Aqueous Mercury Removal with Carbonaceous and Iron Sulfide Sorbents and Their Applicability as Thin-Layer Caps in Mercury-Contaminated Estuary Sediment

Abstract

This study aimed to investigate the Hg removal efficiency of iron sulfide (FeS), sulfurized activated carbon (SAC), and raw activated carbon (AC) sorbents influenced by salinity and dissolved organic matter (DOM), and the effectiveness of these sorbents as thin layer caps on Hg-contaminated sediment remediation via microcosm experiments to decrease the risk of release. In the batch adsorption experiments, FeS showed the greatest Hg2+ removal efficiencies, followed by SAC and AC. The effect of salinity levels on FeS was insignificant. In contrast, the Hg2+ removal efficiency of AC and SAC increased as increasing the salinity levels. The presence of DOM tended to decrease Hg removal efficiency of sorbents. Microcosm studies also showed that FeS had the greatest Hg sorption in both freshwater and estuary water; furthermore, the methylmercury (MeHg) removal ability of sorbents was greater in the freshwater than that in the estuary water. Notably, for the microcosms without capping, the overlying water MeHg in the estuary microcosm (0.14−1.01 ng/L) was far lesser than that in the freshwater microcosms (2.26−11.35 ng/L). Therefore, Hg compounds in the freshwater may be more bioavailable to microorganisms in methylated phase as compared to those in the estuary water. Overall, FeS showed the best Hg removal efficiency, resistance to salinity, and only slightly affected by DOM in aqueous adsorption experiments. Additionally, in the microcosms, AC showed as the best MeHg adsorber that help inhibiting the release of MeHg into overlying and decreasing the risk to the aqueous system.

Ecological and Health Risk of Soils, Sediments, and Water Contamination

“…The HAP and OSP showed the highest removal efficiencies towards Ni, Cr, Cu, and Zn, with CB taking the third place. However, the FeS and CB played a more significant role in Hg removal, corresponding to the findings by Ch'ng et al [9]. The mobility of heavy metals in aquatic environments by desorption from sediments into the surface water is controlled by many biological and chemical factors, making the surface water a major intermediate source of toxic metals in benthic sediments.…”

“…The main approach is to allow the sediment left in place but decreasing further contamination from resuspension of contaminants by the capping layer [8]. Ch'ng investigated mercury (Hg) removal efficiency of iron sulfide (FeS), sulfurized activated carbon (SAC), and raw activated carbon (AC) sorbents influenced by salinity and dissolved organic matter (DOM), and the efficiency of these sorbents as thin layer caps on the remediation of Hg-contaminated estuary sediment to decrease the risk of release [9]. They elucidated that FeS on Hg removal was not significantly affected by salinity levels and maintained with high removal efficiency.…”