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The purpose of this work is to study the dynamics between the matrix of a contaminated marine sediment, its contaminants and various desorbing solutions by means of equilibrium tests, sedimentation trials and zeta potential, with the focus on assessing optimum enhancing solutions for decontamination purposes. Materials and methods The sediment samples were analysed to determine their physico-chemical characteristics: particle size distribution, solids concentration, total organic carbon (TOC), content of heavy metals, organic contaminants, mineralogical phases, zeta potential and buffer capacity. Twelve extracting solutions of different nature were used for equilibrium tests, in which the dynamic behaviour of the sediment was evaluated. Elemental analysis was carried out for the sediment samples and the solutions before and after the tests. Results and discussionThe sediment was mainly composed of clay and lime, with a high content of iron, which has a strong influence on sorption-desorption processes. The sediment had a considerable buffer capacity at low and high pH values. The desorption of the metals was not proportional to pH. The highest decrease in the concentration of metals from the sediment was obtained with 0.2 M ethylenediaminetetra-acetic acid (EDTA) and 1 M nitric acid, while the lowest degree of metal extraction occurred in pure water and potassium iodide (KI). Conclusions The most important parameters for contaminant release were complexation ability of the solution for the sediment components and pH of the solution. A promising design for the remediation treatment for the investigated sediment includes complexation and strong acid agents.

Purpose The study focuses on the use of surfactants as enhancing solutions in electrokinetic remediation trials on sediments, with the hypothesis that they will allow heavy metals to desorb from organic matter, and thus favour their removal to the solution. Materials and methods A total of 15 remediation trials were conducted. As enhancing solutions, four different non-ionic commercial surfactants were used, either alone or in combination with citric acid (CA) or ethylenediaminetetraacetic acid (EDTA) in both compartments. A comparison with distilled water was also performed. 30–40 VDC was applied between activated titanium electrodes. The pH, electroosmotic flow (EOF), mineralogy of the samples (before and after the electrokinetic tests), and the percentage of removal of Cr, Ni, Cu, Zn, As, Cd, Pb, and Hg were determined. Results and discussion Every test showed an increase in current intensity during the first hours, and in certain cases, additional intensity peaks were found during the trial, which were mostly attributed to the establishment of EOF episodes. Depending on the case, EOF was transferred to the anolyte or the catholyte. Reversal of EOF occurred in one case, but was not detected in the others. Cr was primarily removed when CA was used. In the catholite, Ni, Cu, Zn, and Pb were extracted preferentially with EDTA. Surfactant B was more effective at removing Zn and As. Only a few treatments removed Cd with CA and surfactant C extracting the most. Hg was detected in the electrolytes of some experiments, being extracted with surfactant A in the catholyte in all cases, and with surfactant B and surfactant C with EDTA. Cr, Ni, Cu, Zn, Cd, and Pb were preferentially collected in the anolyte. Cu and Zn were found in trace levels in the catholyte. Conclusions Surfactants have been shown to help with metal solubilisation to different degrees depending on the metal. Each metal has a unique optimal species combination in the enhancing electrolyte. The direction of the EOF is determined by the chemical conditions of the system as a whole, not by the type of surfactant. Surfactants in combination with CA and EDTA improve desorption in general, which has been attributed to an increase in charge density passed during the tests rather than a symbiotic enhancement between both types of enhancing solutions.