The remediation of soil contaminated with organic compounds and heavy metals, alone or as a mixture, has becoming an environmental issue of worldwide concern. In the current study, four soils with variable TOC contents were sampled from two industrial sites, representing the high dose perfluorinated compounds (PFCs) and heavy metals (antimony, Sb and lead, Pb) contaminated soils. Two Fe rich waste materials (slag and Fe charcoal) produced during the melting process of iron and titanium ore were tested as remediation agents, with the target of immobilizing pollutants in the soil systems, preventing them from contaminating the environment.
Both materials were tested for their remediation efficacy of heavy metals (Pb and Sb) and PFCs contaminated soils. The slag and Fe-charcoal are rich in Fe and calcium (Ca), the abundant Fe oxyhydroxides endows both sorbents high affinity for metals. Together with the formation of Ca‒Pb/Sb‒Fe precipitates, Sb adsorption to slag and Fe-charcoal ranged from 8.2 ‒ 30.7 μg g-1 and 4.7 ‒ 26.3 μg g-1 respectively. For Pb, slag showed an adsorption of 3.0 ‒8.2 μg g-1, and this value of Fe-charcoal was 8.8 ‒ 13.7 μg g-1. Generally, organic matter in the soil system hindered the adsorption of both Sb and Pb by slag, most likely due to competition for the active sites on the sorbent. However, Fe-charcoal showed better performance with high TOC soils, which can be attributed to the formation of organo-metal complexes that helped the sequestration of Sb and Pb. Fe-charcoal showed promising performances in the immobilization of PFCs in mineral soil with low TOC content, the Freundlich constant (KF) ranged between 5.1 ‒6.5 (μg kg-1) (μg L-1)-n, with the nF values of 0.33 ‒ 0.44. However, the high organic content of the high TOC-soils drastically hindered the adsorption of PFCs by Fe-charcoal.
In general, both slag and Fe-charcoal can be used as reliable remediation agents for Pb and Sb contaminated soils, while the utilization of Fe-charcoal requires moderate to low content of organic carbon in the bulk soil for PFCs immobilization. The result of this study gives the option of reusing these Fe rich wasted materials as promising sorbents for both heavy metals and organic pollutants. Possible uses of these sorbents can be as soil amendments related to the heavily polluted industrial sites remediation or used as barriers in landfills for sorption of leachate contaminants.