characteristics of cadmium. Cadmium: effect on the human body. Heavy metal poisoning. Seven colors of the rainbow

DEFINITION

Cadmium located in the fifth period of the II group of the secondary (B) subgroup of the Periodic Table.

Relates to elements d-families. Metal. Designation - CD. Ordinal number - 48. Relative atomic mass - 112.41 a.m.u.

Electronic structure of the cadmium atom

The cadmium atom consists of a positively charged nucleus (+48), inside which there are 48 protons and 64 neutrons, and 48 electrons move around in five orbits.

Fig.1. Schematic structure of the cadmium atom.

The distribution of electrons in orbitals is as follows:

48Cd) 2) 8) 18) 18) 2 ;

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 .

The valence electrons of the cadmium atom are those located on 4 d- and 5 s-orbitals. The energy diagram of the ground state takes the following form:

The valence electrons of a cadmium atom can be characterized by a set of four quantum numbers: n(chief quantum), l(orbital), m l(magnetic) and s(spin):

sublevel

Examples of problem solving

EXAMPLE 1

Exercise	How many atomic orbitals p-sublevel is filled for elements with serial numbers 35 and 54? Write down their electronic formulas.
Answer	Elements with serial numbers 35 and 54 are bromine and xenon. We write down their electronic formulas in the ground state: 35 Br1 s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 5 ; 54 Xe1 s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 2 5p 6 . There are 3 orbitals on the p-sublevel, each of which can contain no more than 2 electrons (6 in total). The p-orbitals of bromine and xenon atoms are filled.

EXAMPLE 2

Exercise

What values ​​can quantum numbers take? n, l, m l and m s characterizing the state of electrons in an atom. What values ​​do they take for the outer electrons of the calcium atom?

Answer

The main quantum number n can take values ​​from 1 to infinity, but in reality its limit is the number 7. The orbital quantum number l can take values ​​from 0 to 3. Magnetic quantum number m l takes values ​​from -l through 0 to +l. At the spin quantum number m s there can be only two values: +1/2 and -1/2. Let us write down the electronic configuration of the ground state of the magnesium atom (we will highlight the valence electrons in bold): 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 . The electrons of the outer energy level will be characterized by the following set of quantum numbers: sublevel

Cadmium (Latin Cadmium, denoted by the symbol Cd) is an element with atomic number 48 and atomic mass 112.411. It is an element of a secondary subgroup of the second group, the fifth period of the periodic table of chemical elements of Dmitry Ivanovich Mendeleev. Under normal conditions, the simple substance cadmium is a heavy (density 8.65 g/cm3) soft malleable ductile silvery-white transition metal.

Natural cadmium consists of eight isotopes, six of which are stable: 106Cd (isotope abundance 1.22%), 108Cd (0.88%), 110Cd (12.39%), 111Cd (12.75%), 112Cd (24. 07%), 114Cd (28.85%). For two other natural isotopes, weak radioactivity was detected: 113Cd (isotopic abundance 12.22%, β-decay with a half-life of 7.7∙1015 years) and 116Cd (isotopic abundance 7.49%, double β-decay with a half-life of 3, 0∙1019 years).

The forty-eighth element of the periodic system was discovered by the German professor Friedrich Stromeyer in 1817, this discovery can be called accidental. The fact is that Magdeburg pharmacists, when studying preparations containing zinc oxide ZnO, suspected the presence of arsenic in them. Since zinc oxide is an ingredient in many ointments, powders and emulsions used for various skin diseases, the inspectors categorically banned the sale of all suspicious drugs. Naturally, the manufacturer of medicines, defending its interests, demanded an independent examination. Stromeyer acted as an expert. He isolated a brown-brown oxide from ZnO, reduced it with hydrogen and obtained a silver-white metal, which he called "cadmium" (from the Greek kadmeia - impure zinc oxide, also zinc ore). Regardless of Professor Stromeyer, cadmium was discovered in Silesian zinc ores by a group of German scientists - K. Hermann, K. Carsten and W. Meisner in 1818.

Cadmium absorbs slow neutrons well, for this reason cadmium rods are used in nuclear reactors to control the rate of a chain reaction. Cadmium is used in alkaline batteries and is included as a component in some alloys. So, for example, copper alloys containing about 1% Cd (cadmium bronzes) are used for the manufacture of telegraph, telephone, trolleybus wires, since these alloys have greater strength and wear resistance than copper. A number of fusible alloys, for example, used in automatic fire extinguishers, contain the forty-eighth element. In addition, cadmium is included in some jewelry alloys. This metal is used for cadmium plating of steel products, because it carries an oxide film on its surface, which has a protective effect. The fact is that in sea water and in a number of other media, cadmium plating is more effective than galvanizing. Cadmium has a long history of use in homeopathic medicine. Compounds of the forty-eighth element have also found wide application - cadmium sulfide is used to make yellow paint and colored glasses, and cadmium fluoroborate is an important flux used for soldering aluminum and other metals.

Cadmium is found in the body of all vertebrates; it has been established that it affects carbon metabolism, the activity of a number of enzymes, and the synthesis of hippuric acid in the liver. However, cadmium compounds are poisonous, and the metal itself is a carcinogen. Especially dangerous is the inhalation of vapors of cadmium oxide CdO, fatal cases are not uncommon. The penetration of cadmium into the gastrointestinal tract is also harmful, but no cases of fatal poisoning have been recorded, most likely this is due to the fact that the body itself seeks to get rid of the toxin (vomiting).

Biological properties

It turns out that cadmium is present in almost all living organisms - in terrestrial the content of the forty-eighth element is approximately equal to 0.5 mg per 1 kg of mass, in marine organisms (sponges, intestinal cavities, echinoderms, worms) - from 0.15 to 3 mg / kg, the content of cadmium in plants is about 10-4% (on dry matter). Despite the presence of cadmium in most living organisms, its specific physiological significance has not yet been reliably established. Scientists managed to find out that this element affects carbohydrate metabolism, the synthesis of hippuric acid in the liver, the activity of a number of enzymes, as well as the metabolism of zinc, copper, iron and calcium in the body. There is a suggestion, supported by some research, that microscopic amounts of cadmium in food can stimulate growth in mammals. For this reason, some scientists classify cadmium as a conditionally essential trace element, that is, vital, but toxic in certain doses. Even the body of a perfectly healthy person contains a small amount of cadmium. And yet, despite this, cadmium is classified as one of the most toxic heavy metals - the Russian SanPiN classifies it as a hazard class 2 - highly hazardous substances - which also includes antimony, strontium, phenol and other toxic substances. In the Bulletin "Problems of Chemical Safety" dated April 29, 1999, cadmium appears as "the most dangerous ecotoxicant at the turn of the millennium"!

Like other heavy metals, cadmium is a cumulative poison, that is, it can accumulate in the body - its half-life is from 10 to 35 years. By the age of fifty, the human body is able to accumulate from 30 to 50 mg of cadmium. The main "deposit deposits" of the forty-eighth element in the human body are the kidneys, which contain from 30 to 60% of the total amount of this metal in the body, and the liver (20-25%). The following are able to accumulate cadmium to a lesser extent: the pancreas, spleen, tubular bones, and other organs and tissues. In small quantities, the forty-eighth element is present even in the blood. However, unlike lead or mercury, cadmium does not enter the brain. For the most part, cadmium in the body is in a bound state - in combination with the protein metallothionein - this is a kind of protective mechanism, the body's reaction to the presence of a heavy metal. In this form, cadmium is less toxic, however, even when bound, it does not become harmless - accumulating over the years, this metal can lead to disruption of the kidneys and an increased likelihood of kidney stones. Much more dangerous is cadmium, which is in ionic form, because it is chemically very close to zinc and is able to replace it in biochemical reactions, acting as a pseudo-activator or, conversely, an inhibitor of zinc-containing proteins and enzymes. Cadmium binds to the cytoplasmic and nuclear material of cells and damages them, changes the activity of many hormones and enzymes, which is explained by its ability to bind sulfhydryl (-SH) groups. In addition, the forty-eighth element, due to the proximity of the ionic radii of calcium and cadmium, is able to replace calcium in bone tissue. The same situation is with iron, which cadmium is also able to replace. For this reason, the lack of calcium, zinc and iron in the body can lead to an increase in the absorption of cadmium from the gastrointestinal tract up to 15-20%. It is believed that a harmless daily dose of cadmium for an adult is 1 μg of cadmium per 1 kg of body weight, large amounts of cadmium are extremely hazardous to health.

What are the mechanisms of entry of cadmium and its compounds into the body? Poisoning occurs when drinking water (maximum concentration limit for drinking water is 0.01 mg/l) contaminated with cadmium-containing waste, as well as when eating vegetables and grains growing on lands located near oil refineries and metallurgical enterprises. The use of mushrooms from such territories is especially dangerous, since, according to some information, they are able to accumulate more than 100 mg of cadmium per kg of their own weight. Smoking is another source of cadmium intake into the body, both of the smoker himself and of the people around him, because the metal is found in tobacco smoke. The characteristic signs of chronic cadmium poisoning are, as mentioned earlier, kidney damage, muscle pain, bone tissue destruction, and anemia. Acute food poisoning with cadmium occurs when large single doses are taken with food (15-30 mg) or with water (13-15 mg). At the same time, signs of acute gastroenteritis are observed - vomiting, pain and convulsions in the epigastric region, however, cases of fatal poisoning with cadmium compounds that have entered the body with food are unknown to science, but according to WHO estimates, a lethal single dose can be 350-3500 mg. Much more dangerous is cadmium poisoning by inhalation of its vapors (CdO) or cadmium-containing dust (as a rule, this occurs in industries related to the use of cadmium). Symptoms of such poisoning are pulmonary edema, headache, nausea or vomiting, chills, weakness, and diarrhea. As a result of such poisoning, deaths have been recorded.

The antidote for cadmium poisoning is selenium, which helps to reduce the absorption of the forty-eighth element. However, a balanced intake of selenium is required, this is due to the fact that its excess in the body leads to a decrease in the sulfur content, and this will certainly lead to the fact that cadmium will again become easily absorbed by the body.

It has been established that one cigarette contains from 1 to 2 micrograms of cadmium. It turns out that a person who smokes at least a pack of cigarettes per day receives an additional 20 micrograms of cadmium, at least! The danger lies in the fact that the assimilation of the forty-eighth element through the lungs is maximum - from 10 to 20%, thus, from 2 to 4 micrograms of cadmium is absorbed in the body of a smoker with each pack of cigarettes! The carcinogenic effect of nicotine contained in tobacco smoke, as a rule, is associated with the presence of cadmium, and it is not retained even by carbon filters.

An example of mass chronic cadmium poisoning with numerous deaths was described in the late 1950s. On the territory of Japan, cases of mass disease were recorded, which the locals called "itai-itai", which can literally be translated as "oh-oh, how painful!". Symptoms of the disease were severe lumbar pain, which, as it turned out later, was caused by irreversible kidney damage; severe muscle pain. The widespread spread of the disease and its severe course were caused by high environmental pollution in Japan at that time and the specific diet of the Japanese (rice and seafood accumulate large amounts of cadmium). It was found that those who fell ill with a strange disease consumed about 600 micrograms of cadmium daily!

Despite the fact that cadmium is recognized as one of the most toxic substances, it has also found application in medicine! Thus, inserted into the chest of a patient suffering from heart failure, a nickel-cadmium battery provides energy to a mechanical stimulator of the heart. The convenience of such a battery is that the patient does not have to lie down on the operating table to recharge or replace it. For uninterrupted battery life, it is enough to wear a special magnetized jacket once a week for just an hour and a half.

Cadmium is used in homeopathy, experimental medicine, and more recently it has been used to create new anticancer drugs.

Wood's alloy (Wood's metal), containing 50% bismuth, 12.5% ​​tin, 25% lead, 12.5% ​​cadmium, can be easily melted in boiling water. The alloy was invented in 1860 by a not very famous English engineer B. Wood (B.Wood).Several interesting facts are associated with this low-melting alloy: firstly, the first letters of the components of Wood's alloy form the abbreviation WAX, and secondly, quite often the invention is mistakenly attributed to B.Wood's namesake - the famous American physicist Robert Williams Wood, who was born only eight years later.

Not so long ago, the forty-eighth element of the periodic system entered the “armament” of Scotland Yard: with the help of the thinnest layer of cadmium deposited on the surface being examined, it is possible to quickly identify clear fingerprints of the criminal.

Scientists have established such an interesting fact: cadmium tin in the atmosphere of rural areas has a much greater corrosion resistance than in the atmosphere of industrial areas. Such a coating fails especially quickly if the content of sulfurous or sulfuric anhydrides is increased in the air.

In 1968, one of the US health officials (Dr. Carroll) discovered a direct relationship between mortality from cardiovascular diseases and the content of cadmium in the atmosphere. He came to such conclusions by analyzing the data of 28 cities. In four of them - New York, Chicago, 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.

In addition to the "standard" measures to limit cadmium emissions into the atmosphere, water and soil (filters and cleaners at enterprises, removal of housing and crop fields from such enterprises), scientists are also developing new - promising ones. So American scientists planted water hyacinths in the bay of the Mississippi River, believing that with their help it would be possible to purify water from such undesirable elements as cadmium and mercury.

Story

History knows many "discoveries" that were made during various checks, reviews and revisions. However, such finds are more criminal in nature than scientific. And yet there was such a case when the revision that had begun eventually led to the discovery of a new chemical element. It happened in Germany at the beginning of the 19th century. The district doctor R. Rolov checked the pharmacies of his district, during the audit - in a number of pharmacies near Magdeburg - he discovered zinc oxide, the appearance of which aroused suspicion and suggested the content of arsenic in it. To confirm his assumptions, Rolov dissolved the seized drug in acid and passed it through a solution of hydrogen sulfide, which led to the precipitation of a yellow precipitate, similar to arsenic sulfide. All suspicious medicines - ointments, powders, emulsions, powders - were immediately withdrawn from sale. Such a move outraged the owner of the factory in Schenebek, which produced all the drugs rejected by Rolov. This businessman - Herman, being a chemist by profession, conducted his own examination of the goods. Having tried all the arsenal of experiments known at that time for the detection of arsenic, he was convinced that his products were pure in this respect, and iron, which confused the auditor, gave the yellow color of zinc oxide. Having reported the results of his experiments to Rolov and the authorities of the land of Hanover, Herman demanded an independent examination and a complete "rehabilitation" of his product. As a result, it was decided to find out the opinion of Professor Stromeyer, who headed the Department of Chemistry at the University of Göttingen, and concurrently held the post of Inspector General of all Hanoverian pharmacies. Naturally, Stromeyer was sent for verification not only zinc oxide, but also other zinc preparations from the Shenebek factory, including zinc carbonate, from which this oxide was obtained. By calcining zinc carbonate ZnCO3, Friedrich Stromeyer obtained oxide, but not white, as it should have been, but yellowish. As a result of further research, it turned out that the preparations do not contain either arsenic, as Rolov assumed, or iron, as Herman thought. The reason for the unusual color was a completely different metal - previously unknown and very similar in properties to zinc. The only difference was that its hydroxide, unlike Zn (OH) 2, was not amphoteric, but had pronounced basic properties. Stromeyer named the new metal cadmium, hinting at the strong similarity of the new element with zinc - the Greek word καδμεια (kadmeia) has long denoted zinc ores (for example, smithsonite ZnCO3) and zinc oxide. In turn, this word comes from the name of the Phoenician Cadmus, who, according to legend, was the first to find a zinc stone and discovered its ability to give copper (when smelted from ore) a golden color. According to ancient Greek myths, there was another Cadmus - a hero who defeated the Dragon and built the fortress of Cadmeus on the lands of the enemy defeated by him, around which the great seven-gate city of Thebes subsequently grew. In the Semitic languages, "kadmos" means "eastern", which, perhaps, builds the name of the mineral from the places of its extraction or export from any eastern country or province. In 1818, Friedrich Stromeyer published a detailed description of a new metal, the properties of which he had already studied well. In its free form, the new element was a white metal, soft and not very strong, covered with a brownish oxide film on top. Pretty soon, as is often the case, Strohmeyer's priority in the discovery of cadmium began to be challenged, but all claims were soon rejected. Somewhat later, another German chemist, Kersten, found a new element in Silesian zinc ore and named it mellin (from the Latin mellinus, “yellow like quince”). The reason for this name was the color of the precipitate formed under the action of hydrogen sulfide. To Kersten's chagrin, the Mellin turned out to be Stromeyer's Cadmium. Even later, other names were proposed for the forty-eighth element: in 1821, John proposed calling the new element “klaprothium” - in honor of the famous chemist Martin Klaproth - the discoverer of uranium, zirconium and titanium, and Gilbert “junonium” - after the asteroid discovered in 1804 Juno. But no matter how great Klaproth's merits to science, his name was not destined to gain a foothold in the list of chemical elements: cadmium remained cadmium. True, in the Russian chemical literature of the first half of the 19th century, cadmium was often called cadmium.

Being in nature

Cadmium is a typically rare and rather scattered element, the average content of this metal in the earth's crust (clarke) is estimated at about 1.3 10-5% or 1.6 10-5% by weight, it turns out that cadmium in the lithosphere is approximately 130 mg / t. There is so little cadmium in the bowels of our planet that even germanium, which is considered rare, is 25 times more! Approximately the same ratios for cadmium and other rare metals: beryllium, cesium, scandium and indium. Cadmium is close in abundance to antimony (2 10–5%) and twice as common as mercury (8 10–6%).

The forty-eighth element is characterized by migration in hot groundwater along with zinc (cadmium is found as an isomorphic impurity in many minerals and always in zinc minerals) and other chalcophilic elements, that is, chemical elements prone to the formation of natural sulfides, selenides, tellurides, sulfosalts and sometimes found in the native state. In addition, the forty-eighth element is concentrated in hydrothermal deposits. Volcanic rocks are quite rich in cadmium, containing up to 0.2 mg of cadmium per kg; among sedimentary rocks, clay is the richest in the forty-eighth element - up to 0.3 mg / kg (for comparison, limestones contain cadmium 0.035 mg / kg, sandstones - 0.03 mg / kg). The average content of cadmium in the soil is 0.06 mg/kg. Also, this rare metal is present in water - in dissolved form (sulfate, chloride, cadmium nitrate) and in suspension as part of organo-mineral complexes. Under natural conditions, the forty-eighth element enters groundwater as a result of leaching of non-ferrous metal ores, as well as as a result of the decomposition of aquatic plants and organisms capable of accumulating it. Since the beginning of the 20th century, anthropogenic contamination of natural waters with cadmium has become the predominant factor in the entry of cadmium into water and soil. The content of cadmium in water is significantly affected by the pH of the medium (in an alkaline medium, cadmium precipitates in the form of hydroxide), as well as sorption processes. For the same anthropogenic reason, cadmium is also present in the air. In rural areas, the content of cadmium in the air is 0.1-5.0 ng / m3 (1 ng or 1 nanogram = 10-9 grams), in cities - 2-15 ng / m3, in industrial areas - from 15 to 150 ng /m3. Cadmium is mainly released into the atmospheric air due to the fact that many coals burned at thermal power plants contain this element. Being deposited from the air, cadmium enters the water and soil. The increase in the content of cadmium in the soil is facilitated by the use of mineral fertilizers, because almost all of them contain minor impurities of this metal. From water and soil, cadmium enters plants and living organisms, and further along the food chain can be "supplied" to humans.

Cadmium has its own minerals: howliite, otavite CdCO3, montemponite CdO (contains 87.5% Cd), greenockite CdS (77.8% Cd), xanthochroite CdS(H2O)x (77.2% Cd) cadmoselite CdSe (47% Cd ). However, they do not form their own deposits, but are present as impurities in zinc, copper, lead and polymetallic ores (more than 50), which are the main source of industrial production of the forty-eighth element. Moreover, the main role is played by zinc ores, where the concentration of cadmium ranges from 0.01 to 5% (in sphalerite ZnS). In most cases, the content of cadmium in sphalerite does not exceed 0.4 - 0.6%. Cadmium also accumulates in galena (0.005 - 0.02%), stannite (0.003 - 0.2%), pyrite (up to 0.02%), chalcopyrite (0.006 - 0.12%), however, of these sulfides, cadmium is usually not retrieved.

Cadmium is able to accumulate in plants (most of all in fungi) and living organisms (especially in water), for this reason, cadmium can be found in marine sedimentary rocks - shales (Mansfeld, Germany). The total world resources of cadmium are estimated at 20 million tons, industrial - at 600 thousand tons.

Application

The main consumer of the forty-eighth element is the production of chemical current sources: nickel-cadmium and silver-cadmium batteries, lead-cadmium and mercury-cadmium cells in backup batteries, normal Weston cells. Cadmium nickel batteries (AKN) used in industry are one of the most popular among other chemical current sources. The negative plates of such batteries are made of iron meshes with sponge cadmium as an active agent, and the positive plates are coated with nickel oxide. The electrolyte is a solution of caustic potash (potassium hydroxide). Nickel-cadmium alkaline batteries are more reliable than lead acid batteries. Chemical current sources using cadmium are distinguished by a long service life, stable operation and high electrical characteristics. In addition, recharging these batteries takes less than one hour! However, AKN cannot be recharged without a complete preliminary discharge, and in this they, of course, are inferior to metal hydride batteries.

Another wide field of application of cadmium is the deposition of protective anticorrosive coatings on metals (cadmium plating). Cadmium coating reliably protects iron and steel products from atmospheric corrosion. In the past, cadmium plating was carried out by immersing the metal in molten cadmium, the modern process is carried out exclusively by electrolysis. Cadmium plating is applied to the most critical parts of aircraft, ships, as well as parts and mechanisms designed to operate in tropical climates. It is known that some properties of zinc and cadmium are similar, but cadmium coating has certain advantages over galvanized coating: firstly, it is more resistant to corrosion, and secondly, it is easier to make it even and smooth. In addition, unlike zinc, cadmium is stable in an alkaline environment. Cadmium tin is used quite widely, however, there is an area in which the use of a coating of the forty-eighth element is strictly prohibited - this is the food industry. This is due to the high toxicity of cadmium. Until a certain point, the spread of cadmium coatings was also limited for another reason - when cadmium is applied electrolytically to a steel part, hydrogen contained in the electrolyte can penetrate into the metal, and, as is known, this element causes hydrogen embrittlement in high-strength steels, leading to unexpected destruction of the metal under load . The problem was solved by Soviet scientists from the Institute of Physical Chemistry of the USSR Academy of Sciences. It turned out that a negligible addition of titanium (one atom of titanium per thousand atoms of cadmium) protects the cadmium-plated steel part from the occurrence of hydrogen embrittlement, since the titanium absorbs all the hydrogen from the steel during the coating process.

About a tenth of the world production of cadmium is spent on the production of alloys. The low melting point is one of the reasons for the widespread use of cadmium in low-melting alloys. Such, for example, is Wood's alloy containing 12.5% ​​of the forty-eighth element. Such alloys are used as solders, as a material for obtaining thin and complex castings, in automatic fire-fighting systems, for soldering glass with metal. Solders containing the forty-eighth element are quite resistant to temperature fluctuations. Another distinguishing feature of cadmium alloys is their high antifriction properties. So, an alloy containing 99% cadmium and 1% nickel is used for the manufacture of bearings operating in automobile, aircraft and marine engines. Since cadmium is not sufficiently resistant to acids, including organic acids contained in lubricants, cadmium-based bearing alloys are coated with indium. Alloying copper with small additions of cadmium (less than 1%) makes it possible to make more wear-resistant wires on electric transport lines. Such negligible additions of cadmium can significantly increase the strength and hardness of copper, practically without worsening its electrical properties. Cadmium amalgam (a solution of cadmium in mercury) is used in dental technology for the manufacture of dental fillings.

In the forties of the XX century, cadmium acquired a new role - they began to make control and emergency rods of nuclear reactors from it. The reason element forty-eight quickly became a strategic material was because it absorbs thermal neutrons very well. But the first reactors of the beginning of the "atomic age" worked exclusively on thermal neutrons. Only later it turned out that fast neutron reactors are more promising both for energy and for obtaining nuclear fuel - 239Pu, and cadmium is powerless against fast neutrons, it does not delay them. However, even in the days of thermal neutron reactors, cadmium lost its dominant role, giving way to boron and its compounds.

About 20% of cadmium (in the form of compounds) is used for the production of inorganic dyes. Cadmium sulfide CdS is an important mineral dye formerly called cadmium yellow. Already at the beginning of the 20th century, it was known that cadmium yellow could be obtained in six shades, ranging from lemon yellow to orange. The resulting paints are resistant to weak alkalis and acids, and are completely insensitive to hydrogen sulfide. Paints based on CdS were used in many areas - painting, printing, porcelain painting, they covered passenger cars, protecting them from locomotive smoke. Dyes containing cadmium sulfide were used in the textile and soap industries. However, at present, rather expensive cadmium sulfide is often replaced with cheaper dyes - cadmopone (a mixture of cadmium sulfide and barium sulfate) and zinc-cadmium litopone (the composition, like that of cadmopone, plus zinc sulfide). Another compound of the forty-eighth element - cadmium selenide CdSe - is used as a red paint. However, not only in the production of dyes, compounds of the forty-eighth element have found their application - cadmium sulfide, for example, is also used for the production of film solar cells, the efficiency of which is about 10-16%. In addition, CdS is a fairly good thermoelectric material, which is used as a component of semiconductor materials and phosphors. Sometimes cadmium is used in cryogenic technology, which is associated with its maximum thermal conductivity (relative to other metals) near absolute zero.

Production

The main "suppliers" of the forty-eighth element are by-products of processing zinc, copper-zinc and lead-zinc ores. As for cadmium's own minerals, the only one of interest in obtaining the forty-eighth element is greenockite CdS, the so-called "cadmium blende". Greenockite is mined together with faerite during the development of zinc ores. During the recycling process, cadmium accumulates in the by-products of the process, from where it is then recovered. In the processing of polymetallic ores, as mentioned earlier, cadmium is a by-product of zinc production. These are either copper-cadmium cakes (metal precipitates obtained as a result of cleaning solutions of zinc sulfate ZnSO4 by the action of zinc dust), which contain from 2 to 12% Cd, or poussiers (volatile fractions formed during the distillation production of zinc), containing from 0.7 to 1.1% cadmium. The richest in the forty-eighth element are concentrates obtained during the rectification purification of zinc, they can contain up to 40% cadmium. From copper-cadmium cakes and other products with a high content of the forty-eighth element, it is usually leached with sulfuric acid H2SO4 with simultaneous air aeration. The process is carried out in the presence of an oxidizing agent - manganese ore or recycled manganese sludge from electrolysis baths.

In addition, cadmium is recovered from dust from lead and copper smelters (it can contain 0.5 to 5% and 0.2 to 0.5% cadmium, respectively). In such cases, the dust is usually treated with concentrated H2SO4 sulfuric acid, and then the resulting cadmium sulfate is leached with water. Cadmium sponge is precipitated from the resulting cadmium sulfate solution by the action of zinc dust, after which it is dissolved in sulfuric acid and the solution is purified from impurities by the action of sodium carbonate Na2CO3 or zinc oxide ZnO, it is also possible to use ion exchange methods. Cadmium metal is isolated by electrolysis on aluminum cathodes or by reduction with zinc (displacement of cadmium oxide CdO from CdSO4 solutions by zinc) using centrifugal separator reactors. The refining of cadmium metal usually consists in melting the metal under a layer of alkali (to remove zinc and lead), while using Na2CO3 is possible; treatment of the melt with aluminum (to remove nickel) and ammonium chloride NH4Cl (to remove thallium). Cadmium of higher purity is obtained by electrolytic refining with intermediate purification of the electrolyte, which is carried out using ion exchange or extraction; rectification of the metal (usually under reduced pressure), zone melting or other crystallization methods. Combining the above purification methods, it is possible to obtain metallic cadmium with the content of the main impurities (zinc, copper and others) of only 10-5% by weight. In addition, for the purification of the forty-eighth element, the methods of electrotransfer in liquid cadmium, electrorefining in a melt of sodium hydroxide NaOH, and amalgam electrolysis can be used. When zone melting is combined with electrotransfer, separation of cadmium isotopes can occur along with purification.

The world production of cadmium is largely related to the scale of zinc production and has increased significantly over the past decades - according to 2006 data, about 21 thousand tons of cadmium were produced in the world, while in 1980 this figure was only 15 thousand tons. The growth in consumption of the forty-eighth element continues now. The main producers of this metal are Asian countries: China, Japan, Korea, Kazakhstan. They account for 12 thousand tons of total production. Russia, Canada and Mexico can also be considered major producers of cadmium. The shift in mass production of cadmium towards Asia is due to the fact that in Europe there has been a reduction in the use of the forty-eighth element, and in the Asian region, on the contrary, the demand for nickel-cadmium elements is growing, which forces many to transfer production to Asian countries.

Physical Properties

Cadmium is a silvery-white metal that shimmers blue when freshly cut, but tarnishes in air due to the formation of a protective oxide film. Cadmium is a rather soft metal - it is harder than tin, but softer than zinc, it is quite possible to cut it with a knife. In combination with softness, the forty-eighth element has such important qualities for the industry as malleability and ductility - it is perfectly rolled into sheets and pulled into wire, and can be polished without any problems. When heated above 80 ° C, cadmium loses its elasticity, and so much so that it can easily be crushed into powder. The hardness of cadmium according to Mohs is equal to two, according to Brinell (for an annealed sample) 200-275 MPa. Tensile strength 64 MN/m2 or 6.4 kgf/mm2, relative elongation 50% (at 20 °C), yield strength 9.8 MPa.

Cadmium has a hexagonal close-packed crystal lattice with periods: a = 0.296 nm, c = 0.563 nm, c/a ratio = 1.882, z = 2, crystal lattice energy 116 μJ/kmol. Space group С6/mmm, atomic radius 0.156 nm, ionic radius Cd2+ 0.099 nm, atomic volume 13.01∙10-6 m3/mol. A rod made of pure cadmium, when bent, emits a weak crack like tin (“tin scream”) - this is metal microcrystals rubbing against each other, however, any impurities in the metal destroy this effect. In general, in terms of its physical, chemical and pharmacological properties, cadmium belongs to the group of heavy metals, having the most similarities with zinc and mercury.

The melting point of the forty-eighth element (321.1 °C) is quite low and can be compared with the melting points of lead (327.4 °C) or thallium (303.6 °C). However, it differs from the melting points of metals similar in a number of properties - lower than that of zinc (419.5 ° C), but higher than that of tin (231.9 ° C). The boiling point of cadmium is also low - only 770 ° C, which is quite interesting - lead, like most other metals, has a large difference between melting and boiling points. For example, lead has a boiling point (1745°C) 5 times greater than its melting point, and tin, whose boiling point is 2620°C, is 11 times greater than its melting point! At the same time, zinc, similar to cadmium, has a boiling point of only 960 °C at a melting point of 419.5 ° C. The coefficient of thermal expansion for cadmium is 29.8 10-6 (at 25 °C). Below 0.519 K, cadmium becomes a superconductor. The thermal conductivity of the forty-eighth element at 0 ° C is 97.55 W / (m K) or 0.233 cal / (cm sec ° C). The specific heat capacity of cadmium (at 25°C) is 225.02 J/(kg K) or 0.055 cal/(g°C). The temperature coefficient of electrical resistance of the forty-eighth element in the temperature range from 0 °C to 100 °C is 4.3 10-3, the specific electrical resistance of the forty-eighth element (at a temperature of 20 °C) is 7.4 10-8 ohm m (7.4 10-6 ohm cm). Cadmium is diamagnetic, its magnetic susceptibility is -0.176.10-9 (at a temperature of 20 °C). The standard electrode potential is -0.403 V. The electronegativity of cadmium is 1.7. The effective cross section of capture of thermal neutrons is 2450-2900-10 ~ 28 m2. Work function of electrons = 4.1 eV.

The density (at room temperature) of the forty-eighth element is 8.65 g/cm3, which makes it possible to classify cadmium as a heavy metal. According to the classification of N. Reimers, metals with a density of more than 8 g/cm3 should be considered heavy. Thus, heavy metals include Pb, Cu, Zn, Ni, Cd, Co, Sb, Sn, Bi, Hg. And although cadmium is lighter than lead (density 11.34 g/cm3) or mercury (13.546 g/cm3), it is heavier than tin (7.31 g/cm3).

Chemical properties

In chemical compounds, cadmium always exhibits valency 2 (configuration of the outer electron layer 5s2) - the fact is that the atoms of the elements of the secondary subgroup of the second group (zinc, cadmium, mercury), like the atoms of the elements of the copper subgroup, have a d-sublevel of the second outside electronic layer is completely filled. However, for elements of the zinc subgroup, this sublevel is already quite stable, and the removal of electrons from it requires a very large expenditure of energy. Another characteristic feature of the elements of the zinc subgroup, which brings them closer to the elements of the copper subgroup, is their tendency to complex formation.

As already mentioned, the forty-eighth element is located in the same group of the periodic system with zinc and mercury, occupying an intermediate position between them, for this reason a number of chemical properties of all these elements are similar. For example, oxides and sulfides of these metals are practically insoluble in water.

In dry air, cadmium is stable, but in humid air, a thin film of CdO oxide slowly forms on the metal surface, protecting the metal from further oxidation. With strong incandescence, cadmium burns out, also turning into cadmium oxide - a crystalline powder from light brown to dark brown in color (the difference in color gamut is partly due to particle size, but to a greater extent is the result of crystal lattice defects), CdO density 8.15 g /cm3; above 900 °C cadmium oxide is volatile, and at 1570 °C it completely sublimates. Vapors of cadmium react with water vapor to release hydrogen.

Acids react with cadmium to form salts of this metal. Nitric acid HNO3 easily dissolves the forty-eighth element, while nitric oxide is released and nitrate is formed, which gives the hydrate Cd (NO3) 2 4H2O. From other acids - hydrochloric and dilute sulfuric - cadmium slowly displaces hydrogen, this is explained by the fact that in the series of voltages the forty-eighth element is further than zinc, but ahead of hydrogen. Unlike zinc, cadmium does not interact with alkali solutions. Cadmium reduces ammonium nitrate NH4NO3 in concentrated solutions to ammonium nitrite NH4NO2. Above the melting point, cadmium combines directly with halogens, forming colorless compounds - cadmium halides. CdCl2, CdBr2 and CdI2 are very easily soluble in water (53.2% by mass at 20 °C), cadmium fluoride CdF2 (4.06% by mass at 20 °C) is much more difficult to dissolve, which is completely insoluble in ethanol. It can be obtained by the action of fluorine on a metal or hydrogen fluoride on cadmium carbonate. Cadmium chloride is obtained by reacting cadmium with concentrated hydrochloric acid or by chlorinating the metal at 500°C. Cadmium bromide is obtained by metal bromination or by the action of hydrogen bromide on cadmium carbonate. When heated, cadmium reacts with sulfur to form CdS sulfide (lemon yellow to orange red), insoluble in water and dilute acids. When cadmium is fused with phosphorus and arsenic, phosphides and arsenides of compositions Cd3P2 and CdAs2 are formed, respectively, with antimony - cadmium antimonide. Cadmium does not react with hydrogen, nitrogen, carbon, silicon and boron. CdH2 hydride and Cd3N2 nitride, which readily decompose on heating, were obtained indirectly.

Solutions of cadmium salts are acidic due to hydrolysis, caustic alkalis precipitate white hydroxide Cd (OH) 2 from them. Under the action of very concentrated alkali solutions, it is converted into hydroxocadmates, such as Na2. Cadmium hydroxide reacts with ammonia to form soluble complexes:

Cd(OH)2 + 6NH3 H2O → (OH)2 + 6H2O

In addition, Cd(OH)2 goes into solution under the action of alkali cyanides. Above 170°C, it decomposes to CdO. The interaction of cadmium hydroxide with hydrogen peroxide in an aqueous solution leads to the formation of peroxides of various compositions.

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, serial 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

What is cadmium? It is a heavy metal that comes from the smelting of other metals such as zinc, copper or lead. It is widely used for the manufacture of nickel-cadmium batteries. In addition, cigarette smoke also contains such an element. As a result of continuous exposure to cadmium, very severe diseases of the lungs and kidneys occur. Consider the features of this metal in more detail.

Scope of cadmium

Most of the industrial use of this metal is for protective coatings that protect metals from corrosion. Such a coating has a great advantage over zinc, nickel or tin, because it does not peel off during deformation.

What else can be the use of cadmium? It is used to produce alloys that are remarkably machinable. Cadmium alloys with minor additions of copper, nickel and silver are used for the manufacture of bearings for automobile, aircraft and marine engines.

Where else is cadmium used?

Welders, metallurgists, and workers associated with the textile, electronics, and battery industries are most at risk of cadmium poisoning. Nickel-cadmium batteries are used in mobile phones and other electronic devices. This metal is also used in the production of plastics, paints, metal coatings. Many soils that are regularly fertilized can also contain this toxic metal in large quantities.

cadmium: properties

Cadmium as well as its compounds are characterized as but small amounts of the element in the environment have not been proven to cause cancer. Inhalation of metal particles in industrial production does contribute to the development of lung cancer, but if contaminated food is eaten, they do not pose a risk of developing cancer.

How does cadmium enter the human body?

Everyone has long known that cigarette smoke contains cadmium. This heavy metal enters the body of a smoker in an amount twice as large as in the body of a person who is not subject to such a bad habit. However, passive smoking can be harmful.

Leafy vegetables, cereals and potatoes grown in soil containing high levels of cadmium can be hazardous. The liver and kidneys of marine life and animals are also famous for the increased content of this metal.

Many industrial enterprises, especially metallurgical ones, emit large amounts of cadmium into the atmosphere. People living near such enterprises are automatically included in the risk group.

Some agricultural areas actively use phosphate fertilizers, which contain a small amount of cadmium. Products grown on this land pose a potential threat to humans.

The impact of cadmium on the human body

Thus, we have analyzed what cadmium is. The impact on the human body of this heavy metal can cause negative consequences. In any living organism, it is found in small quantities, and its biological role has not yet been fully elucidated. Usually cadmium is associated with a negative function.

Its toxic effect is based on the blocking of sulfur-containing amino acids, which leads to disruption of protein metabolism and damage to the cell nucleus. This heavy metal promotes the removal of calcium from the bones and affects the nervous system. It can accumulate in the kidneys and liver, and it is excreted from the body very slowly. This process can take decades. Cadmium is usually excreted in urine and feces.

Inhalation of cadmium

This element enters the body of industrial workers by inhalation. To prevent this, use effective protective equipment. Neglect of this rule leads to sad consequences. If you inhale cadmium, the effect of such a metal on the human body is manifested as follows: the body temperature rises, chills and muscle pain appear.

After some time, damage to the lungs occurs, chest pain, shortness of breath, cough. In severe cases, this condition causes the death of the patient. Inhalation of air containing cadmium contributes to the development of kidney disease and osteoporosis. The risk of lung cancer increases several times.

The intake of cadmium with food

Why is cadmium dangerous in water and food? With the regular use of contaminated foods and water, this metal begins to accumulate in the body, which leads to negative consequences: kidney function is disrupted, bone tissue is weakened, the liver and heart are affected, and in severe cases death occurs.

Eating foods contaminated with cadmium can cause stomach irritation, nausea, abdominal pain, diarrhea, and vomiting. In addition, flu-like symptoms appear, swelling of the larynx develops, and tingling occurs in the hands.

Causes of cadmium poisoning

Heavy metal poisoning most often occurs in children, diabetics, pregnant and lactating women, people who abuse smoking. In Japan, cadmium intoxication occurs as a result of eating contaminated rice. In this case, apathy develops, the kidneys are affected, the bones soften and deform.

The industrialized areas, where oil refineries and metallurgical enterprises are located, are famous for the fact that the soil there is contaminated with cadmium. If plant products are grown in such places, then there is a high probability that heavy metal poisoning will occur.

The element can accumulate in large quantities in tobacco. If the raw material is dried, then the metal content increases dramatically. The entry of cadmium into the body occurs both during active and during the occurrence of lung cancer directly depends on the content of the metal in the smoke.

Treatment for poisoning

Cadmium:

• damage to the central nervous system;
• sharp pain in the bones;
• protein in the urine;
• stones in the kidneys;
• genital dysfunction.

If acute poisoning occurs, the victim should be kept warm, he needs to be provided with fresh air and peace. After washing the stomach, he should be given warm milk, to which a little baking soda is added. There are no antidotes for cadmium. To neutralize the metal, Unitiol, steroids and diuretics are used. Complex treatment involves the use of cadmium antagonists (zinc, iron, selenium, vitamins). The doctor may prescribe a general strengthening diet containing a large amount of fiber and pectin.

Possible consequences

A metal such as cadmium has a very serious effect on the human body, and if poisoning with this element occurs, the consequences can be dangerous. It displaces calcium from the bones, contributing to the development of osteoporosis. In adults and children, the spine begins to bend and bones deform. In childhood, such poisoning leads to encephalopathy and neuropathy.

Conclusion

Thus, we have analyzed what constitutes such a heavy metal as cadmium. The effect on the human body of this element is quite serious. Gradually accumulating in the body, it leads to the destruction of many organs. You can even get poisoned by cadmium if you eat contaminated foods in large quantities. The consequences of poisoning are also quite dangerous.

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 expected 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 serving 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 converted into metal (and the world output has been fluctuating between 17-20 thousand tons per year for decades), so the prospects for recycling 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.