Selenium (Se) Element: Important Uses, Properties, Health Effects

Selenium is a metallic element with the atomic number 34 and is represented by the symbol ‘Se’ in the periodic table. It is classified as a nonmetal and belongs to the p-block of group 16 of the periodic table. It has five allotropic forms that are classified in three groups as red Se, gray Se, and black Se. Selenium is generally categorized as a nonmetal, yet several of its allotropes exhibit metalloid properties.

The element’s natural state is red Se, which appears as a red irregular powdered material. When rapidly heated, it turns black Se. This vitreous allotrope is physically brittle as well as lustrous. Selenium occurs in the minerals crookesite (Cu, Tl, Ag)₂Se and clausthalite (PbSe).

History of Selenium

• Jons Jacob Berzelius and Johan Gottlieb Gahn (both Swedish chemists) discovered selenium for the first time in 1817.
• Both chemists owned a chemistry plant near Gripsholm, Sweden, that produced sulfuric acid by using the lead-based chamber process. Because the pyrite from the Falun Mine left red contaminants in the lead chambers that made the workers sick, it was assumed to be an arsenic compound, and its use in the production of acid was discontinued.
• Berzelius suggested that the contamination was caused by impurities present in recently imported pyrite ores. The chemical has qualities similar to tellurium and sulfur, but it was eventually proven to be a new element.
• However, the absence of tellurium compounds in the Falun Mine minerals necessitate Berzelius to reanalyze the red precipitate, and in 1818 he wrote a letter to Alexander John Gaspard Marcet (Genevan physician) describing a newly discovered element similar to sulfur and tellurium.
• The name for the element Selenium derives from the Greek word “Selene,” which was the name for the Greek goddess of the moon, which was inspired by the mineral Tellurium, which was named after the Greek goddess of the earth.

Occurrence of Selenium

• Selenium accounts for only 0.000005 to 0.000006 percent of Earth’s crust, which makes it one of the planet’s rarest elements, even less common than silver.
• It is rarely found in its elemental form and is only found in a few minerals, such as pyrite, where it partially replaces sulfur.
• Selenium occurs in a variety of inorganic forms, including selenide, selenate, and selenite, however, these minerals are uncommon. Selenium is most typically found as an impurity, replacing a small portion of the sulfur found in numerous metal sulfide ores.
• Selenium is most often extracted from selenide in sulfide ores such as copper, nickel, or lead.
• Typically, industrial selenium extraction includes the extraction of selenium dioxide from copper refining leftovers.
• Around 40% of the selenium in the original ore may concentrate in copper deposited through electrolytic processes. A ton of smelted copper yields around 1.5 kilos of selenium.
• Selenium is extracted worldwide for commercial purposes; Germany, Japan, the United States, China, Belarus, and Russia are the largest producers, among others.

Isotopes of Selenium

selenium has six naturally occurring isotopes that are stable: ⁷⁴Se, ⁷⁶Se, ⁷⁷Se, ⁷⁸Se, ⁸⁰Se and ⁸²Se. Selenium isotopes are primarily used to create medicinal and industrial radioisotopes.

Naturally occurring isotopes

Elemental Properties of Selenium

Physical Properties of Selenium

• Selenium is a fascinating element because of its three main allotropes. Temperature changes are what drive it to switch between multiple forms: red,grey,and black.
• Selenium has an atomic number of 34 and is a semi metal which is a either silvery or red.
• The density of Selenium is: Grey: 4.81 grams per cubic centimeter. Red: 4.39 grams per cubic centimeter.
• Black: 4.28 grams per cubic centimeter.
• When heated swiftly, black Se is created, but grey Se is formed when heated slowly, at roughly 180 °C.
• Selenium is brittle, which means it can be broken into pieces when force is applied to it.
• Selenium is a photoconductor, which implies that it can convert light energy into electrical energy.
• Selenium is a semiconductor, which means it conducts electricity but not as well as conductors.
• Selenium has a distinct odor of decaying horse.

Chemical Properties of Selenium

Selenium is a nonmetal that has the property of being highly reactive. According to the Pauling Scale, selenium has an electronegativity value of 2.55, making it more reactive than hydrogen.

Selenium contains two unpaired electrons in its valence shell, allowing it to easily bind with other elements. It is rarely discovered in its elemental condition.

Chemical Reaction of Selenium

• Reaction of Selenium with Water

Selenium(IV) oxide reacts with water to form selenious acid.

SeO₂(s) + H₂O(l) → H₂SeO₃(aq)

• Reaction of Nickel with Air

In the presence of air, selenium ignites to generate the solid dioxide selenium (IV) oxide, SeO₂.

Se₈ (s) + 8 O₂ (g) → 8SeO₂ (s)

• Reaction of Nickel with the Halogens

Selenium reacts with fluorine, F₂, and burns to form the hexafluoride selenium (VI) fluoride.

Se₈ (s) + 24F₂ (g) → 8SeF₆ (l) [orange]

Selenium reacts with fluorine, F₂, at 0°C to form the tetrafluoride selenium(IV) fluoride.

Se₈(s) + 16 F₂(g) → 8 SeF₄(s) [colourless]

Selenium combines with chlorine (Cl₂) to generate diselenium dichloride, Se₂Cl₂.

Se₈ + 4 Cl₂ → 4 Se₂Cl₂ (l) [orange]

Selenium combines with bromine (Br₂) to generate diselenium dibromide, Se₂Br₂.

Se₈ + 4 Br₂ → 4 Se₂Br₂ (l) [orange]

Selenium also reacts under controlled conditions with the other halogens:

Selenium reacts with chlorine, Cl₂, to form the tetrahalide selenium (IV) chloride.

Se₈(s) + 16 Cl₂(g) → 8 SeCl₄(s)

Selenium reacts with bromine, Br₂, to form the tetrahalide selenium (IV) bromide.

Se₈(s) + 16 Br₂(g) → 8 SeBr₄(s)

Selenium reacts with iodine, I₂, to form the tetrahalide selenium (IV) iodide.

Se₈(s) + 16 I₂(g) → 8 SeI₄(s)

• Reaction of Selenium with Acids

Selenium does not react with dilute non-oxidizing acids.

Uses Of Selenium

Selenium has numerous uses in modern industries which include:

Used In Industries

Selenium is being used in different industries that include the glass-making industry,heat-stabilized pigment industries, the stainless steel industry, the rubber industry, and many more.

Glass making industry: The glass-making industry consumes nearly half of the selenium that is produced. It is added to glass during the manufacturing procedure to negate the green tint caused by the impurities of iron and essentially decolorize it.When added in higher concentrations, selenium gives the glass a ruby-red color

Stainless Steel industry: The addition of selenium to stainless steel, which is tough and difficult to machine, makes it so easily and freely machinable that it can be readily handled on automatic screw machines.

Heat-stable pigment industry: Selenium is commonly found in a variety of heat-stable pigments used in a variety of sectors, including ceramics, enamels, paints, rubber, and polymers. These are resistant to UV rays and contaminants.

Used As Alloys

Lead selenium has a strong tensile strength and conductivity. It is also corrosion resistant, which aids in the prevention of intergranular corrosion. Selenium is one of the most significant energy-critical elements (ECEs), which are essential for power synthesis, storage, and transmission.When mixed with other elements, it produces advantageous alloys such as selenium tellurium alloy and leads selenium alloy, which is employed in a variety of energy-related operations.

Selenium alloy is widely utilized in the production of ammunition, tank linings, pipes, and tubular grids.

Used In Solar Panels and Photoconductors

Selenium is a photovoltaic element, which means it can convert light to electricity. It is utilized in solar panels,(photovoltaic panels), to generate energy using sunlight because of its feature. Thin films of amorphous selenium are utilized in x-ray detectors as photoconductors, capturing x-ray photons and converting them into electric charges.

Used In Batteries

Lithium-selenium (Li-Se) batteries create a good energy storage system in the lithium battery family. These batteries are an excellent substitute for sulfur-containing batteries, and they provide additional benefits such as improved electrochemical performance and electrical conductivity.

Used In Electrical component

For the purpose of converting alternating current (AC) into direct current (DC) in various appliances, selenium rectifiers are utilized. It makes use of selenium as a semiconductor. They serve as current limiters and protect the rectifier in an instance of a short circuit.

Used As A Fertilizer

Selenium is a trace element that increases plant development in a variety of ways and is thought to be useful in boosting food security. To combat selenium depletion, selenium or its derivatives are incorporated into fertilizers as liquids or nanoparticles. Plants can potentially boost output and improve grain or fruit quality if they acquire enough selenium from the soil.

It is also used in anti-dandruff shampoo because of its anti-fungal properties.

Health Effects Of Selenium

Selenium is a rare element that is found in water and several foods. While people only require a trace amount it has some health benefits. Some of the benefits are;

Acts as an antioxidant

It may reduce risk of certain cancer

Helps in mental health

Helps in thyroid health

May protect from heart disease

• Typically, exposure to selenium through the air occurs only at work. It can produce dizziness, tiredness, and mucous membrane irritation. When the level of contamination is extremely high, fluid accumulation in the lungs and bronchitis may ensue.
• A buildup of fluid in the lungs, garlic breath, bronchitis, pneumonitis, bronchial asthma, nausea, chills, fever, headache, sore throat, shortness of breath, conjunctivitis, vomiting, stomach discomfort, diarrhea, and an enlarged liver can all result from excessive selenium fume exposure.
• In some cases, selenium poisoning could be fatal.

Environmental Effects of Selenium

The behavior of selenium in the environment is heavily influenced by its interactions with other compounds as well as the environmental circumstances at a given site and time. Low levels of selenium can end up in soils or water as a result of rock weathering.There is evidence that selenium can accumulate in organisms’ bodily tissues and then be transmitted up the food chain.

Animals that absorb or accumulate exceptionally high levels of selenium can suffer from reproductive failure and birth abnormalities.

Watch out for the video about Selenium.

References

• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
• Magnetic susceptibility of the elements and inorganic compounds, in Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
• Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
• https://www.rsc.org/periodic-table/element/34/selenium
• https://pubchem.ncbi.nlm.nih.gov/compound/Selenium
• https://www.lenntech.com/periodic/elements/se.htm
• https://www.chemicool.com/elements/selenium.html
• Mary Elvira Weeks, The discovery of the elements. VI. Tellurium and selenium, J. Chem. Educ.
• Vivi Ringnes, Origin of the Names of Chemical Elements., J. Chem. Educ.
• Thomas Jefferson National Accelerator Facility – Office of Science Education, It’s Elemental – The Periodic Table of Elements, accessed December 2014.