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Biochar was tested as an active capping material for oil spill contaminated sediment and its performance was compared to activated carbon and organoclay. Polydimethyilsiloxane fibers were used as passive samplers to evaluate the vertical porewater concentration of selected polycyclic aromatic hydrocarbons through the sea-sediment and the capping layer (1 cm resolution). Experiments were carried out on the laboratory scale using 7.5 cm (∼500 g) of contaminated sea-sediment that were capped with 3 cm (∼150 g) of capping materials. The porewater concentrations of the polycyclic aromatic hydrocarbons were compared using a reactive-diffusion model. Biochar showed a greater capping efficiency than activated carbon and organoclay. For example, anthracene porewater concentrations in the first centimetre of capping material, after 1 month, were reduced by 69%, 56% and 99% respectively for activated carbon, organoclay and biochar. The porewater concentrations were used to model the long term (≥12 months) behaviour of various cap configurations with a numerical simulations. Biochar can be considered a cost-effective alternative to the more consolidated sorbent materials. [ABSTRACT FROM AUTHOR]

Due to anthropogenic activities, heavy metals are discharged into the hydrosphere and deposit onto the sediment. Heavy metals remobilize through physical disturbance and change in environmental conditions, posing a risk to environments and human health. Among several remediation methods, active layer capping is considered to be more feasible due to its financial and technical advantages; however, its long-term effects remain unknown. To overcome this problem, this work applied a novel, recoverable amendment, sulfurized magnetic biochar (SMBC), to remediate multiple heavy metal (Cu, Ni, Zn, Cr, Hg, and MeHg) contaminated sediment. Physiochemical characterization shows magnetite (Fe 3 O 4) crystalline in both magnetic biochar (MBC) and SMBC, with such characteristics resulting in a greater surface area (324.9 and 346.3 m2/g) than BC (39.6 m2/g) and SBC (65.0 m2/g). FeS crystalline was also observed in SMBC, which plays an important role in controlling heavy metal release from sediment. Microcosm experiments indicated the effectiveness of SMBC in lowering aquatic Cu, Ni, Zn, Hg, and MeHg releases was significantly greater than the other three biochar materials. Notably, the recovery of SMBC by magnetism was 87%, demonstrating the exceptional recoverability of SMBC from seawater and sediment. Based on its robust capability in lowering Cu, Ni, Zn, Hg, and MeHg release and excellent recoverability from seawater and sediment, this technique represents a practical alternative to conventional approaches for heavy metal immobilization from sediment. [Display omitted] • Sulfurized magnetic biochar (SMBC) was used to remediate metal-containing sediment. • SMBC had high surface area (346.3 m2/g) and micropore surface area (297.2 m2/g). • SMBC effectively immobilized the most heavy metals (Cu, Ni, Zn, Hg, and MeHg). • FeS in SMBC plays an important role in controlling heavy metal release. • SMBC was successfully recovered via magnetic separation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Geopolymers are novel active capping materials for contaminated sediments. • Metal(loid) bioavailability decreased compared to unamented sediment. • Slag-based geopolymer was more effective than metakaolin geopolymer or vermiculite. • The overall best material, alkali-activated slag, was suitable for Al, Cu, Fe and Ni. • Metakaolin geopolymer was suitable for Cu, Cr, and Fe and vermiculite for Al and Zn. Abstract Metal(loid) contamination in sediments is a widespread environmental issue. Sediments act normally as metal(loid) sinks, but if chemical conditions (such as pH or redox potential) change, they can become sources of secondary pollution. Consequently, various strategies for both in and ex situ remediation of contaminated sediments have been developed. One promising method is active capping, which involves the injection of adsorbents as a layer on the sediment surface or the mixing of adsorbents within the sediment. Adsorbents decrease the bioavailability of metal(loid)s. In the present work, the suitability of alkali-activated blast-furnace-slag, metakaolin geopolymer, and exfoliated vermiculite were evaluated for in situ stabilization of two metal(loid)-contaminated lake sediments through laboratory-scale experiments. The results indicated that adsorbent amendments had metal(loid)-specific performance: alkali-activated blast-furnace slag was suitable for Al, Cu, Fe, and Ni; metakaolin geopolymer for Cu, Cr (total), and Fe; and vermiculite for Al and Zn. None of the materials could stabilize Ba, Sr, or Ti. Furthermore, the amendments performed differently in two different lake sediments, implying that the effectiveness of the amendments needs to be confirmed on a case-by-case basis. [ABSTRACT FROM AUTHOR]