From: Public Services and Procurement Canada
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:
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:
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.
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.
None.
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.
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.
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.
Additives that enhance the formation of glass, such as sands high in borosilicate, may be added to the contaminated material prior to vitrification treatment.
The following sites provide application examples:
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.
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
Emissions monitoring (choice of parameters, types of samples and type of intervention [source, risk or local requirements])
Atmospheric/Steam Emissions—Non-point Sources
Air/steam—by-products
Run-off
Perimeter control of piles of materials, if applicable
Groundwater—displacement
Doesn’t apply
N/A
Groundwater—chemical/ geochemical mobilization
Groundwater quality monitoring (applicable if vitrified materials are used as backfill)
Groundwater—by-product
Accident/Failure—damage to public services
File checks and licensing prior to excavation, development of excavation and emergency procedures
Accident/Failure—leak or spill
Risk review, development of accident and emergency response plans, monitoring and inspection of unsafe conditions
Accident/Failure—fire or explosion
Other—dewatering, water decontamination, minor sewage discharges
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
Other—Exposure to radioactive material during excavation and handling of materials to be treated and in the management of vitrified materials
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
