Volatile elements major

By its great mass, the Sun constitutes the major part of the Solar System. In this sense, it is more representative than the planets, which have been the scene of intensive chemical fractionation. The composition of the solar photosphere can thus be compared with the contents of meteorites, stones that fall from the sky, a second source of information on the composition of the protosolar cloud, provided that volatile elements such as hydrogen, helium, carbon, nitrogen, oxygen and neon are excluded. Indeed, the latter cannot be gravitationally bound to such small masses as meteorites and tend to escape into space over the long period since their formation. 

The size distribution of the particulate matter in the 0.01-5 ym size range is analyzed on line using an electrical mobility analyzer and an optical particle counter. Samples of particles having aerodynamic diameters between 0.05 and 4 ym are classified according to size using the Caltech low pressure cascade impactor. A number of analytical procedures have been used to determine the composition distribution in these particles. A discrete mode of particles is observed between 0.03 and 0.1 ym. The major components of these particles are volatile elements and soot. The composition of the fine particles varies substantially with combustor operating conditions. 

Table 5 further documents that major differences in elemental concentrations do not only exist between different types of tyres, but also between the tread and the wall of a tyre. Most of the elements are preferentially contained in the tyre walls relative to the tread. The wall is particularly enriched in A1 and Ti, as well as in the volatile elements Cl, Br (in track tyres), and Sb (Table 5). Tyre fuel consists most likely predominantly of wall material, and therefore, it is expected that tyre fuel will exhibit concentrations at the upper end of the range listed in Table 5. Of further note are the environmentally critical and volatile elements Hg and Pb, which range between 8 ppb and 0.4 ppm and 5 ppb and 65 ppm, respectively.

Many trace elements are present in coal ashes at concentration levels far in excess of average crustal values. Although new uses are being found for fly ashes, there remains an excess production that ends in lagoons, ash mounds and landfill sites. In the ashes produced in coal-fired power plants trace elements are present in minerals such as quartz, mullite and magnetite, but their overall contribution to the bulk is minimal. The trace elements present in the glass are quantitatively more important, but for the more volatile elements it is surface association that is particularly important, because this is the major location in the ash for some elements and they are potentially leachable. 

The use of hollow cathode lamps is sufficient for the majority of elements. The low intensity and short service life of these lamps when used for volatile elements such as As, Te, Se, Bi, etc. may, however, be a problem when determining traces of these elements. Electrodcless lamps or high intensity lamps (with auxiliary hot cathode) can be used in these cases to enhance the quality of analysis of these elements. 

Satisfactory mass balances for the SRC pilot plant and the Livermore oil shale retort can be made for most trace elements measured to date. The major exception is the volatile element Hg, which will probably balance somewhat better after careful measurements of the oflFgas streams have been made. 

Figure 13 Major and moderately volatile elements in carbonaceous chondrites and in the Earth s mantle. All data are normalized to the RLE Ti. There is a single trend for RLE, Mg-Si, and moderately volatile elements. The Earth may be viewed as an extension of the carbonaceous chondrite trend. The low Cr content in the present mantle (full symbol) is the result of Cr partitioning into the core. The open symbol is plotted at the extension of the carbonaceous chondrite trend. Data for ordinary chondrites are plotted for comparison. Similar chemical trends in carbonaceous chondrites and the Earth are evident. H-chondrites are very different (sources Wolf and Palme, 2001 Wasson and...

The potential components that might have delivered volatile elements to the Earth are the PSN (the major reservoir in the Solar System) and solid matter bodies such as meteorites and comets. The composition of meteoritic volatiles is thought to have been derived from the PSN through elemental and isotopic fractionation. Contributions from sources outside the Solar System such as pre-solar grains or species affected by interstellar chemistry are attested by the discovery of pre-solar grains in primitive meteorites on one hand, and by the large variation of the D/H ratio in the Solar System on another hand, but their extent is a matter of debate. A comparison of the abundances of... 

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