Selenium is a chemical element, and its chemical symbol is Se, a nonmetal. It can be used as photosensitive materials, catalysts for electrolytic manganese industry, essential nutrients for animals and beneficial nutrients for plants.
selenium element name: Selenium
element symbol: Se
element English name: selenium
element type: nonmetallic element
atomic volume: (cubic centimeter/mole)
16.45
element content in seawater: (ppm).
Pacific ocean surface .15
crustal content: (ppm)
.5
highest content found in natural environment: (ppm)
3
relative atomic mass: 78.89
atomic number: 34
oxidation state:. Se+6
Other Se-2
chemical bond energy: (kJ /mol)
se-h35
se-c245
se-o343
se-f285
se-cl245
se-se33
cell parameters:
a = 95.4pm
b.
α = 9
β = 9.81
γ = 9
number of protons: 34
number of neutrons: 45
molar mass: 79
atomic radius: 1.22
period: 4
.
ionization energy (kJ/ mol)
M - M+ 94.9
M+ - M2+ 244
M2+ - M3+ 2974
M3+ - M4+ 4144
M4+ - M5+ 659
M5+ - M6+ 7883
M6+ - M7+ 1499
M7+ - M 8+195
M8+-M9+233
M9+-M1+272
Mohs hardness: 2
Common valence: +4, +6
Isotope: Se-74Se-76Se-77Se. Se-8 Se-82
Elemental substance: selenium
Chemical symbol: Se
Color and state: solid with gray metallic luster
Sound propagation rate: (m/S)
335
Density: 4.81g/cm3;
melting point: 217℃
boiling point: 684.9℃
discoverer: Younce Jacob Bezirius (J? Ns Jakob Berzelius) Discovery date: 1817
Discovery process:
In 1817, Betzelius of Sweden made selenium from the sticky substance at the bottom of the lead chamber of a sulfuric acid plant.
element description:
one of the sparse elements. Among the six known solid allotropes, three crystals (α-single italic, β-single italic, and gray triangular crystal) are the most important. It also exists in the form of three amorphous solids; Red and black amorphous glassy selenium. The former is brittle with a density of 4.26 g/cm 3; The density of the latter is 4.28g/cm3. The first ionization energy is 9.752 electron volts. When selenium burns in the air, it gives off a blue flame and generates selenium dioxide (SeO2). It can also directly react with various metals and nonmetals, including hydrogen and halogen. It cannot react with non-oxidizing acids, but it is soluble in concentrated sulfuric acid, nitric acid and strong alkali. Hydrogen selenide dissolved in water can precipitate many heavy metal ions into particulate selenides [1]. Selenium and metal with oxidation state of +1 can generate two selenides, namely positive selenide (M2Se) and acid selenide (MHSe). The aqueous solution of positive alkali metal and alkaline earth metal selenides will dissolve elemental selenium and generate polyselenium compounds (M2Sen), which is similar to the formation of polysulfides by sulfur.
Source of elements:
It can be recovered from anode mud of electrolytic copper and waste materials such as flue dust and acid mud of sulfuric acid plant.
The main uses of selenium are:
1. Photosensitive materials; For example, the photocopying of dry printing, which makes use of the sensitivity of amorphous selenium to light, can make colored glass containing iron compounds fade. It is also used as paint, enamel, glass and pigments and plastics in ink. It is also used to make photovoltaic cells, rectifiers, optical instruments, photometers, etc. Selenium can be used as photocell and solar cell in electronic industry, and it is also used in television and radio fax. Selenium can color or decolorize the glass. The high-quality signal lens glass contains 2% selenium, and the flat glass containing selenium is used as the heat transmission plate of solar energy and the infrared filter of laser window.
2. catalyst for electrolytic manganese industry; In metallurgy, the amount of selenium in electrolytic manganese industry accounts for a large proportion of the total selenium output in China. In addition, carbon steel, stainless steel and copper alloy containing selenium have good machinability and can be cut at high speed, and the machined parts have smooth surfaces. Alloys of selenium and other elements are used to make low-voltage rectifiers, photovoltaic cells and thermoelectric materials. Selenium can be used as oxidant and catalyst in organic synthesis in the form of compounds, which can be applied in petroleum industry. Adding selenium to rubber can enhance its wear resistance. Selenium and selenium compounds are added into lubricating grease.
3. Essential nutrients for animals and beneficial nutrients for plants. Selenium is an important component of some antioxidant enzymes (glutathione peroxidase) and selenium-p protein in animals and human bodies, which plays a role in balancing the redox atmosphere in vivo. Studies have proved that selenium can improve the immunity of animals, and the research on the influence of selenium on immunity and cancer prevention is a hot issue in this field internationally. Therefore, selenium can be used as a trace additive in animal feed, and trace element fertilizers can be added to plant fertilizers to improve the selenium content of agricultural and sideline products. Selenium has been regarded as an essential trace element for human body. At present, the recommended intake for adults by China Nutrition Society is 5-25 micrograms per day, while the intake of selenium in two-thirds of China is lower than the minimum recommended value. Therefore, China is a region with abundant selenium resources and a large area of selenium deficiency, which is also the reason why international scholars are interested in China.
auxiliary data of elements
Compared with its congener element sulfur, the content of selenium in the earth's crust is much less. Minerals with elemental selenium are extremely difficult to find. At present, the only area in the world where selenium is independently mineralized is located in Enshi, Hubei, China.
Selenium was found in the lead chamber where pyrite was burned to produce sulfuric acid. It was another chemical element discovered in 1817 after Bezirius discovered cerium and thorium. He named this new element selenium. He also found allotropes of selenium. He reduced the oxide of selenium to obtain orange amorphous selenium; Slowly cooling the molten selenium to obtain gray crystal selenium; Let selenide decompose naturally in the air to obtain black crystal selenium.
selenium
sodium selenite
Function and application: In vivo, selenium and vitamin E cooperate to protect cell membrane and prevent oxidation of unsaturated fatty acids. Trace selenium can prevent cancer and protect the liver.
It is mainly used for the prevention and treatment of selenium deficiency patients, endemic disease-Keshan disease, and selenium deficiency patients who rely on intravenous high nutrition for a long time. Because of the toxicity of inorganic selenium salt, it was banned in food and feed in Japan in 1993, and it supported the use of organic forms of selenium such as selenium-containing proteins and amino acids, or selenium-rich agricultural and sideline products with higher safety.
administration and dosage: orally, adults need 5 ~ 5mg per month.
1 ~ 5mg for children.
each sodium selenite tablet contains 1 mg of sodium selenite (equivalent to 457 μ g of selenium), and adults over 11 years old take 2 tablets each time.
For children aged 2-4, take half a tablet once a day; 5 years old, take 1 tablet each time; Side effects: taking too much selenium can cause poisoning, and the maximum safe dose per day is 4 μg g.
the function of selenium:
the function of selenium is broad, as detailed in the following aspects, but its principle is mainly two: first, it constitutes antioxidant enzymes in vivo, which can protect cell membranes from oxidative damage and maintain their permeability; Second, Se -P protein can chelate toxic substances such as heavy metals and reduce the toxicity of toxic substances.
Selenium is called "the king of cancer prevention" by scientists (formerly known as "the king of cancer prevention")
Scientific research has found that the level of blood selenium is closely related to the occurrence of cancer. A large number of survey data show that the selenium content in food and soil in a region is directly related to the incidence of cancer. For example, if the selenium content in food and soil in this region is high, the incidence and mortality of cancer will be low, on the contrary, the incidence and mortality of cancer in this region will be high. Facts show that selenium is closely related to the occurrence of cancer. At the same time, the scientific community also recognizes that selenium has the function of preventing cancer and is the "king of cancer prevention" of trace elements in human body.
Professor Clark from the Cancer Center of the University of Arizona conducted a 13-year controlled trial on 1312 cancer patients. The results showed that the death rate of cancer decreased by 5% and the total incidence of cancer decreased by 37%, including lung cancer by 46%, intestinal cancer by 58% and prostate cancer by 63%.
In 23, the US Food and Drug Administration (FDA) clearly stated that "selenium can reduce the risk of cancer" and "selenium can produce anticancer effect in human body".
In China, selenium has been written into the chemistry textbook (page 96 of the second volume of grade 9) and the medical textbook of colleges and universities (page 262 of trace elements and health), "Selenium can inhibit the growth of cancer cells and the synthesis of DNA RNA and protein, inhibit the transcription of oncogenes and interfere with the metabolism of carcinogens".
Antioxidant effect:
Selenium is a component of glutathione peroxidase (GSH-Px), and each mole of GSH-Px contains 4 grams of atomic selenium. This enzyme catalyzes the redox reaction between reduced GSH and peroxide, so it can play an antioxidant role and is an important free radical scavenger (5-5 times that of vitamin E). In vivo, GSH-Px and vitamin E have different antioxidant mechanisms, and they can complement each other and have synergistic effects.
It is scientifically confirmed that due to the high antioxidant effect of selenium, proper supplementation can prevent organ aging and pathological changes, delay aging, enhance immunity, resist diseases, resist toxic heavy metals, alleviate the side effects of radiotherapy and chemotherapy, and prevent cancer.
Enhance immunity:
Organic selenium can scavenge free radicals, eliminate toxins, resist oxidation, effectively inhibit the production of lipid peroxide, prevent blood clots, remove cholesterol and enhance human immune function.
Prevention of diabetes:
Selenium is the active component of glutathione peroxidase, which can prevent the oxidative damage of islet β cells, make them function normally, promote sugar metabolism, reduce blood sugar and urine sugar, and improve the symptoms of diabetic patients.
Prevention of cataracts:
The retina is easily damaged due to more exposure to computer radiation. Selenium can protect the retina, enhance the smoothness of vitreous body, improve vision and prevent cataracts.
Prevention of cardiovascular and cerebrovascular diseases:
Selenium is an important element to maintain the normal function of the heart, and it can protect and repair the heart. The decrease of human blood selenium level will lead to the decrease of the function of scavenging free radicals in the body, resulting in the increase of harmful substance deposition, the increase of blood pressure, the thickening of blood vessel wall, the decrease of vascular elasticity, the slow blood flow and the decrease of oxygen delivery function, thus inducing the increase of the incidence of cardiovascular and cerebrovascular diseases. However, scientific selenium supplementation has a good effect on preventing cardiovascular and cerebrovascular diseases, hypertension and arteriosclerosis.
Prevention of Keshan disease, Kaschin-Beck disease and arthritis:
Selenium deficiency is the main cause of Keshan disease, Kaschin-Beck disease and two endemic diseases. Selenium supplementation can prevent bone marrow lesions and promote repair, while promoting disulfide bonds against metal elements to detoxify in protein synthesis. It has good preventive and therapeutic effects on patients with these two endemic diseases and arthritis.
Detoxification and detoxification:
Selenium has a strong binding force with metals, which can resist the toxicity of cadmium to kidneys, gonads and central nervous system. Selenium combines with mercury, lead, tin, thallium and other heavy metals in the body to form a metal selenium protein complex to detoxify and detoxify.
Prevention and treatment of liver diseases and protection of liver:
After 16 years of epidemiological investigation in high-incidence areas of liver cancer, Chinese medical expert Yu Shuyu found that the blood selenium content of residents in high-incidence areas of liver cancer was lower than that in low-incidence areas of liver cancer, and the incidence of liver cancer was negatively correlated with the blood selenium level. She confirmed to 13, residents in Qidong County, Jiangsu Province that selenium supplementation can reduce the incidence of liver cancer by 35% and the incidence of people with a family history of liver cancer by 5%.
To sum up, "selenium" is essential to human body and cannot be made by ourselves. Therefore, the World Health Organization recommends that 2 μg selenium be supplemented every day, which can effectively prevent the high incidence of many diseases. Dr. Baboia Lola, a world nutritionist and president of the Biochemistry Society, said: "Selenium" is the most important mineral nutrient to prolong life span, which is reflected in its comprehensive protection of human body. We should not think of it only when we are sick.
absorption and metabolism of selenium, the total amount of selenium in human body is 6~2 mg. Selenium is distributed in all tissues, organs and body fluids, with the highest concentration in kidney. It mainly exists in the form of complex of selenium and protein in tissues. Selenium is mainly absorbed in the small intestine, and the absorption rate of selenium in food is 6%~8%. Most of the selenium absorbed into the body by the intestine is excreted by urine after metabolism. Urine selenium is a good index to judge the profit and loss of selenium in human body. Other ways of selenium excretion are feces and sweat. The absorption, transport, discharge, storage and distribution of selenium in the body will be affected by many external factors. Mainly the chemical form and quantity of selenium in diet. In addition, gender, age, health status, and the presence of compounds such as sulfur, heavy metals and vitamins in food also have an impact. Animal experiments show that selenium is mainly absorbed in duodenum, slightly absorbed in jejunum and ileum, but not in stomach. Selenium excreted in urine accounts for 5%-6% of selenium excretion. When high dietary selenium is ingested, the urinary selenium excretion will increase, otherwise it will decrease, and the kidney plays a regulatory role.
Some foods contain high selenium, such as seafood, edible fungi, meat, eggs, broccoli, garlic and other foods. Nutritionists also advocate supplementing organic selenium with selenium-enriched foods, such as selenium-enriched rice, selenium-enriched eggs, selenium-enriched mushrooms and selenium-enriched foods.