A Laboratory Experiment: Remediation of Metal-Contaminated Marine Sediments with Medium Coarse Sand, Fine Sand, Silty Fine Sand and Clay Caps

In recent years, there has been an increasing demand for disposal of marine dredging materials. In suit capping (ISA) is an effective method for recycling these materials by using capping substances to keep pollutants in storage for an extended period. This research aims to evaluate the effectiveness of medium coarse sand, fine sand, silty fine sand, and clay proposed for capping marine sediments contaminated with trace heavy metals (including AS, Cd, Cr, and Cu) in marine sediments. The metal-contaminated sediment, capping substances and seawater are added to the experimental device successively and the effects of different cap substances and thicknesses on metal spillage within 48 h are monitored by ion chromatography. Results demonstrate that, due to the physical isolation, stabilization and chemical isolation of the capping method, the concentration of heavy metal ions reaches a stable state after 48 h of diffusion when the thickness of the capping material remains unchanged. The release barrier effect of 5 cm caps of the four tested materials on heavy metals can reach more than 90%. It’s noted that the higher the water depth, the higher the concentration of heavy metal. Additionally, the diffusion effect of heavy metal ions in contaminated soil is positively correlated with the thickness of caps. Suitable particle size gradation makes the capping effect of clay the best among the four test materials: after 48 h, the blocking effect of 9 cm clay on the release of heavy metals can reach 99%.