Geoscience Reference
In-Depth Information
Fig. 8.48 Monometal sequential addition of Pb ? Cd or Cd ? Pb to the a Oxisol, b Ultisol,
and c Mollisol soils. S, E, and R represent the amount of sorbed, exchanged, or replaced metal,
respectively. The numbers following the letter designations indicate the order of metal addition to
the soils (Appel et al. 2008 )
the oxidized one. This behavior shows that parathion-organic complexes are
stronger than parathion-mineral ones. Assuming that changes in OM content are
solely responsible for changes in contaminant desorption, it is possible to estimate
desorption curves for mineral and organic fractions. Figure 8.49 shows the cal-
culated parathion desorption in water solutions from the (a) mineral and (b)
organic fractions of Golan and Meron soils. The slopes of the desorption curves of
the mineral fraction are rather steep (especially for Golan soil), indicating that
adsorption is totally reversible. In the range of the concentration studied, only very
small amounts of parathion appear to be released from the OM.
The properties of both OM and clay minerals may affect the release of contam-
inants from adsorbed surfaces. Zhang et al. ( 1990 ) report that desorption (in aqueous
Search WWH ::




Custom Search