Mobility of elements

The porosity and permeability of CP are the most important factors determining their ability to sorb and immobilize BAS. For solving these problems, it was necessary to synthesize various types of porous and permeable CP differing in the mobility of elements of the crosslinked structure and in the rigidity of the polymer backbone. For biological problems related to the application of CP as biosorbents, it has been found necessary to use CP with a marked structural inhomogeneity. 

In order to study the mobility of elements of crosslinked structure of CP, it is suitable to use their microdisperse forms [30-35]. On the one hand, in potentiome-tric titration the equilibrium is quickly attained for these forms and on the other hand the effect of light scattering in spectral methods of investigation (e.g., polarized luminescence) can be greatly decreased. 

The possibility of conformational changes in chains between chemical junctions for weakly crosslinked CP in ionization is confirmed also by the investigation of the kinetic mobility of elements of the reticular structure by polarized luminescence [32, 33]. Polarized luminescence is used for the study of relaxation properties of structural elements with covalently bonded luminescent labels [44,45]. For a microdisperse form of a macroreticular MA-EDMA (2.5 mol% EDMA) copolymer (Fig. 9 a, curves 1 and 2), as compared to linear PM A, the inner structure of chain parts is more stable and the conformational transition is more distinct. A similar kind of dependence is also observed for a weakly crosslinked AA-EDMA (2.5 mol%) copolymer (Fig. 9b, curves 4 and 5). 

The interpretation of the relationships obtained here is based on the same principles of polyfunctional interaction between CP and organic ions which are considered in sections 3.1-3.3. The dispersion of CP grains to a certain size (1-10 pm) yields particles retaining the ability of polyfunctional interaction with organic ions. Simultaneously with increasing dispersion, the mobility of elements of the crosslinked structure also increases, which favors additional interaction. Further dispersion of CP (d 0.1 pm) gives so weak networks that the spatial effect of polyfunctional interaction with organic ions drastically decreases similar to linear polyelectrolytes [64]. 

Biological and volcanic activities also have roles in the natural mobilization of elements. Plants can play multiple roles in this process. Root growth breaks down rocks mechanically to expose new surfaces to chenaical weathering, while chemical interactions between plants and the soil solution affect solution pFF and the concentration of salts, in turn affecting the solution-mineral interactions. Plants also aid in decreasing the rate of mechanical erosion by increasing land stability. These factors are discussed more fully in Chapters 6 and 7. 

Tatsumi et al. (1986) noted that the mobility of elements in fluids released during dehydration of serpentinite increased with ionic radius. This correctly predicts the greater mobility of the LILE relative to the HFSE and REE but does not account for the observed U/Th fractionation in arc lavas. 

Table 4.3 Relative mobility of elements in the different surface environments (taken from Plant and Raiswell, 1994 based on that of Andrews-Jones, 1968)...

Wintsch R. P. and Kvale C. M. (1994) Differential mobility of elements in burial diagenesis of siliciclastic rocks. J. Sedim. Res. 64, 349-361. 

Figure 9.1. Dynamic interactive processes governing solubility, availability, and mobility of elements in soils.

As described earlier, movement of adsorbed elements in soils generally requires that a sequence of processes occurs, beginning with desorption or dissolution followed by diffusion and convection. Readsorption or precipitation can then immobilize the element at another location in the soil. Relative mobility of elements depends on several important factors, including ... 

The important consequence of the irreversibility illustrated by Figure 9.6 is that not many of the initially sorbed ions are able to desorb once the concentration of these ions is lowered in solution. This is behavior inconsistent with the ion exchange model of leaching described in the last section. That model would overpredict mobility of elements that are retained by chemisorption or precipitation reactions. 

The main drawbacks of the reviewed methods are that they determine migration mobility of elements or their analytical components summarily, independently of their migration form, and do not supply an idea of their migration distance. 

Table 3.19 Migration mobility of elements vs. redox environment (A.l.Perelman, 1972)... 

Notwithstanding the discussion above, it should be emphasised that the lanthanides are among the least mobile of elements under geological conditions, and remain as the single, most useful group of elements for the quantitative modelling of igneous processes. 

Hereafter we consider one-dimentional case for simplicity. If the mobility of elements are not dependent on their positions in the space, the Cahn-Hillirad equation for a Fe-X-Y ternary alloy is given by... 

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