Background: Mercury (Hg) is recognized as one of the 10 most toxic elements and is much more persistent in soils than in other environmental compartments. However, an effective, environmentally friendly, economical, and applicable at large-scale technology for the remediation of soils contaminated by Hg has not yet been established. This study evaluates the feasibility of a new carbon foam-based product for the remediation of three soils contaminated with Hg, and infers the mobilization or immobilization mechanism through a detailed study of Hg speciation. Results: Soil treatment with the carbon foams, one of them impregnated with goethite, reduced Hg availability by between 75 and 100%. Mercury associated to humic acid (Hg-HA) determined the proportion of mobility and availability of Hg when soils were treated with carbon foams. When the pH dropped, the structure of HA changed causing the Hg-HA to become part of the unavailable fraction of the soil along with HgS. The carbon foam impregnated with goethite did not mobilize Fe as occurred with ZVI nanoparticles. The presence of acid groups on the surface of the foam (carboxyl, quinone and phenolic groups) can bind metal cations strongly improving Fe immobilization. Conclusions: A novel carbon foam-based amendment was efficient in immobilizing Hg in all the soils studied. The carbon foam impregnated with goethite, in addition to not mobilizing Fe, had the additional advantage of its lesser effect on the electrical conductivity of the soil. This novel approach could be considered as a potential amendment for other sites contaminated with Hg and/or other metal(loid)s.
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