Introduction to Contaminated Site Management - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 44

( 2006 ) demonstrated that by the addition of lime and limestone to a contaminated
Cambisol with 7 mg/kg cadmium, 2,174 mg/kg lead and 270 mg/kg zinc, the mobile
(0.01 mol/l CaCl 2 extractable) fractions dropped by 50, 20 and 80% for cadmium,
lead and zinc, respectively. The pH was increased from 5.7 to 7.3. Consequently, the
metal concentrations in straw and grains of wheat were significantly reduced.
Száková et al. ( 2007 ) found substantial differences in reduction of the mobile
(0.01 mol/L aqueous CaCl 2 ) fractions of metals when applying lime, limestone,
and zeolite to contaminated soils. However, although the mobile fraction of cad-
mium and zinc indeed decreased, the mobile fraction of lead was hardly affected
and the mobile fraction of arsenic even increased in some of the treated spots. The
availability of arsenic was more affected by different characteristics of experimental
soils than by individual soil amendments. Moon et al. ( 2004 ) contributed the fixa-
tion of arsenic to inclusion of arsenic in pozzolani cement reaction products and the
formation of calcium-arsenic precipitates.
Ameliorating soil materials can be of natural origin, such as clay or bauxite
residue. Alternatively, several by-products of production processes are used for
this purpose. Red mud, a by-product of the aluminium industry, for example, has
been identified as an effective amendment for in situ fixation of heavy metals in
soil because of the high content of Fe and Al oxides (Zhang et al. 2002 ). Friesl
et al. ( 2003 ) demonstrated the efficiency of the amendment of red mud (10 g/kg)
in four soils, in the vicinity of a former Pb-Zn smelter in Austria, highly polluted
with (among others) Zn (2,713 mg/kg) and Cd (19.7 mg/kg). This resulted in the
reduction of metal extractability of 70% for Cd and 89% for Zn.
Other cements used as fixation material are sulfoaluminate cement, powdered
activated carbon, quick lime (Guha et al. 2006 ), and ferrous sulphate (Warren et al.
2003 ). These authors showed that accelerated carbonated treatment substantially
reduces the availability and, hence, the risks, of mercury in soil.
One disadvantage of the amendment of immobilizing soil materials may be the
presence of other contaminants, which implies that the immobilization of specific
metals is accompanied by the introduction of other contaminants. Red mud, for
example, includes arsenic, chromium and vanadium (Friesl et al. 2003 ). Therefore,
the optimal application of immobilizing materials to soils requires the optimum bal-
ance between an effective binding of metals and minimizing the negative effects of
other contaminants. Friesl et al. ( 2004 ), for example showed that, at a red mud addi-
tion of more than 5% of total soil weight, the disadvantages of introducing other
contaminants exceeds the advantage of fixation of metals.
Grotenhuis and Rijnaarts ( Chapter 21 of this topic) give a detailed description of
in situ remediation technologies.

1.6.4.3 Ex Situ Remediation Technologies

The US Environmental Protection Agency includes 14 different ex situ remedi-
ation technologies in their Annual Status report on contaminated sites treatment
technologies (US EPA 2007 ); these are Bioremediation, Chemical treatment,