Arsenic: its chemistry, its occurrence in the earth and its release into industry and the environment
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Arsenic: its chemistry, its occurrence in the earth and its release into industry and the environment Ian D. Rae1 Received: 1 April 2020 / Accepted: 12 September 2020 © Springer Nature Switzerland AG 2020
Abstract Arsenic is widespread in the environment where it occurs combined with metals and sulfur and as secondary minerals in combination with oxygen. Its atomic structure allows it to be trivalent or pentavalent, and its properties lead to its classification as a metalloid in the periodic classification of the elements. Arsenic trioxide is a by-product of the smelting of metal sulfide ores and can contaminate other industrial products such as sulfuric acid. Arsenic from mineral deposits can also be solubilized and be present in groundwater, where it presents a health and environmental hazard, and in the sea, where it can be taken up by marine animals in the form of arseno-betaines. Although arsenates resemble phosphates in their chemistry, and can be transported with them in living systems, arsenate cannot replace phosphate in plant and animal metabolism as has sometimes been postulated. Keywords Arsenic · Metalloid · Orpiment · Realgar · Mining · Cobalt blue · Sulfuric acid · Arsenobetaine · Phosphate metabolism
Introduction Despite being one of the elements that has high recognition among non-scientists, arsenic is not abundant in the earth’s crust. A range of concentrations has been reported because of variations in the composition of the crust at different depths and geographic locations, but an average of 1.8 mg/kg is the accepted value [1]. This makes it the 52nd most abundant element in the earth’s crust, just behind wellknown elements such as uranium (#48), bromine (#49) and tin (#50). Arsenic has atomic number 33 and exists in nature as a single isotope having 32 neutrons and atomic mass 74.922 Da. It is 1 of only 21 mononuclidic elements. Balancing the charge on the arsenic nucleus are 33 electrons that are arranged in four shells with occupancies designated by superscripts as 1 s22s2p63s23p6d104s2p3. The atomic structures of the atoms are covered in any comprehensive textbook of general or inorganic chemistry of the sort prescribed for undergraduate learning [2, 3]. The five electrons in the * Ian D. Rae [email protected] 1
School of Chemistry, University of Melbourne, Melbourne, VIC 3030, Australia
outer shell of the arsenic atom, a configuration that is also present in the atoms of other members of the vertical group (N, P, Sb, Bi), account for the tri- and pentavalency, most of which is expressed in covalent links, either directly as in AsCl3 or with oxygen in the trivalent anions arsenite (AsO33−) and arsenate (AsO43−).
Arsenic in the periodic classification of the elements Co-discoverers of the periodic system, Dmitri Mendeleev, Julius Lothar Meyer, William Odling and John Newlands, all placed arsenic in a group with nitrogen and phosphorus already in the 1860s, indicating that they shared chemical properties [4]. A portion of today’s version of the periodic table is
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