Contaminated sites with organic contamination such as low to high boiling hydrocarbons can now be remedied very well with thermal in situ methods such as solid heat sources (thermal conductive heating, TCH). Heavy metals that can occur on co-contaminated sites in combination with organic contaminations, on the other hand, are not removed by this remediation method. The heavy metals bound in the soil could be mobilized again through changes in the soil structure during thermal remediation.
Renewed mobilization of heavy metals would cause a major environmental risk, as they could be transferred into the groundwater and spread. However, whether there is an increased mobilization of heavy metals has not yet been monitored during a remediation using TCH.
In order to be able to carry out a thermal remediation of co-contaminated sites, a study is required that excludes the mobilization of the heavy metals and thus the transport of pollutants, since a relocation of pollutants would be contrary to the goal of contaminated site remediation.
Therefore, this master's thesis deals with the investigation of five contaminated soils, in which pH-dependent leaching tests in accordance with EN 14429 and various mineralogical and chemical investigation methods are intended to clarify how the speciation of heavy metals changes before and after thermal treatment and how these changes affects their leachability.
The results show that the leachability of barium and lead was highest at a temperature of 500 °C, of zinc at 105 °C and of chromium and arsenic at 300 °C, while the leachability of zinc was lowest at 300 ° C. The low mobility of lead in the temperature range of 105 – 300 ° C could be explained by the formation of poorly soluble calcium lead phosphate. In another sample, the silicate binding of lead was responsible for a high level of leaching. From this it can be concluded that a silicate lead compound causes high mobility, whereas a bond in calcium lead phosphate is associated with low mobility.