Reduktion af krom(VI) i grundvand ved hjælp af jernspåner

Summary

Based on the detected contamination with Cr(VI) on Sct. Clara Vej in Rosklde, Denmark a series of columntests has been conducted. The goal has been to design an on-site filter consisting of zero-valent iron to treat groundwater from the site. The groundwater is pumped to the surface in order to achieve a lowering of the groundwatertable in order to escavate chromium contaminated soil from the area. The background for the use of zero-valent iron is its corresponding function in the so called ‘reactive barriers’ for in-situ treatment of soils contaminated with chlorinates solvents and chromium(VI).

The focus of the columntest has been to establish the capacity for the specific type of iron to be used, i.e. the ‘Conelly-type’ under the relevant conditions. The dependence of the capacity has been evaluated for the following parameters: Level of concentration, flowrate, pH and mixing with sand.

The conclusion drawn on basis of the generated results are summarized below:

• It is demonstrated that a filter consisting of zero-valent iron has a certain capacity with respect to reducing chromium(VI) to chromium(III): After a certain period the effect of the filter will decrease dramatically
• Tests where the zero-valent iron was mixed with sand did not show an increase in the capacity of the iron.
• Tests revealed no direct relation between the level of concentration and the capacity for concentrations of 20-300 ppm.
• Flow velocities up to the level expected at Sct. Clara Vej did not directly alter the capacities.
• pH-adjustment of the inlet showed a significant effect on the capacities. Only adjustment to pH=4 was examined.

Based on the collected results it is concluded that the suggested design of the on-site filter will be sufficient, and that the filter will have a working period of approximately half a year under the conditions at the site.