Enhanced remediation of organotin compounds and metal(loid)s in polluted sediments: Chemical stabilization with mining-wastes and nZVI versus physical soil washing

Here we describe two innovative approaches for remediating sediments contaminated with organotin compounds (OTCs, mainly TBT) and metal(loid)s. The first involves chemical stabilization through amendments with nanoscale zero-valent iron (nZVI), dunite mining waste, and coal tailings, materials that have not been previously studied for OTC remediation. The second focuses on physical soil washing, using grain-size separation and magnetic separation to isolate the most polluted fractions, thereby reducing the volume of contaminated material destined for landfills. The results for the first approach indicated that OTC degradation occurred mainly through nZVI application, with concurrent immobilization of As and mobilization of Cu. Furthermore, combining nZVI with coal tailings enhanced OTC degradation whereas dunite mining waste effectively immobilized Zn. In turn, in the second approach, grain-size separation efficiently removed coarse material (>500 μm) with low pollutant concentrations. Subsequent magnetic separation selectively concentrated less than 5% of the initial volume of sediment in a magnetic fraction that showed the highest contaminant content. Therefore, 95% of material revealed lower contaminant concentrations than the feed material. These findings highlight the potential of combining physical soil washing, which significantly reduces the volume of contaminated sediments, with chemical stabilization, which can effectively stabilize the polluted fractions isolated in the physical treatment.