Geoscience Reference
In-Depth Information
Fig. 16.13 Parathion losses
from a glass surface, a water
solution, and a dry Ca
2+
-
kaolinite at 40 C (Saltzman
et al.
1974
)
ð
16
:
3
Þ
where M represents an exchangeable cation. In other experiments, Saltzman et al.
(
1974
) found that, after 60 days, the quantities of parathion converted to diethyl
phosphate were 72 % for Ca
2+
-kaolinite, 34 % for Na
+
-kaolinite, and 19 % for
Al
3+
-kaolinite. The amount of p-nitrophenol recovered in the case of Na
+
- and
Ca
2+
-kaolinite was equal to that of the
14
C-labeled fraction of the water-soluble
product, indicating that hydrolysis was the only path of degradation and extraction
was apparently complete. In addition to the availability of OH
-
, the cation charge
and radius affect the rate of hydrolysis.
Surface catalysis affects the kinetics of the process as well. Saltzman et al.
(
1974
) note that in the case of Ca
2+
-kaolinite, parathion decomposition proceeds in
two stages with different first-order rates (Fig.
16.14
). In the first stage, parathion
molecules specifically adsorbed on the saturating cation are quickly hydrolyzed by
