114
M. Hempel and j. Thoeming
Table l. Sources and uses of mercury with respect to its chemical form (Jasinski 1995)
Chemical form
Elemental mercury
Inorganic mercury (Hg 21)
Inorganic mercury (Hg212)
Organic mercury
e.g. phenylmercury,
methoxyethylmercury
Source or use
Chlorine-alkali-manufacturing
Dental fillings
Gold mining
Electrical equipment (batteries, switches)
Instruments (thermometers, barometers)
Electrical equipment (batteries)
Skin care products
Medicinal products
Wood impregnation
Electrical equipment (batteries)
Medicinal products
Fungicides
Pesticides
Pigments (paints)
Medicinal products
Generally, we differentiate between protection techniques, which aim to
immobilize or isolate the Hg, and cleanup techniques, which aim to separate the
Hg from soil. These cleanup methods could be divided into on site methods,
where the contaminated soil is excavated and subsequently treated, and in situ
methods, where the soil is treated, e.g. by leaching, in the ground.
3
Cleanup Methods Applied in Practice
3.1
Physical Treatment
Physical treatment of excavated soil is a method, by which the Hg is removed
from the soil by wet classification. A simplified process scheme of a wet
classification process is shown in Fig. 1. The process basically consists of the
following steps: a sorting step where the soil is separated from other material, for
example rubble; a dry classification where coarse material like uncontaminated
gravel is removed by sieving; an intensive mixing step where the medium and
small fractions (e.g. <50 mm) are mixed with water and a separation step where
the washed clean medium fraction (e.g. <50 mm and >0.1 mm) is removed from
the sludge or fine fraction which is enriched with Hg. The Hg is often
concentrated in the fine fraction, which is usually dewatered before leaving the
wet classification plant.
In practice, no chemical additives are usually used during the above
procedure. Several techniques are available for mixing the medium and small
fraction with water. In the mixing step, techniques are used by which the energy
M. Hempel and j. Thoeming
Table l. Sources and uses of mercury with respect to its chemical form (Jasinski 1995)
Chemical form
Elemental mercury
Inorganic mercury (Hg 21)
Inorganic mercury (Hg212)
Organic mercury
e.g. phenylmercury,
methoxyethylmercury
Source or use
Chlorine-alkali-manufacturing
Dental fillings
Gold mining
Electrical equipment (batteries, switches)
Instruments (thermometers, barometers)
Electrical equipment (batteries)
Skin care products
Medicinal products
Wood impregnation
Electrical equipment (batteries)
Medicinal products
Fungicides
Pesticides
Pigments (paints)
Medicinal products
Generally, we differentiate between protection techniques, which aim to
immobilize or isolate the Hg, and cleanup techniques, which aim to separate the
Hg from soil. These cleanup methods could be divided into on site methods,
where the contaminated soil is excavated and subsequently treated, and in situ
methods, where the soil is treated, e.g. by leaching, in the ground.
3
Cleanup Methods Applied in Practice
3.1
Physical Treatment
Physical treatment of excavated soil is a method, by which the Hg is removed
from the soil by wet classification. A simplified process scheme of a wet
classification process is shown in Fig. 1. The process basically consists of the
following steps: a sorting step where the soil is separated from other material, for
example rubble; a dry classification where coarse material like uncontaminated
gravel is removed by sieving; an intensive mixing step where the medium and
small fractions (e.g. <50 mm) are mixed with water and a separation step where
the washed clean medium fraction (e.g. <50 mm and >0.1 mm) is removed from
the sludge or fine fraction which is enriched with Hg. The Hg is often
concentrated in the fine fraction, which is usually dewatered before leaving the
wet classification plant.
In practice, no chemical additives are usually used during the above
procedure. Several techniques are available for mixing the medium and small
fraction with water. In the mixing step, techniques are used by which the energy