Removal of mercury from marine sediments by the combined application of a biodegradable non-ionic surfactant and complexing agent in enhanced-electrokinetic treatment

In this work, the Hg removal potentiality of an electrokinetic (EK) decontamination treatment enhanced by a biodegradable complexing agent (MGDA) also in combination with a biodegradable surfactant (Tween (R) 80) was investigated to decontaminate heavily contaminated marine sediments. The main results revealed that the nature of sediments and their interactions with different enhancing agents significantly influenced the remediation processes. A general increase of pH values along the sediment specimen was observed due to the strong buffering capacity of the carbonates, which are the main constituent minerals. This, in combination with the high organic matter and sulphide sediment content, resulted in very poor contaminant mobilization without any appropriate conditioning agents. The use of EDTA as a processing fluid resulted in a modest increase in Hg removal of similar to 15%, whereas a further improvement in the Hg removal rate (similar to 39%) was achieved by replacing EDTA with MGDA as the anodic solution in response to its ability to form stable negative complexes with mercury, which can be moved towards the anode. A significantly higher Hg-removal of similar to 71% was obtained by the simultaneous use of MGDA and Tween (R) 80 due to their synergic action in remedial processes and, especially, due to the improved selective action of the non-ionic surfactant adopted in favour of organo-Hg-complex removal. Compared with other Hg-removal technologies, the investigated enhanced-EK treatment allows the achievement of remediation targets, which can hardly met by one-stage processes. The data can be useful for predicting the remediation activity responses, as well as for guiding the design and scaling-up of EK treatment of Hg-contaminated sediments. In addition, the knowledge of the investigated Hg-removal mechanism can provide basic information, which is helpful for improving the development of further novel enhanced-EK technologies. (C) 2016 Elsevier Ltd. All rights reserved.