Mechanism of Hg(II) immobilization in sediments by sulfate-cement amendment

Abstract

Reactive amendments such as Portland and super-sulfate cements offer a promising technology for immobilizing metalloid contaminants such as mercury (Hg) in soils and sediments through sequestration in less bioavailable solid forms. Tidal marsh sediments were reacted with dissolved Hg(II) in synthetic seawater and fresh water solutions, treated with Portland cement and FeSO4 amendment, and aged for up to 90 days. Reacted solids were analyzed with bulk sequential extraction methods and characterized by powder X-ray diffraction (XRD), electron microscopy, and synchrotron X-ray absorption spectroscopy at the Hg LIII- and S K-edge. In amended sediments, XRD, SEM and sulfur K-edge XANES indicated formation of gypsum in seawater experiments or ettringite-type (Ca6Al2(SO4)3(OH)12.26H2O) phases in fresh water experiments, depending on the final solution pH (seawater ∼8.5; freshwater ∼10.5). Analysis of Hg EXAFS spectra showed Cl and Hg ligands in the first- and second-coordination shells at distances characteristic of a polynuclear chloromercury(II) salt, perhaps as a nanoparticulate phase, in both seawater and fresh water experiments. In addition to the chloromercury species, a smaller fraction (∼20-25%) of Hg was bonded to O atoms in fresh water sample spectra, suggesting the presence of a minor sorbed Hg fraction. In the absence of amendment treatment, Hg sorption and resistance to extraction can be accounted for by relatively strong binding by reduced S species present in the marsh sediment detected by S XANES. Thermodynamic calculations predict stable aqueous Hg-Cl species at seawater final pH, but higher final pH in fresh water favors aqueous Hg-hydroxide species. The difference in Hg coordination between aqueous and solid phases suggests that the initial Hg-Cl coordination was stabilized in the cement hydration products and did not re-equilibrate with the bulk solution with aging. Collectively, results suggest physical encapsulation of Hg as a polynuclear chloromercury(II) salt as the primary immobilization mechanism.

Control of mercury and methylmercury in contaminated sediments using biochars: A long-term microcosm study

“…Different reactive materials are available for stabilizing Hg, including activated carbon (AC) (Gilmour et al, 2013;Hilber and Bucheli, 2010;Patmont et al, 2015), zerovalent Fe (Weisener et al, 2005), sulfurized clay (Gibson et al, 2011), sulfate-type cements (Serrano et al, 2012;Serrano et al, 2016), sulfur and iron (Zhong et al, 2018), and biochars (Ahmad et al, 2014;Li et al, 2017;Liu et al, 2016). However, most of the reactive materials are expensive and not practical for large contaminated sites, resulting M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 4 in the need to identify cost-effective materials to control Hg for remediation of large areas.…”

Evaluation of mercury stabilization mechanisms by sulfurized biochars determined using X-ray absorption spectroscopy

“…Micro-X-ray fluorescence (µ-XRF) mapping has also been widely used to characterize the spatial distribution of Hg in various materials [36][37][38][39][40]. One drawback of µ-XRF mapping is that the fluorescence received by the detector is the sum of the signal along the incident beam path through the sample.…”

Design of Research on Performance of a New Iridium Coordination Compound for the Detection of Hg2+

“…In the molecular design of these two coordination compounds, the sulfur atom is introduced therein, which, as a soft base, could react with the soft acid Hg 2+ , thus to realize the detection of Hg 2+ . The result of research will provide the theoretical and technical support for further development and ultimate commercial application of the phosphorescent chemical sensor [ 59 , 60 , 61 , 62 ].…”