Stabilization characteristics of metal ions in marine-contaminated sediments by recycled aggregate

Recycling and reusing of recycled aggregate (RA) is a significant contribution to environmental conservation for sustainable development. However, the recycling of RA is mainly limited to the use of road construction in low-specification applications. In this study, we evaluated the contribution of the stabilization (or immobilization) of heavy metals (Ni, Zn, Cd, and Pb) in marine-contaminated sediment by RA. Recycled aggregate was obtained by natural drying and grinding for use in the experiments. The RA was mixed with marine-contaminated sediment at 5 wt%. The amendments were applied in a wet-curing stabilization process for 5 months. For the stabilization, sequential extraction procedure, toxicity characteristic leaching procedure (TCLP), waste official test (WOT), and potential ecological risk index (PERI) were adopted as the evaluating methods. The results were used to test for an in situ stabilization effect. The results showed that the marine-contaminated sediment was polluted by heavy metals such as Ni and Zn. From the results of sequential extraction, compared to raw sediment, Ni, Cd, Pb, and Zn in the residual fraction increased 16.9, 14.4, 12.7, and 5.0%, respectively, after 5 months of composite treatment. Moreover, after the stabilization treatment with RA, the bioavailability and eco-toxicity of the heavy metals were significantly reduced as the mobile, bioavailable heavy metal fractions were transformed into relatively stable (less bioavailable) fractions. Results indicated that RA treatments were effective in reducing the mobilization of heavy metals in marine-contaminated sediments. Overall, the results of this study suggest that RA can be recycled into an effective marine-contaminated sediment-stabilizing agent.