Geoscience Reference
In-Depth Information
Fig. 12.3 Transport of Pb
2+
in association with in situ mobilized colloids in a packed, Na
+
-
saturated soil column following a decrease in solution ionic strength. Colloidal Al was used as a
key element to quantify the colloid concentration. The inlets show that elevated colloidal Al and
Pb
2+
concentrations were observed for at least 50 pore volumes after the change in feed solution
(Kretzschmar et al.
1999
). Reprinted from Kretzschmar et al. (
1999
). Copyright 1999 with
permission from Elsevier
who examined pH ranging between 3 and 7. It was observed that both dissolved
lead and lead adsorbed on colloids increase with an increase in pH (Fig.
12.6
a);
this is related to the organic content of the adsorbing phase (Fig.
12.6
b). Specif-
ically, the colloidal Pb fraction increased continuously from almost zero at pH 3 to
1,200 mg/kg at pH 7. Klitzke et al. (
2008
) also found that the ratio between
colloidal and dissolved Pb in soil suspension is affected by the counter-ion va-
lency: Pb shows a much stronger mobilization in the presence of the monovalent
K
+
than in the presence of the divalent Ca
2+
(Fig.
12.7
).
In the previous examples, we discussed the case of heavy metal-facilitated
transport when they are bound on colloidal fractions in the soil-subsurface
domain. However, in many instances, heavy metals are disposed on the land
surface together with organic residues of urban or agricultural origin. Sewage
sludge disposal, for example, encompasses simultaneous disposal on land surface
