What do we know about selenium? At school chemistry lessons, we were told that selenium is a chemical element, we could solve various chemical equations and observe reactions with its participation. But there are so many elements in the periodic table that it is impossible to cover the entire amount of information. Therefore, everything is stated quite briefly.
In this article, you can get acquainted with the element called "selenium" in detail. What is it, what are its properties, where in nature can this element be found and how is it used in industry. In addition, it is important to know what effect it has on our body.
What is selenium
Selenium (element Selenium) is a chemical element, an analogue of sulfur, which belongs to the 16th group (according to the earlier classification - to the 6th) of the periodic table. The atomic number of the element is 34, and the atomic mass is 78.96. The element exhibits predominantly non-metallic properties. In nature, selenium is a complex of six isotopes that usually accompanies sulfur. That is, it is found in places where sulfur is mined. So, the mysterious selenium -what is it and why is it so valuable? It has many useful properties.
The history of the discovery of selenium
This chemical element was discovered by the Swedish chemist and mineralogist Jöns Jakob Berzelius in 1817.
In the scientific literature there is a story of the discovery of the mineral, told by the scientist himself.
He says that at that time he, along with another scientist named Johan Gottlieb Gan (who became famous as the discoverer of manganese and studied its properties), was researching a method for producing sulfuric acid in the city of Gripsholm.
In the course of laboratory experiments in sulfuric acid, red precipitates were found with an admixture of a light brown hue of the substance. When interacting with a blowpipe, a light rare smell emanated from sedimentary materials and a lead bead was formed. Berlin scientist Martin Klaproth argued that the presence of a characteristic odor indicates the presence of tellurium. A colleague of Berzelius also noted that in the mines where this sulfur for acid is mined (in Falun), a similar smell is also felt.
Hoping to find a rare, recently discovered metal (tellurium) in solution, scientists began to study the sediment in more detail, but to no avail. After Berzelius collected all the products that had accumulated over several months of obtaining sulfuric acid by burning sulfur, and also began to explore.
Research has shown that a new, previously unknown element has similar properties to tellurium, but is not. So the periodic table got a new element- selenium.
Origin of element name
The story of the origin of the name of the new element is quite interesting. The periodic table of Mendeleev defines the new element as Selenium (Se). It got its name from the name of our natural satellite.
Initially, in Russian publications, the element was called "selenium" (in the tenth years of the XIX century). Later, after 1835, the name "selenium" was adopted.
Properties of selenium
Selenium formula – Se. The melting point of the substance is 217 (α-Se) and 170–180 degrees Celsius (β-Se), and it boils at a temperature of 6850.
The oxidation states that selenium exhibits in the reactions: (-2), (+2), (+4), (+6), it is resistant to air, oxygen, water, hydrochloric acid and dilute sulfuric acid.
Dissolves in high concentration nitric acid, aqua regia, dissolves longer in alkaline environment with oxidation.
Shapes of selenium
There are two modifications of selenium:
- Crystalline (monoclinic selenium a- and b-forms, hexagonal selenium g-forms).
- Amorphous (powdery, colloidal and glassy forms of selenium).
Modification of amorphous red selenium. What it is? One of the unstable element modifications. Powdered and colloidal forms of selenium are obtained by reducing the substance from a solution of selenious acid H2SeO3.
Black vitreous selenium can be obtained by heating an element of any modification to a temperature220 degrees Celsius with rapid cooling.
Hexagonal selenium has a gray color. This modification, the most stable thermodynamically, can also be obtained by heating to the melting point with further cooling to a temperature of 180-210 degrees Celsius. It is necessary to withstand such a temperature regime for some time.
Selenium oxide
There are a number of oxides that are formed by the interaction of selenium and oxygen: SeO2, SeO3, SeO, Se 2O5. At the same time, SeO2 and SeO3 are selenium anhydrides (H2SeO 3) and selenic (H2SeO4) acids, which form selenite and selenate s alts. SeO2 (highly soluble in water) and is the most stable.
Interesting experiments on selenium
Before starting experiments with this element, it is worth remembering that any compounds with selenium are poisonous, so it is necessary to take all safety measures, for example, wear protective equipment and conduct reactions in a fume hood.
The color of selenium appears in a pleasant reaction. If sulfur dioxide, which is a good reducing agent, is passed through a flask with selenous acid, the resulting solution will turn yellow, then orange, and finally blood red.
Weak solution will make it possible to obtain amorphous colloidal selenium. If the concentration of selenous acid is high, then during the reaction, a red to maroon powder will precipitate. This willamorphous powdered selenium elemental form.
In order to bring a substance into a glassy state, it is necessary to heat it and cool it sharply. The color will change to black, but the red tint can only be seen if you look at the light.
Crystalline monoclinic selenium will be a bit more difficult to obtain. To do this, take a small amount of red powder and mix with carbon disulfide. It is necessary to connect a reflux condenser to the vessel with the mixture and boil for 2 hours. Soon, a light orange liquid with a slight green tint will begin to form, which will need to be slowly evaporated in a container under filter paper.
Use of selenium
Selenium was first used in the ceramic and glass industries. This is what the "Handbook of Rare Metals" of 1965 edition tells us about.
Selenium is added to the glass mass in order to discolor the glass, to eliminate the greenish tint, which gives an admixture of iron compounds. To obtain ruby glass in the glass industry, a compound of selenium and cadmium (cadmoselite CdSe) is used. In the production of ceramics, cadmoselite gives it a red color and also stains enamels.
A little selenium is used as a filler in the rubber industry and also in the steel industry to make the resulting alloys fine-grained.
Most semiconductor technology is made using selenium. This was the main reason for the increase in the cost of such a substance,like selenium. The price increased from $3.3 to $33 per kilogram in 1930 and 1956 respectively.
The cost of selenium on the world market in 2015 was $68 per 1 kg. Whereas in 2012 a kilogram of this metal cost about $130 per kilogram. Demand for selenium (the price confirms this) is falling due to high supply.
The substance is also widely used in the manufacture of photographic equipment.
Presence of selenium in the human body
Our body contains approximately 10-14 milligrams of this substance, which is concentrated to a greater extent in organs such as the liver, kidneys, heart, spleen, testicles and spermatic cords in men, as well as in the nuclei of cells.
The need of the human body for such a trace element as selenium is low. Only 55-70 micrograms for adults. The maximum daily dose is considered to be 400 micrograms. However, there is a disease called Keshan disease that occurs when this element is deficient. Until about the 60s, selenium was considered a toxic substance that has a negative effect on the human body. But after a detailed study, the opposite conclusions were drawn.
Often, when a pathological selenium content is detected, doctors can prescribe special preparations containing a combination of zinc-selenium-magnesium, substances that, in combination, will make up for its deficiency in the body. Of course, not excluding foods that contain selenium.
Effect on the body
Selenium plays a very important role in the processvital functions of the organism:
- it activates the immune system - "stimulates" leukocytes to more actively affect harmful microorganisms (viruses);
- slows down the aging process in the body;
- reduces the risk of arrhythmia, sudden coronary death or anoxia by slowing cholesterol oxidation;
- accelerates blood flow to the brain, activating mental activity, relieves symptoms of blues and depression (fatigue, lethargy, depression and restlessness);
- slows down the development of cancer cells with antioxidant properties;
- actively selenium fights free radicals;
- when interacting with vitamin E acts as an anti-inflammatory agent.
Of course, one cannot ignore such an important property of a trace element as help in the fight against dangerous viruses: HIV/AIDS, hepatitis, Ebola.
Due to the presence of selenium, the virus lingers inside the cell; substance prevents the spread of the virus throughout the body. But if there is not enough selenium, then its function does not work properly.
Intake of selenium in combination with iodine will help stop the progressive thyroid disease (thyroxine deficiency), and in some cases stimulate the regression of the disease (more often in children).
Also in medicine, selenium is used to prevent diabetes, as it accelerates the consumption of glucose by the body.
The drug with vitamins can be prescribed to pregnant women. It helps to cope with the symptoms of toxicosis, relieve fatigue andwill cheer you up.
Selenium deficiency
Why can there be a lack of such a substance as selenium in the body? What is it - "deficiency of selenium" and how to deal with it? In fact, this is an unpleasant disease, despite the fact that it occurs quite rarely.
It is important to know that the worst enemy of this substance is, of course, carbohydrates - starchy, sweet. In combination with them, selenium is very poorly absorbed by the body and this may result in its deficiency.
What are the signs of a shortage? First of all, it is worth noting that with a deficiency of selenium, efficiency and general mood will decrease.
Lack of selenium weakens the immune system, as a result of which the body becomes more susceptible to various diseases, both mental and physical.
Also, with a deficiency of this substance in the body, the process of assimilation of vitamin E is disrupted.
The main signs of selenium deficiency are: pain in muscles and joints, premature fatigue, anemia, exacerbated diseases of the kidneys and pancreas.
But if you feel any of the symptoms, in no case should you self-medicate with medication. Be sure to visit a doctor and consult about the need to take certain drugs. Otherwise, you can independently cause an excess of selenium, which is worse in some cases. For example, if a person with cancer takes selenium uncontrollably, chemo (chemotherapy) may not work.
Excess selenium
Saturation with selenium also has a negative effect on the body. The main signs of a surplus are: damage to the hair and nails, damage to the teeth, fatigue and permanent nervous breakdowns, loss of appetite, the appearance of dermatitis, arthritis, as well as yellowness and peeling of the skin.
But if you do not work at selenium mining facilities, or do not live near places where this substance is mined, then you can not be afraid of excess selenium in the body.
Foods rich in selenium
Most of all selenium is found in meat and liver - pork, beef, chicken, duck or turkey liver. For example, 100 grams of turkey liver contains 71, and pork - 53 micrograms of selenium.
100 grams of octopus meat contains 44.8 micrograms of selenium. Also, the diet should include foods such as shrimp, red fish, eggs, corn, rice, beans, barley groats and lentils, wheat, peas, broccoli, inactive baker's yeast (treated with water heated to 60 degrees). Don't forget about nuts - pistachios, almonds, walnuts and peanuts also contain selenium, albeit in small amounts.
It is also worth remembering that the substance is lost during food processing, canned food and concentrates contain half as much selenium as fresh food. Therefore, whenever possible, it is necessary to consume as many fresh foods with selenium as possible.
