Biomedical Engineering Reference
In-Depth Information
Soil or sediment-water
interface
Sediment prole
and analysis
Inorganic and
organic pollutant
Laboratory tests
Sediment and surface water
composition; sequential extraction
permeability; leaching;
partitioning; environmental mobility;
kow, Kd,
Soil/sediment
and water
samples
Prediction of transport
of pollutants
Assessment of impacts
FIGURE 10.3
Schematic showing procedures required to evaluate potential for pollutant
transport.
Soil washing is a process that uses water to remove contaminants from soil and
sediments by physical and/or chemical techniques. Contaminated sediments are
problematic as they can potentially release contaminants severely impacting water
quality. Soil washing involves the addition of a solution with the contaminated soil
to transfer the contaminants to the wash solution. It is most appropriate for weaker
bound metals in the form of hydroxides, oxides, and carbonates. Mercury, lead,
cadmium, copper, nickel, zinc, and chromium can be recovered by electrochemi-
cal processes if the levels of organic compounds are not significant. Metals can
also be removed from precipitation or ion exchange. Precipitation is not appli-
cable for metal sulfides. Pretreatment to remove uncontaminated coarser fractions
can be used. Various additives can be employed such as bases, surfactants, acids,
or chelating agents. Nitric, hydrochloric, and sulfuric acids can be used. However,
if sulfuric acid is used, 50% of the amount is required compared to hydrochloric
acid (Papadopoulos et al., 1997).
Figure 10.4 illustrates a typical soil-washing process where the separation
consists of size separation, washing, rinsing, and other technologies similar to
those used in the mineral processing industry. Larger particles are separated
from the smaller ones as they have lower contamination levels. The smaller vol-
umes of soil can be treated less expensively. Surfactants may be added in the
washing water. The more contaminated size range is 0.24-2 mm due to the sur-
face charges of the soil clay particles that attract anionic metal contaminants and
the organic fraction that binds organic contaminants. Wash water and additives
should be recycled, or treated prior to disposal. The mechanical dewatering of
particles is performed via a filter press, conveyer filtration, centrifugal separa-
tion, etc. Froth flotation by the introduction of air bubbles into a slurry may also
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