Occurrence and History

Selenium was discovered in 1817 by J. J. Berzelius (1779-1848) and J. G. Gahn (1745-1818) in the sediment taken from the lead chamber of a sulfuric acid plant in Gripsholm, Sweden. Its name was derived from the Greek word aekr]vr] (selene), for moon, because of its chemical similarity to tellurium-earth. 

Tellurium was the first of the three elements S, Se, and Te to be recognized as an element. F. J. Muller von Reichenstein (ca. 1740-1825) extracted it from a Transylvanian ore and identified it as a new metal in 1782, while M. H. Klaproth (1743-1817) isolated it in 1798 and named it from the Latin tellus, meaning earth. 

The most important minerals of sulfur The most abundant minerals of selenium and tellurium 

Polonium, completing the elements of Group 16, is radioactive and one of the rarest naturally occurring elements (about 3 x 10 % of the Earth s crust). The main natural source of polonium is uranium ores, which contain about lO g of Po per ton. The isotope 210-Po, occurring in uranium (and also thorium) minerals as an intermediate in the radioactive decay series, was discovered by M. S. Curie in 1898. 

Eighteen isotopes of sulfur, 17 of selenium, 21 of tellurium, and 27 of polonium have been registered of these, 4 sulfur, 6 selenium, and 8 tellurium isotopes are stable, while there is no stable isotope of polonium. None of the naturally occurring isotopes of Se is radioactive its radioisotopes are by-products of the nuclear reactor and neutron activation technology. The naturally occurring, stable isotopes of S, Se, and Te are included in Table 1.2. 

Worldwide, the same concentrations are foimd in the air neon is contained with 18 vppm, krypton with 1.14 vppm and xenon with 0.086 vppm (see Table 2.1). Except helium, which occurs enriched in some natural gas sources, all other noble gases are extracted from air. In view of the low concentrations of neon, krypton and xenon large quantities of air have to be processed in order to produce these noble gases on an industrial scale. Radon (Rn) as the heaviest and radioactive noble gas develops from radioactive decay processes and occurs in extremely small traces in the air (6 10 vppm). In medicine, radon serves as a-source in cancer therapy. 

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Chemie, Leipzig-Berlin, 1926, pp. 1-35. History and occurrence of the noble gases. 

The number (1 — golden mean. The significance of this number has been known since ancient times. Livio (2002) gives a very entertaining account of its history and occurrence in art, architecture, music, and nature. 

D.R. Peck, The history and occurrence of phosphorus, in Mellor s Comprehensive Treatise on Inorganic and Theoretical Chemistry, Vol. 8, Supp. 3, Longman, London, 1971. 

Bundschuh, X, Litter, M.I., Parvez, R, Roman-Ross, G., Nicolli, H.B., Jean, J.-S., Liu, C.-W., Lopez, D., Armienta, M.A., Guilherme, L.R.G., Cuevas, A.H., Cornejo, L., Cumbal, L. Toujaguez, R. (2012a) One century of arsenic exposure in Latin America a review of history and occurrence from 14 countries. Science of the Total Environment, 429,2-35. 

Ulrich (1987) Ulrich, D. Egyptian blue and green frit Characterisation, history and occurrence, synthesis PACT 17 (1987) 323-332... 

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