Behavior of cadmium, lead and zinc at the sediment–water interface by electrochemically initiated processes

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Physicochemical and engineering aspects, 2003-07, Vol.222 (1), p.261-271
• Main Authors: Shrestha, Reena, Fischer, R., Rahner, D.
• Format: Article
• Language: English
• Subjects: Heavy metals; Mobilization/accumulation; Redox barrier; Sediment
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/S0927-7757(03)00231-0

Nowadays, electrokinetic remediation is one of the popular and cheapest in situ remediation techniques for contaminated soils. This method uses a low-level electrical energy and is known for removal of heavy metals like, cadmium, chromium, copper, iron, lead, mercury, nickel, zinc and the metalloid arsenic from polluted and spiked soils. The driving force is the migration of those ions in the soil body by the applied electric field. In most cases the heavy metals are concentrated near the cathode depending on the actual pH profile and the solubility products of formed non-soluble compounds (oxides, oxihydroxides, carbonates etc.). Sometimes it is also possible to deposit heavy metals directly at the cathode surface (e.g. copper, cadmium). Often it is necessary to add an acid to prevent the precipitation during such an electrochemical process. Therefore, the mobilization and accumulation of cadmium, lead and zinc at the sediment–water interface with different positions and conditions of the electrode arrangement was studied. The tests were carried out with a natural heavy metal containing sediment from the river Weisse Elster of Germany. The results showed that they were mobilized by the effects of the anodic polarization and transported by migration from sediment into the water–sediment interface. By constructing a pH-barrier at the sediment–water interface, those metals were precipitated at the steep pH-gradient. The metals were accumulated at the sediment–water interface. In the opposite situation, where the cathode is at the sediment surface, the alkaline front penetrates into the sediment and a fixation of amphoteric metals at weak alkaline and a mobilization at strong alkaline conditions occurs. In our view, the electrode arrangement anode in the sediment–cathode in the water body with a relatively small distance between both electrodes to create a steep pH- and Eh-gradient is the best arrangement for the predicted mobilization and accumulation of those heavy metals. After this it should be possible to mobilize them in a relative short time and to remove the concentrated heavy metals from the solid phase by reversing the polarity of the electrodes. This will be a possibility to support the in-situ-cleaning of sediments by constructing a pH- and Eh-barrier to eliminate the heavy metals.