Fig. 1. Diagram showing steps in the vitrification process for metal, including (A) insertion of electrodes and placement of graphite and glass frit starter path to initiate vitrification, (B) subsidence of the soil during vitrification and (C) placement of backfill over vitrified monolith.
Vitrification is a solidification/stabilization process requiring thermal energy. It involves insertion of electrodes into the soil which must be able to carry a current, and then to solidify, as it cools (Fig. 1). Toxic gases can also be produced during vitrification. Full-scale applications exist for arsenic, lead and chromium contaminated soils. Mixed wastes can also be treated in this manner. High clay and moisture contents and debris can affect the efficiency of the process. These solidification/stabilization processes are suitable for contamination in shallow depths and of large volume. Leaching of the contaminants must, however, be carefully monitored as is the case for vitrification, the formation of a glassy solid.