Abstract
The soil flushing technique has been investigating for its potential ability in restoring heavy metal contaminated soils. The technique is further efficient when using chelating agents, such as EDTA and EDDS, in the flushing solution so that to promote the desorption of the metal. However, different problems are involved in the application of this technique such as the extraction of the EDTA- metal complex, which can migrate towards the deeper no contaminated soil layers and release the adsorbed metal during its transport; in this case the metal is re-adsorbed to the no contaminated soil and the free-EDTA can reach the water table leading to an environmental damage and to a no-efficient remediation treatment. It leads to the need to be able to predict the effects of flushing EDTA through a contaminated soil on metal extraction and desorption in advance. The aim of this paper is to provide a tool able to simulate the chelating process and the lead (Pb) desorption and re-adsorption to the soil by means of the implementation of a self-made 1D numerical model. The model takes into account first- order reaction both for the adsorption and desorption process and it was calibrated and validated using two set of experimental data. The experiments used columns of different dimensions filled with both lead-contaminated and no contaminated soil in variable amounts. The experimental results confirm the lead transport and re-adsorption in the deeper no contaminated soil layer. The model is assessed able to simulate the soil flushing process in both the cases of metal desorption or re-adsorption to the soil, as confirmed by the good fit between the column outlet values and the experimental Pb concentration in the leachate in the two tests.