We developed a methodology for the cost optimization of electrokinetic treatment porous media contaminated by toxic metals. A two-dimensional reactive-transport model was implemented to simulate the transport of chemical species by diffusion, electromigration and electroosmosis, coupled with a geochemical model which calculates precipitation and dissolution of species, adsorption and desorption reactions, and aqueous speciation. The model was applied to the case study of an electrokinetic remediation prototype plant built in Livorno (Italy), treating 150 m(3) of dredged sediments contaminated by toxic metals. The plant consisted of an ex-situ treatment basin equipped with electrodic wells arranged on a rectangular grid, connected to an electrolyte management system for catholyte and anolyte pH control. We validated the model by comparing the simulated electric field with the measured electric potential and the simulated pH profiles with the pH values of field samples. Good agreement was achieved between the modelled and measured data. On the basis of the validated model, we performed a parametric study to evaluate the influence of electrode distance and sediment buffering capacity on treatment costs and calculated the overall cost as a function of these two parameters. The results and costs were evaluated in terms of Pb removal, which was taken as the representative toxic metal. The results revealed the existence of distinct minima, representing the best set of parameters which optimized the overall treatment costs. We believe that the methodology and results obtained can be employed as a valuable tool to support the evaluation and design of electrokinetic remediation systems. (C) 2017 Elsevier B.V. All rights reserved.