Apparent distribution coefficient

This straightforward application is obvious for type I systems only, for which coprecipitation diagrams like Figure 3 can be calculated and experimentally verified. As can be seen from Figures 4 and 5, the apparent distribution coefficient, X, for systems of... 

The constant is the apparent distribution coefficient for the distribution of a substance between the swelling medium inside and outside the gel particles. 

As shown in the last line of Table 23.5, for PCB33 the three-phase model has little effect on the calculated Kd value. Both values are much smaller than the observed one, although the uncertainty of the latter is large. In contrast, for PCB 185 the new calculated apparent distribution coefficient is reduced as compared to the large particle value of Table 23.4 (from 70 to 45 m3kg l). 

Apparent distribution coefficients for indomethacin are tabulated below(31). Additional information is given in the references. 

Distribution coefficients calculated from extraction data are influenced by (1) the value used for the salt-to-metal ratio, (2) the fraction of equilibrium obtained during the extraction, and (3) the extent of side reactions. Distribution coefficients calculated from extraction data are defined in this study as apparent distribution coefficients (Kdf)... 

Because of the above uncertainties in estimating actual weights of liquid salt and molten plutonium at equilibrium, it is more practical (although not rigorous) to base the salt-to-metal ratio on the weights of the salt and metal fed to the extraction rather than on the estimated weights of the salt and metal at equilibrium. This puts a low bias on the value of the salt-to-metal ratio and a high bias on the value of the apparent distribution coefficient. 

The synergistic mixture (HDEHP + TOPO) was used in Experiment 3 (runs 3a-3b). The DF Cm/Am values obtained were very similar (7 and 7.5) and not higher than previously, while DF Am/Cm are respectively 1,300 and 6,100 with two and three scrub stages. The aqueous raffinate was found to contain hexavalent and trivalent americium (the apparent distribution coefficient in the final extraction stage was 0.2). 

Many national programs plan to surround containers of their nuclear waste in a geologic repository, with a backfill of compacted bentonite clay (Fig. 13.33). A chief function of the clay backfill is to adsorb radionuclides and so retard their release from the engineered barrier system. Conca (1992) measured the apparent diffusion coefficient (D ) and apparent distribution coefficient (K [ml/g]) of some radionuclides in bentonite clay as a function of clay moisture content and compaction density. Measurements were made for clay densities from 0.2 to 2.0 g/cm, which correspond to porosities of 93 to 25%, respectively. With decreasing porosity, values declined by roughly 10 to 10 -fold. However, for the same porosity reduction, values were usually lowered by 10-fold and more, indicating less adsorption with compaction (Fig. 13.38). 

Figure 13.38 Apparent distribution coefficients of some radionuclides in bentonite as a function of bentonite compaction density. Except for Np, adsorption of the radionuclides decreases with increasing compaction (decreasing porosity). After Conca (1992).

Kershaw, P.J., Pentreath, R.J., Harvey, B.R., Lovett, M.B. Boggis, S.J. (1986) Apparent distribution coefficients of transuranium elements in UK coastal waters. In Application of Distribution Coefficients to Radiological Assessment Models, eds, T.H. Sibley and C. Myttenaere, 227-87. Elsevier Applied Science Publishers, London and New York,... 

On the other hand, the simplicity of Eqs. (7.2-1) and (7.2-2) and their accuracy over the intended range favor their use fen- prettminary calculations. They permit consideration of the effects of inextractabte materials (e.g., salts or dissolved solids) ou the liquid-liquid equilibrium and the temperature with the introduction of relatively few adjustable parameters. In addition, they can be expanded into a polynomial form to account for situations whem the logarithm of the apparent distribution coefficient is not a linear function of one of the important variables. Several examples are given In Fig. 7.2-1, which is taken from Tawfik.1... 

Figure 10.31 Equilibrium apparent distribution coefficient of neptunium in the system 30 percent TBP-dodecane-HNOj-HNOs-HjO, from [G12].-2S - 35° -50°C.

Figure 9. Effect of hindered diffusion on the solute distribution curves and the apparent distribution coefficient...

Figure 10. (a) Distribution curves for a 2.5 X 10 M solution of several fluorides and of HCl. Growth rate 5 microns a second. No stirring. No relation exists between the apparent distribution coefficients fk computed from the slope of the cation curve) and the diffusion coefficients of the cations... 

In the presentation of this writers experimental results (below) the term apparent distribution coefficient is taken to mean the interface distribution coeflBcient computed according to Equation 5 and the five assumptions listed with Equation 3. The adjective apparent acknowledges the fact that these assumptions may not be satisfied. The k-values shown in Figures 9 to 17 are apparent distribution coeflBcients according to this definition. 

Very hydrophobic analytes Low solubility in the aqueous phase. They are totally incorporated into the micelle and cannot be separated Addition of CDs to achiral surfactant solutions, which can include hydrophobic compounds changing the apparent distribution coefficients between the micelle and the non-micellar phases... 

Two aspects of solubilization which remain to be investigated, are the variation of the apparent distribution coefficient with so-lubilizate concentration in the micellar ph.ase, and the mechanism of the incorporation of solubilizate into micelle. Since a micelle is assumed to consist of a hydrocarbon core (in liquid state), and surrounded by a palisade layer of hydrophilic group. Fig. 1, the following possible ways have been suggested for the incorporation of a solubilizate in a micelle [5,74] (a) adsorption on the surface of the micelle, (b) deep or short penetration into the palisade layer, and (c) dissolution into the (liquid like) hydrocarbon core. These mechanisms of incorporation are closely related to the structure of the micelle. However, the effect of solubilizate on the structure of the micelle has not been satisfactori 1y studied in the current literature [75,76,77]. 

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