Immobilization and recycling of contaminated marine sediments in cement-based materials incorporating iron-biochar composites.

Sustainable stabilization/solidification (S/S) incorporating biochar for hazardous wastes has attracted increasing attention. In this study, contaminated marine sediments were remediated and recycled as useful materials via cement-based S/S process incorporating iron-biochar composites derived from incinerated sewage sludge ash (ISSA) and peanut shell. Results showed that incorporation of 20% iron-biochar composites notably increased the Cr immobilization (52.8% vs 92.1-99.7%), while attained similar As (70%) and Cu (95%) immobilization efficiencies compared to the control group (CK) prepared with plain cement as the binder based on the Toxicity Characteristic Leaching Procedure. S/S products with the addition of ISSA derived iron-biochar composite had a mechanical strength of 5.0 MPa, which was significantly higher than its counterparts derived from pure iron oxide or pristine biochar (< 4.5 MPa). Microstructural and spectroscopic characterizations and chemical leaching experiments demonstrated that reduction of Cr(VI) to Cr(III) followed by formation of Cr-Fe precipitates by zero valent iron in iron-biochar composites contributed to the enhanced immobilization efficacy of Cr(VI) compared to CK. Overall, these results demonstrated the potential of applying ISSA and peanut shell derived iron-biochar composites as additives in the cement-based S/S treatment for contaminated sediments.