Agriculture Reference
In-Depth Information
2000
Isotherms - Linear Assumption
n
= 10
Case A
1500
Case B
1000
500
0
0
10
20
30
Concentration (mg/L)
FIGURE 1.5
Nonlinear isotherms with 10 fractions (
n
= 1) based on the linear model assumption.
1.6 Effect of Soil Properties
Buchter et al. (1989) studied the retention of 15 elements by 11 soils from 10
soil orders to determine the effects of element and soil properties on the
magnitude of the Freundlich parameters
K
f
and
b
. They also explored the
correlation of the Freundlich parameters with selected soil properties and
found that pH, cation-exchange capacity (CEC), and iron/aluminum oxide
content were the most important factors for correlation with the partitioning
coefficients. The names, taxonomic classification, and selected properties of
the 11 soils used in their study are listed in Table 1.2, and estimated values
for
K
f
and
b
for selected heavy metals are given in Table 1.3. A wide range of
K
f
values, from 0.0419 to 4.32 × 10
7
ml g
-1
, were obtained, which illustrates the
extent of heavy metals affinity among various soil types. Such a wide range
of values was not obtained for the exponent parameter
b
, however. The mag-
nitude of
K
f
and
b
was related to both soil and element properties. Strongly
retained elements such as Cu, Hg, Pb, and V had the highest
K
f
values. The
transition metal cations Co and Ni had similar
K
f
and
b
values, as did the
group IIB elements Zn and Cd. Oxyanion species tended to have lower
b
val-
ues than did cation species. Soil pH and CEC were significantly correlated to
log
K
f
values for cation species. High pH and high CEC soils retained greater
quantities of the cation species than did low pH and low CEC soils. A sig-
nificant negative correlation between soil pH and the Freundlich parameter
b
was observed for cation species, whereas a significant positive correlation
between soil pH and
b
for Cr(VI) was found. Greater quantities of anion spe-
cies were retained by soils with high amounts of amorphous iron oxides,
aluminum oxides, and amorphous material than were retained by soils with
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