INSITU VITRIFICATION OF SOILS CONTAINING VARIOUS METALS

In situ vitrification (ISV) converts contaminated soil into a glass and crystalline product by melting it with electrical energy. Pacific Northwest Laboratory, the developer of ISV, is currently conducting research to extend the technology to buried wastes and underground tanks for the U.S. Department of Energy. Since these types of wastes are anticipated to contain high concentrations of metals, new processing techniques are being developed and tested. In addition, the effects of metals on melt shape and on the solubility of heavy metals are being studied and tested. An electrode feeding technique has been developed and tested for processing high concentrations of metals. Instead of predrilling casings for electrode installation into the contaminated soil to be vitrified, electrode feeding allows the electrodes to be inserted as the vitrified soil melts downward. This concept has been successfully tested four times on engineering-scale equipment, which is 1/100th the capacity of large-scale equipment. Preliminary information has been collected on the influence of metals on melt on melt shape and on the solubility of heavy metals in the molten soil. Test results indicate that metals could be used to achieve greater depths with ISV. Also, although the presence of metals can cause heavy metals to reduce and alloy with the molten metal pool at the bottom of the vitrified soil, the metallic phase passes all criteria for product durability. Additional and larger scale testing is needed to confirm these conclusions.