EDTA chelating process for lead removal. Evaluation of approaches by means of a reactive transport model

A 1D reactive model is developed to simulate the EDTA chelating process in a lead (Pb)-contaminated saturated soil. The model is implemented using a multistep numerical approach in order to avoid numerical diffusion assuring at the same time the algorithm stability. The model takes into account first-order reactions where the lead species are splitted into three fractions: C1 (easily mobilized lead), C2 (lead associated with iron and manganese oxides), and C3 (lead bound to organic matter and in the residual fraction). Two different mobilization kinetics (Bslow^ and Bfast^) are considered for each fraction. The model was therefore calibrated and validated using laboratory experimental data. A sequential extraction procedure was conducted to evaluate the lead mobilization due to the EDTA flushing through the column and to take into account the different soil fraction at which the metal is bound. Several remediation scenarios are used to show the suitability of the model to provide information and knowledge of the best EDTA feed and flux conditions for the lead extraction from soil. The model can therefore be considered as a tool to know in advance the performances of a remediation treatment and to optimize the extraction process minimizing the chelating agent costs and its effects on the soil.