Individual Trace Elements

So far, no mention has been made of the individual trace elements. At the beginning of this work, it was found that the proportions of the trace elements in the ash vary from original coal to filtered coal extract solution. Some of the original results for Point of Ayr coal are shown in Table 5 (9). 

Thus, the previous work gives different ways of reducing the overall ash level in the filtered extract solution, with indications of the effect on individual trace elements. However, all these methods require alteration to process parameters and it was thought that it might be useful to provide an alternative which would be an add-on to the existing process. The observation that solvent insolubles of filtered extract contain high proportions of trace elements could provide the basis for a method based on solvent de-ashing of a filtered extract These results are described in the next section. 

As indicated previously, it is important to look at the individual trace elements in the coal extract solution. Table 9 shows the concentration of trace elements in the ash from the original extract and the filtrate produced after toluene extraction. This was for an extract with an ash level of 350 ppm, extracted with toluene at 165 C to give a filtrate with an ash level of 100 ppm. The results show that there are some differences, with Ca reducing and Fe and Ti increasing their proportions. However, the changes are not great and it would be expected that if the filtrate were fed to the hydrocracker it would deposit trace elements as observed previously Q), except, of course, there would be a smaller quantity overall. 

A more recent analytical tabulation covering individual trace elements, amino acids, and volatile fatty acids, together with proximate analyses, ADF, MADF, NDF, cellulose, lignin, starch, water soluble carbohydrates, etc., has the title UK Tables of Nutritive Value and Chemical Composition of Feedingstuffs (MAFF, 1990). 

Reviews on the stability and storage of individual trace elements have been made by several... 

In the test method, the coal or coke to be analyzed is ashed under controlled conditions, digested by a mixture of aqua regia and hydrofluoric acid, and finally dissolved in 1% nitric acid. The concentration of individual trace elements is determined by either inductively coupled plasma-atomic emission spectrometry (ICPAES) or inductively coupled plasma-mass spectrometry (ICPMS). Selected elements that occur at concentrations below the detection limits of ICPAES can be analyzed quantitatively by graphite furnace atomic absorption spectrometry (GFAA). 

This study also presented some limited data on partitioning of trace elements during combustion. The partitioning of individual trace elements between bottom ash, fly ash, and uncollected... 

Modern technology utilizes fluidized bed boilers, pressurized fluidized bed boilers, and gasification of coal to improve energy extraction and minimize potential pollutants. The lower temperatures of those processes affect the fate of the individual trace elements that are emitted or are associated with the residues from the consumed coal (Table 2 Clarke, 1993). 

Estuarine environments in particular are often sites of intense human and animal activity (e.g. sites of leisure pursuits and breeding grounds for many species of birds) so the level of contamination of intertidal sediments is of particular interest in relation to environmental health. Total concentrations of individual trace elements in UK estuaries, for example, vary widely (Table 2.1), reflecting the natural sediment characteristics (e.g. organic content and surface area), and the level of anthropogenic contamination of individual systems (Bryan Langston, 1992). The order of variability of concentrations of individual elements in Table 2.1 is Sn > As > Cu > Pb > Hg > Ag > Zn > Cd > Se > Cr > Mn > Co > Ni > Fe, which to some extent can be considered as the order of anthropogenic influence. 

Volatilization is usually utilized for separating individual trace elements from the sample before the determination. The methods based on volatilization are concerned mainly with non-metallic and amphoteric elements which have high vapour pressure in the elemental form (e.g., chlorine, bromine, sulphur), or in compounds with halogen, hydrogen, or oxygen. Other volatilization methods exist for the separation of certain elements, such as the distillation of boron as methyl borate. 

The total element concentration is an initial indication of the occurrence and distribution of individual trace elements in the environment, but in many cases it does not permit an assessment of their effects. To assess such effects it is necessary to determine the speciation, i.e. the chemical form of the element concerned in the environmental sample to be analyzed and deduce possible effects on organisms and communities of organisms from this. 

If a soil can be shown to be derived directly from igneous rock, it is possible to draw conclusions about its trace element content with some accuracy. It is, however, much more difficult to predict the trace element composition of sedimentary rocks and the problem of prediction is greatly complicated by the processes of weathering and metamorphism. Mitchell has pointed out [75] that in sedimentary rocks, unexpected accumulations of individual trace elements can occur and has reported that in analysing about 250 Scottish limestones, one was found to contain up to 1 per cent boron, although the level generally encountered was below 10 ppm. 

Although nutritional problems based on deficiencies or on excessive concentrations of individual trace elements, which can be related to the geochemical origins of soils, affect only a small proportion of land under cultivation, there are numerous other instances of problems of this kind in limited areas. There are problems of molybdenum deficiency in plants, on soils which have inherently low contents of molybdenum, in New Zealand,... 

Since the trends in the behaviour of the trace elements are the subject of the present study, rather than the differences between individual trace elements, whether in relation to the SP, particle size or surface emichment, the adjusted bulk concentrations are preferred to the enrichment factors (EF) used in some earlier papers. 

Trace elements are those elements of the periodic table that occur in animals or humans in amounts measured in mg per kg of body weight or less. The trace elements essential for health are usually required by humans in amounts measured in mg per day these elements include copper, iron, manganese, and zinc. The individual trace elements are discussed elsewhere in the encyclopedia. Since 1980, the term ultratrace element has appeared in the nutritional literature. Ultratrace elements have been defined as those elements with estimated dietary requirements usually less than Imgkg, and often less than 50pgkg of diet for laboratory animals. For humans, the term often is used to indicate an element with an established, estimated, or suspected requirement of less than 1 mg per day or generally indicated by pg per day. At least 18 elements could... 

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