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The objectives of this study are to assess the effectiveness of limestone (LS), steel slag (SS), and activated carbon (AC) as capping materials to sequester trace metals including As, Cd, Cr, Cu, Ni, Pb, and Zn in heavily contaminated marine sediments and to minimize the release of these metals into the water column. A flat flow tank was filled with 10 mm of capping material, contaminated sediments, and seawater, and the metal concentrations were monitored over 32 d. After completion of the flow tank experiments, the sediments below the capping material were sampled and were sequentially extracted. SS effectively reduced the As, Cr, Cu, Ni, Pb, and particularly Cd elution from the contaminated sediments to the overlying seawater. Adsorption and surface precipitation were the key mechanisms for interrupting the release of cationic trace metals by SS. LS was appropriate for interrupting the release of only Cu and Pb with high hydrolysis reaction constants. AC capping could interrupt the release of Cr, Cu, Ni, and particularly Zn from the sediments by binding with the metals via electrostatic interaction. The results obtained from the sequential extraction revealed that LS capping is appropriate for stabilizing Zn, whereas AC is appropriate for Cd and Pb. LS, SS, and AC can be applied effectively for remediation of sediments contaminated by trace metals because it interrupts their release and stabilizes the trace metals in the sediments. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to develop a novel integrated active capping system and to investigate its efficiency in the remediation of nitrobenzene-contaminated sediment. An integrated Fe(0)–sorbent–microorganism remediation system was proposed as an in situ active capping technique to remediate nitrobenzene-contaminated sediment. In this system, nitrobenzene was reduced to aniline by Fe(0), which has a much better biodegradability. The sorption capacity and structural properties of cinder was measured to examine its applicability as the sorbent and matrix for this integrated capping system. Indigenous microorganisms from Songhuajiang River sediment, which was contaminated by nitrobenzene and aniline in Chinese Petrochemical Explosion in Jilin, were acquired one month after the explosion and used in this active capping system to degrade nitrobenzene and its reduced product, aniline. A bench-scale remediation experiment was conducted on a mimicked nitrobenzene-contaminated sediment to investigate the efficiency of the integrated capping system and the synergistic effects of the combined components in the active capping system. The results show that this integrated active capping system can effectively block the release of target pollutants into the upper-layer water and remove the compounds from the environment. [ABSTRACT FROM AUTHOR]

Abstract: Collateral Channel is a heavily polluted former navigation slip to the Chicago Sanitary and Ship Canal (Illinois, USA). Characterization of sediment cores taken in the channel show high levels of heavy metals, polycyclic aromatic hydrocarbons (PAHs) and other contaminants in deposited sediment dating back to the 1800''s. Of these, PAHs were the contaminants of greatest concern based upon exceedance of sediment contamination criteria (Σ16 PAHs up to 1500mg/kg). Benthic animal counts revealed a lack of biodiversity, with relatively low levels of small tubificid oligochaetes (generally <3000/m2) in surficial sediments. Comparison of surficial sediment contaminant levels between 1995 and 2005 showed few decreases in contaminant levels, indicating a lack of “natural recovery” processes occurring in the channel. These results led to an analysis of sediment amendments for an active capping demonstration project in the channel using transport models developed in our previous work (Viana et al., 2008). Based on the sediment characterization and modeling results, the active capping design will be focused on organic contaminant sequestration through the use of organoclay. A site-specific difficulty is the substantial rates of gas ebullition from anaerobic organic matter biodegradation in the sediments, particularly in the summer months. These gases can open advective channels that may result in substantial pollution release and compromise cap effectiveness, and thus the capping scenario must control for such releases. The active capping layer will underlay a sloped sand layer and a high permeability gas venting system to allow biogenically-produced gas migration to shoreline collectors through an innovative support grid. The cap will include an overlaying wetland to remove nutrients from the adjoining Chicago River and provide a public recreational space. [Copyright &y& Elsevier]

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]