Fact sheet: Vitrification—ex situ

From: Public Services and Procurement Canada

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Description

ex situ vitrification (ESV) is a remediation technology that uses electricity to heat excavated contaminated soils and sludges to extremely high temperatures (1,600 to 2,000 0C) to produce an inert glass product. Most inorganic contaminants are incorporated into the glass product and organic contaminants are either destroyed by pyrolysis or volatilized from the contaminated matrix and collected by a vapor extraction system. The glass product is chemically stable and leach-resistant and is often used as construction or fill material. ESV glass products may be stored or disposed of according to their specific stability and toxicity.

ESV techniques may be performed by two processes: plasma torches or electric arc furnaces. With plasma torch technology, contaminated soils are fed into a rotating brick or stone stove. The soils are held against the side by centrifugal force. During rotation, the soil moves through the plasma (ionized gas) generated by a stationary torch. To remove the molten material from the stove, the rotation slows and the molten material flows through a bottom opening. With the electric arc furnace, contaminated soils are fed into a furnace where they are heated by carbon electrodes. The molten material exits the vitrification chamber and cools to form an inert glass product.

ESV techniques can simultaneously treat organic and inorganic contamination. The United States Department of Energy has developed a transportable vitrification system for treating mixed contaminated materials. This system is currently being tested.

Source:

Implementation of the technology

Soils, sludge, excavated sediments or mine tailings are first sieved to separate and remove (or grind) oversized materials (over 60 mm in diameter). If the water content is too high, drying may be necessary.

In the plasma vitrification process, the contaminated matrix is placed in a rotary furnace. Rotating movements allow the contaminated materials to be held onto the furnace walls by centrifugal force, and to pass through a plasma beam (ionized gas) produced by stationary torches. As the speed of rotation decreases, the molten material formed flows to an opening at the bottom of the furnace.

In the electric arc process, contaminated materials are heated in a furnace using carbon electrodes. The molten material is also recovered at the bottom of the furnace.

In both cases, the molten material produced is cooled to form the inert glass product.

During vitrification, the gases released must be treated before being released into the atmosphere. The gas treatment can be carried out by adsorption on granular activated carbon, by condensation or by thermal oxidation. The thermal oxidation process uses direct flame, flameless or catalytic oxidizers.

Implementation of ex situ vitrification rehabilitation may include:

  • mobilization, access to the site and setting up temporary facilities;
  • the installation of an electricity supply system;
  • excavation of contaminated materials (soil, sludge, sediment or mine tailings);
  • segregation of contaminated materials to remove large materials;
  • the installation of the vitrification unit, if it is installed on the site, or the transport of contaminated materials to a fixed unit;
  • the installation of a gas treatment and air emission control system, and its connection to the vitrification unit;
  • transportation of glass products for off-site disposal or use as fill or construction material on-site;
  • restoration of the site following soil excavation.

Materials and Storage

Excavation and segregation of contaminated materials require conventional and commonly available construction equipment as well as civil engineering and earthmoving methods. The contractor may create temporary piles of contaminated material while waiting for treatment. Soil piles must be covered to prevent dust from being propagated and to limit the run-off of contaminated particles caused by poor weather conditions.

The implementation of vitrification requires the installation of some specialized equipment. Transportable commercial equipment is available for the treatment process. Chemicals may be required as additives in the vitrification process and mixed with contaminated materials prior to treatment.

The electricity required can be supplied through a trailer containing diesel generators, in cases where the construction of a connection to the power grid would be impracticable.

Residues and Discharges

Vitrification produces solid residues (inert glass product). Storage, management and disposal or re-use depend on the type of contaminants that have been treated. Everything must be done according to the applicable standards and laws.

Gaseous emissions produced during vitrification are treated. Used adsorbent materials (granular activated carbon) or other products used in this treatment must be collected and disposed off-site in an authorized centre.

Recommended analyses for detailed characterization

Chemical analysis

  • pH
  • Organic matter content
  • Metals concentrations
  • Contaminant concentrations present in the following phases:
    • adsorbed

Physical analysis

  • Soil water content
  • Soil granulometry
  • Soil thermal conductivity

Recommended trials for detailed characterization

None.

Other information recommended for detailed characterization

Phase III

  • Volume of contaminated material to treat

Notes:

Certain contaminants are incompatible with ex situ vitrification, and treatability studies are generally required. The need and type of additives to be added to contaminated materials must also be determined to produce an inert glass material. Finally, it is important to identify the properties of the glass material to be produced to select the appropriate usage, storage or disposal procedure for the material.

Applications

  • Vitrification applies to a broad range of solid media (soils, waste, sludge, sediments, etc.).
  • This process has been tested on a variety of volatile and semi-volatile organic compounds, organic compounds including dioxins and furans and polychlorinated biphenyls, and inorganic compounds such as metals and radionuclides.
  • Immobilization of inorganic compounds is permanent.
  • The glass material is very resistant to leaching and is stronger than concrete. The vitrification technique makes it possible to treat inorganic and organic contamination simultaneously. The U.S. Department of Energy has developed a transportable system.

Applications to sites in northern regions

Remote sites are subject to high mobilization and monitoring costs, limited equipment availability and short work periods. As this rehabilitation technique requires considerable and complex equipment and high energy consumption, vitrification is not well suited to northern and remote environments.

Treatment type

Treatment type
Treatment typeApplies or Does not apply
In situ
Does not apply
Ex situ
Applies
Biological
Does not exist
Chemical
Does not exist
Control
Applies
Dissolved contamination
Does not exist
Free Phase
Does not exist
Physical
Applies
Residual contamination
Applies
Resorption
Applies
Thermal
Applies

State of technology

State of technology
State of technologyExist or Does not exist
Testing
Exist
Commercialization
Exist

Target contaminants

Target contaminantsApplies, Does not apply or With restrictions
Aliphatic chlorinated hydrocarbons
Applies
Chlorobenzenes
Applies
Explosives
Does not apply
Metals
Applies
Monocyclic aromatic hydrocarbons
Applies
Non metalic inorganic compounds
Applies
Pesticides
With restrictions
Petroleum hydrocarbons
With restrictions
Phenolic compounds
With restrictions
Policyclic aromatic hydrocarbons
With restrictions
Polychlorinated biphenyls
Applies

Treatment time

Treatment time
Treatment timeApplies or Does not apply
Less than 1 year
Applies
1 to 3 years
Does not apply
3 to 5 years
Does not apply
More than 5 years
Does not apply

Long-term considerations (following remediation work)

If glass materials are reused at the site as fill material, the downstream area of—the site must be monitored after the application of the treatment to ensure that there is no contamination released from the glass material.

Secondary by-products and/or metabolites

  • Vitrification doesn’t reduce the radioactivity of radionuclides. Glass materials containing radioactive compounds must be stored in facilities that protect the environment from radiation exposure.
  • Gas emissions during the vitrification procedure must be collected and treated.
  • Ex situ vitrification rapidly volatilizes volatile and semi-volatile organic compounds as well as volatile radionuclides, including Caesium-137, Strontium- 90, and tritium.

Limitations and Undesirable Effects of the Technology

  • Vitrification processes require substantial quantities of energy.
  • The vitrification process releases combustion gases that must be collected and treated.
  • Excavation is not always possible when there is infrastructure (underground or above ground) within or near the contaminated site.
  • Excavation of soils contaminated with radioactive compounds increases the risk of radiation exposure.
  • When processing radioactive material, there may be an accumulation of radioactive gas in the gas emission collection system.
  • Vitrification is not applicable for large quantities of flammable or explosive materials.
  • The transportable vitrification system is limited in the type of contaminated materials that can be treated and effectively vitrified in the system. The system is not designed to treat large debris, or soils rich in organic matter or free metals. Some residues with unique properties, such as pure chemicals, oxidizing agents or explosives, cannot be processed by the transportable system.
  • This technology for remediation of contaminated sites is poorly accepted by the public.
  • Costs of using electricity generated by diesel are generally higher.

Complementary technologies that improve treatment effectiveness

Additives that enhance the formation of glass, such as sands high in borosilicate, may be added to the contaminated material prior to vitrification treatment.

Required secondary treatments

  • Debris greater than 60 mm in diameter are generally removed or pulverized prior to processing.
  • Gaseous emissions must be collected and treated.

Application examples

The following sites provide application examples:

Performance

Demonstration studies examining ex situ vitrification were conducted to treat contaminated soil originating from several sites located within the United States (such as Oak Ridge, TN and Washington, DC). These demonstrations indicated that ex situ vitrification technologies can be implemented and are efficient. The transportable vitrification system is sometimes used on contaminated sites under the supervision of the U.S. Department of Energy.

Measures to improve sustainability or promote ecological remediation

  • Use of energy-efficient equipment.
  • Process optimization to reduce waste and consumables.
  • Evaluation of on-site use of treated materials for construction or backfilling to reduce trucking and backfilling.
  • Use of waste or products derived from industrial processes, if relevant, as additives or reagents.

Potential impacts of the application of the technology on human health

Main Exposure Mechanisms

Applies or Doesn’t Apply

Monitoring and Mitigation

Dust

Applies

Monitoring of conditions favourable to dispersion during the excavation of the soil to be treated and sieving if applicable.

Atmospheric/Steam Emissions—Point Sources or Chimneys

Applies

Emissions monitoring (choice of parameters, types of samples and type of intervention [source, risk or local requirements])

Atmospheric/Steam Emissions—Non-point Sources

Applies

Emissions monitoring (choice of parameters, types of samples and type of intervention [source, risk or local requirements])

Air/steam—by-products

Applies

Emissions monitoring (choice of parameters, types of samples and type of intervention [source, risk or local requirements])

Run-off

Applies

Perimeter control of piles of materials, if applicable

Groundwater—displacement

Doesn’t apply

N/A

Groundwater—chemical/ geochemical mobilization

Applies

Groundwater quality monitoring (applicable if vitrified materials are used as backfill)

Groundwater—by-product

Doesn’t apply

N/A

Accident/Failure—damage to public services

Applies

File checks and licensing prior to excavation, development of excavation and emergency procedures

Accident/Failure—leak or spill

Applies

Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions

Accident/Failure—fire or explosion

Applies

Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions

Other—dewatering, water decontamination, minor sewage discharges

Applies

Monitoring of discharges (choice of parameters, types of samples and type of intervention) and monitoring of the efficiency of collection and treatment.

Other—Manipulation of contaminated soils, sludge and / or sediments

Applies

Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions

Other—Exposure to radioactive material during excavation and handling of materials to be treated and in the management of vitrified materials

Applies

Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions

References

Author and update

Composed by : Josée Thibodeau, M.Sc, National Research Council

Updated by : Martin Désilets, B.Sc., National Research Council

Updated Date : November 27, 2013

Latest update provided by : Nathalie Arel, P.Eng., M.Sc., Christian Gosselin, P.Eng., M.Eng. and Sylvain Hains, P.Eng., M.Sc., Golder Associés Ltée

Updated Date : March 22, 2019

Version:
1.2.1