Кадмий номер в таблице менделеева

Cadmium, ₄₈Cd

Cadmium
Pronunciation	​(KAD-mee-əm)
Appearance	silvery bluish-gray metallic
Standard atomic weight Ar°(Cd)
	112.414±0.004 112.41±0.01 (abridged)[1]
Cadmium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Zn ↑ Cd ↓ Hg silver ← cadmium → indium
Atomic number (Z)	48
Group	group 12
Period	period 5
Block	d-block
Electron configuration	[Kr] 4d10 5s2
Electrons per shell	2, 8, 18, 18, 2
Physical properties
Phase at STP	solid
Melting point	594.22 K ​(321.07 °C, ​609.93 °F)
Boiling point	1040 K ​(767 °C, ​1413 °F)
Density (near r.t.)	8.65 g/cm3
when liquid (at m.p.)	7.996 g/cm3
Heat of fusion	6.21 kJ/mol
Heat of vaporization	99.87 kJ/mol
Molar heat capacity	26.020 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 530 583 654 745 867 1040
Atomic properties
Oxidation states	−2, +1, +2 (a mildly basic oxide)
Electronegativity	Pauling scale: 1.69
Ionization energies	1st: 867.8 kJ/mol 2nd: 1631.4 kJ/mol 3rd: 3616 kJ/mol
Atomic radius	empirical: 151 pm
Covalent radius	144±9 pm
Van der Waals radius	158 pm
Spectral lines of cadmium
Other properties
Natural occurrence	primordial
Crystal structure	​hexagonal close-packed (hcp)
Speed of sound thin rod	2310 m/s (at 20 °C)
Thermal expansion	30.8 µm/(m⋅K) (at 25 °C)
Thermal conductivity	96.6 W/(m⋅K)
Electrical resistivity	72.7 nΩ⋅m (at 22 °C)
Magnetic ordering	diamagnetic[2]
Molar magnetic susceptibility	−19.8×10−6 cm3/mol[3]
Young’s modulus	50 GPa
Shear modulus	19 GPa
Bulk modulus	42 GPa
Poisson ratio	0.30
Mohs hardness	2.0
Brinell hardness	203–220 MPa
CAS Number	7440-43-9
History
Discovery and first isolation	Karl Samuel Leberecht Hermann and Friedrich Stromeyer (1817)
Named by	Friedrich Stromeyer (1817)
Main isotopes of cadmium v e
Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct 106Cd 1.25% stable 107Cd syn 6.5 h ε 107Ag 108Cd 0.89% stable 109Cd syn 462.6 d ε 109Ag 110Cd 12.47% stable 111Cd 12.80% stable 112Cd 24.11% stable 113Cd 12.23% 7.7×1015 y β− 113In 113mCd syn 14.1 y β− 113In IT 113Cd 114Cd 28.75% stable 115Cd syn 53.46 h β− 115In 116Cd 7.51% 3.1×1019 y β−β− 116Sn
Category: Cadmium view talk edit | references

Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of its compounds, and like mercury, it has a lower melting point than the transition metals in groups 3 through 11. Cadmium and its congeners in group 12 are often not considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states. The average concentration of cadmium in Earth’s crust is between 0.1 and 0.5 parts per million (ppm). It was discovered in 1817 simultaneously by Stromeyer and Hermann, both in Germany, as an impurity in zinc carbonate.

Cadmium occurs as a minor component in most zinc ores and is a byproduct of zinc production. Cadmium was used for a long time as a corrosion-resistant plating on steel, and cadmium compounds are used as red, orange and yellow pigments, to color glass, and to stabilize plastic. Cadmium use is generally decreasing because it is toxic (it is specifically listed in the European Restriction of Hazardous Substances Directive^[4]) and nickel-cadmium batteries have been replaced with nickel-metal hydride and lithium-ion batteries. One of its few new uses is in cadmium telluride solar panels.

Although cadmium has no known biological function in higher organisms, a cadmium-dependent carbonic anhydrase has been found in marine diatoms.

Characteristics[edit]

Physical properties[edit]

Cadmium is a soft, malleable, ductile, silvery-white divalent metal. It is similar in many respects to zinc but forms complex compounds.^[5] Unlike most other metals, cadmium is resistant to corrosion and is used as a protective plate on other metals. As a bulk metal, cadmium is insoluble in water^[6] and is not flammable; however, in its powdered form it may burn and release toxic fumes.^[7]

Chemical properties[edit]

Although cadmium usually has an oxidation state of +2, it also exists in the +1 state. Cadmium and its congeners are not always considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states.^[8] Cadmium burns in air to form brown amorphous cadmium oxide (CdO); the crystalline form of this compound is a dark red which changes color when heated, similar to zinc oxide. Hydrochloric acid, sulfuric acid, and nitric acid dissolve cadmium by forming cadmium chloride (CdCl₂), cadmium sulfate (CdSO₄), or cadmium nitrate (Cd(NO₃)₂). The oxidation state +1 can be produced by dissolving cadmium in a mixture of cadmium chloride and aluminium chloride, forming the Cd₂²⁺ cation, which is similar to the Hg₂²⁺ cation in mercury(I) chloride.^[5]

Cd + CdCl₂ + 2 AlCl₃ → Cd₂(AlCl₄)₂

The structures of many cadmium complexes with nucleobases, amino acids, and vitamins have been determined.^[9]

Isotopes[edit]

Naturally occurring cadmium is composed of eight isotopes. Two of them are radioactive, and three are expected to decay but have not done so under laboratory conditions. The two natural radioactive isotopes are ¹¹³Cd (beta decay, half-life is 7.7×10¹⁵ y) and ¹¹⁶Cd (two-neutrino double beta decay, half-life is 2.9×10¹⁹ y). The other three are ¹⁰⁶Cd, ¹⁰⁸Cd (both double electron capture), and ¹¹⁴Cd (double beta decay); only lower limits on these half-lives have been determined. At least three isotopes – ¹¹⁰Cd, ¹¹¹Cd, and ¹¹²Cd – are stable. Among the isotopes that do not occur naturally, the most long-lived are ¹⁰⁹Cd with a half-life of 462.6 days, and ¹¹⁵Cd with a half-life of 53.46 hours. All of the remaining radioactive isotopes have half-lives of less than 2.5 hours, and the majority have half-lives of less than 5 minutes. Cadmium has 8 known meta states, with the most stable being ^113mCd (t_1⁄2 = 14.1 years), ^115mCd (t_1⁄2 = 44.6 days), and ^117mCd (t_1⁄2 = 3.36 hours).^[10]

The known isotopes of cadmium range in atomic mass from 94.950 u (⁹⁵Cd) to 131.946 u (¹³²Cd). For isotopes lighter than 112 u, the primary decay mode is electron capture and the dominant decay product is element 47 (silver). Heavier isotopes decay mostly through beta emission producing element 49 (indium).^[10]

One isotope of cadmium, ¹¹³Cd, absorbs neutrons with high selectivity: With very high probability, neutrons with energy below the cadmium cut-off will be absorbed; those higher than the cut-off will be transmitted. The cadmium cut-off is about 0.5 eV, and neutrons below that level are deemed slow neutrons, distinct from intermediate and fast neutrons.^[11]

Cadmium is created via the s-process in low- to medium-mass stars with masses of 0.6 to 10 solar masses, over thousands of years. In that process, a silver atom captures a neutron and then undergoes beta decay.^[12]

History[edit]

Cadmium (Latin cadmia, Greek καδμεία meaning «calamine», a cadmium-bearing mixture of minerals that was named after the Greek mythological character Κάδμος, Cadmus, the founder of Thebes) was discovered in contaminated zinc compounds sold in pharmacies in Germany^[13] in 1817 by Friedrich Stromeyer.^[14] Karl Samuel Leberecht Hermann simultaneously investigated the discoloration in zinc oxide and found an impurity, first suspected to be arsenic, because of the yellow precipitate with hydrogen sulfide. Additionally Stromeyer discovered that one supplier sold zinc carbonate instead of zinc oxide.^[4] Stromeyer found the new element as an impurity in zinc carbonate (calamine), and, for 100 years, Germany remained the only important producer of the metal. The metal was named after the Latin word for calamine, because it was found in this zinc ore. Stromeyer noted that some impure samples of calamine changed color when heated but pure calamine did not. He was persistent in studying these results and eventually isolated cadmium metal by roasting and reducing the sulfide. The potential for cadmium yellow as pigment was recognized in the 1840s, but the lack of cadmium limited this application.^[15][16][17]

Even though cadmium and its compounds are toxic in certain forms and concentrations, the British Pharmaceutical Codex from 1907 states that cadmium iodide was used as a medication to treat «enlarged joints, scrofulous glands, and chilblains».^[18]

In 1907, the International Astronomical Union defined the international ångström in terms of a red cadmium spectral line (1 wavelength = 6438.46963 Å).^[19][20] This was adopted by the 7th General Conference on Weights and Measures in 1927. In 1960, the definitions of both the metre and ångström were changed to use krypton.^[21]

After the industrial scale production of cadmium started in the 1930s and 1940s, the major application of cadmium was the coating of iron and steel to prevent corrosion; in 1944, 62% and in 1956, 59% of the cadmium in the United States was used for plating.^[4][22] In 1956, 24% of the cadmium in the United States was used for a second application in red, orange and yellow pigments from sulfides and selenides of cadmium.^[22]

The stabilizing effect of cadmium chemicals like the carboxylates cadmium laurate and cadmium stearate on PVC led to an increased use of those compounds in the 1970s and 1980s. The demand for cadmium in pigments, coatings, stabilizers, and alloys declined as a result of environmental and health regulations in the 1980s and 1990s; in 2006, only 7% of to total cadmium consumption was used for plating, and only 10% was used for pigments.^[4]
At the same time, these decreases in consumption were compensated by a growing demand for cadmium for nickel-cadmium batteries, which accounted for 81% of the cadmium consumption in the United States in 2006.^[23]

Occurrence[edit]

Cadmium makes up about 0.1 ppm of Earth’s crust. It is much rarer than zinc, which makes up about 65 ppm.^[24] No significant deposits of cadmium-containing ores are known. The only cadmium mineral of importance, greenockite (CdS), is nearly always associated with sphalerite (ZnS). This association is caused by geochemical similarity between zinc and cadmium, with no geological process likely to separate them. Thus, cadmium is produced mainly as a byproduct of mining, smelting, and refining sulfidic ores of zinc, and, to a lesser degree, lead and copper. Small amounts of cadmium, about 10% of consumption, are produced from secondary sources, mainly from dust generated by recycling iron and steel scrap. Production in the United States began in 1907,^[17] but wide use began after World War I.^[25][26]

Metallic cadmium can be found in the Vilyuy River basin in Siberia.^[27]

Rocks mined for phosphate fertilizers contain varying amounts of cadmium, resulting in a cadmium concentration of as much as 300 mg/kg in the fertilizers and a high cadmium content in agricultural soils.^[28][29] Coal can contain significant amounts of cadmium, which ends up mostly in coal fly ash.^[30] Cadmium in soil can be absorbed by crops such as rice. Chinese ministry of agriculture measured in 2002 that 28% of rice it sampled had excess lead and 10% had excess cadmium above limits defined by law. Some plants such as willow trees and poplars have been found to clean both lead and cadmium from soil.^[31]

Typical background concentrations of cadmium do not exceed 5 ng/m³ in the atmosphere; 2 mg/kg in soil; 1 μg/L in freshwater and 50 ng/L in seawater.^[32] Concentrations of cadmium above 10 μg/L may be stable in water having low total solute concentrations and p H and can be difficult to remove by conventional water treatment processes.^[33]

Production[edit]

Cadmium is a common impurity in zinc ores, and it is most often isolated during the production of zinc. Some zinc ores concentrates from zinc sulfate ores contain up to 1.4% of cadmium.^[34] In the 1970s, the output of cadmium was 6.5 pounds (2.9 kg) per ton of zinc.^[34] Zinc sulfide ores are roasted in the presence of oxygen, converting the zinc sulfide to the oxide. Zinc metal is produced either by smelting the oxide with carbon or by electrolysis in sulfuric acid. Cadmium is isolated from the zinc metal by vacuum distillation if the zinc is smelted, or cadmium sulfate is precipitated from the electrolysis solution.^[26][35]

The British Geological Survey reports that in 2001, China was the top producer of cadmium with almost one-sixth of the world’s production, closely followed by South Korea and Japan.^[36]

• 

  History of the world production of cadmium

• 

  Cadmium production in 2010.

Applications[edit]

Cadmium is a common component of electric batteries, pigments,^[37] coatings,^[38] and electroplating.^[39]

Batteries[edit]

In 2009, 86% of cadmium was used in batteries, predominantly in rechargeable nickel-cadmium batteries. Nickel-cadmium cells have a nominal cell potential of 1.2 V. The cell consists of a positive nickel hydroxide electrode and a negative cadmium electrode plate separated by an alkaline electrolyte (potassium hydroxide).^[40] The European Union put a limit on cadmium in electronics in 2004 of 0.01%,^[41] with some exceptions, and in 2006 reduced the limit on cadmium content to 0.002%.^[42] Another type of battery based on cadmium is the silver-cadmium battery.

Electroplating[edit]

Cadmium electroplating, consuming 6% of the global production, is used in the aircraft industry to reduce corrosion of steel components.^[39] This coating is passivated by chromate salts.^[38] A limitation of cadmium plating is hydrogen embrittlement of high-strength steels from the electroplating process. Therefore, steel parts heat-treated to tensile strength above 1300 MPa (200 ksi) should be coated by an alternative method (such as special low-embrittlement cadmium electroplating processes or physical vapor deposition).

Titanium embrittlement from cadmium-plated tool residues resulted in banishment of those tools (and the implementation of routine tool testing to detect cadmium contamination) in the A-12/SR-71, U-2, and subsequent aircraft programs that use titanium.^[43]

Nuclear fission[edit]

Cadmium is used in the control rods of nuclear reactors, acting as a very effective neutron poison to control neutron flux in nuclear fission.^[39] When cadmium rods are inserted in the core of a nuclear reactor, cadmium absorbs neutrons, preventing them from creating additional fission events, thus controlling the amount of reactivity. The pressurized water reactor designed by Westinghouse Electric Company uses an alloy consisting of 80% silver, 15% indium, and 5% cadmium.^[39]

Televisions[edit]

QLED TVs have been starting to include cadmium in construction. Some companies have been looking to reduce the environmental impact of human exposure and pollution of the material in televisions during production.^[44]

Anticancer drugs[edit]

Complexes based on heavy metals have great potential for the treatment of a wide variety of cancers but their use is often limited due to toxic side effects. However, scientists are advancing in the field and new promising cadmium complex compounds with reduced toxicity have been discovered.^[45]

Compounds[edit]

Cadmium oxide was used in black and white television phosphors and in the blue and green phosphors of color television cathode ray tubes.^[46] Cadmium sulfide (CdS) is used as a photoconductive surface coating for photocopier drums.^[47]

Various cadmium salts are used in paint pigments, with CdS as a yellow pigment being the most common. Cadmium selenide is a red pigment, commonly called cadmium red. To painters who work with the pigment, cadmium provides the most brilliant and durable yellows, oranges, and reds – so much so that during production, these colors are significantly toned down before they are ground with oils and binders or blended into watercolors, gouaches, acrylics, and other paint and pigment formulations. Because these pigments are potentially toxic, users should use a barrier cream on the hands to prevent absorption through the skin^[37] even though the amount of cadmium absorbed into the body through the skin is reported to be less than 1%.^[7]

In PVC, cadmium was used as heat, light, and weathering stabilizers.^[39][48] Currently, cadmium stabilizers have been completely replaced with barium-zinc, calcium-zinc and organo-tin stabilizers. Cadmium is used in many kinds of solder and bearing alloys, because it has a low coefficient of friction and fatigue resistance.^[39] It is also found in some of the lowest-melting alloys, such as Wood’s metal.^[49]

Semiconductors[edit]

Cadmium is an element in some semiconductor materials. Cadmium sulfide, cadmium selenide, and cadmium telluride are used in some photodetectors and solar cells. HgCdTe detectors are sensitive to mid-infrared light ^[39] and used in some motion detectors.

Laboratory uses[edit]

Helium–cadmium lasers are a common source of blue or ultraviolet laser light. Lasers at wavelengths of 325, 354 and 442 nm are made using this gain medium; some models can switch between these wavelengths. They are notably used in fluorescence microscopy as well as various laboratory uses requiring laser light at these wavelengths.^[50][51]

Cadmium selenide quantum dots emit bright luminescence under UV excitation (He-Cd laser, for example). The color of this luminescence can be green, yellow or red depending on the particle size. Colloidal solutions of those particles are used for imaging of biological tissues and solutions with a fluorescence microscope.^[52]

In molecular biology, cadmium is used to block voltage-dependent calcium channels from fluxing calcium ions, as well as in hypoxia research to stimulate proteasome-dependent degradation of Hif-1α.^[53]

Cadmium-selective sensors based on the fluorophore BODIPY have been developed for imaging and sensing of cadmium in cells.^[54] One powerful method for monitoring cadmium in aqueous environments involves electrochemistry. By employing a self-assembled monolayer one can obtain a cadmium selective electrode with a ppt-level sensitivity.^[55]

Biological role and research[edit]

Cadmium has no known function in higher organisms and is considered toxic.^[56] Cadmium is considered an environmental pollutant that causes health hazard to living organisms.^[57] Administration of cadmium to cells causes oxidative stress and increases the levels of antioxidants produced by cells to protect against macro molecular damage.^[58]

However a cadmium-dependent carbonic anhydrase has been found in some marine diatoms.^[59] The diatoms live in environments with very low zinc concentrations and cadmium performs the function normally carried out by zinc in other anhydrases. This was discovered with X-ray absorption near edge structure (XANES) spectroscopy.^[59][60]

Cadmium is preferentially absorbed in the kidneys of humans. Up to about 30 mg of cadmium is commonly inhaled throughout human childhood and adolescence.^[61] Cadmium is under research regarding its toxicity in humans, potentially elevating risks of cancer, cardiovascular disease, and osteoporosis.^{[62][63][64][65]}

Environment[edit]

The biogeochemistry of cadmium and its release to the environment has been the subject of review, as has the speciation of cadmium in the environment.^[66][67]

Safety[edit]

Cadmium

Hazards
GHS labelling:[68]
Pictograms
Signal word	Danger
Hazard statements	H301, H330, H341, H350, H361fd, H372, H410
Precautionary statements	P201, P202, P260, P264, P273, P304+P340+P310
NFPA 704 (fire diamond)	4 0 0

Individuals and organizations have been reviewing cadmium’s bioinorganic aspects for its toxicity.^[69] The most dangerous form of occupational exposure to cadmium is inhalation of fine dust and fumes, or ingestion of highly soluble cadmium compounds.^[4] Inhalation of cadmium fumes can result initially in metal fume fever, but may progress to chemical pneumonitis, pulmonary edema, and death.^[70]

Cadmium is also an environmental hazard. Human exposure is primarily from fossil fuel combustion, phosphate fertilizers, natural sources, iron and steel production, cement production and related activities, nonferrous metals production, and municipal solid waste incineration.^[4] Other sources of cadmium include bread, root crops, and vegetables.^[71]

There have been a few instances of general population poisoning as the result of long-term exposure to cadmium in contaminated food and water. Research into an estrogen mimicry that may induce breast cancer is ongoing.^[71] In the decades leading up to World War II, mining operations contaminated the Jinzū River in Japan with cadmium and traces of other toxic metals. As a consequence, cadmium accumulated in the rice crops along the riverbanks downstream of the mines. Some members of the local agricultural communities consumed the contaminated rice and developed itai-itai disease and renal abnormalities, including proteinuria and glucosuria.^[72] The victims of this poisoning were almost exclusively post-menopausal women with low iron and low body stores of other minerals. Similar general population cadmium exposures in other parts of the world have not resulted in the same health problems because the populations maintained sufficient iron and other mineral levels. Thus, although cadmium is a major factor in the itai-itai disease in Japan, most researchers have concluded that it was one of several factors.^[4]

Cadmium is one of six substances banned by the European Union’s Restriction of Hazardous Substances (RoHS) directive, which regulates hazardous substances in electrical and electronic equipment, but allows for certain exemptions and exclusions from the scope of the law.^[73]

The International Agency for Research on Cancer has classified cadmium and cadmium compounds as carcinogenic to humans.^[74] Although occupational exposure to cadmium is linked to lung and prostate cancer, there is still uncertainty about the carcinogenicity of cadmium in low environmental exposure. Recent data from epidemiological studies suggest that intake of cadmium through diet is associated with a higher risk of endometrial, breast, and prostate cancer as well as with osteoporosis in humans.^{[75][76][77][78]} A recent study has demonstrated that endometrial tissue is characterized by higher levels of cadmium in current and former smoking females.^[79]

Cadmium exposure is associated with a large number of illnesses including kidney disease,^[80] early atherosclerosis, hypertension, and cardiovascular diseases.^[81] Although studies show a significant correlation between cadmium exposure and occurrence of disease in human populations, a molecular mechanism has not yet been identified. One hypothesis holds that cadmium is an endocrine disruptor and some experimental studies have shown that it can interact with different hormonal signaling pathways. For example, cadmium can bind to the estrogen receptor alpha,^[82][83] and affect signal transduction along the estrogen and MAPK signaling pathways at low doses.^[84][85][86]

The tobacco plant absorbs and accumulates heavy metals such as cadmium from the surrounding soil into its leaves. Following tobacco smoke inhalation, these are readily absorbed into the body of users.^[87] Tobacco smoking is the most important single source of cadmium exposure in the general population. An estimated 10% of the cadmium content of a cigarette is inhaled through smoking. Absorption of cadmium through the lungs is more effective than through the gut. As much as 50% of the cadmium inhaled in cigarette smoke may be absorbed.^[88]
On average, cadmium concentrations in the blood of smokers is 4 to 5 times greater than non-smokers and in the kidney, 2–3 times greater than in non-smokers. Despite the high cadmium content in cigarette smoke, there seems to be little exposure to cadmium from passive smoking.^[89]

In a non-smoking population, food is the greatest source of exposure. High quantities of cadmium can be found in crustaceans, mollusks, offal, frog legs, cocoa solids, bitter and semi-bitter chocolate, seaweed, fungi and algae products. However, grains, vegetables, and starchy roots and tubers are consumed in much greater quantity in the U.S., and are the source of the greatest dietary exposure there.^[90] Most plants bio-accumulate metal toxins such as cadmium and when composted to form organic fertilizers, yield a product that often can contain high amounts (e.g., over 0.5 mg) of metal toxins for every kilogram of fertilizer. Fertilizers made from animal dung (e.g., cow dung) or urban waste can contain similar amounts of cadmium. The cadmium added to the soil from fertilizers (rock phosphates or organic fertilizers) become bio-available and toxic only if the soil pH is low (i.e., acidic soils).

Zinc, copper, calcium, and iron ions, and selenium with vitamin C are used to treat cadmium intoxication, though it is not easily reversed.^[80]

Regulations[edit]

Because of the adverse effects of cadmium on the environment and human health, the supply and use of cadmium is restricted in Europe under the REACH Regulation.^[91]

The EFSA Panel on Contaminants in the Food Chain specifies that 2.5 μg/kg body weight is a tolerable weekly intake for humans.^[90] The Joint FAO/WHO Expert Committee on Food Additives has declared 7 μg/kg body weight to be the provisional tolerable weekly intake level.^[92] The state of California requires a food label to carry a warning about potential exposure to cadmium on products such as cocoa powder.^[93]

The U.S. Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit (PEL) for cadmium at a time-weighted average (TWA) of 0.005 ppm. The National Institute for Occupational Safety and Health (NIOSH) has not set a recommended exposure limit (REL) and has designated cadmium as a known human carcinogen. The IDLH (immediately dangerous to life and health) level for cadmium is 9 mg/m³.^[94]

Lethal dose[95]	Organism	Route	Time
LD50: 225 mg/kg	rat	oral	n/a
LD50: 890 mg/kg	mouse	oral	n/a
LC50: 25 mg/m3	rat	n/a	30 min

In addition to mercury, the presence of cadmium in some batteries has led to the requirement of proper disposal (or recycling) of batteries.

Product recalls[edit]

In May 2006, a sale of the seats from Arsenal F.C.’s old stadium, Highbury in London, England was cancelled when the seats were discovered to contain trace amounts of cadmium.^[96] Reports of high levels of cadmium use in children’s jewelry in 2010 led to a US Consumer Product Safety Commission investigation.^[97] The U.S. CPSC issued specific recall notices for cadmium content in jewelry sold by Claire’s^[98] and Wal-Mart^[99] stores.

In June 2010, McDonald’s voluntarily recalled more than 12 million promotional Shrek Forever After 3D Collectible Drinking Glasses because of the cadmium levels in paint pigments on the glassware.^[100] The glasses were manufactured by Arc International, of Millville, NJ, USA.^[101]

See also[edit]

• Red List building materials
• Toxic heavy metal

References[edit]

Further reading[edit]

• Hartwig, Andrea (2013). «Chapter 15. Cadmium and cancer». In Astrid Sigel; Helmut Sigel; Roland K. O. Sigel (eds.). Cadmium: From Toxicology to Essentiality. Metal Ions in Life Sciences. Vol. 11. Springer. pp. 491–507. doi:10.1007/978-94-007-5179-8_15. ISBN 978-94-007-5178-1. PMID 23430782.

External links[edit]

• Cadmium at The Periodic Table of Videos (University of Nottingham)
• ATSDR Case Studies in Environmental Medicine: Cadmium Toxicity U.S. Department of Health and Human Services
• National Institute for Occupational Safety and Health – Cadmium Page
• NLM Hazardous Substances Databank – Cadmium, Elemental

Cadmium, ₄₈Cd

Cadmium
Pronunciation	​(KAD-mee-əm)
Appearance	silvery bluish-gray metallic
Standard atomic weight Ar°(Cd)
	112.414±0.004 112.41±0.01 (abridged)[1]
Cadmium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Zn ↑ Cd ↓ Hg silver ← cadmium → indium
Atomic number (Z)	48
Group	group 12
Period	period 5
Block	d-block
Electron configuration	[Kr] 4d10 5s2
Electrons per shell	2, 8, 18, 18, 2
Physical properties
Phase at STP	solid
Melting point	594.22 K ​(321.07 °C, ​609.93 °F)
Boiling point	1040 K ​(767 °C, ​1413 °F)
Density (near r.t.)	8.65 g/cm3
when liquid (at m.p.)	7.996 g/cm3
Heat of fusion	6.21 kJ/mol
Heat of vaporization	99.87 kJ/mol
Molar heat capacity	26.020 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 530 583 654 745 867 1040
Atomic properties
Oxidation states	−2, +1, +2 (a mildly basic oxide)
Electronegativity	Pauling scale: 1.69
Ionization energies	1st: 867.8 kJ/mol 2nd: 1631.4 kJ/mol 3rd: 3616 kJ/mol
Atomic radius	empirical: 151 pm
Covalent radius	144±9 pm
Van der Waals radius	158 pm
Spectral lines of cadmium
Other properties
Natural occurrence	primordial
Crystal structure	​hexagonal close-packed (hcp)
Speed of sound thin rod	2310 m/s (at 20 °C)
Thermal expansion	30.8 µm/(m⋅K) (at 25 °C)
Thermal conductivity	96.6 W/(m⋅K)
Electrical resistivity	72.7 nΩ⋅m (at 22 °C)
Magnetic ordering	diamagnetic[2]
Molar magnetic susceptibility	−19.8×10−6 cm3/mol[3]
Young’s modulus	50 GPa
Shear modulus	19 GPa
Bulk modulus	42 GPa
Poisson ratio	0.30
Mohs hardness	2.0
Brinell hardness	203–220 MPa
CAS Number	7440-43-9
History
Discovery and first isolation	Karl Samuel Leberecht Hermann and Friedrich Stromeyer (1817)
Named by	Friedrich Stromeyer (1817)
Main isotopes of cadmium v e
Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct 106Cd 1.25% stable 107Cd syn 6.5 h ε 107Ag 108Cd 0.89% stable 109Cd syn 462.6 d ε 109Ag 110Cd 12.47% stable 111Cd 12.80% stable 112Cd 24.11% stable 113Cd 12.23% 7.7×1015 y β− 113In 113mCd syn 14.1 y β− 113In IT 113Cd 114Cd 28.75% stable 115Cd syn 53.46 h β− 115In 116Cd 7.51% 3.1×1019 y β−β− 116Sn
Category: Cadmium view talk edit | references

Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, silvery-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it demonstrates oxidation state +2 in most of its compounds, and like mercury, it has a lower melting point than the transition metals in groups 3 through 11. Cadmium and its congeners in group 12 are often not considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states. The average concentration of cadmium in Earth’s crust is between 0.1 and 0.5 parts per million (ppm). It was discovered in 1817 simultaneously by Stromeyer and Hermann, both in Germany, as an impurity in zinc carbonate.

Cadmium occurs as a minor component in most zinc ores and is a byproduct of zinc production. Cadmium was used for a long time as a corrosion-resistant plating on steel, and cadmium compounds are used as red, orange and yellow pigments, to color glass, and to stabilize plastic. Cadmium use is generally decreasing because it is toxic (it is specifically listed in the European Restriction of Hazardous Substances Directive^[4]) and nickel-cadmium batteries have been replaced with nickel-metal hydride and lithium-ion batteries. One of its few new uses is in cadmium telluride solar panels.

Although cadmium has no known biological function in higher organisms, a cadmium-dependent carbonic anhydrase has been found in marine diatoms.

Characteristics[edit]

Physical properties[edit]

Cadmium is a soft, malleable, ductile, silvery-white divalent metal. It is similar in many respects to zinc but forms complex compounds.^[5] Unlike most other metals, cadmium is resistant to corrosion and is used as a protective plate on other metals. As a bulk metal, cadmium is insoluble in water^[6] and is not flammable; however, in its powdered form it may burn and release toxic fumes.^[7]

Chemical properties[edit]

Although cadmium usually has an oxidation state of +2, it also exists in the +1 state. Cadmium and its congeners are not always considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states.^[8] Cadmium burns in air to form brown amorphous cadmium oxide (CdO); the crystalline form of this compound is a dark red which changes color when heated, similar to zinc oxide. Hydrochloric acid, sulfuric acid, and nitric acid dissolve cadmium by forming cadmium chloride (CdCl₂), cadmium sulfate (CdSO₄), or cadmium nitrate (Cd(NO₃)₂). The oxidation state +1 can be produced by dissolving cadmium in a mixture of cadmium chloride and aluminium chloride, forming the Cd₂²⁺ cation, which is similar to the Hg₂²⁺ cation in mercury(I) chloride.^[5]

Cd + CdCl₂ + 2 AlCl₃ → Cd₂(AlCl₄)₂

The structures of many cadmium complexes with nucleobases, amino acids, and vitamins have been determined.^[9]

Isotopes[edit]

Naturally occurring cadmium is composed of eight isotopes. Two of them are radioactive, and three are expected to decay but have not done so under laboratory conditions. The two natural radioactive isotopes are ¹¹³Cd (beta decay, half-life is 7.7×10¹⁵ y) and ¹¹⁶Cd (two-neutrino double beta decay, half-life is 2.9×10¹⁹ y). The other three are ¹⁰⁶Cd, ¹⁰⁸Cd (both double electron capture), and ¹¹⁴Cd (double beta decay); only lower limits on these half-lives have been determined. At least three isotopes – ¹¹⁰Cd, ¹¹¹Cd, and ¹¹²Cd – are stable. Among the isotopes that do not occur naturally, the most long-lived are ¹⁰⁹Cd with a half-life of 462.6 days, and ¹¹⁵Cd with a half-life of 53.46 hours. All of the remaining radioactive isotopes have half-lives of less than 2.5 hours, and the majority have half-lives of less than 5 minutes. Cadmium has 8 known meta states, with the most stable being ^113mCd (t_1⁄2 = 14.1 years), ^115mCd (t_1⁄2 = 44.6 days), and ^117mCd (t_1⁄2 = 3.36 hours).^[10]

The known isotopes of cadmium range in atomic mass from 94.950 u (⁹⁵Cd) to 131.946 u (¹³²Cd). For isotopes lighter than 112 u, the primary decay mode is electron capture and the dominant decay product is element 47 (silver). Heavier isotopes decay mostly through beta emission producing element 49 (indium).^[10]

One isotope of cadmium, ¹¹³Cd, absorbs neutrons with high selectivity: With very high probability, neutrons with energy below the cadmium cut-off will be absorbed; those higher than the cut-off will be transmitted. The cadmium cut-off is about 0.5 eV, and neutrons below that level are deemed slow neutrons, distinct from intermediate and fast neutrons.^[11]

Cadmium is created via the s-process in low- to medium-mass stars with masses of 0.6 to 10 solar masses, over thousands of years. In that process, a silver atom captures a neutron and then undergoes beta decay.^[12]

History[edit]

Cadmium (Latin cadmia, Greek καδμεία meaning «calamine», a cadmium-bearing mixture of minerals that was named after the Greek mythological character Κάδμος, Cadmus, the founder of Thebes) was discovered in contaminated zinc compounds sold in pharmacies in Germany^[13] in 1817 by Friedrich Stromeyer.^[14] Karl Samuel Leberecht Hermann simultaneously investigated the discoloration in zinc oxide and found an impurity, first suspected to be arsenic, because of the yellow precipitate with hydrogen sulfide. Additionally Stromeyer discovered that one supplier sold zinc carbonate instead of zinc oxide.^[4] Stromeyer found the new element as an impurity in zinc carbonate (calamine), and, for 100 years, Germany remained the only important producer of the metal. The metal was named after the Latin word for calamine, because it was found in this zinc ore. Stromeyer noted that some impure samples of calamine changed color when heated but pure calamine did not. He was persistent in studying these results and eventually isolated cadmium metal by roasting and reducing the sulfide. The potential for cadmium yellow as pigment was recognized in the 1840s, but the lack of cadmium limited this application.^[15][16][17]

Even though cadmium and its compounds are toxic in certain forms and concentrations, the British Pharmaceutical Codex from 1907 states that cadmium iodide was used as a medication to treat «enlarged joints, scrofulous glands, and chilblains».^[18]

In 1907, the International Astronomical Union defined the international ångström in terms of a red cadmium spectral line (1 wavelength = 6438.46963 Å).^[19][20] This was adopted by the 7th General Conference on Weights and Measures in 1927. In 1960, the definitions of both the metre and ångström were changed to use krypton.^[21]

After the industrial scale production of cadmium started in the 1930s and 1940s, the major application of cadmium was the coating of iron and steel to prevent corrosion; in 1944, 62% and in 1956, 59% of the cadmium in the United States was used for plating.^[4][22] In 1956, 24% of the cadmium in the United States was used for a second application in red, orange and yellow pigments from sulfides and selenides of cadmium.^[22]

The stabilizing effect of cadmium chemicals like the carboxylates cadmium laurate and cadmium stearate on PVC led to an increased use of those compounds in the 1970s and 1980s. The demand for cadmium in pigments, coatings, stabilizers, and alloys declined as a result of environmental and health regulations in the 1980s and 1990s; in 2006, only 7% of to total cadmium consumption was used for plating, and only 10% was used for pigments.^[4]
At the same time, these decreases in consumption were compensated by a growing demand for cadmium for nickel-cadmium batteries, which accounted for 81% of the cadmium consumption in the United States in 2006.^[23]

Occurrence[edit]

Cadmium makes up about 0.1 ppm of Earth’s crust. It is much rarer than zinc, which makes up about 65 ppm.^[24] No significant deposits of cadmium-containing ores are known. The only cadmium mineral of importance, greenockite (CdS), is nearly always associated with sphalerite (ZnS). This association is caused by geochemical similarity between zinc and cadmium, with no geological process likely to separate them. Thus, cadmium is produced mainly as a byproduct of mining, smelting, and refining sulfidic ores of zinc, and, to a lesser degree, lead and copper. Small amounts of cadmium, about 10% of consumption, are produced from secondary sources, mainly from dust generated by recycling iron and steel scrap. Production in the United States began in 1907,^[17] but wide use began after World War I.^[25][26]

Metallic cadmium can be found in the Vilyuy River basin in Siberia.^[27]

Rocks mined for phosphate fertilizers contain varying amounts of cadmium, resulting in a cadmium concentration of as much as 300 mg/kg in the fertilizers and a high cadmium content in agricultural soils.^[28][29] Coal can contain significant amounts of cadmium, which ends up mostly in coal fly ash.^[30] Cadmium in soil can be absorbed by crops such as rice. Chinese ministry of agriculture measured in 2002 that 28% of rice it sampled had excess lead and 10% had excess cadmium above limits defined by law. Some plants such as willow trees and poplars have been found to clean both lead and cadmium from soil.^[31]

Typical background concentrations of cadmium do not exceed 5 ng/m³ in the atmosphere; 2 mg/kg in soil; 1 μg/L in freshwater and 50 ng/L in seawater.^[32] Concentrations of cadmium above 10 μg/L may be stable in water having low total solute concentrations and p H and can be difficult to remove by conventional water treatment processes.^[33]

Production[edit]

Cadmium is a common impurity in zinc ores, and it is most often isolated during the production of zinc. Some zinc ores concentrates from zinc sulfate ores contain up to 1.4% of cadmium.^[34] In the 1970s, the output of cadmium was 6.5 pounds (2.9 kg) per ton of zinc.^[34] Zinc sulfide ores are roasted in the presence of oxygen, converting the zinc sulfide to the oxide. Zinc metal is produced either by smelting the oxide with carbon or by electrolysis in sulfuric acid. Cadmium is isolated from the zinc metal by vacuum distillation if the zinc is smelted, or cadmium sulfate is precipitated from the electrolysis solution.^[26][35]

The British Geological Survey reports that in 2001, China was the top producer of cadmium with almost one-sixth of the world’s production, closely followed by South Korea and Japan.^[36]

• 

  History of the world production of cadmium

• 

  Cadmium production in 2010.

Applications[edit]

Cadmium is a common component of electric batteries, pigments,^[37] coatings,^[38] and electroplating.^[39]

Batteries[edit]

In 2009, 86% of cadmium was used in batteries, predominantly in rechargeable nickel-cadmium batteries. Nickel-cadmium cells have a nominal cell potential of 1.2 V. The cell consists of a positive nickel hydroxide electrode and a negative cadmium electrode plate separated by an alkaline electrolyte (potassium hydroxide).^[40] The European Union put a limit on cadmium in electronics in 2004 of 0.01%,^[41] with some exceptions, and in 2006 reduced the limit on cadmium content to 0.002%.^[42] Another type of battery based on cadmium is the silver-cadmium battery.

Electroplating[edit]

Cadmium electroplating, consuming 6% of the global production, is used in the aircraft industry to reduce corrosion of steel components.^[39] This coating is passivated by chromate salts.^[38] A limitation of cadmium plating is hydrogen embrittlement of high-strength steels from the electroplating process. Therefore, steel parts heat-treated to tensile strength above 1300 MPa (200 ksi) should be coated by an alternative method (such as special low-embrittlement cadmium electroplating processes or physical vapor deposition).

Titanium embrittlement from cadmium-plated tool residues resulted in banishment of those tools (and the implementation of routine tool testing to detect cadmium contamination) in the A-12/SR-71, U-2, and subsequent aircraft programs that use titanium.^[43]

Nuclear fission[edit]

Cadmium is used in the control rods of nuclear reactors, acting as a very effective neutron poison to control neutron flux in nuclear fission.^[39] When cadmium rods are inserted in the core of a nuclear reactor, cadmium absorbs neutrons, preventing them from creating additional fission events, thus controlling the amount of reactivity. The pressurized water reactor designed by Westinghouse Electric Company uses an alloy consisting of 80% silver, 15% indium, and 5% cadmium.^[39]

Televisions[edit]

QLED TVs have been starting to include cadmium in construction. Some companies have been looking to reduce the environmental impact of human exposure and pollution of the material in televisions during production.^[44]

Anticancer drugs[edit]

Complexes based on heavy metals have great potential for the treatment of a wide variety of cancers but their use is often limited due to toxic side effects. However, scientists are advancing in the field and new promising cadmium complex compounds with reduced toxicity have been discovered.^[45]

Compounds[edit]

Cadmium oxide was used in black and white television phosphors and in the blue and green phosphors of color television cathode ray tubes.^[46] Cadmium sulfide (CdS) is used as a photoconductive surface coating for photocopier drums.^[47]

Various cadmium salts are used in paint pigments, with CdS as a yellow pigment being the most common. Cadmium selenide is a red pigment, commonly called cadmium red. To painters who work with the pigment, cadmium provides the most brilliant and durable yellows, oranges, and reds – so much so that during production, these colors are significantly toned down before they are ground with oils and binders or blended into watercolors, gouaches, acrylics, and other paint and pigment formulations. Because these pigments are potentially toxic, users should use a barrier cream on the hands to prevent absorption through the skin^[37] even though the amount of cadmium absorbed into the body through the skin is reported to be less than 1%.^[7]

In PVC, cadmium was used as heat, light, and weathering stabilizers.^[39][48] Currently, cadmium stabilizers have been completely replaced with barium-zinc, calcium-zinc and organo-tin stabilizers. Cadmium is used in many kinds of solder and bearing alloys, because it has a low coefficient of friction and fatigue resistance.^[39] It is also found in some of the lowest-melting alloys, such as Wood’s metal.^[49]

Semiconductors[edit]

Cadmium is an element in some semiconductor materials. Cadmium sulfide, cadmium selenide, and cadmium telluride are used in some photodetectors and solar cells. HgCdTe detectors are sensitive to mid-infrared light ^[39] and used in some motion detectors.

Laboratory uses[edit]

Helium–cadmium lasers are a common source of blue or ultraviolet laser light. Lasers at wavelengths of 325, 354 and 442 nm are made using this gain medium; some models can switch between these wavelengths. They are notably used in fluorescence microscopy as well as various laboratory uses requiring laser light at these wavelengths.^[50][51]

Cadmium selenide quantum dots emit bright luminescence under UV excitation (He-Cd laser, for example). The color of this luminescence can be green, yellow or red depending on the particle size. Colloidal solutions of those particles are used for imaging of biological tissues and solutions with a fluorescence microscope.^[52]

In molecular biology, cadmium is used to block voltage-dependent calcium channels from fluxing calcium ions, as well as in hypoxia research to stimulate proteasome-dependent degradation of Hif-1α.^[53]

Cadmium-selective sensors based on the fluorophore BODIPY have been developed for imaging and sensing of cadmium in cells.^[54] One powerful method for monitoring cadmium in aqueous environments involves electrochemistry. By employing a self-assembled monolayer one can obtain a cadmium selective electrode with a ppt-level sensitivity.^[55]

Biological role and research[edit]

Cadmium has no known function in higher organisms and is considered toxic.^[56] Cadmium is considered an environmental pollutant that causes health hazard to living organisms.^[57] Administration of cadmium to cells causes oxidative stress and increases the levels of antioxidants produced by cells to protect against macro molecular damage.^[58]

However a cadmium-dependent carbonic anhydrase has been found in some marine diatoms.^[59] The diatoms live in environments with very low zinc concentrations and cadmium performs the function normally carried out by zinc in other anhydrases. This was discovered with X-ray absorption near edge structure (XANES) spectroscopy.^[59][60]

Cadmium is preferentially absorbed in the kidneys of humans. Up to about 30 mg of cadmium is commonly inhaled throughout human childhood and adolescence.^[61] Cadmium is under research regarding its toxicity in humans, potentially elevating risks of cancer, cardiovascular disease, and osteoporosis.^{[62][63][64][65]}

Environment[edit]

The biogeochemistry of cadmium and its release to the environment has been the subject of review, as has the speciation of cadmium in the environment.^[66][67]

Safety[edit]

Cadmium

Hazards
GHS labelling:[68]
Pictograms
Signal word	Danger
Hazard statements	H301, H330, H341, H350, H361fd, H372, H410
Precautionary statements	P201, P202, P260, P264, P273, P304+P340+P310
NFPA 704 (fire diamond)	4 0 0

Individuals and organizations have been reviewing cadmium’s bioinorganic aspects for its toxicity.^[69] The most dangerous form of occupational exposure to cadmium is inhalation of fine dust and fumes, or ingestion of highly soluble cadmium compounds.^[4] Inhalation of cadmium fumes can result initially in metal fume fever, but may progress to chemical pneumonitis, pulmonary edema, and death.^[70]

Cadmium is also an environmental hazard. Human exposure is primarily from fossil fuel combustion, phosphate fertilizers, natural sources, iron and steel production, cement production and related activities, nonferrous metals production, and municipal solid waste incineration.^[4] Other sources of cadmium include bread, root crops, and vegetables.^[71]

There have been a few instances of general population poisoning as the result of long-term exposure to cadmium in contaminated food and water. Research into an estrogen mimicry that may induce breast cancer is ongoing.^[71] In the decades leading up to World War II, mining operations contaminated the Jinzū River in Japan with cadmium and traces of other toxic metals. As a consequence, cadmium accumulated in the rice crops along the riverbanks downstream of the mines. Some members of the local agricultural communities consumed the contaminated rice and developed itai-itai disease and renal abnormalities, including proteinuria and glucosuria.^[72] The victims of this poisoning were almost exclusively post-menopausal women with low iron and low body stores of other minerals. Similar general population cadmium exposures in other parts of the world have not resulted in the same health problems because the populations maintained sufficient iron and other mineral levels. Thus, although cadmium is a major factor in the itai-itai disease in Japan, most researchers have concluded that it was one of several factors.^[4]

Cadmium is one of six substances banned by the European Union’s Restriction of Hazardous Substances (RoHS) directive, which regulates hazardous substances in electrical and electronic equipment, but allows for certain exemptions and exclusions from the scope of the law.^[73]

The International Agency for Research on Cancer has classified cadmium and cadmium compounds as carcinogenic to humans.^[74] Although occupational exposure to cadmium is linked to lung and prostate cancer, there is still uncertainty about the carcinogenicity of cadmium in low environmental exposure. Recent data from epidemiological studies suggest that intake of cadmium through diet is associated with a higher risk of endometrial, breast, and prostate cancer as well as with osteoporosis in humans.^{[75][76][77][78]} A recent study has demonstrated that endometrial tissue is characterized by higher levels of cadmium in current and former smoking females.^[79]

Cadmium exposure is associated with a large number of illnesses including kidney disease,^[80] early atherosclerosis, hypertension, and cardiovascular diseases.^[81] Although studies show a significant correlation between cadmium exposure and occurrence of disease in human populations, a molecular mechanism has not yet been identified. One hypothesis holds that cadmium is an endocrine disruptor and some experimental studies have shown that it can interact with different hormonal signaling pathways. For example, cadmium can bind to the estrogen receptor alpha,^[82][83] and affect signal transduction along the estrogen and MAPK signaling pathways at low doses.^[84][85][86]

The tobacco plant absorbs and accumulates heavy metals such as cadmium from the surrounding soil into its leaves. Following tobacco smoke inhalation, these are readily absorbed into the body of users.^[87] Tobacco smoking is the most important single source of cadmium exposure in the general population. An estimated 10% of the cadmium content of a cigarette is inhaled through smoking. Absorption of cadmium through the lungs is more effective than through the gut. As much as 50% of the cadmium inhaled in cigarette smoke may be absorbed.^[88]
On average, cadmium concentrations in the blood of smokers is 4 to 5 times greater than non-smokers and in the kidney, 2–3 times greater than in non-smokers. Despite the high cadmium content in cigarette smoke, there seems to be little exposure to cadmium from passive smoking.^[89]

In a non-smoking population, food is the greatest source of exposure. High quantities of cadmium can be found in crustaceans, mollusks, offal, frog legs, cocoa solids, bitter and semi-bitter chocolate, seaweed, fungi and algae products. However, grains, vegetables, and starchy roots and tubers are consumed in much greater quantity in the U.S., and are the source of the greatest dietary exposure there.^[90] Most plants bio-accumulate metal toxins such as cadmium and when composted to form organic fertilizers, yield a product that often can contain high amounts (e.g., over 0.5 mg) of metal toxins for every kilogram of fertilizer. Fertilizers made from animal dung (e.g., cow dung) or urban waste can contain similar amounts of cadmium. The cadmium added to the soil from fertilizers (rock phosphates or organic fertilizers) become bio-available and toxic only if the soil pH is low (i.e., acidic soils).

Zinc, copper, calcium, and iron ions, and selenium with vitamin C are used to treat cadmium intoxication, though it is not easily reversed.^[80]

Regulations[edit]

Because of the adverse effects of cadmium on the environment and human health, the supply and use of cadmium is restricted in Europe under the REACH Regulation.^[91]

The EFSA Panel on Contaminants in the Food Chain specifies that 2.5 μg/kg body weight is a tolerable weekly intake for humans.^[90] The Joint FAO/WHO Expert Committee on Food Additives has declared 7 μg/kg body weight to be the provisional tolerable weekly intake level.^[92] The state of California requires a food label to carry a warning about potential exposure to cadmium on products such as cocoa powder.^[93]

The U.S. Occupational Safety and Health Administration (OSHA) has set the permissible exposure limit (PEL) for cadmium at a time-weighted average (TWA) of 0.005 ppm. The National Institute for Occupational Safety and Health (NIOSH) has not set a recommended exposure limit (REL) and has designated cadmium as a known human carcinogen. The IDLH (immediately dangerous to life and health) level for cadmium is 9 mg/m³.^[94]

Lethal dose[95]	Organism	Route	Time
LD50: 225 mg/kg	rat	oral	n/a
LD50: 890 mg/kg	mouse	oral	n/a
LC50: 25 mg/m3	rat	n/a	30 min

In addition to mercury, the presence of cadmium in some batteries has led to the requirement of proper disposal (or recycling) of batteries.

Product recalls[edit]

In May 2006, a sale of the seats from Arsenal F.C.’s old stadium, Highbury in London, England was cancelled when the seats were discovered to contain trace amounts of cadmium.^[96] Reports of high levels of cadmium use in children’s jewelry in 2010 led to a US Consumer Product Safety Commission investigation.^[97] The U.S. CPSC issued specific recall notices for cadmium content in jewelry sold by Claire’s^[98] and Wal-Mart^[99] stores.

In June 2010, McDonald’s voluntarily recalled more than 12 million promotional Shrek Forever After 3D Collectible Drinking Glasses because of the cadmium levels in paint pigments on the glassware.^[100] The glasses were manufactured by Arc International, of Millville, NJ, USA.^[101]

See also[edit]

• Red List building materials
• Toxic heavy metal

References[edit]

Further reading[edit]

• Hartwig, Andrea (2013). «Chapter 15. Cadmium and cancer». In Astrid Sigel; Helmut Sigel; Roland K. O. Sigel (eds.). Cadmium: From Toxicology to Essentiality. Metal Ions in Life Sciences. Vol. 11. Springer. pp. 491–507. doi:10.1007/978-94-007-5179-8_15. ISBN 978-94-007-5178-1. PMID 23430782.

External links[edit]

• Cadmium at The Periodic Table of Videos (University of Nottingham)
• ATSDR Case Studies in Environmental Medicine: Cadmium Toxicity U.S. Department of Health and Human Services
• National Institute for Occupational Safety and Health – Cadmium Page
• NLM Hazardous Substances Databank – Cadmium, Elemental

Энергия ионизации

Чем ближе электрон к центру атома — тем больше энергии необходимо, что бы его оторвать.
Энергия, затрачиваемая на отрыв электрона от атома называется энергией ионизации и обозначается E_o.
Если не указано иное, то энергия ионизации — это энергия отрыва первого электрона, также существуют энергии
ионизации для каждого последующего электрона.

Энергия ионизации Cd:
E_o = 868 кДж/моль

— Что такое ион читайте в статье.

---

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Группа	12	Температура плавления	321,069 ° С, 609,924 ° F, 594,219 К
Период	5	Точка кипения	767 ° С, 1413 ° F, 1040 К
Блокировать	d	Плотность (г см -3 )	8,69
Атомный номер	48	Относительная атомная масса	112,414
Состояние при 20 ° C	Твердый	Ключевые изотопы	114 кд
Электронная конфигурация	[Kr] 4д 1 0 5с 2	Количество CAS	7440-43-9

Кадмий — элемент двенадцатой группы, пятого периода периодической системы химических элементов Д. И. Менделеева, с атомным номером 48. Обозначается символом Cd. Простое вещество кадмий при нормальных условиях — мягкий ковкий тягучий переходный металл серебристо-белого цвета. Устойчив в сухом воздухе, во влажном на его поверхности образуется плёнка оксида, препятствующая дальнейшему окислению металла. Кадмий и многие его соединения ядовиты.

Кадмий
← Серебро | Индий →
48 Zn ↑ Cd ↓ Hg 48Cd
Внешний вид простого вещества
Мягкий ковкий серебристо-серый металл
Элементарный кадмий
Свойства атома
Название, символ, номер	Ка́дмий / Cadmium (Cd), 48
Атомная масса (молярная масса)	112,411(8) а. е. м. (г/моль)
Электронная конфигурация	[Kr] 4d10 5s2
Радиус атома	154 пм
Химические свойства
Ковалентный радиус	148 пм
Радиус иона	(+2e) 97 пм
Электроотрицательность	1,69 (шкала Полинга)
Электродный потенциал	−0,403
Степени окисления	2
Энергия ионизации (первый электрон)	867,2 (8,99) кДж/моль (эВ)
Термодинамические свойства простого вещества
Плотность (при н. у.)	8,65 г/см³
Температура плавления	594,1 K (321 °C)
Температура кипения	1038 K (764,85 °C)
Уд. теплота плавления	6,11 кДж/моль
Уд. теплота испарения	59,1 кДж/моль
Молярная теплоёмкость	26,0 Дж/(K·моль)
Молярный объём	13,1 см³/моль
Кристаллическая решётка простого вещества
Структура решётки	гексагональная
Параметры решётки	a=2,979 c=5,618 Å
Отношение c/a	1,886
Температура Дебая	209 K
Прочие характеристики
Теплопроводность	(300 K) 96,9 Вт/(м·К)
Номер CAS	7440-43-9

История открытия

Открыт немецким профессором Ф. Штромейером в 1817 году. Провизоры Магдебурга при изучении оксида цинка ZnO заподозрили в нём примесь мышьяка. Штромейер выделил из ZnO коричнево-бурый оксид, восстановил его водородом и получил серебристо-белый металл, который получил название кадмий.

Происхождение названия

Штромейер назвал кадмий по греческому названию руды, из которой в Германии добывали цинк, — καδμεία. В свою очередь, руда получила своё название в честь Кадма, героя древнегреческой мифологии.

Нахождение в природе

Среднее содержание кадмия в земной коре — 130 мг/т, в морской воде — 0,11 мкг/л. Кадмий относится к редким, рассеянным элементам: он содержится в виде изоморфной примеси во многих минералах и всегда в минералах цинка. Известно всего лишь 6 кадмиевых минералов. Весьма редкими минералами кадмия являются гринокит CdS (77,8 % Cd), хоулиит (то же), отавит CdCO₃, монтепонит CdO (87,5 % Cd), кадмоселит CdSe (47 % Cd), ксантохроит CdS(H₂O)_х (77,2 % Cd). Основная масса кадмия рассеяна в большом числе минералов (более 50), преимущественно в сульфидах цинка, свинца, меди, железа, марганца и ртути. Максимальная концентрация отмечена в минералах цинка и, прежде всего, в сфалерите (до 5 %). В большинстве же случаев содержание кадмия в сфалерите не превышает 0,4—0,6 %. В других сульфидах, например, в станине содержание кадмия — 0,003—0,2 %, в галените — 0,005—0,02 %, в халькопирите — 0,006—0,12 %; из этих сульфидов кадмий обычно не извлекается.

Кадмий не образует самостоятельных месторождений, а входит в состав руд месторождений других металлов. Относительно высоко содержание кадмия в рудах среднетемпературных свинцово-цинковых и частично медно-колчеданных месторождений.

Почва содержит 0,06 мг/кг, глина — 0,3 мг/кг.

Нахождение в продуктах

ПДК кадмия в воде согласно СанПиН 2.1.4.1074-01 «Питьевая вода. Гигиенические требования к качеству воды централизованных систем питьевого водоснабжения. Контроль качества. Гигиенические требования к обеспечению безопасности систем горячего водоснабжения» — 1 мкг/л

Ископаемый уголь, древесный уголь, ПЭТ тара, древесные гранулы пеллеты (до 0,5 мг/кг), рыба (0,2 мг/кг), какао-порошок (0,5 мг/кг), почки животных (1 мг/кг), рис (0,06 мг/кг), сигарета (0,002 мг/кг), пшеничный хлеб (0,03 мг/кг), маргарин (0,042 мг/кг), говядина/свинина (0,016 мг/кг), креветки (1,2 мг/кг)

Получение

Единственный минерал, который представляет интерес в получении кадмия — гринокит, так называемая «кадмиевая обманка». Его добывают вместе со сфалеритом при разработке цинковых руд. В ходе переработки кадмий концентрируется в побочных продуктах процесса, откуда его потом извлекают. В настоящее время производится около 20000 тонн кадмия в год.

Физические свойства

Кадмий — серебристо-белый мягкий металл с гексагональной решёткой. Температура плавления — 321 °C, температура кипения — 770 °C. Если кадмиевую палочку изгибать, то можно услышать слабый треск — это трутся друг о друга микрокристаллы металла (так же трещит и пруток олова); любые примеси в металле уничтожают этот эффект. Кадмий твёрже олова, но мягче цинка — его можно резать ножом. При нагревании выше 80 °C кадмий теряет упругость до такой степени, что его можно истолочь в порошок.

Химические свойства

Кадмий расположен в одной группе периодической системы с цинком и ртутью, занимая промежуточное место между ними, поэтому некоторые химические свойства этих элементов сходны. На воздухе кадмий устойчив и не утрачивает металлического блеска. Вступает в реакцию с кислородом лишь при нагревании до 350 °C с образованием оксида кадмия . Сульфиды и оксиды этих элементов практически нерастворимы в воде. С углеродом кадмий не взаимодействует и карбидов не образует. Вступает в реакции с кислотами-неокислителями выделяя водород:

Сплавы

Кадмий используется как компонент твёрдых припоев (сплавов на основе серебра, меди, цинка) для снижения их температуры плавления. Около 10 % производимого кадмия — компонент ювелирных и легкоплавких сплавов. Сплав кадмия с золотом имеет зеленоватый цвет.

Защитные покрытия

40 % производимого кадмия используется для нанесения антикоррозионных покрытий на металлы. Кадмирование стальных деталей даёт большую устойчивость против коррозии, особенно в морской воде.

Кадмирование — это электролитическая процедура нанесения кадмиевых покрытий на поверхность металлоизделий. Кадмием покрывают высокоуглеродистые, инструментальные и нержавеющие стали, а кадмирование хлористо-аммонийное наносят на высокопрочные стали.

Химические источники тока

Около 20 % кадмия идёт на изготовление кадмиевых электродов, применяемых в аккумуляторах (никель-кадмиевых и серебряно-кадмиевых), нормальных элементах Вестона, в резервных батареях (свинцово-кадмиевый элемент, ртутно-кадмиевый элемент) и др.

Пигменты

Около 20 % кадмия используется для производства неорганических красящих веществ (сульфиды и селениды, смешанные соли, например, сульфид кадмия — кадмий лимонный).

Цена

Цена на кадмий в августе 2011 года составила примерно $3 за 1 кг.

Другие сферы применения

• Сульфид кадмия применяется для производства плёночных солнечных батарей с КПД около 10—16 %, а также как очень хороший термоэлектрический материал.
• Кадмий используется как компонент полупроводниковых материалов и люминофоров.
• Кадмий очень хорошо захватывает тепловые нейтроны (среднее сечение радиационного захвата тепловых нейтронов изотопом ¹¹⁴Cd составляет 20600 барн). Поэтому кадмий служит для изготовления регулирующих стержней для атомных реакторов и в качестве защиты от нейтронов. Иногда эти свойства используются в экспериментальных моделях противоопухолевой терапии (нейтрон-захватная терапия).
• Фтороборат кадмия — важный флюс, применяемый для пайки алюминия и других металлов.
• Теплопроводность кадмия вблизи абсолютного нуля — наивысшая среди всех металлов, поэтому кадмий иногда применяется для криогенной техники.
• Экранирование гамма-спектрометров от естественного радиационного фона: «свинцовый домик», в котором располагается спектрометрический датчик, выстилается изнутри медным и кадмиевым слоями для экранирования паразитного излучения свинца, искажающего гамма-спектр измеряемого вещества.

Ограничение применения

В 2016 году принят Технический регламент Евразийского экономического союза «Об ограничении применения опасных веществ в изделиях электротехники и радиоэлектроники» (ТР ЕАЭС 037/2016), по которому содержание кадмия в изделиях электротехники и радиоэлектроники не должно превышать 0,01 % по весу однородного материала (Приложение N 2). В Европейском союзе действует аналогичная директива RoHS, существенно ограничивающая использование кадмия.

Физиологическое действие

Кадмий и многие его соединения ядовиты (в больших концентрациях). Особенно опасным случаем является вдыхание паров его оксида (CdO). Вдыхание в течение 1 минуты воздуха с содержанием 2,5 г/м³ оксида кадмия, или 30 секунд при концентрации 5 г/м³ является смертельным. Кадмий является канцерогеном.

В качестве первой помощи при остром кадмиевом отравлении рекомендуется свежий воздух, полный покой, предотвращение охлаждения. При раздражении дыхательных путей — тёплое молоко с содой, ингаляции 2%-ным раствором NaHCO₃. При упорном кашле — кодеин, дионин, горчичники на грудную клетку, необходима врачебная помощь. Противоядием при отравлении, вызванном приёмом внутрь кадмиевых солей, служит альбумин с карбонатом натрия.

Острая токсичность

Пары кадмия, многие его соединения токсичны, что связано, в частности, с его способностью связывать серосодержащие ферменты и аминокислоты.

Симптомы острого отравления кадмием — рвота и судороги.

Хроническая токсичность

Кадмий — кумулятивный яд (способен накапливаться в организме).

Санитарно-экологические нормативы

В питьевой воде ПДК для кадмия 0,001 мг/дм³ (СанПиН 2.1.4.1074-01).

Механизм токсического действия

Механизм токсического действия кадмия заключается, по-видимому, в связывании карбоксильных, аминных и особенно сульфгидрильных групп белковых молекул, в результате чего угнетается активность ферментных систем. Растворимые соединения кадмия после всасывания в кровь поражают центральную нервную систему, печень и почки, нарушают фосфорно-кальциевый обмен. Хроническое отравление приводит к анемии и разрушению костей.

Кадмий в норме в небольших количествах присутствует в организме здорового человека. Кадмий легко накапливается в быстроразмножающихся клетках (например, в опухолевых или половых). Он связывается с цитоплазматическим и ядерным материалом клеток и повреждает их. Он изменяет активность многих гормонов и ферментов. Это обусловлено его способностью связывать сульфгидрильные (-SH) группы.

Изотопы

Из восьми природных изотопов кадмия шесть стабильны, для двух изотопов обнаружена слабая радиоактивность. Это ¹¹³Cd (изотопная распространённость 12,22 %, бета-распад с периодом полураспада 7,7⋅10¹⁵ лет) и ¹¹⁶Cd (изотопная распространённость 7,49 %, двойной бета-распад с периодом полураспада 3,0⋅10¹⁹ лет).