Abundance, distribution and extraction

None of the three elements is particularly abundant in the earth s crust though several minerals contain them as major constituents. As can be seen from Table 13.1, arsenic occurs about halfway down the elements in order of abundance, grouped with several others near 2 ppm. Antimony has only one-tenth of this abundance and Bi, down by a further factor of 20 or more, is about as unabundant as several of the commoner platinum metals and gold. In common with all the post-transition-element metals. As, Sb and Bi are chalcophiles, i.e. they occur in association with the chalcogens S, Se and Te rather than as oxides and silicates. 

Arsenic minerals are widely distributed throughout the world and small amounts of the free element have also been found. Common 

Until the late H)80s the USA was the principal supplier of while arsenic (i e. AsiOi) but it now relies entirely on imports. World production has been steady for many years at about 52fX10 tonnes pa and the main producers are France (lOOOOtpa), Sweden (lOOOOtpa). Russia (SOOOtpa) and Chile (VOOOlpa). The price of refined oxide was about 480 per tonne in 1989 and commercial grade As metal (99%+) was about 2.20/kg in 1990. Fligh purity As (99.99%+) was 45 (Xl/kg and zone-refined semiconductor grade even more expensive. 

The main use of elemental As is in alloys with Pb and to a lesser extent Cu. Addition of small concentrations of As improves die properties of Pb/Sb for storage batteries (see below ), up to 0.75% improves the hardness and castabilily of type metal, and 0 5-2.0% improves the sphericity of Pb ammunition. Automotive body solder is Pb (92%),, Sb (5 0%), Sn (2.5%) and As (0.5%). Intcrnxitallic compounds with Al, Ga and In give the 111-V semiconductors (p 255) of which GaAs and InAs are of particular value for light-emitting diodes (LEDs), tunnel diodes, infrared emitters, laser windows and Hall-effect devices (p. 258). 

Tlie use of As comjiounds as herbicides and pest controls in agriculture is now considerably restricted because of environmental considerations though arsenic acid itself. AsO(OH).v, is still used in die formulation of wood preservatives. The oxide is widely used to decolorize glass. 

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World annual production of bismuiii and its compounds has hovered around 4000 tonnes of contained Bi for many years and a similar amount of secondary (refinety) Bi i.s also produced. Production has been dominated by China, Japan, Pern, Bolivia, Mexico, Canada, USA and Australia which, between them, account for almost of all supplies. I+iccs for the free dement have fluctuated wildly since ihe 1970s, from , 4.tX)/kg to 44.0fWlcg at die end of 1990 it was 6..30/kg. Consumption of Ihc tneial and ils compounds has also been unusual, usage in the USA dropping by a factor of 2 from 1973 to 1975, for example. I he main uses arc in pharmaceuticals, fusible alloys (including (ype inelal, p. 547), and metallurgical additives. 

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The tannins are synthesized by plants and are abundantly distributed in many different forms of plant life. Common sources of tannins include for example, the bark, leaves, fruit and roots of many plants most tannins, however, have been and are still derived from the bark of a few trees and shrubs, such as oak, chestnut, hemlock, mangrove, quebracho, and wattle, from which they are generally extracted with water. 

The alkaloids were best isolated from the ethanol extract of the plant material, partially fractionated by counter-current distribution, and subsequently purified by preparative chromatography. Of the 11 known Cephalotaxus alkaloids (105-115 in Figs. 8 and 9), cephalotaxine (105a) is ubiquitous and the most abundant (up to 64% of the total alkaloid extract) in all species examined. C. wilsoniana Hay., which yields only minor quantities of cephalotaxine, is the exception, however it is rich in Homoerythrina alkaloids,... 

Gamma-ray, X-ray, optical and infrared line spectroscopy of SNe and SNRs have been used to observe nucleosynthesis and the abundance distribution of elements freshly synthesized (both radioactive isotopes and stable decay products) and to extract dynamical information about the explosion. In particular the radioactive isotopes provide unique tracers of nucleosynthetic processes (what, where and how much) and its related dynamics. The best examples are the observations of gamma-ray lines in supernovae, but X-ray line spectroscopy of decay products of radioactive nuclei have also been attempted, and specific elements in numerous SNRs and a few SNe identified. 

As the parent of actinium in this series it was named protoactinium, shortened in 1949 to protactinium. Because of its low natural abundance its chemistry was obscure until 1960 when A. G. Maddock and co-workers at the UK Atomic Energy Authority worked up about 130g from 60 tons of sludge which had accumulated during the extraction of uranium from UO2 ores. It is from this sample, distributed to numerous laboratories throughout the world, that the bulk of our knowledge of the element s chemistry was gleaned. 

The study of biochemical natural products has also been aided through the application of two-dimensional GC. In many studies, it has been observed that volatile organic compounds from plants (for example, in fruits) show species-specific distributions in chiral abundances. Observations have shown that related species produce similar compounds, but at differing ratios, and the study of such distributions yields information on speciation and plant genetics. In particular, the determination of hydroxyl fatty acid adducts produced from bacterial processes has been a successful application. In the reported applications, enantiomeric determination of polyhydroxyl alkanoic acids extracted from intracellular regions has been enabled (45). 

Several factors indicate that the amino acids detected in all of these carbonaceous chondrites are indigenous and that they must have originated abiotically. First, the presence of protein and non-protein amino acids, with approximately equal quantities of D and L enantiomers points to a nonbiological origin and precludes terrestrial contamination. In addition, the non-extractable fraction of the Murchison is significantly heavier in 13C than terrestrial samples. Finally, the relative abundances of some compounds detected resemble those of products formed in prebiotic synthesis experiments. The aliphatic hydrocarbons are randomly distributed in chain length, and the C2, C3, and C4 amino acids have the highest concentrations (i.e., the most easily synthesized amino acids with the least number of possible structures are most abundant) [4]. 

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