The pH dependency of the removal of Cu, Zn and Pb by electrodialytic soil remediation from
different industrially polluted soils was examined. From 18 experiments performed with five different
soils, it was found that the order of mobilization due to a pH decrease was Zn > Cu > Pb. It
was found, too, that each of the elements was removed at higher soil pH in calcareous soils (about
12% carbonates) than in soils with a carbonate content of less than 3.7%. In soils rich in carbonates,
precipitation of heavy metal carbonates is an important retention mechanism and the heavy metal
carbonates are dissolved at higher pH values than the pH at which heavy metals are desorbed in
non-calcareous soils. Thus, the relation between the soil pH and the mobility of the heavy metal in
the electric field is not only dependent on the heavy metal in focus, but also on the fraction of the
heavy metal precipitated as carbonates.