Changes of heavy metal chemical bonds in thermally treated soils

The cleaning performance of thermal decontamination methods for heavy metals is reviewed by means of a 8-step sequential extraction process. With the help of this extraction process different soils of varying contents (acidity, proportion of clay, carbonates, C/org, heavy metals and KAK) are treated thermally at temperature levels of 300 C, 600 C, 800 C and 1000 C. Thereafter, the changes of the typical forms of heavy metal bonds in soil are determined. It was proven that a decontamination in the strict sense of the word does not occur because the heavy metals zinc, lead, chrome, nickel and copper, with the exception of cadmium, cannot be removed at a temperature of 1000 C. A further conclusion is that a successful decontamination in form of a mineral incorporation of heavy metals is not feasible unless temperatures exceed 600 C. Still, a considerable proportion of heavy metals remains mobile also over longer time in soils with a low level of clay (e.g. Podzol) or a high proportion of carbonate even if temperatures exceed 600 C. (orig.)