Remediation Techniques for Hg-Contaminated Sites
119
3.3
Immobilization of Contaminated Soil
Due to technical, environmental, geographical, social or financial reasons, a
cleanup of contaminated soil is often not feasible. In these cases, methods which
are not intended to remove mercury are applied. These techniques of
immobilization, isolation, solidification and stabilization aim to reduce the risk
to mankind and the ecosystem without a cleanup (B6lsing 1993; Mull 1993;
Miiller-Kirchenbauer et al. 1993). A large variety of techniques are available and
may be classified into the following groups.
3.3.1
Physical Barriers
The installation of physical/mechanical barriers helps to reduce the lateral and
vertical mobilization of the pollutant. Lateral barriers consist of sealing walls
connected to a natural or an artificial aquiclude or impermeable bed as the
bottom barrier. A top sealing layer is installed to reduce the ingress of rainwater
and the emission of gas and dust. For vertical and horizontal sealing, there are a
great variety of techniques and commercial suppliers, showing differences in
material, ageing, chemical resistance and costs. Meschede and Vogelsberger
(1995) used an impermeable base and cover comprised of two layers of asphalt
concrete and a layer of sulphur to act as a mercury immobilization barrier.
3.3.2
Geohydro/ogical Isolation
If a natural impermeable bed is not present and a man-made bottom barrier
(injection system) is impossible to realize, geohydrological isolation is another
possibility to isolate the polluted site. This is usually performed by a series of
pumping wells, often combined with a water infiltration system and lateral barriers.
3.3.3
Solidification and Stabilization
These on-site techniques involve mixing the contaminated soil with, for example,
cement, gypsum, calcium carbonate or lime, along with other binders such as fly
ash or furnace slag silicate reagents. Specialized suppliers add reagents to bind
with the metal. Some suppliers use silicate compounds to solidify and stabilize
contaminated soils and sludges. After pre-treatment where coarse material is
separated out, a silicate reagent and water are added, mixed and then poured into
confining pits or cast into moulds (Hazardous Waste Control 1992; Silicate
Technology Corporation 1992).
Another typical treatment process begins by adding water and the chemical
additive to the contaminated soil (Funderburk and de Percin 1992). Subsequent-
119
3.3
Immobilization of Contaminated Soil
Due to technical, environmental, geographical, social or financial reasons, a
cleanup of contaminated soil is often not feasible. In these cases, methods which
are not intended to remove mercury are applied. These techniques of
immobilization, isolation, solidification and stabilization aim to reduce the risk
to mankind and the ecosystem without a cleanup (B6lsing 1993; Mull 1993;
Miiller-Kirchenbauer et al. 1993). A large variety of techniques are available and
may be classified into the following groups.
3.3.1
Physical Barriers
The installation of physical/mechanical barriers helps to reduce the lateral and
vertical mobilization of the pollutant. Lateral barriers consist of sealing walls
connected to a natural or an artificial aquiclude or impermeable bed as the
bottom barrier. A top sealing layer is installed to reduce the ingress of rainwater
and the emission of gas and dust. For vertical and horizontal sealing, there are a
great variety of techniques and commercial suppliers, showing differences in
material, ageing, chemical resistance and costs. Meschede and Vogelsberger
(1995) used an impermeable base and cover comprised of two layers of asphalt
concrete and a layer of sulphur to act as a mercury immobilization barrier.
3.3.2
Geohydro/ogical Isolation
If a natural impermeable bed is not present and a man-made bottom barrier
(injection system) is impossible to realize, geohydrological isolation is another
possibility to isolate the polluted site. This is usually performed by a series of
pumping wells, often combined with a water infiltration system and lateral barriers.
3.3.3
Solidification and Stabilization
These on-site techniques involve mixing the contaminated soil with, for example,
cement, gypsum, calcium carbonate or lime, along with other binders such as fly
ash or furnace slag silicate reagents. Specialized suppliers add reagents to bind
with the metal. Some suppliers use silicate compounds to solidify and stabilize
contaminated soils and sludges. After pre-treatment where coarse material is
separated out, a silicate reagent and water are added, mixed and then poured into
confining pits or cast into moulds (Hazardous Waste Control 1992; Silicate
Technology Corporation 1992).
Another typical treatment process begins by adding water and the chemical
additive to the contaminated soil (Funderburk and de Percin 1992). Subsequent-