Salt-fractionation factor

This in turn gives the ratio of these two quantities, the salt-fractionation factor s, as... 

For low surface potentials ( s < 1), the salt-fractionation factors calculated (a) via the coulombic attraction theory and the electric integral solved by Equation 4.20 (i.e., via the Donnan equilibrium) and (b) via the coulombic attraction theory and the electric... 

Some Illustrative Values of the Salt-Fractionation Factor (s) as a Function of the Surface Potential (y/0)... 

Note r is the sol concentration, c is the salt concentration of the solution added to the crystals, W is the number of washes that the crystals were given and Ns is the number of samples used under each set of conditions. Measured salt concentrations in the supernatant fluid cex and the gel phase cgd and the salt fractionation factor s=cex/cgel, are given in the form a <7, where a is the average result and exits standard deviation. The exception is the r = 0.01, c = 0.03 M result, for which only the average values are given. 

FIGURE 5.5 The salt fractionation effect in n-butylammonium vermiculite swelling. The salt fractionation factor s = ceJc x is plotted as a function of cex, the salt concentration in the supernatant fluid. The solid line shows the coulombic attraction theory prediction, s = 2.8. 

As far as I am aware, independent experimental evidence for the values of the surface potential and salt fractionation factor have not been obtained for any system other than the n-butylammonium vermiculite gels. For this isolated system, the predicted values of 5 from the Donnan equilibrium and the new equilibrium based on the coulombic attraction theory, namely 4.0 and 2.8, respectively, are definitely distinguished by the experimental results. It would be highly desirable to obtain further tests of our prediction for 5 in systems of interacting plate macroions, both in clay science and lamellar surfactant phases. 

The indirect method of deducing the isotope composition of ore fluids is more frequently used, because it is technically easier. Uncertainties arise from several sources uncertainty in the temperature of deposition, and uncertainty in the equations for isotope fractionation factors. Another source of error is an imprecise knowledge of the effects of fluid chemistry ( salt effect ) on mineral-water fractionation factors. 

Many salt minerals have water of crystallization in their crystal structnre. Such water of hydration can provide information on the isotope compositions and/or temperatures of brines from which the minerals were deposited. To interpret snch isotope data, it is necessary to know the fractionation factors between the hydration water and the solntion from which they are deposited. Several experimental studies have been made to determine these fractionation factors (Matsno et al. 1972 Mat-subaya and Sakai 1973 Stewart 1974 Horita 1989). Becanse most saline minerals equilibrate only with highly saline solutions, the isotopic activity and isotopic concentration ratio of water in the solntion are not the same (Sofer and Gat 1972). Most studies determined the isotopic concentration ratios of the sonrce solntion and as Horita (1989) demonstrated, these fractionation factors have to be corrected using the salt effect coefficients when applied to natural settings (Table 3.2). 

Table 3.2 Experimentally determined fractionation factors of salt minerals and their corrections using salt effect coefficients (after Horita 1989)...

Horita J (1988) Hydrogen isotope analysis of natural waters using an H2-water equilibration method a special implication to brines. Chem Geol 72 89-94 Horita J (1989) Stable isotope fractionation factors of water in hydrated salt minerals. Earth Planet Sci Lett 95 173-179... 

Fig. 9. Comparison of REE fractionation in the salt with fractionation factors X, determined by Byrne et al. (1996) from experimental data for REE coprecipitation with phosphate. REE fractionation in the salt is illustrated by the ratio of samples R 4254/R 4250, which are the two extreme samples of the salt profile. The A values are plotted in reciprocal form in order to show REE fractionation in the remaining solution from which phosphate has precipitated.

Combined effects. Because temperature, pressure and solution composition all affect the physical properties of water, these three variables can act in concert to influence fractionation factors (Horita et al., in press Hu and Clayton, in press). Increases in pressure and NaCl concentration both work to decrease the fluid s affinity for deuterium. The isotopic effect is most pronounced at low pressures and NaCl concentrations, which relates to the fact that the largest changes in the density of the fluid occurs over this region of pressure-composition space. It appears that the fractionation factor and the density of aqueous NaCl solutions are closely related to each other. With additional systematic experiments, empirical equations can be designed that relate the isotope salt effects and the density of aqueous solutions. 

No experimental results for the actual Shilov system point clearly in any direction. Analysis of the methane obtained when [MePt Cls] was reduced in a mixture of H2O/D2O indicated a KIE around 9 at 0°C, a borderline number, and one whose interpretation is made more difficult by the possible involvement of so-called fractionation factors [36]. Further study, perhaps making use of the [MePt Clsl salt described above, might be worthwhile, although complicated by the necessarily heterogeneous reactions of this insoluble material. 

Chromatography by ion exchange on a sulfonated poly(styrene-co-divinyl benzene) phase has been proposed as a replacement for titrimetry.57 Eluted by a dilute solution of a neutral salt such as sodium ethanesulfonate, the conductance of the protons can be measured in the absence of a suppressor from sub-millimolar to molar concentration. The response factors of mono-, di-, and trichloroacetic acid and of o-phthalic acid were large and essentially equivalent to ethanesulfonic acid, while the response factor of acetic acid was far smaller. A syringe pump has generated pressures as high as 72,000 psi (5000 bar) in a capillary column packed with 1 p particles, generating a fraction capacity of 300 peaks in 30 minutes.58... 

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