Remediation Techniques for Hg-Contaminated Sites
127
form Hg(o). More recently, Rugh et al. (1996) described the potential of
transgenic plants to remediate Hg-contaminated soil.
5
Conclusions
Due to financial and technological constraints, there are only a few possibilities
for treating mercury-contaminated sites. Wet classification is applied in many
cases. In the 1980s, diverse types of techniques were tested and used. At present,
the authors do not expect significant developments, which suggests that wet
classification will be used for a larger number of applications. The technique is
realized in small mobile plants as well as in large >100 tlh plants. It is a relatively
cheap cleanup method. Regulatory authority permission is often less timeconsuming than for thermal techniques.
Thermal methods are now in the stadium of diversification. Different types of
techniques, often only on the laboratory scale, have been described. Only a few
techniques are applied full scale. Thermal removal has the advantage that it
reduces the Hg-containing material to a minimum. There are still problems, e.g.
with porous fine material such as bricks and sludge. It is quite time-consuming
to obtain regulatory permission for a thermal plant. Besides, the acceptance in
the neighbourhood of a thermal plant is typically poor. The measures which have
to be taken for occupational health are more expensive than in any other applied
technique.
Compared with thermal treatment, hydro metallurgical extraction processes
would have the following advantages:
- low costs at small operation scales,
- higher public acceptance,
- less emissions: wastewater can be avoided due to recirculation of the spent
liquid,
- potentiality of in-situ treatment in the case of electrokinetic techniques,
- high flexibility for treating multi-metal contaminations,
- larger thermodynamic separation factors, which leads to a lower energy
consumption.
In contrast, the disadvantages are the following:
- care has to be taken to avoid corrosion of the plant facilities,
- in the case of chlorination processes, the formation of (1) chlorinated
compounds is likely if the soil contains organic matter and also (2) chlorine
emissions,
- leaching agents could cause the dissolution of a significant fraction of the soil,
e.g. acid dissolution of carbonates could lead to a mass defect of more than
75% in the case of limestone
With respect to different geological and environmental situations, there are a
large number of techniques to immobilize mercury in soils and rocks. However,
127
form Hg(o). More recently, Rugh et al. (1996) described the potential of
transgenic plants to remediate Hg-contaminated soil.
5
Conclusions
Due to financial and technological constraints, there are only a few possibilities
for treating mercury-contaminated sites. Wet classification is applied in many
cases. In the 1980s, diverse types of techniques were tested and used. At present,
the authors do not expect significant developments, which suggests that wet
classification will be used for a larger number of applications. The technique is
realized in small mobile plants as well as in large >100 tlh plants. It is a relatively
cheap cleanup method. Regulatory authority permission is often less timeconsuming than for thermal techniques.
Thermal methods are now in the stadium of diversification. Different types of
techniques, often only on the laboratory scale, have been described. Only a few
techniques are applied full scale. Thermal removal has the advantage that it
reduces the Hg-containing material to a minimum. There are still problems, e.g.
with porous fine material such as bricks and sludge. It is quite time-consuming
to obtain regulatory permission for a thermal plant. Besides, the acceptance in
the neighbourhood of a thermal plant is typically poor. The measures which have
to be taken for occupational health are more expensive than in any other applied
technique.
Compared with thermal treatment, hydro metallurgical extraction processes
would have the following advantages:
- low costs at small operation scales,
- higher public acceptance,
- less emissions: wastewater can be avoided due to recirculation of the spent
liquid,
- potentiality of in-situ treatment in the case of electrokinetic techniques,
- high flexibility for treating multi-metal contaminations,
- larger thermodynamic separation factors, which leads to a lower energy
consumption.
In contrast, the disadvantages are the following:
- care has to be taken to avoid corrosion of the plant facilities,
- in the case of chlorination processes, the formation of (1) chlorinated
compounds is likely if the soil contains organic matter and also (2) chlorine
emissions,
- leaching agents could cause the dissolution of a significant fraction of the soil,
e.g. acid dissolution of carbonates could lead to a mass defect of more than
75% in the case of limestone
With respect to different geological and environmental situations, there are a
large number of techniques to immobilize mercury in soils and rocks. However,