Release behavior of heavy metals during treatment of dredged sediment by microwave-assisted hydrogen peroxide oxidation

•Chemical oxidation is used to remediate river sediment.•The oxidation reduction potential of sediment slurry was greatly increased.•The final pH of sediment slurry was markedly decreased.•High release of metals was found during microwave-assisted H2O2 oxidation.•Metals in residue were found higher stability and lower risk to the environment.

Chemical oxidation is often used to remediate river sediment contaminated with organic contaminants, which might cause the release of heavy metals. However, the mechanisms of the heavy metals release are not fully understood. In this work, dredged sediment was collected from Xiawan River in Hunan province, China, and the release behavior of heavy metals from the sediment treated with microwave-assisted hydrogen peroxide oxidation (MW-H2O2) process was investigated. The release efficiency of Cu, Cd and Zn was stable with pH varying from 0 to 4.0 and declined dramatically when the pH went higher than 4.0. H2O2 was advantageous to improve the release efficiency for Cu, Zn and Pb with H2O2 concentration from 0 M to 0.2 M, and from 0 M to 0.1 M for Cd. The release efficiency of Cu and Pb increased significantly with increasing microwave temperature from 25 °C to 85 °C and microwave time from 0 min to 6 min. After treatment by MW-H2O2 process, the metals in the sediment have higher stability and thus lower risk to the environment.