Elements occurrence

B. Jezowska-Trzebiatowska, S. Kopacz and T. Mikul-SKl, The Rare Earth Elements, Occurrence and Technology, Elsevier, Amsterdam, 1990, 540 pp. 

Comparative Media Evaluation. Table 4 is a summary of trace element occurrences for water, sediment, fish and rocks in Oregon as compared with concentrations measured elsewhere in the world. Details of the comparison parameters are provided in the footnotes to Table 4. The table indicates that no excessively high concentrations of potentially toxic trace elements exist in Willamette River water relative to "uncontaminated sites. 

Table 4. Summary of Trace Element Occurrences for Water, Sediment, Fish and Rocks in Oregon and Elsewhere with Comparisons...

BGS (British Geological Survey) (1989) Trace Element Occurrence in British Groundwaters. Research Report SD/89/3, British Geological Survey (BGS), Key worth. 

A final section draws attention to the human alteration of river chemistry during the past hundred years, particularly for Na, K, Cl, and it is important to differentiate anthropogenic from natural inputs. Trace element occurrence is covered by Gaillardet (see Chapter 5.09). 

Antropova, L.V., 1975. Forms of Element Occurrence in Dispersion Flalos of Ore Deposits. Ncdra, Leningrad, 145 pp. (in Russian). 

Analysing the distribution of elements and compounds related to petroleum occurrences... 

The Co-Occurrence Matrix is a function of two variables i and j, the intensities of two pixels, each in E it takes its elements in N (set of natural integers). 

The scheme of dispersion effects displayed in engineering materials of different structures was considered and an analysis of the causes of their occurrence was performed in our work. The spectrum of structural noise is considered as an element of unified spectral characteristics, reflected interaction of the ultrasonic field with given parameters and heterogeneous medium... 

We may note (a) the common occurrence of oxidation state +2 where the 4s electrons have been formally lost, (b) the increase in the number of oxidation states from scandium to manganese in the latter element, the oxidation state + 7 corresponds to the formal loss of the and 3d electrons, (c) the sharp decrease in the number of oxidation states after manganese—suggesting that removal of the paired id electrons is less easy (d) the oxidation state 0, occurring for many of the later elements in the series. ... 

Structural keys describe the chemical composition and structural motifs of molecules represented as a Boolean array. If a certain structural feature is present in a molecule or a substructure, a particular bit is set to 1 (true), otherwise to 0 (false). A bit in this array may encode a particular functional group (such as a carboxylic acid or an amidelinkage), a structural element (e.g., a substituted cyclohexane), or at least n occurrences of a particular element (e.g., a carbon atom). Alternatively, the structural key can be defined as an array of integers where the elements of this array contain the frequency of a specific feature in the molecule. 

The occurrence of the elements carbon, nitrogen, and oxygen manifests itself in the isotope patterns occurring for all molecular or fragment ions. For small numbers of carbon atoms, the... 

For organometailic compounds, the situation becomes even more complicated because the presence of elements such as platinum, iron, and copper introduces more complex isotopic patterns. In a very general sense, for inorganic chemistry, as atomic number increases, the number of isotopes occurring naturally for any one element can increase considerably. An element of small atomic number, lithium, has only two natural isotopes, but tin has ten, xenon has nine, and mercury has seven isotopes. This general phenomenon should be approached with caution because, for example, yttrium of atomic mass 89 is monoisotopic, and iridium has just two natural isotopes at masses 191 and 193. Nevertheless, the occurrence and variation in patterns of multi-isotopic elements often make their mass spectrometric identification easy, as depicted for the cases of dimethylmercury and dimethylplatinum in Figure 47.4. 

Some elements contain a fixed number of neutrons, as with fluorine (P = 9, N = 10) and phosphorus (P = 15, N = 16). For their natural occurrences, atoms of any one such element all have the same mass (F= 19 P = 31). 

Occurrence in Nature. About 99.6% of the earth s mass results from 32 of the chemical elements. The remaining 0.4% is apportioned among 64 elements, all of which are present as traces. Iodine is one of these 64. Estimates about abundance of the constituent elements of the Hthosphere place iodine 46th on a restricted Hst of 59 elements (37 very rare elements are excluded) and 61st on a Hst in which 96 elements are included. Iodine is, indeed, one of the scarcest of the nonmetaUic elements in the total composition of the earth (3). 

Although not abundant in quantity, iodine is distributed in rocks, soils, waters, plants, animal tissues, and foodstuffs (3,4). Excepting the possible occurrence of elemental iodine vapor in the air near certain iodine-rich springs, iodine never occurs free in nature. It is always found combined with other elements. 

Phosphorus [7723-14-0] is a nonmetaUic element having widespread occurrence in nature as phosphate compounds (see Phosphoric acid and phosphates). Fluorapatite [1306-03-4], Ca F(P0 2> is the primary mineral in phosphate rock ores from which useful phosphoms compounds (qv) ate produced. The recovery from the ore into commercial chemicals is accompHshed by two routes the electric furnace process, which yields elemental phosphoms and the wet acid process, which generates phosphoric acid. The former is discussed herein (see Furnaces, electric). Less than 10% of the phosphate rock mined in the world is processed in electric furnaces. Over 90% is processed by the wet process, used primarily to make fertilisers (qv). 

Occurrence and Recovery. Rhenium is one of the least abundant of the naturally occurring elements. Various estimates of its abundance in Earth s cmst have been made. The most widely quoted figure is 0.027 atoms pet 10 atoms of silicon (0.05 ppm by wt) (3). However, this number, based on analyses for the most common rocks, ie, granites and basalts, has a high uncertainty. The abundance of rhenium in stony meteorites has been found to be approximately the same value. An average abundance in siderites is 0.5 ppm. In lunar materials, Re, when compared to Re, appears to be enriched by 1.4% to as much as 29%, relative to the terrestrial abundance. This may result from a nuclear reaction sequence beginning with neutron capture by tungsten-186, followed by p-decay of of a half-hfe of 24 h (4) (see Extraterrestrial materials). 

Occurrence of rhenium and molybdenum together in nature is a consequence of the similarities of these elements. Both elements have a high affinity for sulfide ion. Moreover, the radii of Re" " and Mo" ", 0.74 nm and 0.70 nm, respectively, ate almost identical, so that ReS2 [12038-63-0] and M0S2 have similar crystal stmctures with almost identical dimensions (see Molybdenumcompounds). 

Occurrence. The metal sulfides, which are scattered throughout most of the world, have been an important source of elemental sulfur. The potential for recovery from metal sulfides exists, although these sources are less attractive economically and technologicaky than other sources of sulfur. Nevertheless sulfide ores are an important source of sulfur in other forms, such as sulfur dioxide and sulfuric acid. 

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