = CdO + H 2
Compared to its neighbor in group IIB - Zn, cadmium reacts more slowly with acids:
Cd + 2HCl = CdCl 2 + H 2
The reaction occurs most easily with nitric acid:
3Cd + 8HNO 3 = 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 capable of reducing ammonium nitrate to nitrite NH 4 NO 2:
NH 4 NO 3 + Cd = NH 4 NO 2 + CdO
Cadmium is oxidized by solutions of Cu(II) or Fe(III) salts:
Cd + CuCl 2 = Cu + CdCl 2;
2FeCl 3 + Cd = 2FeCl 2 + CdCl 2
Above the melting point, cadmium reacts with halogens (cm. HALOGEN) with the formation of halides:
Cd + Cl 2 = 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 = Na 2 SO 4 + Cd(OH) 2 Ї
Cadmium hydroxide is practically insoluble in alkalis, although the formation of hydroxide complexes 2– has been observed during prolonged boiling in very concentrated solutions of alkalis. Thus, amphoteric (cm. AMPHOTERIC) the properties of CdO oxide and cadmium hydroxide Cd(OH) 2 are much less pronounced than those of the corresponding zinc compounds.
Due to complex formation, cadmium hydroxide Cd(OH) 2 easily dissolves in aqueous solutions of ammonia NH 3:
Cd(OH) 2 + 6NH 3 = (OH) 2
Application
40% of cadmium produced is used to apply anti-corrosion coatings to metals. 20% of cadmium is used for the manufacture of cadmium electrodes used in batteries and Weston normal cells. About 20% of cadmium is used in the production of inorganic dyes, specialty solders, semiconductor materials and phosphors. 10% cadmium is a component of jewelry and low-melting alloys, plastics.
Physiological action
Cadmium vapor and its compounds are toxic, and cadmium can accumulate in the body. In drinking water, the maximum permissible concentration for cadmium is 10 mg/m3. Symptoms of acute poisoning with cadmium salts are vomiting and convulsions. Soluble cadmium compounds, after absorption 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 .

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

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- (symbol Cd), a silvery-white metal from the second group of the periodic table. First isolated in 1817. Found in greenockite (in sulphide form), it is mainly obtained as a by-product of the extraction of zinc and lead. Easy to forge... Scientific and technical encyclopedic dictionary

Cd (from Greek kadmeia zinc ore * a. cadmium; n. Kadmium; f. cadmium; i. cadmio), chemical. element of group II periodic. Mendeleev system, at.sci. 48, at. m. 112.41. There are 8 stable isotopes found in nature: 106Cd (1.225%) 108Cd (0.875%),... ... Geological encyclopedia

Husband. metal (one of the chemical principles or non-decomposable elements) found in zinc ore. Cadmium, related to cadmium. Admist, containing cadmium. Dahl's Explanatory Dictionary. IN AND. Dahl. 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, melting point 321.1°C. Cadmium is used for applying anti-corrosion coatings to metals, making electrodes, producing pigments,... ... Illustrated Encyclopedic Dictionary

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