Fraction carbonate

FIG. 2. The dependence of the carbon fraction. v = Cl/(lSi] + [C ) on the gas-flow ratio r = [CH4]/([SiH4] -I- ICH4I) for films deposited in the ASTER system [ASTI (filled circles) and AST2 (filled triangles)] and for films deposited in a similar system (ATLAS) [ATLI (open circles) and ATL2 (open triangles)]. (From R, A. C. M. M. van Swaaij, Ph.D. Thesis, Universiteit Utrecht, Utrecht, the Netherlands, 1994. with permission.)... 

In Figure 3b and c the absolute atomic concentrations of carbon and silicon, respectively, are shown as a function of the carbon fraction. As expected, the carbon concentration increases upon alloying. In contrast, the silicon content decreases rapidly, which implies that the material becomes less dense. As it was reported that the Si—Si bond length does not change upon carbon alloying [116], it thus... 

Figure 8. Partition coefficients (Kd) for Th and Pa and the fractionation factor (F) between Th and Pa plotted as a function of the opal and calcium carbonate percentage in settling particulate material. Note the tendency for the Kd for Th to increase with increasing carbonate fraction and decrease with increasing opal fraction. Pa shows the opposite behavior so that F increases with low opal fraction or high carbonate fraction. This plot is modified from Chase et al. (in press-b) but excludes the continental margin data also shown in that study and instead focuses exclusively on open-ocean sites.

The protocol involving NaOAc-HOAc at pH 5 was first proposed and used by Jackson (1958) to remove carbonates from calcareous soils to analyze soil cation exchange characteristics (Grossman and Millet, 1961). Other researchers used HOAc for the extraction of metals from sediments and soils (Nissenbaum, 1972 Mclaren and Crawford, 1973). Tessier et al. (1979) first used the NaOAc-HOAc solution at pH 5 to dissolve the carbonate fraction from sediments. Since then, the NaOAc-HOAc buffer has been widely used as a specific extractant for the carbonate phase in various media (Tessier et al., 1979 Hickey and Kittrick, 1984 Rapin et al., 1986 Mahan et al., 1987 Han et al., 1992 Clevenger, 1990 Banin et al., 1990). Despite its widespread use, this step is not free from difficulties, and further optimization is required in its application. Questions arise with regard to this step in the elemental extraction from noncalcareous soils, the dissolution capacity and dissolution rates imposed by the buffer at various pHs, and the possibility that different carbonate minerals may require different extraction protocols (Grossman and Millet, 1961 Tessier et al., 1979). 

The following sections summarize the studies on the dissolution technique for the carbonate fraction from arid and semi-arid soils with different amounts and types of carbonate minerals. In addition, the selectivity and effectivity of the NaOAc-HOAc extraction technique at varying pHs to extract the carbonate phase, and only the carbonate phase, from soils is examined (Han and Banin, 1995). 

Figure 4.1. Removal of carbonate from Israeli arid soils as indicated by the X-ray diffractograms after extraction of the carbonate fraction by NaOAc-HOAc solutions at various pHs for 16 hours. C calcite d = 3.04 A, and D dolomite, d = 2.89 A. Number 1, 2, 3, 4, 5, and 6 indicate non-treated soil (No. 1), treatments (No. 2-6) with NaOAc-HOAc solutions at pH 7.0, 6.0, 5.5, 5.0 and 4.0, respectively (after Han and Banin, 1995. Reprinted from Commun Soil Sci Plant Anal, 26, Han and Banin A., Selective sequential dissolution techniques for trace metals in arid-zone soils The carbonate dissolution step, p 563, Copyright (1995), with permission from Taylor Francis US)...

In summary, sodium acetate buffer solutions at pH 5.5 and at the soil to solution ratio of 1 25 only extract the carbonate from calcareous soils with 10-20% of carbonate, and, at pH 5.0, all of the carbonate from soils with 30-50% of carbonate is dissolved. A second extraction with a fresh buffer solution is required for soils with more than 50% carbonate. The dissolution kinetics of carbonate showed that six hours of extraction are generally sufficient for complete carbonate dissolution. The part of the carbonate fraction not dissolved at the carbonate fraction step is mainly... 

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. 

Cadmium in native arid soils predominates in the carbonate fraction. In 45 uncontaminated Israeli soils, Cd is mainly present in the carbonate bound fraction (43.5% 22.3%), followed by the easily reducible oxide bound fraction (22% 19.5%) (Table 5.4) (Banin et al., 1997a). The... 

In arid soils from California, U.S., 73% of the Cd exists in the carbonate fraction and only 13% in the residual fraction (Emmerich et al., 1982). In the delta of the Guadalquiver River of southwestern Spain, more than 50% of Cd is present in the carbonate fraction, and the Cd in the exchangeable fraction increases in polluted soils (Ramos et al., 1994). 

In Californian soils amended with sewage sludge for seven years, Ni is mostly present in the residual (64%), the organically bound (12%) and the carbonate fractions (18%) (Chang et al., 1984). Nickel in the carbonate fraction is found to increase with time in arid zone soils amended with sludge (Knudtsen and O Connor, 1987). In the sludge-amended calcareous soils of Southeast Spain, the residual and the carbonate bound Ni fractions are the major solid-phase (Moral et al., 2005). 

Lead has been found to reside mainly in the carbonate and the residual fractions in arid soils. In Californian soils, most of the Pb is in the carbonate fraction (55%), compared to 20% in the residual fraction (Sposito et al., 1982). In Israeli arid soils, Pb is predominately in the residual and the crystalline Fe oxide bound fractions (Han and Banin, 1999). In the delta of the Guadalquiver River of Southwestern Spain, Pb is primarily present in the Fe-Mn oxide bound fraction, followed by the carbonate fraction, while the organic and the exchangeable fractions are small (Ramos et al., 1994). In uncontaminated arid soils of China, Pb is mainly in the residual fraction, followed by the carbonate and the oxide bound fractions (Jin et al., 1996). 

Amendment with soluble copper in arid Israeli soils, particularly at high loading levels, resulted in initial perturbation and increased the amounts of copper in the exchangeable and the carbonate fractions in the loessial soil. This also occurred with the carbonate and the organic bound fractions (Fig. 6.10, Fig. 6.1). Even so, the soils converged quite rapidly... 

During the saturation regime, fluxes of reduced-species of Mn, as measured by the decrease in its content in the ERO fraction (mg kg 1 sec-1), were somewhat faster (by a factor of 1.43/0.828 = 1.7) in the sandy soil than in the loessial soil. The reduced Mn species was split in both of the soils between the exchangeable and the carbonate fractions. The rate of increase of Mn in the carbonate fraction was somewhat faster (6.9/4.14 = 1.7) in the loessial soil than in the sandy soil, whereas the attachment of Mn2+ to the... 

Banin et al. (1990) reported that most of the Pb in Israeli sewage sludge was bound in the reducible oxide fraction (46%), followed by the readily reducible oxide (20%) and the carbonate (18.7%) fractions. McGrath and Cegarra (1992) found that Pb mainly existed in the residual and the carbonate fractions. 

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