In Situ Vitrification Treatment 1
In situ vitrification (ISV) uses electrical power to heat and melt soil, sludge, mine tailings, buried wastes, and sediments contaminated with organic, inorganic, and metal-bearing hazardous wastes. The molten material cools to form a hard, monolithic, chemically inert, stable glass and crystalline product that incorporates and immobilizes the thermally stable inorganic compounds and heavy metals in the hazardous waste. The slag product material is glass-like with very low leaching characteristics.
Organic wastes are initially vaporized or pyrolyzed by the process. These contaminants migrate to the surface, where the majority are then burned within a hood covering the treatment area; the remainder are treated in an off-gas treatment system.
ISV uses a square array of four electrodes that are inserted into the surface of the ground. Electrical power is applied to the electrodes which, through a starter path or graphite and glass frit, establish an electric current in the soil. The electric current generates heat and melts the starter path and the soil; typical soil melt temperature is 2,900°F to 3,600°F. An electrode feed system (EFS) drives the electrodes in the soil as the molten mass continues to grow downward and outward until the melt zone reaches the desired depth and width. The process is repeated in square arrays until the desired volume of soil has been vitrified. The process can typically treat up to 1,000 tons of material in one melt setting.
ISV technology has been under development and testing since 1980 [1, p. 1].2 ISV was developed originally for possible application to soils contaminated with radioactive materials. In this application, trans-uranium radionuclides are incorporated in the vitrified mass. At this time there is only one vendor of commercially available in situ vitrification systems. The technology description, status, and performance data are quoted from the published work of this vendor.
ISV is the proposed remediation technology at eight sites, six of which are EPA Superfund sites [2; 3]. Full-scale units have been constructed. Even so, the technology should be considered emerging in its full-scale application to Superfund sites. EFS mechanisms have recently been developed for pilot- and full-scale systems. This chapter provides information on the technology applicability, limitations, the types of residuals produced, the latest performance data, site requirements, the status of the technology, and sources for further information.
Site-specific treatability studies are the best means of establishing the applicability and projecting the likely performance of an ISV system. Determination of whether ISV is the best treatment alternative will be based on multiple site-specific factors, cost, and effectiveness. The EPA Contact indicated at the end of this chapter can assist in the location of other contacts and sources of information necessary for such treatability studies.