Electrokinetic remediation of soils polluted by heavy metals (mercury in particular)

• Due to an electric field, Hg0 can be mobilized without using oxidizing chemicals.
• A proper management of hydraulic fluids allows to minimize pH adjustments.
• A significant abatement of Hg pollution can be obtained in short times.
• The outcomes from pilot-scale tests encourage further tests in field.

The electrokinetic approach, for the extraction of contaminants from a soil matrix, requires the application of electric fields of suitable intensity, through saturated portions of the soil. When aimed at the removal of species present in metallic form (like mercury) or as poorly conductive minerals (like some sulfides), pollutants require to be preliminary dissolved, an action that can be facilitated by adding appropriate chemicals. In this paper, we show that the presence of an electric field is decisive, possibly because the pollutant-containing particles were able to act as polarizable species (and thus as improper electrodes). At first, tests were performed on small amounts of soil (about 200 g, in plastic bench cells); then, the process was scaled up, testing approximately 400 kg of soil. A 60% of total mercury was removed, in less than 3 months, by adopting specific expedients, in terms of hydraulic control as well as of plant design.

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