Decontamination of Soils by Membrane Processes: Characterization of Membranes under Working Conditions

An electrodialytic soil remediation process was applied for the removal of cadmium (1000 mg/kg of dry soil) from spiked kaolin. The method consists of the application of a dc electric current to the soil placed between ion-exchanger membranes, which allows for the separation of the soil from electrode solutions. Characterization of cationic and anionic membranes was done by measuring the membrane potential and electrical resistance under operating conditions. Experimental results and modeling indicate that both membranes work close to ideal conditions (t+ ~1), although a small fraction of the H+ ions (tH+membrane ~0.13tH+solution) is allowed to circulate through the anionic membrane and less than 1% of OH- ions pass through the cationic one. A model for ion transport involved in the process across both ion-exchanger membranes used in soil remediation was also developed, and good agreement was obtained when compared with the experimental results. Cadmium analysis of different sections of the soil column showed a high removal from the zones closer to the anode and a significant accumulation in the vicinity of the cathode.