Sodium selenate is the inorganic compound with the formula , not to be confused with sodium selenite. It exists as the anhydrous salt, the heptahydrate, and the decahydrate. These are white, water-soluble solids. The decahydrate is a common ingredient in multivitamins and

livestock feed Fodder (), also called provender (), is any agricultural foodstuff used specifically to feed domesticated livestock, such as cattle, rabbits, sheep, horses, chickens and pigs. "Fodder" refers particularly to food given to the animals (includin ...

as a source of selenium. The anhydrous salt is used in the production of some glass. Although the selenates are much more toxic, many physical properties of sodium selenate and sodium sulfate are similar.

Production

Sodium selenate is produced by oxidation of selenium, first with

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...

, producing

selenous acid Selenous acid (or selenious acid) is the chemical compound with the formula . Structurally, it is more accurately described by . It is the principal oxoacid of selenium; the other being selenic acid. Formation and properties Selenous acid is a ...

. The selenous acid is neutralized to form sodium selenite. The sodium selenite is

oxidized Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...

in a basic medium

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscous than water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as a dilute solution (3%� ...

to form a

selenate The selenate ion is . Selenates are analogous to sulfates and have similar chemistry. They are highly soluble in aqueous solutions at ambient temperatures. Unlike sulfate, selenate is a somewhat good oxidizer; it can be reduced to selenite o ...

, which is then spray-dried. :Se + 2HNO → HSeO + NO + NO :HSeO + NaCO → NaSeO + HO + CO :NaSeO + HO → NaSeO + HO. It was prepared shortly after the discovery of

selenium Selenium is a chemical element with the symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate between the elements above and below in the periodic table, sulfur and tellurium, ...

by Jöns Jacob Berzelius in 1817.

Industrial uses

Glass manufacturing

One of the earliest applications of sodium selenate was in the

glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...

industry. Selenium produces a red hue in glass. The molten glass is treated with sodium selenate and then

arsenic trioxide Arsenic trioxide, sold under the brand name Trisenox among others, is an inorganic compound and medication. As an industrial chemical, whose major uses include in the manufacture of wood preservatives, pesticides, and glass. As a medication, it ...

to reduce the compound and provide elemental selenium. Sodium selenate is also used as a decolorizing agent in glass production. The red hue it gives glass is complementary to the green hue given by

ferrous oxide Iron(II) oxide or ferrous oxide is the inorganic compound with the formula FeO. Its mineral form is known as wüstite. One of several iron oxides, it is a black-colored powder that is sometimes confused with rust, the latter of which consists of ...

s in the manufacturing process. When used together, the two compound produce a colourless glass.

Pesticide

Sodium selenate is a common ingredient in some insecticides used against

mite Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear e ...

aphid Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A t ...

s, and mealybugs. For most

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...

s, a dose of 10mg/kg is enough to be fatal. It is also used in some fungicides.

Bio-fortification of crops

Sodium selenate is effectively used for bio-fortification of crops hence fortifying food/feed to mitigate selenium deficiency in humans and livestock. It can be applied as foliar spray or via rooting medium e.g. added in fertilizers.

Dietary supplement

Chosen for its selenium content and high solubility, sodium selenate is a common ingredient in over-the-counter vitamin supplements. Selenium is a trace

essential element In the context of nutrition, a mineral is a chemical element required as an essential nutrient by organisms to perform functions necessary for life. However, the four major structural elements in the human body by weight (oxygen, hydrogen, carbon ...

. Sodium selenate and selenite are also common in premix animal feed. Neither compound has demonstrated a difference in the amount of selenium absorbed. The US FDA regulates that animal feed contain no more than 5ppm selenium content. Controversy arose in 2009 when a group of 21 polo horses died from selenium poisoning from an incorrectly mixed dietary supplement.

Toxicology

The US FDA and European Union currently classify sodium selenate as toxic, primarily if ingested or inhaled. Testing on rats showed a dose of 1.6mg/kg to be lethal. A low lethal dose as this places the chemical as being 2 to 3 times more toxic than sodium cyanide. As such, it is extremely toxic and must be handled with care. For a person, this dosage corresponds to 112mg, or, in terms of 200µg pills, 560 pills. Chronic exposure to sodium selenate can cause severe lung, kidney, and liver damage. Overexposure to selenium in the diet leads to a condition known as selenosis. Selenosis occurs at blood levels greater than 100µg/dL. Symptoms include gastrointestinal upsets, hair loss, white blotchy nails, garlic breath odour, fatigue, irritability, and mild nerve damage.

References

{{Sodium compounds Selenates Sodium compounds