Sorption Isotherms - Transport and Fate of Chemicals in Soils: Principles and Applications - page 16

low amounts of these minerals. Several anion species were not retained by
high pH soils. Despite the fact that element retention by soils is the result of
many interacting processes and that many factors influence retention, signif-
icant relationships among retention parameters and soil and element prop-
erties exist even among soils with greatly different characteristics. Buchter
et al. (1989) made the following conclusions:

1. pH is the most important soil property that affects K f and b.

2. CEC influences K f for cation species.

3. The amounts of amorphous iron oxides, aluminum oxides, and
amorphous material in soils influence both cation and anion reten-
tion parameters.

4. Except for Cu and Hg, transition metal (Co and Ni) and group lIB
cations (Zn and Cd) have similar K f and b values for a given soil.

5. Significant relationships between soil properties and retention
parameters exist even in a group of soils with greatly different
characteristics.

The relationships between soil properties and retention parameters
(e.g., Figure 1.6) can be used to estimate retention parameters when reten-
tion data for a particular element and soil type are lacking, but soil property
data are available. For example, the retention characteristics of Co, Ni, Zn,
and Cd are sufficiently similar that these elements can be grouped together

1.5

Co
Ni
Zn

Cd
Cr

1.3

1.0

A

0.8

0.5

B

0.3

0 2

4 6

pH

8 10

FIGURE 1.6
Correlation between soil pH and Freundlich parameter b . Curve A is a regression line for Co,
Ni, Zn, and Cd ( b = 1.24 − 0.0831 pH, r = 0.83 ** ). Curve B is for Cr(VI) ( b = −0.0846 + 0.116 pH, r =
0.98 ** ). (After Buchter et al., 1989.)