NATO/CCMS Pilot Study Evaluation of Demonstrated and ... - CLU-IN

NATO/CCMS Pilot Project on Contaminated Land and Groundwater (Phase III) January 2001
4.2 FORMATION OF SURFACE BARRIERS FOR THE PYRITE CINDERS AND CALAMINA
RESIDUES
Laboratory tests showed that mixing of pyrite cinders or calamina red mud with bentonite would not
reduce drastically the hydraulic conductivity, so that to achieve the formation of a low permeability layer,
i.e., k: ≤10 -7 cm/sec. Alternative materials, such as alumina red mud stabilised with gypsum and a sandbentonite
mixture, are currently evaluated under field scale for the rehabilitation of calamina red muds
and pyrite cinders respectively. Preliminary results showed that covering of the pyrite cinders with a sand-
10% bentonite layer, 30 cm thick, reduced the volume of leachates by 72%. The reduction in the
cumulative mass of metals dissolved was 90% for iron, copper and zinc, 83% for arsenic and 75% for
lead.
4.3 CHEMICAL STABILISATION OF METALS IN OXIDIC WASTES AND SOILS
For Lavrion oxidic tailings, phosphates, fly ash, and biological sludge, added to amounts 0.9, 8, and 10%
w/w, were proven to be efficient stabilisers reducing Pb and Cd leachability well below the regulatory
limits. The most successful additives for Lavrion soils were phosphates, lime, red mud, and fly ash at a
dose of 1.4, 5, 5 and 7.5% w/w respectively. Alumina red mud stabilised with 5% gypsum was proven to
be a successful stabilising agent for Montevecchio soils.
Given that inorganic materials (e.g., phosphates, fly ash, and lime) do not support plant growth, whereas
the application of organic materials (e.g., biological sludge, peated lignite) has a beneficial effect on the
production of biomass, the rehabilitation scheme currently tested under field scale involves mixtures of
inorganic and organic materials including phosphates and peated lignite.
4.4 LEACHING METHODS FOR THE CLEAN-UP OF CONTAMINATED SOILS
The HCl-CaCl2 process was selected as the most efficient treatment option for Montevecchio soils, due to
their low calcite content, whereas the Na2CaEDTA process was considered as the best alternative for the
calcareous soils of Lavrion. The results indicated that it is possible to achieve a high extraction of heavy
metals, e.g., Pb 93-95%, Zn 78-85%, Cd 71-95% etc. The contaminants are recovered in a solid residue,
corresponding to approximately 76 kg per ton soil on a dry basis. Finally, fresh water required for the
final washing of treated soil was estimated to be approximately 1.6m 3 per ton soil.
5. COSTS
Cost estimates of rehabilitation technologies examined will be available upon evaluation of field-scale
test results.
REFERENCES
1. Cambridge, M. et al, 1995: "Design of a Tailing Liner and Cover to Mitigate Potential Acid Rock
Drainage: A Geochemical Engineering Project" presented at the 1995 National Meeting of the
American Society for Surface Mining and Reclamation, Gillette, Wyoming.
2. Daniel, D.E., Koerner, R.M., 1993: Cover systems in geotechnical practice for waste disposal, ed.
D.E. Daniel, Chapman and Hall, London, pp. 455-496.
3. Elliot, H.A., Brown, G.A. & Shields, G.A., Lynn, J.H., 1989. Restoration of metal-polluted soils
by EDTA extraction. In Seventh International Conference on Heavy Metals in the Environment,
Geneva, vol.2, pp. 64-67.
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