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 familiarize yourself in detail with an element called "selenium". What is it, what are its properties, where in nature you can find this element and how it is used in industry. In addition, it is important to know what effect it has on our body.
What is selenium?
Selenium (Selenium element) is a chemical element, an analogue of sulfur, which belongs to the 16th group (according to an 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 consisting of six isotopes, usually accompanied by sulfur. That is, it is found in places of sulfur production. So, the mysterious selenium - what is it and why is it so valuable? It has many useful properties.
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 history of the discovery of the mineral, told by the scientist himself.
He says that at that time he, together with another scientist named Johan Gottlieb Gan (who became famous as a pioneer of manganese and studied its properties), conducted research on the method of producing sulfuric acid in the city of Gripsholm.
During laboratory experiments in sulfuric acid, sediments of a red substance mixed with a light brown hue were found. When interacting with the soldering tube, a slight rare smell emanated from the sedimentary materials and a lead kinglet formed. Berlin scientist Martin Klaprot argued that the presence of a characteristic odor indicates the presence of tellurium. A colleague of Berzelius also noted that a similar smell is also felt in the mines where this sulfur for acid is mined (in Falun).
In the hope of finding a rare recently discovered metal (tellurium) in solution, the scientists began a more detailed study of the precipitate, but it was all in vain. After Berzelius collected all the products that accumulated over several months of sulfuric acid production by burning sulfur, and also began to research.
Studies have shown that a new, previously unknown element has similar properties to tellurium, but it is not. So the periodic table received a new element - selenium.
Origin of item name
The history of the origin of the name of the new element is quite interesting. The periodic table defines the new element as Selenium (Se). It got its name from the name of our natural satellite.
Initially, in Russian editions the element was called "selenium" (in the tenths of the XIX century). Later, after 1835, the name "selenium" was adopted.
Selenium Properties
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 685 0 .
The oxidation state that selenium manifests in the reactions: (-2), (+2), (+4), (+6), it is resistant to air, oxygen, water, hydrochloric acid and dilute sulfuric acid.
It can be dissolved in high concentration nitric acid, “aqua regia”, it dissolves for a longer time in an alkaline environment with oxidation.
Selenium Forms
There are two modifications of selenium:
- Crystalline (monoclinic selenium of a- and b-forms, hexagonal selenium of g-form).
- Amorphous (powdery, colloidal and vitreous forms of selenium).
Modification of amorphous red selenium. What it is? One of the unstable modifications of the element. Powdered and colloidal forms of selenium are obtained by reducing the substance from a solution of selenic acid H 2 SeO 3 .
Black glassy selenium can be obtained by heating an element of any modification to a temperature of 220 degrees Celsius with rapid cooling.
Hexagonal selenium is gray. This modification, the most stable thermodynamically, can also be obtained by heating to the melting temperature 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: SeO 2 , SeO 3 , SeO, Se 2 O 5 . Moreover, SeO 2 and SeO 3 are anhydrides of selenic (H 2 SeO 3 ) and selenic (H 2 SeO 4 ) acids, which form salts of selenite and selenate. Selenium oxide SeO 2 (readily 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 you need to take all safety measures, for example, wear protective equipment and carry out reactions in a fume hood.
The color of selenium manifests itself during a pleasant reaction to the eye. If sulfur dioxide gas, which is a good reducing agent, is passed through a flask with selenic acid, the resulting solution will turn yellow, then orange, and eventually blood red.
A weak solution will make it possible to obtain amorphous colloidal selenium. If the concentration of selenic acid is high, then the powder will precipitate from red to maroon in the course of the reaction. It will be an amorphous powdery selenium of elemental form.
In order to bring the 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 be seen only if you look at the clearance.
Crystalline monoclinic selenium will be a little more difficult to obtain. To do this, take a small amount of red powder and mix with carbon disulfide. A reflux condenser must be connected to the vessel with the mixture and boiled 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 the filter paper.
Application of selenium
For the first time, selenium began to be used in the ceramic and glass industries. This is what the Rare Metals Handbook of the 1965 edition tells us.
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 paints enamels.
A little selenium is used as a filler in the rubber industry, as well as in the steel industry, so that the resulting alloys have a fine-grained structure.
Most semiconductor technology is manufactured using selenium. This was the main reason for the increase in the cost of such a substance as selenium. The price increased from 3.3 to 33 dollars per 1 kilogram in 1930 and 1956, respectively.
The cost of selenium on the world market in 2015 amounted to 68 dollars per 1 kg. Whereas in 2012, a kilogram of this metal cost about $ 130 per kilogram. Demand for selenium (confirmation of price) is falling due to high supply.
The substance is also widely used in the manufacture of photographic equipment.
The presence of selenium in the human body
Our body contains approximately 10-14 milligrams of this substance, which is concentrated more in organs such as the liver, kidneys, heart, spleen, testicles and spermatic cord 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 400 micrograms. Nevertheless, 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 identifying the pathological content of selenium, doctors can prescribe special preparations containing a combination of zinc-selenium-magnesium, substances that in a complex will make up for its deficiency in the body. Of course, not excluding products that contain selenium.
Effects on the body
Selenium has a very important role in the body's vital functions:
- it activates the immune system - “stimulates” white blood cells for a more active effect on harmful microorganisms (viruses);
- slows down the aging process in the body;
- reduces the risks of arrhythmias, sudden coronary death or oxygen starvation due to the slowdown of cholesterol oxidation;
- accelerates blood flow to the brain, activating mental activity, relieves symptoms of spleen and depression (fatigue, lethargy, depression and anxiety);
- inhibits the development of cancer cells, possessing antioxidant properties;
- Selenium actively fights free radicals;
- when interacting with vitamin E, acts as an anti-inflammatory agent.
Of course, one cannot ignore such an important trace element property as helping in the fight against dangerous viruses: HIV / AIDS, hepatitis, Ebola.
Due to the presence of selenium, the virus is retained within the cell; the substance prevents the spread of the virus throughout the body. But if selenium is not enough, then its function does not work properly.
Taking selenium in combination with iodine will help stop a progressive thyroid disease (lack of thyroxine), and in some cases it stimulates the regression of the disease (more often in children).
Also in medicine, selenium is used to prevent diabetes, because it accelerates the consumption of glucose by the body.
The drug with vitamins can be prescribed for pregnant women. It helps to cope with the symptoms of toxicosis, relieve fatigue and cheer up.
Selenium deficiency
Why may there be a shortage of a substance such as selenium in the body? What is “selenium deficiency” 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 - flour, sweet. In combination with them, selenium is very poorly absorbed by the body and this may cause its lack.
What are the signs of deficiency? First of all, it is worth noting that with a deficiency of selenium, working capacity 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 the muscles and joints, premature fatigue, anemia, kidney and pancreas diseases worsen.
But if you feel any of the symptoms, in no case should you engage in medical self-medication. It is imperative 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 an oncological disease takes uncontrolled intake of selenium, chemistry (chemotherapy) may not work.
Excess selenium
Oversaturation with selenium also produces a negative effect on the body. The main signs of surplus are: damage to hair and nails, tooth damage, fatigue and permanent nervous disorders, 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 production facilities, or do not live near the places where this substance is extracted, then you can not be afraid of excess selenium in the body.
Selenium-rich foods
Most 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 products such as shrimp, red fish, eggs, corn, rice, beans, barley groats and lentils, wheat, peas, broccoli, inactive baker's yeast (processed with water heated to 60 degrees). Do not forget about nuts - pistachios, almonds, walnuts and peanuts also contain selenium, albeit in small quantities.
It is also worth remembering that when processing products, the substance is lost, canned foods and concentrates contain half as much selenium as fresh products. Therefore, whenever possible, it is necessary to consume as many fresh products with selenium content as possible.