Figure 4-18: Typical Gravity Separation System
The separation processes are used for
removing contaminated concentrates from soils, to leave relatively
uncontaminated fractions that can then be regarded as treated soil. Ex situ separation can be performed by many processes.
and sieving/physical separation are two well-developed processes that have long been
primary methods for treating municipal wastewaters. Magnetic separation, on the other
hand, is a much newer separation process that is still being tested.
Gravity separation is a solid/liquid separation process, which relies on a density
difference between the phases. Equipment size and effectiveness of gravity separation
depends on the solids settling velocity, which is a function of the particles size,
density difference, fluid viscosity, and particle concentration (hindered settling).
Gravity separation is also used for removing immiscible oil phases, and for classification
where particles of different sizes are separated. It is often preceded by coagulation and
flocculation to increase particle size, thereby allowing removal of fine particles.
Magnetic separation is used to extract slightly magnetic radioactive particles from
host materials such as water, soil, or air. All uranium and plutonium compounds are
slightly magnetic while most host materials are nonmagnetic. The process operates by
passing contaminated fluid or slurry through a magnetized volume. The magnetized volume
contains a magnetic matrix material such as steel wool that extracts the slightly magnetic
contamination particles from the slurry.
Sieving and physical separation processes use different size sieves and screens to
effectively concentrate contaminants into smaller volumes. Physical separation is based on
the fact that most organic and inorganic contaminants tend to bind, either chemically or
physically, to the fine (i.e., clay and silt) fraction of a soil. The clay and silt soil
particles are, in turn, physically bound to the coarser sand and gravel particles by
compaction and adhesion. Thus, separating the fine clay and silt particles from the
coarser sand and gravel soil particles would effectively concentrate the contaminants into
a smaller volume of soil that could then be further treated or disposed.
The target contaminant groups for ex situ separation processes are SVOCs,
fuels, and inorganics (including radionuclides). The technologies can be used on selected
VOCs and pesticides. Magnetic separation is specifically used on heavy metals,
radionuclides, and magnetic radioactive particles, such as uranium and plutonium
Physical separation often precedes chemical extraction treatment based on
the assumption that most of the contamination is tied to the finer soil fraction, which
alone may need to be treated. Separation is also useful when heavy metal contaminants
occur as particulates (e.g., in small-arms ranges). One advantage of physical separation
processes is that high throughputs can be achieved with relatively small equipment.
Factors that may limit the applicability and effectiveness of these
- High clay and moisture content will increase treatment cost.
- Gravity separation processes rely on a difference in the solids and liquid phase
densities. Specific gravity of particles will effect settling rate and process efficiency.
Additionally, settling velocity is dependent on the viscosity of the suspending fluid,
which must be known to estimate process efficiency and to size equipment.
- Special measures may be required to mitigate odor problems, resulting from organic
sludge that undergoes septic conditions.
A detailed discussion of data elements is provided in Subsection 2.2.1 (Data Requirements for Soil, Sediment,
and Sludge). In addition, particle size distribution; soil type, physical form, handling
properties, and moisture content; contaminant type and concentration; texture; and organic
content need to be investigated.
Gravity separation and sieving/physical separation are full-scale,
well-established technologies used mostly for treatment of wastewater and contaminated
soil, sediment, and sludge. Magnetic separation is a promising new technique used to
remove radioactive contaminants from soils. It has recently been tested at the bench-scale
level at DOE sites.
Additional cost information can be found in the
Hazardous, Toxic, and Radioactive Wastes (HTRW) Historical Cost Analysis System (HCAS)
developed by Environmental Historical Cost Committee of Interagency Cost Estimation Group.
Technologies for Site Cleanup: Annual Status Report (ASR), Tenth Edition,
Technologies: Field Scale Demonstration Project in North America,
of Remediation Case Studies, Volume 4, June, 2000, EPA
Nottingham Trent University,1995. Interim Status
Report, Enhancement Techniques for Ex Situ Separation
Processes Particularly With Regard to Fine Particles, Nottingham,
Guide to Documenting and Managing Cost and Performance Information for
Remediation Projects - Revised Version, October, 1998, EPA 542-B-98-007
Battelle Memorial Institute, 1995. ReOpt. V3.1,
by Battelle Memorial Institute for DOE under Contract DE/AC06/76RLO 1830.
1995. High Gradient Magnetic Separation (HGMS), Los
Alamos National Laboratory (LANL), LALP-94-264.
DOE, April 1995. Technology Catalogue, Second Edition, Office
of Environmental Management & Office of Technology Development, DOE/EM-0235.
Points of Contact:
General FRTR Agency Contacts
Technology Specific Web Sites:
Government Web Sites
Non Government Web Sites
list of vendors offering Ex Situ Physical/Chemical Soil Treatment is
available from EPA
REACH IT which combines information from three established EPA databases,
the Vendor Information System for Innovative Treatment Technologies (VISITT),
the Vendor Field Analytical and Characterization Technologies System (Vendor
FACTS), and the Innovative Treatment Technologies (ITT), to give users access to
comprehensive information about treatment and characterization technologies and
Health and Safety: