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Results for “HgS precipitation”

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5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Impact of dissolved organic matter on mercury and methylmercury sorption to activated carbon in soils: implications for remediation

Activated carbon (AC) amendments have shown promise in reducing inorganic mercury (Hg(II) complexes, “Hg”) and methylmercury (MeHg) risk in contaminated soils. However, the effectiveness of AC in Hg and MeHg immobilization has varied among studies, suggesting that site biogeochemistry might dictate efficacy. In this study, we examined the effect of dissolved organic matter (DOM) on MeHg and Hg sorption to AC. We evaluated the impact of Suwannee River Humic Acid (SRHA) on sorption to AC directly using an isotherm approach and in a soil/AC mixture using slurry microcosms. Aqueous sorption coefficients to AC (log K AC ) for Hg-SRHA and MeHg-SRHA complexes were one to two orders of magnitude lower (Hg-SRHA = 4.53, MeHgSRHA = 4.35) than those for chloride complexes (HgCl 2 = 6.55, MeHgCl = 4.90) and more closely resembled the log K AC of SRHA (3.64). In anoxic, sulfidic soil slurries, the K AC for sulfide species appeared stronger than for chloride or SRHA species for both Hg and MeHg. AC significantly reduced porewater concentrations of both ambient MeHg and a fresh Me 199 Hg spike, and the addition of up to 60 mg L -1 SRHA did not reduce sorption to AC. The AC also reduced ambient Hg and 201 Hg porewater concentrations, but as SRHA concentration increased, the magnitude of solid phase sorption decreased. Speciation modeling revealed that SRHA may have impacted Hg distribution to the solid phase by reducing HgS precipitation. In conclusion, this study highlights the need for site-specific evaluation of AC efficacy and the value in developing biogeochemical models of AC performance for Hg control.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Sonochemical oxidation and stabilization of liquid elemental mercury in water and soil

Over 3000 mercury (Hg)-contaminated sites worldwide contain liquid metallic Hg [Hg(0) 1 ] representing a continuous source of elemental Hg(0) in the environment through volatilization and solubilization in water. Currently, there are few effective treatment technologies available to remove or sequester Hg(0) 1 in situ. We investigated sonochemical treatments coupled with complexing agents, polysulfide and sulfide, in oxidizing Hg(0) 1 and stabilizing Hg in water, soil and quartz sand. Results indicate that sonication is highly effective in breaking up and oxidizing liquid Hg(0) 1 beads via acoustic cavitation, particularly in the presence of polysulfide. Without complexing agents, sonication caused only minor oxidation of Hg(0) 1 but increased headspace gaseous Hg(0) g and dissolved Hg(0) aq in water. However, the presence of polysulfide essentially stopped Hg(0) volatilization and solubilization. As a charged polymer, polysulfide was more effective than sulfide in oxidizing Hg(0) 1 and subsequently stabilizing the precipitated metacinnabar (β-HgS) nanocrystals. Sonochemical treatments with sulfide yielded incomplete oxidation of Hg(0) 1 , likely resulting from the formation of HgS coatings on the dispersed µm-size Hg(0) 1 bead surfaces. Sonication with polysulfide also resulted in rapid oxidation of Hg(0) 1 and precipitation of HgS in quartz sand and in the Hg(0) 1 -contaminated soil. This research indicates that sonochemical treatment with polysulfide could be an effective means in rapidly converting Hg(0) 1 to insoluble HgS precipitates in water and sediments, thereby preventing its further emission and release to the environment. We suggest that future studies are performed to confirm its technical feasibility and treatment efficacy for remediation applications.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Modeling CO 2 -Brine-Rock Interaction Including Mercury and H 2 S Impurities in the Context of CO 2 Geologic Storage

This study uses modeling and simulation approaches to investigate the impacts on injectivity of trace amounts of mercury (Hg) in a carbon dioxide (CO 2 ) stream injected for geologic carbon sequestration in a sandstone reservoir at ~2.5 km depth. At the range of Hg concentrations expected (7-190 ppbV, or ~ 0.06-1.6 mg/std.m 3 CO 2 ), the total volumetric plugging that could occur due to complete condensation of Hg, or due to complete precipitation of Hg as cinnabar, results in a very small porosity change. In addition, Hg concentration much higher than the concentrations considered here would be required for Hg condensation to even occur. Concentration of aqueous Hg by water evaporation into CO 2 is also unlikely because the higher volatility of Hg relative to H 2 O at reservoir conditions prevents the Hg concentration from increasing in groundwater as dry CO 2 sweeps through, volatilizing both H 2 O and Hg. Using a model-derived aqueous solution to represent the formation water, batch reactive geochemical modeling show that the reaction of the formation water with the CO 2 -Hg mixture causes the pH to drop to about 4.7 and then become buffered near 5.2 upon reaction with the sediments, with a negligible net volume change from mineral dissolution and precipitation. Cinnabar (HgS(s)) is found to be thermodynamically stable as soon as the Hg-bearing CO 2 reacts with the formation water which contains small amounts of dissolved sulfide. Liquid mercury (Hg(l)) is not found to be thermodynamically stable at any point during the simulation. Two-dimensional radial reactive transport simulations of CO 2 injection at a rate of 14.8 kg/s into a 400 m-thick formation at isothermal conditions of 106°C and average pressure near 215 bar, with varying amounts of Hg and H 2 S trace gases, show generally that porosity changes only by about ±0.05% (absolute, i.e., new porosity = initial porosity ±0.0005) with Hg predicted to readily precipitate from the CO 2 as cinnabar in a zone mostly matching the single-phase CO 2 plume. The precipitation of minerals other than cinnabar, however, dominates the evolution of porosity. Main reactions include the replacement of primarily Fe-chlorite by siderite, of calcite by dolomite, and of K-feldspar by muscovite. Chalcedony is also predicted to precipitate from the dissolution of feldspars and quartz. Although the range of predicted porosity change is quite small, the amount of dissolution and precipitation predicted for these individual minerals is not negligible. These reactive transport simulations assume that Hg gas behaves ideally. To examine effects of non-ideality on these simulations, approximate calculations of the fugacity coefficient of Hg in CO 2 were made. Results suggest that Hg condensation could be significantly overestimated when assuming ideal gas behavior, making our simulation results conservative with respect to impacts on injectivity. The effect of pressure on Henry’s constant for Hg is estimated to yield Hg solubilities about 10% lower than when this effect is not considered, a change that is considered too small to affect the conclusions of this report. Although all results in this study are based on relatively mature data and modeling approaches, in the absence of experimental data and more detailed site-specific information, it is not possible to fully validate the results and conclusions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Photochemical reactions between mercury (Hg) and dissolved organic matter decrease Hg bioavailability and methylation

Atmospheric deposition of mercury (Hg) to surface water is one of the dominant sources of Hg in aquatic environments and ultimately drives methylmercury (MeHg) toxin accumulation in fish. It is known that freshly deposited Hg is more readily methylated by microorganisms than aged or preexisting Hg; however the underlying mechanism of this process is unclear. Here we report that Hg bioavailability is decreased by photochemical reactions between Hg and dissolved organic matter (DOM) in water. Photo-irradiation of Hg-DOM complexes results in loss of Sn(II)-reducible (i.e. reactive) Hg and up to an 80% decrease in MeHg production by the methylating bacterium Geobacter sulfurreducens PCA. Loss of reactive Hg proceeded at a faster rate with a decrease in the Hg to DOM ratio and is attributed to the possible formation of mercury sulfide (HgS). Lastly, these results suggest a new pathway of abiotic photochemical formation of HgS in surface water and provide a mechanism whereby freshly deposited Hg is readily methylated but, over time, progressively becomes less available for microbial uptake and methylation.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2018

Removal of inorganic mercury by selective extraction and coprecipitation for determination of methylmercury in mercury-contaminated soils by chemical vapor generation inductively coupled plasma mass spectrometry (CVG-ICP-MS)

A procedure is developed for selective extraction of methylmercury (CH 3 Hg + ) from heavily Hg-contaminated soils and sediments for determination by chemical vapor generation inductively coupled plasma mass spectrometry (CVG-ICP-MS). Soils artificially contaminated with 40 μg g –1 inorganic mercury (Hg 2+ ) or methylmercury chloride (CH 3 HgCl) were agitated by shaking or exposing to ultrasounds in dilute hydrochloric acid (HCl) or nitric acid (HNO 3 ) solutions at room temperature. Extractions in HCl (5 or 10% v/v) resulted in substantial leaching of Hg 2+ from soils, whereas 5% (v/v) HNO 3 provided selectivity for quantitative extraction of CH 3 Hg + with minimum Hg 2+ leaching. Agitation with ultrasounds in 5% (v/v) HNO 3 for about 3 min was sufficient for extraction of all CH 3 Hg + from soils. Coprecipitations with Fe(OH) 3 , Bi(OH) 3 and HgS were investigated for removal of residual Hg 2+ in soil extracts. Hydroxide precipitations were not effective. Thiourea or l-cysteine added to soil extracts prior to hydroxide precipitation improved precipitation of Hg 2+ , but also resulted in removal of CH 3 Hg + . HgS precipitation was made with dilute ammonium sulfide solution, (NH 4 ) 2 S. Adding 30 μL of 0.35 mol L –1 (NH 4 ) 2 S to soil extracts in 5% (v/v) HNO 3 resulted in removal of all residual Hg 2+ without impacting CH 3 Hg + levels. Vapor generation was carried out by reacting Hg 2+ -free soil extracts with 1% (m/v) NaBH 4 . No significant interferences were observed from (NH 4 ) 2 S on the vapor generation from CH 3 Hg + . The slopes of the calibration curves for CH 3 HgCl standard solutions in 5% (v/v) HNO 3 with and without (NH 4 ) 2 S were similar. Limits of detection (LOD, 3s method) were around 0.08 μg L –1 for 5% (v/v) HNO 3 blanks (n = 10) and 0.10 μg L –1 for 5% (v/v) HNO 3 + 0.005 mol L –1 (NH 4 ) 2 S blanks (n = 10). Percent relative standard deviation (%RSD) for five replicate measurements varied between 3.1% and 6.4% at 1.0 CH 3 HgCl level. The method is validated by analysis of two certified reference materials (CRM); purely Methylmercury sediment (SQC1238, 10.00 ± 0.291 ng g –1 CH 3 Hg + ) and Hg-contaminated Estuarine sediment (ERM – CC580, 75 ± 4 ng g–1 CH 3 Hg + and 132 ± 3 μg g –1 total Hg). CH 3 Hg + values for SQC1238 were between 13.0 and 13.2 ng g –1 , and 79 and 81 ng g –1 for ERM – CC580. Hg-contaminated soils (57–96 μg g –1 total Hg) collected from the floodplains of Oak Ridge, TN were analyzed for CH 3 Hg + using the procedure by CVG-ICPMS. CH 3 Hg + levels ranged from 30 to 51 ng g –1 and did not correlate with total Hg levels (R 2 = 0.01).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗