UNDERSTANDING VARIATION IN PARTITION COEFFICIENT, Kd ...

up tables was based in part on their correlation coefficients. Perhaps more importantly, the
independent variables had to be a parameter that is readily available to modelers. For instance,
particle size and pH are often available to modelers whereas such parameters as iron oxide or
surface area are not as frequently available. The estimated ranges for the minimum and maximum
K d values were based on regression estimates of the 95 percent error (P < 0.05). The central
estimates were based primarily on values calculated using the appropriate regression equations.
5.8.6.2.1 Limits of K d Values with Respect to pH, CEC and Clay Content Values
A full factorial table was created that included 3 pH categories and 3 CEC categories, resulting in
9 cells (Table 5.13). Each cell contains an estimated minimum and maximum K d value. As the
pH or the CEC of a system increases, so does the strontium K d values.
A second table was created based on Table 5.13, in which clay content replaced CEC as an
independent variable (subset of Table 5.13). This second table was created because it is likely
that clay content data will be more readily available for modelers than CEC data. To accomplish
this, clay contents associated with the CEC values used to delineate the different categories were
calculated using regression equations (see Appendix H). for additional details).
5.8.6.2.2 Limits of K d Values with Respect to Dissolved Calcium Concentrations
Of the 63 experiments reporting strontium K d values, 32 also reported dissolved calcium
concentrations (Appendix H). The mean calcium concentration in this data set was 56 mg/l, with
a minimum of 0 mg/l and a maximum of 400 mg/l. Calcium concentration had a correlation with
strontium K d values, r = -0.17. Although this correlation is insignificant, it does show that the
relationship between these 2 parameters is negative. This inverse relationship can be attributed to
calcium competing with strontium for adsorption sites on the solid phase.
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