Electroremediation:  Removal of Heavy Metals from Soils by Using Cation Selective Membrane

When the electroremediation is used to remove heavy metals from soils, metals may precipitate as hydroxides near the cathode where the pH is raised, which limits the remediation efficiency. The pH rise is caused by the genera tion of hydroxyl ions as a result of cathodic hydrogen evolution reaction during the remediation. In previous studies, a method to deal with the pH impact was developed. In the method, to prevent the transport of the hydroxyl ions into the soil being treated, a length of tube filled with solution and containing no soil is placed between the cathode and the soil. The heavy metals can then preciptate in the water instead of in the soil. In this study, a new method is proposed and developed. A cation selective membrane is placed in front of the cathode to stop the advancement of hydroxyl front toward the anode. This can considerably reduce the water volume needed, while ensuring that the soil being treated is at low pH condition. Thus, metal precipitation could not occur in the soil and heavy metals may migrate out of the soil, and precipitate in the water. Some unexpected phenomena were encounted and solved. Bench-scale experiments have been conducted to remove copper from sand by the method. The experimental results show that a removal efficiency higher than 90% can be reached.