Trace element release

Another source of metallic contamination in the studied region comes from the residual oil combustion used for electric utilities and fluvial and terrestrial transportation. Using the selected emission factors (quantity of trace element released by quantity of material consumed) given by Nriagu and Pacyna (1988) and Nriagu (1989), the electric-power production installed in the Amazonian states and the fuel consumption used for transportation (Ministerio de Minas... 

Loppi, S., Cenni, E., Bussotti, F., Ferretti, M., 1997. Epiphytic lichens and tree leaves as biomonitors of trace elements released by geothermal power plants. Chem. Ecol. 14, 31-38. 

The solubility and reactivity of Fe(III) and Mn(IV) oxides are regulated by pH and Eh. They are soluble under reducing or acidic conditions, thus resulting in the release of trace elements. As discussed before, Mn(IV) oxides are present in a dissolved form at a higher Eh and pH than Ee(III) oxides. Thus, any trace elements released as a result of the dissolution of Mn(IV) oxides can be retained by Ee(III) oxides. 

B.W. Callen, B.F. Lowenberg, S. Lugowski, R.N.S. Sodhi, and J.E. Davies, Nitric acid passivation of Ti6A14V reduces thickness of surface oxide layer and increases trace element release . Journal of Biomedical Materials Research, 29, 279-290 (1995). 

Callen, B. W., Lowenbeig, B. F., Lugowski, S., et al., Nitric Acid Passivation of Ti6A14V Reduces Thickness of Surface Oxide Layer and Increases Trace Element Release, Jourtml of Biomedical Materials Research, Vol. 29, 1995, pp. 279-290. 

The mercury cell operates efficiently because of the higher overpotential of hydrogen on mercury to achieve the preferential formation of sodium amalgam. Certain trace elements, such as vanadium, can lower the hydrogen overpotential, however, resulting in the release of hydrogen in potentially dangerous amounts. 

Concern over the release of hazardous trace elements from the burning of coal has been highlighted by the 1990 Clean Air Act Amendments. Most toxic elements are associated with ash-forming minerals in coal (5). As shown in Table 1, levels of many of these toxic metals can be significantly reduced by physical coal cleaning (6). 

Despite the difficulties, there have been many efforts in recent years to evaluate trace metal concentrations in natural systems and to compare trace metal release and transport rates from natural and anthropogenic sources. There is no single parameter that can summarize such comparisons. Frequently, a comparison is made between the composition of atmospheric particles and that of average crustal material to indicate whether certain elements are enriched in the atmospheric particulates. If so, some explanation is sought for the enrichment. Usually, the contribution of seaspray to the enrichment is estimated, and any enrichment unaccounted for is attributed to other natural inputs (volcanoes, low-temperature volatilization processes, etc.) or anthropogenic sources. 

Group 3 elements which are not mostly vaporized in the boiler (1423 K) V, Cr, Mn, Co, Ni Referring to the classification, we investigated the temperature dependency of release of trace metals in coal combustion. We already reported the behavior of these three types of elements during high temperature coal processing and reported elsewhere . So in this paper, we investigated the effect of atmosphere for the emission behavior of trace elements. 

A current area of interest is the use of AB cements as devices for the controlled release of biologically active species (Allen et al, 1984). AB cements can be formulated to be degradable and to release bioactive elements when placed in appropriate environments. These elements can be incorporated into the cement matrix as either the cation or the anion cement former. Special copper/cobalt phosphates/selenates have been prepared which, when placed as boluses in the rumens of cattle and sheep, have the ability to decompose and release the essential trace elements copper, cobalt and selenium in a sustained fashion over many months (Chapter 6). Although practical examples are confined to phosphate cements, others are known which are based on a variety of anions polyacrylate (Chapter 5), oxychlorides and oxysulphates (Chapter 7) and a variety of organic chelating anions (Chapter 9). The number of cements available for this purpose is very great. 

Here we might note that cobalt(II) hydroxide, but not the oxide, also forms cements (Allen et al., 1984 Mansion Gleed, 1985 Prosser et al., 1986). It also is used in controlled-release devices for supplying trace elements to cattle and sheep. Nothing is known of its structure. 

Mansion, R. Gleed, P. T. (1985). Reaction cements as materials for the sustained release of trace elements into the digestive tract of cattle and sheep. II. Release of cobalt and selenium. Journal of Veterinary Pharmacology Therapeutics, 8, 374-81. 

In a similar way there has been a passing reference to a cobalt oxychloride cement (Prosser et ai, 1986). No explicit details of the fabrication or chemical behaviour of this material were provided, but the ingredients were listed among series of acids and bases for forming cements as agents for the sustained release of trace elements to grazing animals. The implication of this paper was that cobalt oxide would function as the base... 

Residual. This fraction mainly contains primary and secondary minerals, which hold elements within their crystal structure. This fraction also contains trace elements remained from the extraction of all previous fractions (e.g., humin bound). These metals/trace elements are not expected to be released into soil solutions over a reasonable time span under conditions normally encountered in nature. 

The contents of trace elements extracted by the buffer solutions depend upon the solution s acid capacity in dissolving carbonate from soils. Trace elements dissolved by the buffer solution increased with decreasing pH of the buffer solution (Table 4.3). Release of trace elements by the buffer solutions at pH 6.0 was much smaller from calcareous soils with more than 30% of CaCC>3. The dissolution of trace elements by the buffers paralleled with the dissolution of Ca and Mg. The correlation coefficients between Ca and trace elements were as follows Cd (0.92), Pb (0.87), Zn (0.90), Ni (0.90), Cr (0.91), V (0.54) and Co (0.70) and between Mg and trace elements were Cd (0.88), Pb (0.80), Zn (0.79), Ni (0.87), Cr (0.58), V (0.69) and Co (0.80), (all with n = 32). 

The cumulative sums of selected major and trace metals extracted by the two SSD procedures from representative arid-zone soils are shown in Fig. 4.6. As can be seen from the figure, the Rehovot procedure is stronger in attacking desired fractions, such as the carbonate bound, Mn oxide bound and organically bound fractions. Extraction of certain major elements, indicating selectivity, specificity and completeness of extraction of given soil components, was found to differ between the two procedures. Calcium and Mg were more completely extracted from the carbonate fraction in arid zone soils by the Rehovot procedure. Calcium and relevant trace elements bound in the carbonate fraction, which were not completely dissolved by the Bonn procedure at this step, were released at the following steps, such as the ERO, OM or RO fractions. 

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