Simulation-based analysis of the differences in the removal rate of chlorides, nitrates and sulfates by electrokinetic desalination treatments

Due to their abundance in the natural environment, chloride, nitrate and sulfate salts are considered the main responsible for the salt-induced decay processes in building materials and sculptures. Electro-desalination techniques, enhanced with carbonated clay buffer poultice placed between the surface of the stone and the electrodes, have been successfully applied for the prevention of salt-induced deterioration problems of masonry and other construction materials. However, it has been experimentally observed that, in this type of treatments, the removal rate of sulfates is considerably slower than chlorides and nitrates.A physicochemical model for electrochemically induced reactive-transport processes is described and used for a theoretical analysis of the influence of the chemical interactions on the removal rate of the target ions. Simulations for the electro-desalination of a brick sample contaminated with a combination of these target ions are shown. Results from simulations show that the lower removal efficiency of sulfates is related to the precipitation of gypsum inside the porous body. Modifications of the existing technique are suggested based on the simulation results.