A simulation study of mercury immobilization in estuary sediment microcosm by activated carbon/clay-based thin-layer capping under artificial flow and turbation

• Published in: The Science of the total environment Vol. 708; p. 135068
• Main Authors: Ting, Yu, Ch'ng, Boon-Lek, Chen, Chi, Ou, Meng-Yuan, Cheng, Yung-Hua, Hsu, Che-Jung, Hsi, Hsing-Cheng
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.03.2020
• Subjects: Mercury; Methylmercury; Sediment turbation; Thin layer capping; Sediment turbation; Thin layer capping; Mercury; Methylmercury
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.135068

[Display omitted] •AC + kaolin and AC + bentonite were efficient to reduce Hg in overlying water.•AC + montmorillonite was inefficient to reduce Hg and may cause Hg breakthrough.•Sulfate, Fe, and Hg are co-dependent and can be highly impacted by turbation.•Direct evidences that AC/clay thin caps reduce sediment-to-water Hg flux are shown.•Sediment MeHg may increase due to caps, but would not release with stable caps. In-situ thin layer capping (TLC) is a promising sediment remediation approach that has been shown effective in immobilizing contaminants from releasing to natural biotas and human beings. This research intended to comprehend the effectiveness of Hg immobilization by TLC under turbation condition via a microcosm study. Three TLC caps with different activated carbon (AC)/clay combinations were applied to actual Hg-contaminated estuary sediment (76.0 ± 2.6 mg-Hg/kg). The caps with AC (3%) + bentonite (3%) and AC (3%) + kaolin (3%) were efficient in reducing both total mercury (THg) and methylmercury (MeHg) concentrations in overlying water by 75–95% and 64–98%, respectively, in the later stage of 75-d operation. In contrast, the AC (3%) + montmorillonite (3%) cap did not show a significant reduction on THg and MeHg in the overlying water, probably due to the unstable, suspension property of montmorillonite. The stable caps showed higher resistance to Hg breakthrough under occasional turbation events; however, a labile cap appeared to have dramatic Hg breakthrough when turbation occurred. It is therefore essential to note that with unstable caps, turbation events may result in unwanted secondary resuspension of contaminants.