Microwave Treatment of Hazardous Wastes: “Fixation” of Chromium in Soil

It has been found that chromium (hexavalent)-impregnated soil treated in a microwave field can be rendered non-hazardous as defined by federal regulations. Another requirement for feasibly effecting site remediation by any technology is that the heavy metal does not become leachable in the future.That it is possible to prevent leaching after treatment was demonstrated by spectroscopic studies. The hexavalent chromium phase in the chromium-impregnated soil became non-detectable; chromium reappeared in two new crystalline phases: chromite (FeCr204) and chromic oxide (Cr203), respectively.Ills the appearance of the chromite phase which suggests the following model to guide the development of microwave-based processes to treat this class of hazardous wastes cost-effectively: The hematite phase, initially present in the soil, is “Iossy”, and absorbs microwave energy; this phase can interact with the dichromate phase in the presence of other soil constituents to effect the formation of a non-hazardous phase. This type of interaction should be more cost-effective than soil vitrification because the expenditure of energy should be less. In contrast to physical stabilization processes, the possibility of subsequent leaching of a hazardous nature is eliminated. This model leads to general guidelines for the development ofmicrowave-based processes to remediate soils contaminated with a heavy toxic metal: (a) Determine if a “lossy” native mineral is present; (b) Determine if this “lossy” native mineral interacts with the toxic heavy metal within the soil matrix to form a non-hazardous substance.