Hg Emissions Research Articles

Health risk assessment of gaseous elemental mercury (GEM) in Mexico City.

Emissions of gaseous elemental mercury (GEM or Hg0) from different sources in urban areas are important subjects for environmental investigations. In this study, atmospheric Hg measurements were conducted to investigate air pollution in the urban environment by carrying out several mobile surveys in Mexico City. This work presents atmospheric concentrations of GEM in terms of diurnal variation trends and comparisons with criteria for pollutant concentrations such as CO, SO2, NO2, PM2.5, and PM10. The concentration of GEM was measured during the pre-rainy period by using a high-resolution active air sampler, the Lumex RA 915 M mercury analyzer. In comparison with those for other cities worldwide, the GEM concentrations were similar or slightly elevated, and they ranged from 0.20 to 30.23 ng m−3. However, the GEM concentration was significantly lower than those in contaminated areas, such as fluorescent lamp factory locations and gold mining zones. The GEM concentrations recorded in Mexico City did not exceed the WHO atmospheric limit of 200 ng m−3. We performed statistical correlation analysis which suggests equivalent sources between Hg and other atmospheric pollutants, mainly NO2 and SO2, emitted from urban combustion and industrial plants. The atmospheric Hg emissions are basically controlled by sunlight radiation, as well as having a direct relationship with meteorological parameters. The area of the city studied herein is characterized by high traffic density, cement production, and municipal solid waste (MSW) treatment, which constantly release GEM into the atmosphere. In this study, we included the simulation with the HYSPLIT dispersion model from three potential areas of GEM release. Emissions from industrial corridors and volcanic plumes localized outside the urban area contribute to the pollution of Mexico City and mainly affect the northern area during specific periods and climate conditions. Using the USEPA model, we assessed the human health risk resulting from exposure to inhaled GEM among residents of Mexico City. The results of the health risk assessment indicated no significant noncarcinogenic risk (hazard quotient (HQ) < 1) or consequent adverse effects for children and adults living in the sampling area over the study period. GEM emissions inventory data is necessary to improve our knowledge about the Hg contribution and effect in urban megacity areas with the objective to develop public safe policy and implementing the Minamata Convention.Supplementary informationThe online version contains supplementary material available at 10.1007/s10661-022-10107-7.

Arctic atmospheric mercury: Sources and changes

Global anthropogenic and legacy mercury (Hg) emissions are the main sources of Arctic Hg contamination, primarily transported there via the atmosphere. This review summarizes the state of knowledge of the global anthropogenic sources of Hg emissions, and examines recent changes and source attribution of Hg transport and deposition to the Arctic using models. Estimated global anthropogenic Hg emissions to the atmosphere for 2015 were ~2220 Mg, ~20% higher than 2010. Global anthropogenic, legacy and geogenic Hg emissions were, respectively, responsible for 32%, 64% (wildfires: 6–10%) and 4% of the annual Arctic Hg deposition. Relative contributions to Arctic deposition of anthropogenic origin was dominated by sources in East Asia (32%), Commonwealth of Independent States (12%), and Africa (12%). Model results exhibit significant spatiotemporal variations in Arctic anthropogenic Hg deposition fluxes, driven by regional differences in Hg air transport routes, surface and precipitation uptake rates, and inter-seasonal differences in atmospheric circulation and deposition pathways. Model simulations reveal that changes in meteorology are having a profound impact on contemporary atmospheric Hg in the Arctic. Reversal of North Atlantic Oscillation phase from strongly negative in 2010 to positive in 2015, associated with lower temperature and more sea ice in the Canadian Arctic, Greenland and surrounding ocean, resulted in enhanced production of bromine species and Hg(0) oxidation and lower evasion of Hg(0) from ocean waters in 2015. This led to increased Hg(II) (and its deposition) and reduced Hg(0) air concentrations in these regions in line with High Arctic observations. However, combined changes in meteorology and anthropogenic emissions led to overall elevated modeled Arctic air Hg(0) levels in 2015 compared to 2010 contrary to observed declines at most monitoring sites, likely due to uncertainties in anthropogenic emission speciation, wildfire emissions and model representations of air-surface Hg fluxes.

Evidence for Interhemispheric Mercury Exchange in the Pacific Ocean Upper Troposphere

AbstractEven though anthropogenic mercury (Hg) emissions to the atmosphere are ∼2.5 times higher in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH), atmospheric Hg concentrations in the NH are only ∼1.5 times higher than in the SH. Global Hg models attribute this apparent discrepancy to large SH oceanic Hg emissions or to interhemispheric exchange of Hg through the atmosphere. However, no observational data set exists to serve as a benchmark to validate whether these coarse‐resolution models adequately represent the complex dynamics of interhemispheric Hg exchange. During the 2015–2016 El Niño, we observed at mount Chacaltaya in the tropical Andes a ∼50% increase in ambient Hg compared to the year before, coinciding with a shift in synoptic transport pathways. Using this event as a case study, we investigate the impact of interhemispheric exchange on atmospheric Hg in tropical South America. We use HYSPLIT to link Hg observations to long‐range transport and find that the observed Hg increase relates strongly to air masses from the tropical Pacific upper troposphere (UT), a region directly impacted by interhemispheric exchange. Inclusion of the modeled seasonality of interhemispheric air mass exchange strengthens this relationship significantly. We estimate that interhemispheric exchange drives Hg seasonality in the SH tropical Pacific UT, with strongly enhanced Hg between July and October. We validate this seasonality with previously published aircraft Hg observations. Our results suggest that the transport of NH‐influenced air masses to tropical South America via the Pacific UT occurs regularly but became more detectable at Chacaltaya in 2015–2016 because of a westward shift in air mass origin.

Concentrations and Species of Mercury in Municipal Sludge of Selected Chinese Cities and Potential Mercury Emissions From Sludge Treatment and Disposal

Municipal sewage has been identified as an important source of mercury (Hg) to the environment, and sewage sludge is the major sink of sewage-borne Hg. Knowledge of Hg species in sludge and potential Hg emissions during sludge treatment/disposal is still limited. A survey on Hg concentrations and species in sewage sludge of 16 provinces and municipalities in China was conducted. Hg was detected in all sewage sludge samples, with total Hg (THg) concentrations ranging from 0.3 to 7.7 mg/kg. Results from sequential chemical extractions (SCE) indicated that sludge-borne Hg mainly occurred in the form of Hg sulfide, with a small amount of organo-chelated Hg (Hg-OM) and HgO, and a negligible amount of soluble Hg. Thermal decomposition results indicated that Hg is generally released from sludge at a temperature range of 200–400°C, with the highest release at 250–350°C (38%–86%), consistent with the thermal decomposition of HgS, Hg-OM, and HgO. THg in sewage samples under ventilation at room temperature remained constant over a month period, indicating negligible Hg emission under such conditions. The mass loading of sludge-borne THg in China for year 2019 was estimated to be 30 tons, about 3.6% of the total anthropogenic THg released (including direct and secondary anthropogenic releases) in China. At the temperature range for sludge incineration, sludge carbonization, and sludge/brick/cement production, most of the Hg in sludge will be released to air due to thermal decomposition of Hg compounds. As such, Hg-capture systems are essential in sludge treatment processes involving high temperatures.

Pilot-scale study of desulfurization wastewater evaporation: Emission and migration characteristics of mercury

The hot flue gas evaporation technology exhibited a significant advantage in desulfurization wastewater zero discharge. However, the mercury emission during the wastewater evaporation process was a potential risk that may limit the popularization and application of this technology. The emission and migration characteristics of mercury were studied on the lab-scale furnace and pilot-scale wastewater evaporation system, respectively. The Hg in the wastewater would undergo the release-oxidation/adsorption process. Approximately 93.6% of Hg existing in the wastewater would firstly release due to the high volatility and component of SO32− and Cl−. Then, the released Hg would be further affected by the oxidation and adsorption mechanism. The generated HCl gas atmosphere and the active substances in the solid content would oxidize most of the released Hg0 and lift the Hg2+ proportion in the flue gas. Besides, the adsorption effect enhanced the conversion from the gaseous Hg to the Hgp, causing a high Hg proportion of 89.4% in the final solid evaporation product. The findings in risk assessment demonstrated that the hot flue gas evaporation technology would not upset the Hg distribution or cause extra Hg emissions for the whole power plant. However, the large water/acid-soluble fraction of Hg in the evaporation product should be considered in the storage and disposal procedure.

Biogeochemical cycle of mercury and controlling technologies: Publications in critical reviews in environmental science & technology in the period of 2017–2021

The Minamata Convention on Mercury (Hg) calls for global efforts to reduce the release and risk of Hg. A better understanding of the global Hg budget, transformation and transport as well as toxicity of Hg in the environment, and the Hg emission controlling technologies, is important to minimize Hg pollution and exposure risks. Here, we summarized recent findings regarding the Hg cycle, transport, transformation, and controlling technologies, based on publications in Critical Review in Environmental Science and Technology (CREST) during 2017–2021. In terms of CREST publications we first focused on the biogeochemical cycle and impacts of Hg in the sensitive environment of the Tibet Plateau, and technologies being used to control Hg0 emission from thermal power plants. Second, we discussed the roles of forest in the global cycle of Hg. Third, we reviewed the transport of Hg at artisanal and small-scale gold mining sites, and the mobility and transformation of Hg species in the environment. This special issue covers the recent studies on the cycle, transport, and transformation of Hg, enhances our abilities to develop better strategies to minimize its risks. There are emerging concerns with climatic change and natural and human perturbations on the biogeochemical cycle of Hg in the environment and futures studies are warranted in these areas as well as the global Hg cycle, transport, and remediation.

What are the likely changes in mercury concentration in the Arctic atmosphere and ocean under future emissions scenarios?

Arctic mercury (Hg) concentrations respond to changes in anthropogenic Hg emissions and environmental change. This manuscript, prepared for the 2021 Arctic Monitoring and Assessment Programme Mercury Assessment, explores the response of Arctic Ocean Hg concentrations to changing primary Hg emissions and to changing sea-ice cover, river inputs, and net primary production. To do this, we conduct a model analysis using a 2015 Hg inventory and future anthropogenic Hg emission scenarios. We model future atmospheric Hg deposition to the surface ocean as a flux to the surface water or sea ice using three scenarios: No Action, New Policy (NP), and Maximum Feasible Reduction (MFR). We then force a five-compartment box model of Hg cycling in the Arctic Ocean with these scenarios and literature-derived climate variables to simulate environmental change. No Action results in a 51% higher Hg deposition rate by 2050 while increasing Hg concentrations in the surface water by 22% and <9% at depth. Both “action” scenarios (NP and MFR), implemented in 2020 or 2035, result in lower Hg deposition ranging from 7% (NP delayed to 2035) to 30% (MFR implemented in 2020) by 2050. Under this last scenario, ocean Hg concentrations decline by 14% in the surface and 4% at depth. We find that the sea-ice cover decline exerts the strongest Hg reducing forcing on the Arctic Ocean while increasing river discharge increases Hg concentrations. When modified together the climate scenarios result in a ≤5% Hg decline by 2050 in the Arctic Ocean. Thus, we show that the magnitude of emissions-induced future changes in the Arctic Ocean is likely to be substantial compared to climate-induced effects. Furthermore, this study underscores the need for prompt and ambitious action for changing Hg concentrations in the Arctic, since delaying less ambitious reduction measures–like NP–until 2035 may become offset by Hg accumulated from pre-2035 emissions.

Graphitic Carbon Nitride for Gaseous Mercury Emission Control: A Review

Mercury emissions from combustion of coal, biomass, and solid waste threaten human life and the environment. As the principal mercury species in flue gas, elemental mercury (Hg0) can easily escape from available air pollution control instruments because of its chemical inertness, high volatility, and aqueous insolubility. Recently, graphitic carbon nitride (g-C3N4) seems to be an intriguing candidate for Hg0 emission control. This review highlights the latest advances in adsorptive and photocatalytic removal of Hg0 by g-C3N4-based composites. Metal oxide (MeOx)- and halide-modified g-C3N4 can effectively capture Hg0 from simulated flue gas. Nonetheless, acidic flue gas components can degrade the performances of MeOx/g-C3N4 adsorbents, while halide-modified g-C3N4 suffers from release of halogen and potential leaching risk of mercury. Metal sulfide (MeSx)-modified g-C3N4 appears to be the best candidate for Hg0 capture owing to its superior tolerance to sulfur dioxide, fast adsorption rate, and high mercury capacity. Combining bismuth oxyhalides (BiOX) with g-C3N4 can promote photocatalytic oxidation of elemental mercury under visible light irradiation; nonetheless, the Hg0 removal efficiency is still unsatisfactory, and the underlying photocatalysis mechanism is not yet clear.

Characteristics and Health Risk Assessment of Mercury Exposure via Indoor and Outdoor Household Dust in Three Iranian Cities

This study aims to increase our current knowledge on the concentration of particulate-bound mercury (PBM) in urban environments of three Iranian cities, where high concentrations of dust particles can act as carriers for mercury transport and deposition. A total of 172 dust samples were collected from Ahvaz, Asaluyeh, and Zabol residential houses and in outdoor air and were analyzed for total mercury content. Ahvaz is a highly industrialized city with large metallurgical plants, refineries, and major oil-related activities, which were assumed to contribute to elevated contents of PBM in this city. Very high levels of Hg contamination in Ahvaz indoor dust samples were calculated (Contamination Factor: CF &gt; 6). Sampling sites in Asaluyeh are influenced by Hg emissions from the South Pars Gas Field. However, the results revealed a relatively lower concentration of PBM in Asaluyeh, with a low-to-moderate level of Hg contamination. This is likely ascribed to the lower content of total mercury in hydrocarbon gases than crude oil, in addition to the absence of metal smelting plants in this city compared to Ahvaz. Zabol, as a city devoid of industrial activity, presented the lowest levels of PBM concentration and contamination. Indoor dust in Ahvaz showed considerable potential to cause a non-carcinogenic health risk for children, mainly through the inhalation of PBM, while the health risk for other cities was below safe limits. The trend of health risk was found in the order of indoor &gt; outdoor and children &gt; adults in all studied cities.

Charge distribution modulation and morphology controlling of copper selenide for an enhanced elemental mercury adsorption activity in flue gas

The abatement of elemental mercury (Hg0) emissions from industrial flue gases remains an enormous challenge. Metal selenides have been demonstrated to be promising Hg0 remediators, and the electron-transfer ability of selenide ligands is one of the key factors that determining the uptake capacity and adsorption rate of Hg0. Herein, a charge distribution modulation strategy was developed to generate desired selenide ligands. The selenide ligands on a tutorial sample, copper selenide (Cu2Se), was artificially modulated to −1 valances (Se1-) via electrostatic adsorption of positively charged head groups of cetyltrimethylammonium bromide (CTAB). Unlike other selenide ligand such as Se2-, the Se1- directly acted as an electron acceptor for Hg0 and realize one-step immobilization of Hg0 as environmentally stable mercury selenide (HgSe). Besides, CTAB was beneficial to construct nanosheets with thinner and larger plates, hence facilitated a sufficient exposure of active sites for binding Hg0. Profiting from the above advantages, the Hg0 adsorption capacity of CTAB modulated Cu2Se (Cu2Se-CTAB) was up to 80.2 mg·g−1, about two times higher than that of bare Cu2Se. Meanwhile, the average Hg0 adsorption rate of Cu2Se-CTAB before achieving saturation was 9.99 mg·g−1·h−1, much faster comparing with 6.90 mg·g−1·h−1 for regular Cu2Se. The Cu2Se-CTAB showed superior Hg0 adsorption performance at 40–80 °C and excellent resistance to flue gas interference, which are crucial for real-world applications. This newly designed method not only provides an excellent Hg0 remediator but also offers a tutorial example for a rational modulation of metal selenides for diverse environmental remediations.

Reconstructing atmospheric Hg levels near the oldest chemical factory in central Europe using a tree ring archive

The Chemical Factory in Marktredwitz (CFM) is known as the oldest chemical factory in Germany (1778–1985), and from the beginning of the 20th century focused primarily on the production of mercury (Hg) compounds. Due to extensive pollution, together with employee health issues, the CFM was shut in 1985 by a government order and remediation works proceeded from 1986 to 1993. In this study, tree ring archives of European Larch (Larix decidua Mill.) were used to reconstruct changes of air Hg levels near the CFM. Mercury concentrations in larch boles decreased from 80.6 μg kg−1 at a distance of 0.34 km–3.4 μg kg−1 at a distance of 16 km. The temporal trend of atmospheric Hg emissions from the CFM reconstructed from the tree ring archives showed two main peaks. The first was in the 1920s, with a maximum tree ring Hg concentration 249.1 ± 43.9 μg kg−1 coinciding with when the factory had a worldwide monopoly on the production of Hg-based seed dressing fungicide. The second peak in the 1970s, with a maximum tree ring Hg concentration of 116.4 ± 6.3 μg kg−1, was associated with a peak in the general usage and production of Hg chemicals and goods. We used the tree ring record to reconstruct past atmospheric Hg levels using a simple model of Hg distribution between the larch tree rings and atmosphere. The precision of the tree ring model was checked against the results of air Hg measurements during the CFM remediation 30 years ago. According to the tree ring archives, the highest air Hg concentrations in the 1920s in Marktredwitz were over 70 ng m−3. Current air Hg levels of 1.18 ng m−3, assessed in the city of Marktredwitz, indicate the lowest air Hg in the past 150 years, underscoring the effective remediation of the CFM premises 30 years ago.

Analysis of mercury emissions and cycles in typical industrial city clusters: a case study in China.

China's Suzhou (SZ), Wuxi (WX), and Changzhou (CZ) (collectively referred to as the SXC area) have developed economies and advanced industrial production, which are typical industrial city clusters. To analyze the Hg flow characteristics, we quantified the Hg emissions and circulation according to six categories (including industrial production, agricultural livestock, vehicle exhaust, solid waste, atmospheric deposition, and runoff). The results showed that the Hg emission from coal accounting for 40.99% of the total circulation. The amount of Hg circulating in SZ is obviously higher than those in WX and CZ, accounting for 47.88% of the total regional emissions. The Hg pollution in SXC area represent an optimistic level. Except that the Hg concentration in the soil in WX is slightly higher than the first-level soil quality standard, the water and atmosphere in the three cities and the soil in SZ and CZ all meet the highest national standards. The study provides in-depth statistics on the Hg cycle characteristics of typical industrial urban agglomerations. It is beneficial to the management of Hg and provides a basis for the implementation of different schemes in different stages of production and emission, so as to effectively prevent the occurrence of serious heavy metal poisoning hazards. This research idea is widely used and can be applied to other regions and other heavy metal elements.

Arctic mercury cycling

Anthropogenic mercury (Hg) emissions have driven marked increases in Arctic Hg levels, which are now being impacted by regional warming, with uncertain ecological consequences. This Review presents a comprehensive assessment of the present-day total Hg mass balance in the Arctic. Over 98% of atmospheric Hg is emitted outside the region and is transported to the Arctic via long-range air and ocean transport. Around two thirds of this Hg is deposited in terrestrial ecosystems, where it predominantly accumulates in soils via vegetation uptake. Rivers and coastal erosion transfer about 80 Mg year−1 of terrestrial Hg to the Arctic Ocean, in approximate balance with modelled net terrestrial Hg deposition in the region. The revised Arctic Ocean Hg mass balance suggests net atmospheric Hg deposition to the ocean and that Hg burial in inner-shelf sediments is underestimated (up to >100%), needing seasonal observations of sediment-ocean Hg exchange. Terrestrial Hg mobilization pathways from soils and the cryosphere (permafrost, ice, snow and glaciers) remain uncertain. Improved soil, snowpack and glacial Hg inventories, transfer mechanisms of riverine Hg releases under accelerated glacier and soil thaw, coupled atmosphere–terrestrial modelling and monitoring of Hg in sensitive ecosystems such as fjords can help to anticipate impacts on downstream Arctic ecosystems.

Chemistry of surface water, precipitation, throughfall, leaves, sediment, soil, and air near a gold mining region in Peru.

Artisanal and small-scale gold mining (ASGM) is the primary global source of anthropogenic mercury (Hg) emissions and a large source of landscape change. ASGM occurs throughout the world, including in the Peruvian Amazon. This data set contains measurements of surface water, precipitation, throughfall, leaves, sediment, soil, and air samples from across the Madre de Dios region of Peru, in locations near and remote from ASGM. These data were collected to determine the fate and transport of Hg across the landscape. Samples were collected in 2018 and 2019. Data predominantly included total Hg and methyl Hg concentrations in surface water, precipitation, throughfall, leaves, sediment, soil, and air. Additional water and soil parameters were also measured to better characterize their chemistry. There are no copyright restrictions; please cite this data paper when the data are used in publication.

Biomass Carbon Magnetic Adsorbent Constructed by One-Step Activation Method for the Removal of Hg0 in Flue Gas.

Elemental mercury (Hg0) emission from industrial boilers equipped in factories such as coal-fired power plants poses serious hazards to the environment and human health. Herein, an iron-modified biomass carbon (Fe/BC) magnetic adsorbent was prepared by a one-step method using pepper straw waste as raw material and potassium oxalate and ferric nitrate as activator and catalyst precursor, respectively. A fixed-bed reactor was used to evaluate the Hg0 removal performance of the Fe/BC adsorbent. The synthesized adsorbent showed a wide temperature window for Hg0 removal. In a N2 + O2 atmosphere, the removal efficiency toward Hg0 was 97.6% at 150 °C. Further, O2 or SO2 could promote the removal of Hg0, while NO could inhibit the conversion of Hg0 over the Fe/BC adsorbent. The consequence of XPS and Hg-TPD showed that lattice oxygen in Fe2O3 and chemisorbed oxygen were the main active sites for Hg0 removal, and HgO was the main mercury species on used Fe/BC. Moreover, Fe/BC adsorbent showed a good regeneration and magnetization performance, which was conducive to the cost reduction of actual industrial application. This study provides a facile approach for efficient removal of Hg0 using biomass-derived carbon material.

Mass flow, enrichment and potential environmental impacts of mercury in a preheater-precalciner cement plant using multiple mining and industrial wastes

Cement plants (CPs) are one of the most important anthropogenic sources of mercury (Hg) emissions in China. Over 1000 cement production lines operate in China and use various raw materials; however, little data on Hg emissions is recorded on site. This study investigated a CP in Guizhou Province that uses multiple mining and industrial wastes as part of the circular economy policy. Among the various raw materials, carbide slag had the highest Hg content (2.6 mg/kg) and contributed half of the Hg input. High Hg concentration (27 mg/kg) in the kiln tail dust and a strong Hg enrichment factor (39) was found, which was determined as the ratio of total Hg accumulated within the clinker production process to the daily Hg input from raw materials and fuel. The clinker had negligible Hg (0.001 mg/kg), while the Hg in cement products (0.04 mg/kg) mostly came from additives and retarders. The estimated atmospheric emission factor of Hg from this CP was 161.5 mg Hg/t clinker, which was much higher than those of other CPs in Guizhou that employ low-Hg raw materials. A five-step sequential extraction experiment with kiln tail dust indicates that Hg mainly existed in fraction of F4 (73–96% of the total Hg, possibly as Hg2Cl2) and that some samples had high proportions of water-soluble Hg (up to 21% of the total), which may be easily released into surrounding water bodies and pose high environmental risks. Using low-Hg raw (or alternative raw) materials and conducting proper disposal of kiln tail dust will reduce the environmental risk of Hg from CPs.

Surface sulfidation modification of magnetospheres from fly ash for elemental mercury removal from coal combustion flue gas

Reduction of elemental mercury (Hg0) emission from coal-fired power plants is an enormous challenge. In this work, magnetospheres separated from fly ash was modified through H2S as an efficient sorbent (i.e., S-MS) for Hg0. Elemental sulfur with high affinity towards Hg0 was formed on the S-MS surface through selective catalytic oxidation of H2S. The sulfidation temperature played an important role in Hg0 adsorption over S-MS, ascribing to the variation of sulfur species on S-MS. The S-MS exhibited above 80% Hg0 adsorption efficiency with a sulfidation temperature of 150 °C for 30 min. The optimal Hg0 adsorption performance was obtained at 50 and 75 °C, implying that the S-MS could be adopted by injecting into the duct upstream of wet electrostatic precipitator (WESP) system. The gaseous Hg0 was immobilized by S-MS as stable mercury sulfide (HgS) owing to the presence of abundant sulfur species that is active for binding Hg0. The leaching ratio of mercury from spent S-MS in WESP effluent was as low as 1%, hence minimizing the secondary mercury pollution from the industrial waste. The cost analysis demonstrates that the mercury removal technology on the basis of magnetospheres adsorbents exhibited much superiority in operation cost compared with commercial activated carbon injection technology. Thus, the S-MS, with specific features, such as high Hg0 adsorption performance, minimized environmental hazardous and recyclability, displayed great potential in Hg0 sequestration.

Elemental mercury (Hg0) removal from coal syngas using magnetic tea-biochar: Experimental and theoretical insights

Mercury is ranked 3rd as a global pollutant because of its long persistence in the environment. Approximately 65% of its anthropogenic emission (Hg0) to the atmosphere is from coal-thermal power plants. Thus, the Hg0 emission control from coal-thermal power plants is inevitable. Therefore, multiple sorbent materials were synthesized using a one-step pyrolysis method to capture the Hg0 from simulated coal syngas. Results showed, the Hg0 removal performance of the sorbents increased by the citric acid/ultrasonic application. T5CUF0.3 demonstrated the highest Hg0 capturing performance with an adsorption capacity of 106.81 µg/g within 60 min at 200 °C under complex simulated syngas mixture (20% CO, 20% H2, 10 ppmV HCl, 6% H2O, and 400 ppmV H2S). The Hg0 removal mechanism was proposed, revealing that the chemisorption governs the Hg0 removal process. Besides, the active Hg0 removal performance is attributed to the high dispersion of valence Fe3O4 and lattice oxygen (α) contents over the T5CUF0.3 surface. In addition, the temperature programmed desorption (TPD) and XPS analysis confirmed that H2S/HCl gases generate active sites over the sorbent surface, facilitating high Hg0 adsorption from syngas. This work represented a facile and practical pathway for utilizing cheap and eco-friendly tea waste to control the Hg0 emission.

Sulfur, lead, and mercury characteristics in South Africa coals and emissions from the coal-fired power plants

Coal-fired power plants (CFPPs) are the dominant source of electricity in South Africa due to coal abundance in the country. However, emissions of SO2, Pb, and Hg have raised serious environmental and public health concerns. Hence, to reduce emissions and utilize coal efficiently, it is essential to estimate emissions trends, understanding existential forms of the elements in coals, and their affinities to minerals, organic matter, and pyrite. Therefore, this paper aimed to assess the forms of elemental occurrence of sulfur (S), lead (Pb), mercury Hg affinities in the coals using statistical correlations and their isotopic compositions. This study also estimated SO2, Pb, and Hg emissions from 1971 to 2018 from the CFPPs based on activity data and emission factors. Based on the results, South African coals mainly comprise equivalent fractions of organic and pyritic S. The Pb were correlated with ash content (R = 0.61), Si, Al, and Ti, which indicates clay mineral-bound Pb. However, the highest Pb206/Pb207 and the lowest Pb208/Pb206 in South Africa coals which contain high inertinite (organic matter) and low S, also reveal organically associated Pb. Similarly, clay minerals linked Hg appeared as of Hg relationship with ash (R = 0.641) and major elements, and the remaining could be an organic matter associated. As an organic matter-associated element least cleanability and readily oxidizing nature, burning South African coals containing a substantial quantity of organic S and organically bound Pb and Hg without washing results in higher emissions. The estimated SO2, Pb, and Hg emissions were 355.84 Gg, 168.91 tons, and 4.17 tons in 1971, and increased to 1468.13 Gg, 696.89 tons, and 17.20 tons in 2018, respectively. The values approximately increased by a factor of 4.

Mercury contamination in the riparian ecosystem during the reservoir discharging regulated by a mega dam.

Mercury (Hg) is extremely poisonous and can be absorbed through touch, inhalation, or consumption. In the living environment, Hg in contaminated sediment can be transferred into grass by the direct absorption through the roots or shoots. The intake of Hg due to Hg emissions may pose a threat to living bodies especially to human beings. The present study aims to provide a novel insight about total mercury (THg) and methyl mercury (MeHg) in a riparian grass (Cynodon dactylon (L).Pers) and sediments during the discharging phase (summertime at 145m water level) in Three Gorges Reservoir (TGR-China); where C. dactylon is a dominant perennial herb in the riparian zone. Yet, the potential risk of Hg contamination in the riparian ecosystem is not thoroughly assessed in the dam regulated reservoir. This study was conducted in the riparian zones of the reservoir formed by a mega dam (Three Gorge Dam) which regulates the water levels during the summer and winter period in the TGR. Our results showed that riparian sediments were acting as a sink for THg and MeHg. Insignificant correlation of THg and MeHg was found between the amphiphyte C. dactylon and its surrounding sediments in the TGR. Bioconcentration factors values for MeHg were found higher than 1 in all study locations in the riparian zones in TGR, which could be due to action of certain bacteria/purely chemical-based methylation on inorganic form of Hg. Additionally, translocation factor indices also highlighted that the amphiphyte C. dactylon was MeHg accumulator in riparian zones. These results suggested that since riparian sediment was found acting as the sink for THg and MeHg during discharging phase, MeHg contamination in the amphiphyte C. dactylon in riparian zones was not caused by the riparian sediments but by other factors, for instance, the anthropogenic activities in the TGR. Finally, this study leads to conclude that amphiphyte C. dactylon can be used as biomonitoring agent for Hg pollution in the TGR.