Assessing the influence of particle size and dissolved organic carbon on heavy metal leaching from construction and demolition waste modified with carbon-rich materials

Construction and demolition waste (CDW) represents a substantial proportion of the overall waste generated in both developed and developing countries, attracting attention due to its large volume, reuse potential, and environmental risks. This study aims to investigate the impact of biochar and activated carbon on the leaching characteristics of copper (Cu) and nickel (Ni) from CDW towards groundwater resources. This research investigates, for the first time, the impact of dissolved organic carbon (DOC) on the mobilization and release of Cu and Ni in biochar-amended CDW. The leaching behavior of Cu and Ni from CDW was assessed using the column leaching test. Activated carbon and wood-derived biochar, produced at temperatures up to 750°C, were incorporated into the columns and applied to CDW at two different rates. Column leachates collected at different intervals were analyzed for Cu and Ni using inductively coupled plasma-mass spectrometry (ICP-MS). During the experiment, the concentrations of Cu and Ni in the effluents of the unamended column decreased by 94.67% and 73.68%, respectively. Applying 2% activated carbon to CDW reduced Cu and Ni leachate release by 30.82% and 33.33%, respectively, compared to 2% pulverized biochar. The results indicated high initial mobilization followed by a rapid decline in leached concentrations of the heavy metals in all treatments. The application of pulverized biochar and activated carbon significantly reduced leaching and cumulative release of heavy metals from CDW into water, whereas crushed biochar elevated mobilization and leached concentrations of Cu and Ni. A positive correlation was obtained between the leached concentrations of Cu and Ni from CDW with DOC. The results indicated that biochar could serve as a promising and cost-effective carbon-rich amendment for immobilizing Cu and Ni within CDW; however, biochar particle size played a critical role in controlling the mobilization and release of heavy metals in CDW.