Laval University

From the SelectedWorks of Fathi Habashi

July, 2017

Two Hundred Years SeleniumFathi Habashi

Available at: https://works.bepress.com/fathi_habashi/217/

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Selenium was discovered in 1817 in the red mud accumulated at the bottom of a sulfuric acid lead chamber plant in which Berzelius

(Fig. 1) was a partner. The acid was manu-factured from pyrite from Falun – the old mine in Sweden (Figure 2). Berzelius named the new element after Selene the goddess of the Moon (Figure 3) in anal-ogy with tellurium meaning Earth which was discovered earlier in 1782 in a gold ore in Transylvania in the Austrian Empire. The element was first mistaken for tellu-rium but on careful examination Berzelius

found that it was a new element. When he digested the mass with aqua regia at mod-erate temperature was able to isolate the new element. He reported that selenium had properties between sulfur and telluri-um. Later he investigated the Falun pyrite and found that it contained 0.15% seleni-um. At present all lead chamber acid plants are shut down and pyrite is no longer used in making sulfuric acid since all plants are using elemental sulfur. Selenium is known in two varieties: grey and red (Figure 4). At present it is a by-product of the extraction of copper and nickel from their sulfide ores. It is concen-trated in the anodic slimes of electrorefin-

ing of these metals to 2 - 15% from which it is obtained by a long processing.Red amorphous selenium is produced by reducing selenous acid with sulfur diox-ide, by crystallization from solution, or by quenching of selenium vapor or molten selenium. It consists of Se8 rings (Figure 5) similar to elemental sulfur, soluble in carbon disulfide giving red solutions from which selenium can be crystallized. Red selenium is an electrical non-conductor. On heating at 100-150°C is transformed into the stable, grey, hexagonal metal-like form in an exothermic reaction (Figure 6, Table 1). In the vapor phase, red sele-nium exists mainly as Se8 rings. At higher temperature these decompose into smaller units, eventually forming Se2 molecules.The grey, hexagonal crystals have metal-lic appearance, and is composed of helical chains which melts at 220°C. It is a semi-conductor whose electrical conductiv-ity increases by a factor >1000 under the influence of light (photoconductivity). The electrical conductivity is strongly depend-

ent on purity. Thus, the conductivity of selenium, including the poorly conducting amorphous form, can be increased consid-erably by traces (a few parts per million) of halide ions or by alloying elements such as tellurium or arsenic. Because the electri-cal properties are sensitive to the presence of crystal defects, the purity of selenium, which can be deliberately controlled by doping or alloying with other elements, plays an important role in its use in electri-cal and electronic applications. The relative abundance in Earth’s crust is 9 x 10-6 %.In its compounds, selenium exhibits the oxidation states -2, +4, and +6. Selenium burns in air to form selenium dioxide, which has the smell of rotten radishes. Selenium is oxidized by nitric acid to sele-

Two Hundred Years Selenium Habashi, F. (1)

Beside selenium discovered in 1817, Jöns Jacob Berzelius (1779-1848) discov-ered cerium in 1814, thorium in 1815, and silicon in 1823. Together with his stu-dent Johan August Arfwedson (1792-1841) he discovered lithium in 1817 and played an important role in the discovery of vanadium.

Fig. 1: Jöns Jacob Berzelius (1779-1848)

Fig. 2: Falun Mine in Sweden

Fig. 4: Grey and red selenium

Fig. 3: A representation of Selene the god-dess of the Moon

Fig. 5: Structure of red selenium [top] and grey selenium [bottom]

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nous acid. Hot, concentrated sulfuric acid dissolves selenium, giving a green color and forming polymeric selenium cations, for example:

Se8 + 3H2SO4 → Se82+ + 2HSO4

- + SO2 + 2H2O

With chlorine, vigorous oxidation to selenium tetrachloride occurs. Selenium reacts with electropositive elements (e.g., many metals) to form selenides and is therefore strongly corrosive, especially at high temperature. With hydrogen, the tox-ic gas hydrogen selenide, H2Se, is formed. Although selenium is an essential trace ele-ment, it is toxic if taken in excess.

Berzelius

Berzelius studied medicine at the Univer-sity of Uppsala and wrote a dissertation in

1802 on galvanotherapy inspired by Volta’s invention of the galvanic pile two years ear-lier. In 1807, he was appointed professor of medicine and pharmacy (later chemistry and pharmacy) in Stockholm, and in 1819 he was appointed secretary of the Academy of Science. There he obtained a laboratory, a library, and an apartment in the Acad-emy building. His students discovered a number of metals: W Heinrich Rose discovered niobium in

1820W Carl Gustaf Mosander discovered lan-

thanum, didymium [which was resolved later into praseodymium, neodymium, samarium, and europium by others], erbium, and terbium in the period 1824-1831

Prominent Berzelius’ students and co workers are shown in Table 2.

Writings

Berzelius’ work in chemistry was remark-able. He was the first to determine accu-rately the atomic weight of the elements. He systematized the chemical language by introducing the chemical symbols for the elements and compounds that we use today. He invented the concepts of cataly-sis and isomerism. He wrote an important textbook of chemistry in Swedish (Figure 7) which was translated into German and then revised and updated into five editions from Swedish manuscripts. Beside these, unauthorized editions appeared in Stutt-

gart (1832-33) in three volumes (1,505 pag-es) and in Quedlinburg (1833-43) in four volumes (2,327 pages). Translations into other languages were also published.Berzelius founded and edited a chemi-cal journal and published a summary of

Fig. 6: Red amorphous selenium is transformed into crystalline variety on heating

Table 1: Crystalline modifications of sele-nium

Table 2 - Prominent Berzelius’ students and coworkers

Red GreyAppearance Red powder Grey

metallicForm ---- Hexagonal

Density 4.42 4.80Melting

point144°C 220.2°C

Solubility in CS2

Slightly soluble

Insoluble

Fig. 7: Berzelius book in Swedish Lärbok i Kemien in six volumes [1808-1830]

Fig. 8 - 10: Berzelius’ Museum

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progress in chemistry each year in the form of Annual Reports which were translated in German. His scientific correspondence with chemists of the time, published after his death in numerous volumes, filled thousands of pages. He also kept a diary of his travels which was published in a 430-page volume.

Legacy

Berzelius’ laboratory equipment, speci-mens, and other personal effects are kept in a Museum maintained by the Academy in Stockholm (Figures 8-14). A statue for

him were erected in Stockholm (Figure 15) in addition to postage stamps (Figure 16) and medals in his honour (Figure 17).

Occurrence of selenium

Ignaz Domeyko discovered in Chile in 1861 a silver-copper mineral in Cacheuta containing 22.4 to 30.8% Se now known as cacheutite. Other minerals containing selenium were later discovered.

Uses

In 1873, the British electrical engineer Willoughby Smith (1828-1891) (Figure 18) found that the electrical resistance of grey selenium was dependent on the ambient light. This led to its use as a cell for sens-ing light. The first commercial products were developed by Werner Siemens in the

mid-1870s. Selenium transmits an electric current proportional to the amount of light falling on its surface. This phenomenon was used in the design of light meters and similar devices. Selenium’s semiconductor properties found numerous other applica-tions in electronics. The development of selenium rectifiers began during the early 1930s.

References- F. Habashi, The Story of Metals - Volume 2,

Métallurgie Extractive Québec 2015. Distrib-uted by Laval University Bookstore, www.zone.ul.ca

- F. Habashi, Chemistry and Metallurgy in the Great Empires, Métallurgie Extractive Québec, Québec City, Canada 2009. Distrib-uted by Laval University Bookstore, www.zone.ul.ca

- M. E. Weeks, The Discovery of the Elements, Journal of Chemical Education, Easton, PA 1956

(1) Fathi Habashi, Department of Mining, Metallurgical, and Materials Engi-neering, Laval University, Quebec City, Canada

Fig. 16: Berzelius stamps in Sweden

Fig. 17: Berzelius medal

Bild 6: Sandwich 1 (unten), Qualität schlecht (Tabelle 2).

Fig. 11 - 13: Chemicals in Berzelius Museum

Fig. 15: Berzelius statue in Stockholm

Fig. 18: Willoughby Smith (1828-1891)Fig. 14: Chemicals prepared by Berzelius

Se2017 – 200 Years of Selenium Reserch

An international selenium conference will be held at Karolinska Institutet in Stockholm on August 13-17, 2017. The conference will cover all fields of current selenium research, with a special focus on biology, medicine, biomedicine and the environment.

www.se2017.se