As part of an evaluation of a newly developed electrodialytic soil remediation technique, we investigated the incubation of a contaminated soil (from a Portuguese wood preservation site polluted with CCA) with potassium diphosphate as a possible catalyst for the removal of heavy metals and metalloids. A chemical sequential extraction scheme (SE) applied to the soil has shown that the potassium diphosphate (0.1 M), used for the attack of forms organically bound, extracted 30% of Cu, 15% of Cr and 23% of As. Two electrodialytic laboratory experiments (E and O) were carried out for 35 days in a laboratory cell, with a current density of 0.2 mA/cm2. In Exp. E the contaminated soil was put in the cell as it was sampled, and in Exp. O, the soil was previously incubated with 0.1 M K4P2O7, for 51 h. The aim was to compare results of process efficiencies by maintaining either acid or basic pH conditions in the soil, both media known to keep solubilization of metals high. Results show that the remediation process was not more efficient in the soil submitted to the pre-treatment, for the considered time length, as total Cu, Cr and Zn soil concentrations were higher after Exp. O than after Exp. E. The K4P2O7 incubation did not succeed in maintaining a basic pH in the soil. However, the soil SE results show that Exp. O put more Cu, Cr and Zn in "soluble and exchangeable forms" than Exp. E. If the process had been run for a longer period, electromigration could have acted more efficiently and these elements are expected to be removed from the soil, increasing the overall efficiency of the process. Addition of extra alkali could have furthered the process.

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