Insights into processes and consequent metal(loid) behavior in dredged estuarine sediments upon electrokinetic treatment

Abstract

The use and reuse of natural and waste materials after treatment has become increasingly crucial as a means of achieving sustainable and environmentally-friendly solutions, and is part of a broader trend towards embracing circular economy principles. This study aims to understand the behavior of different elements (metal(loid)s and non-metals) and minerals during and after electrokinetic remediation (EKR) and to develop an effective approach to monitor its progress and overcome unwanted occurrences. In this regard, estuarine sediments, collected from Tancarville (Seine River estuary, France), were electrokinetically treated using a 64 L laboratory reactor; treatment was done 8 h per day for 21 days. The physico-chemical properties (pH, electric conductivity, and oxido-reduction potential) and current were monitored during treatment. The spatial evolution of the physico-chemical, physical (grain size distribution), mineral (mainly carbonates), organic, and elemental (As, Ca, Cl, Mg, Na, Pb, Sr, Zn, and Zr) characteristics was studied to assess the treatment efficiency. The results showed that the acidic conditions in the anodic sediments caused the dissolution of carbonates (calcite, dolomite, and aragonite), resulting in a considerable reduction in As, Zn, and Pb. Additionally, Cl as well as electric conductivity were significantly reduced from most sediments, which is essential in agricultural practices. Furthermore, materials had precipitated and settled in the anolyte and catholyte chambers, which acted as sorbents for elements that were released from the sediments (mainly Zn and As). Finally, three distinct phases occurred during treatment and were mainly linked to the current intensity and electric conductivity on the one hand, and the dissolution of carbonates and metal(loid) release on the other. This approach can be used to treat sediments and other media to improve the overall efficiency of remediation processes and create an end product with desired characteristics.