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In recent years, electrokinetic (EK) remediation method has been widely considered to remove metal pollutants from contaminated dredged sediments. Chelating agents are used as electrolyte solutions to increase metal mobility. This study aims to investigate heavy metal (HM) (As, Cd, Cr, Cu, Ni, Pb and Zn) mobility by assessing the effect of different chelating agents (ethylenediaminetetraacetic acid (EDTA), ethylenediaminedisuccinic acid (EDDS), nitrilotriacetic acid (NTA) or citric acid (CA)) in enhancing EK remediation efficiency. The results show that, for the same concentration (0.1 mol L(-1)), EDTA is more suitable to enhance removal of Ni (52.8 %), Pb (60.1 %) and Zn (34.9 %). EDDS provides effectiveness to increase Cu removal efficiency (52 %), while EDTA and EDDS have a similar enhancement removal effect on As EK remediation (30.5∼31.3 %). CA is more suitable to enhance Cd removal (40.2 %). Similar Cr removal efficiency was provided by EK remediation tests (35.6∼43.5 %). In the migration of metal-chelate complexes being directed towards the anode, metals are accumulated in the middle sections of the sediment matrix for the tests performed with EDTA, NTA and CA. But, low accumulation of metal contamination in the sediment was observed in the test using EDDS.

A laboratory study was undertaken on the transport and the deposition of suspended particles (silt of modal diametre 6 µm) in three columns of different length, filled with glass beads or gravel. Tracer tests were carried out at various flow velocities by short pulses of a mixture of suspended particles/dissolved tracer. The breakthrough curves were competently described with the analytical solution of a convection dispersion equation with a first-order deposition rate and the hydro-dispersive parameters were deduced. For the same experimental conditions, the results showed a difference in the behaviour of the suspended particles transport and deposition rates within the two porous media tested. The internal structure of both media governs the particle-grain collision frequency as well as the particles trapping. The scale effect was highlighted and affects the dispersivity, the size exclusion effect, the recovery rates and the deposition rates. Longitudinal dispersion increases with mean pore velocity and is described with a nonlinear relationship. The dispersivity increases with the column length. The size exclusion effect is more important in the short column. The recovery rate increases with flow velocity and decreases while increasing column length. The deposition rates increases until a critical flow velocity then decreases. This critical velocity is also sensitive to the scale effect, and increases with the column length.

International audienceThis paper discusses the transport and deposition rate of suspended particles in saturated porous media. The laboratory study used a column where the porous media were subjected to a steady state flow. Two materials were used: gravel and glass beads. Silt particles of 14 µm mean diameter were used as suspended particle tracer. By means of short pulse injection, transport tests using suspended particles and a conservative tracer were performed. The breakthrough curves were well described with the analytical solution of the convection-dispersion equation with first-order deposition rate. The experiments were performed under different flow rates. The particle size distribution, the porous media, and the flow rates tested were the main factors retained in this study to investigate the mechanisms governing the transport and deposition kinetics. The results showed the existence of a flow rate beyond which suspended particles travel faster than the conservative tracer. A decrease of the deposition rate of suspended particles beyond a critical flow velocity is observed too. Such behaviour makes us think of the couple hydrodynamic-gravity forces at high flow rates. As the hydrodynamic force increases particle deposition rates are reduced due to the effect of hydrodynamic forces inhibiting the deposition

The maintenance of harbor waterways generates large amounts of dredged sediments which are often rich in coexisting organic and inorganic contaminants. Electrokinetic remediation treatments have recently been developed for the simultaneous removal of heavy metals and polycyclic aromatic hydrocarbons (PAHs), using various enhancing agents generally tested sequentially. In this study, different processing fluids were tested, alone or mixed, to improve the decontamination of aged model sediment contaminated with cadmium, lead, chromium, copper, zinc, and five PAHs. Nitric acid (NA) and citric acid (CA) were tested to avoid the formation of an alkaline front into the sediment and favor the metals removal, while an anionic surfactant [sodium dodecyl sulfate (SDS)] and a nonionic surfactant (Tween 20) were tested to solubilize and mobilize PAHs. Processing fluids were circulated under a constant voltage gradient of 1 V cm -1 for 10-14 days. NA showed an excellent potential to remove metals (76.8-99.9 % removal) and PAHs (70.3-89.7 % removal) in a single run. Besides, the mixture of Tween 20 and CA, more environmental friendly, could be considered as a relatively good processing fluid for the simultaneous removal of metals (10.3-90.8 % removal) and PAHs (53.6-61.6 % removal) from the fine-grained sediment, while SDS mixed to CA was not a good candidate for this purpose (0.1-65 % removal for metals and 34.1-41.0 % removal for PAHs).

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