A. Badora et al., IMMOBILIZATION OF ZINC AND CADMIUM IN POLLUTED SOILS BY POLYNUCLEAR AL-13 AND AL-MONTMORILLONITE, Journal of soil contamination, 7(5), 1998, pp. 573-588
We investigated the suitability of two aluminum-based binding agents,
polynuclear Al-13 and Al-coated montmorillonite (Al-montmorillonite),
for the immobilization of heavy metals in two contaminated agricultura
l soils:; a loamy luvisol from an arable site in Rafz, Canton Zurich,
Switzerland, and a sandy podsol from Szopienice, Upper Silesia, Poland
. Both soils were polluted by lead, zinc, and cadmium: the soil from S
zopienice by the emissions of a nearby zinc-lead smelter, and the soil
from Rafz by sewage sludge applications. While the samples from Szopi
enice exhibited extremely high loads of these metals, the samples from
Rafz were only moderately contaminated. The samples from both soils w
ere slightly acidic. The Rafz soil contained 2.5% organic matter, that
from Szopienice only 1.5%. Destruction of the organic matter in the S
zopienice samples by H2O2 led to a significant release of Zn and Cd in
to solution. This indicated that organic matter is an important factor
for the immobilization of heavy metals in this soil. The treatment of
the Szopienice samples with 8 mmol Al-13 per kg dry soil resulted in
a considerable mobilization of the two metals. As the pH of the sample
s did not decrease, this effect was presumably due to direct interacti
ons between the applied aluminium and organic matter. After destructio
n of soil organic matter, the two binding agents exhibited an immobili
zing effect on Zn, which, however, was weak compared with the binding
of the metal by the organic matter prior to its destruction. In the ca
se of the Rafz samples, metal mobilization was observed only for Al,,
if applied in high doses (4 and 8 mmol per kg soil), but not for Al-mo
ntmorillonite. In this soil, Al-montmorillonite as well as Al,, at low
doses (1.2 mmol per kg soil and less) decreased soluble zinc concentr
ations significantly. The mobilization of metals at high doses of the
applied binding agents and the dependence of this effect on the type o
f soil show that care has to be taken with this remediation method and
that the proper doses of applied binding agents can be crucial for th
e success of metal immobilization in polluted soils.