Mechanism of electrochemical chloride removal

This paper presents the first laboratory results obtained from continuous monitoring of the free chloride content in concrete blocks during electrochemical chloride removal (ECR). Chloride sensitive electrodes have been embedded at different depths in concrete specimens and the free chloride concentration was measured during ECR. The total chloride content was determined prior to and after the electrochemical treatment. Time and space resolved data on the removal of chloride ions and information concerning the relationship between bound and free chloride was obtained. Due to the removal of free chloride during the treatment, bound chloride is dissolved in order to re-establish the equilibrium between bound and free chlorides. The rate of release of bound chloride is slow compared to the rate of chloride removal and thus the ECR process quickly becomes inefficient. Current off periods allow the system to re-establish the equilibrium between bound and free chlorides. Subsequently, the process is efficient again. The results are discussed with respect to treatment efficiency, treatment procedure and current distribution. It is concluded that the ECR process is currently applied in an inefficient manner and the charge required for the desalination can be reduced significantly. This is also of interest with regard to the risk of undesirable side-effects that currently limit the use of ECR. (c) 2007 Elsevier Ltd. All rights reserved.