The International Information Center for Geotechnical Engineers

Vitrification

Limitations and Disadvantages

 

The size of a melt which can be generated is limited to approximately 40 feet by 40 feet and a maximum depth of about 20 feet with the current ISV technology. The maximum ISV depth obtainable is influenced by several factors, including spacing between electrodes, amount of power available, variations in soil composition and depth to groundwater, soil permeability within an aquifer, and waste and soil density. All of these controlling factors cause a high complexity of in-situ vitrification field set-up.

 

Soil water content and water recharge can also limit ISV applicability. Extra energy input is needed when dealing with wet soil, to dry the soil prior to melting. This extra energy input could increase the cost of remediation by 10 percent.  Therefore, ISV is more economical to implement when the soil to be vitrified has low moisture content.

 

Because vitrification technology is more often used in situ, it may not be appropriate for sites where contaminated soil exists directly to buildings, other structures, or the property line. Staging or the use of insulating refractory walls can be used in some cases, but will probably increase the costs.

 

The treatment soil is limited to a maximum of seven to ten percent organics by weight for effective remediation using the current off-gas treatment equipment. It’s ineffective to process contaminated soils containing more than 10% total organic content (USEPA, 1995b).

 

It is more difficult and unsafe to process sites with flammable liquid or vapor in sealed containers beneath the soil surface. Combustible materials may also present treatment difficulties since the sudden release of gases may exceed the heat load and volumetric capacity of the off-gas treatment system, resulting in a loss of hood vacuum and a potential for fugitive emission releases.

Furthermore, to form a melt, sufficient (typically 2 to 5 percent) monovalent alkali cations (e.g., sodium and potassium) must be present to provide the degree of electrical conductivity needed for the process to operate efficiently. Also it requires sufficient glass-forming materials (e.g., silicon and aluminum oxides) be present within the waste materials to form and support a high-temperature melt. If the natural soil does not meet these requirements, fluxing materials could be added to the base materials, leading to a increasing costs.

 

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