Huaqing Wang

There is an extensive water exchange between river water and groundwater in natural conditions

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.

Internal erosion has long been a major problem associated with earth structures. Laboratory experiments provide a potential insight into the processes involved. The design of dam embankments is usually based on hydraulic criteria. Some of the hydraulic criteria are based on sediment transport theory where the critical velocities are derived from the different approaches comparing the drag force of the particles and the hydraulic load. Many hydraulic criteria for suffusion are based on tests with consistent soil samples or on analytical descriptions of the particle and pore geometry derived from characteristic parameters. An experimental study of soil suffusion is performed on a laboratory column subjected to different flow conditions and soil parameters. The permeability variation along the soil column is controlled. The initiation and the kinetics of soil suffusion are investigated using a laboratory fine grained soil (mixed sand and clay) and a natural soil. Attempts are also made to assess the influence of the clay content and the type of fine particles. The results demonstrate that low hydraulic gradients can cause suffusion. The critical shear stresses for various soil tested differ slightly when the nature of grains and fines are varied. The hydraulic gradient affects the cumulative eroded mass upon a certain threshold value.