Rensning af kromforurenet jord vha. jernspåner og jernsulfat

Summary and conclusions

Chromium contaminated soils often originate from old industries such as plating industries, tanneries and wood preserving facilities. The purpose of this project has been to investigate the potential for treating such soils. Initially this was attempted by the use of zero-valent iron (iron fillings), but the main focus of this project was treatment of chromium contaminated soils by the use of iron sulfate, FeSO₄. Three different soil/waste samples (from a plating industry, an old wood preserving facility and a waste disposal site for tannery waste) were collected, and tests were performed on these samples. The sample from the tannery waste disposal site is different from the other two in that it is an actual waste product rather than a contaminated soil. It also contains very large amounts of chalk and chromium with has consequences for the treatment of the sample.

Based on preliminary results it was soon concluded that treatment with zero-valent iron did not seem a realistic alternative due to the need of too large amounts of iron. The treatment of the soil samples with iron sulfate, however, were more promising. It was demonstrated for all three samples, that the leaching from the samples could be significantly reduced by addition of sufficient iron sulfate. For the most contaminated sample however, relatively large amounts of iron sulfate were needed (corresponding to approximately 130 grams of Fe per kg sample.)

It is concluded, that iron sulfate may have demonstrated its ability to reduce the leaching of chromium. However there are still several unanswered questions, mainly:

• The long term stability of the treated soils. Will the chromium destabilize leading to leaching of chromium on a long time scenario?
• What is the effect of adding iron sulfate to the soils on the leaching of other compounds (for example other harmful metals in the soil) ?
• What is the optimal way to use the iron sulfate ?
• How is the wastewater problem handled ? And does the treatment of the wastewater mean that the overall use of the iron sulfate is not the optimal use of the allocated resources ? May disposal of the soils under safe conditions (i.e. with a membrane of zero-valent iron) represent a better use of the resources ?