Feasibility of Remediation of Heavy-Metal-Contaminated Marine Dredged Sediments by Active Capping with Biochar.

biochar (BC) has been proposed as a potential absorbent in the marine environments. This study attempts to understand the process of active capping using BC to prevent the release of heavy metals (Pb and Cd) from contaminated marine dredged sediments. The capping efficiency was assessed with a series of lab-scale column experiments. Results showed that the BC exhibits rough pore structure and higher specific surface area, as well as more surface organic functional groups, which is favorable for its adsorption capacity and selectivity towards heavy metals. The capping thickness of 2 cm for BC was sufficient to prevent the release of heavy metals from sediments, with the capping efficiency of 47% for Pb and 62% for Cd. Kinetic studies showed that heavy metals released into the overlying water can be described by a three-parameter sigmoidal kinetic model. Importantly, the fractions of heavy metals in the dredged sediments below the capping layer were analyzed to reveal the capping remediation mechanism. The outcomes of the present study indicate that capping with BC is a promising method to regulate the water environment by preventing the release of heavy metals from the contaminated dredged sediments.