Gaseous Mercury Emissions Research Articles

Multi-layered physical factors govern mercury release from soil: Implications for predicting the environmental fate of mercury

Despite the recognised risks of human exposure to mercury (Hg), the drivers of gaseous elemental mercury (GEM) emissions from the soil remain understudied. In this study, we aimed to identify the environmental parameters that affect the GEM flux from soil and derive the correlations between environmental parameters and GEM flux. Principal component analysis (PCA), factor analysis (FA), and structural equation modelling (SEM) were performed on samples from forest and non-forest sites. The associated results revealed the impact of each environmental parameter on GEM flux, either due to the interaction between the parameters or as a coherent set of parameters. An introductory correlation matrix examining the relationship between two components showed a negative correlation between GEM flux and atmospheric pressure at the two sites, as well as strong correlations between atmospheric pressure and soil temperature. In cases of non-forest open sites with no trees, the PCA and FA results were consistent, indicating that atmospheric pressure, solar irradiance, and soil moisture—defined as primary causality—are largely independent drivers of GEM flux. In contrast, the PCA and FA results for the forest areas with high humidity, tree coverage, and shade were inconsistent, confirming the hypothesis that primary causality affects GEM flux rather than consequent parameters driven by primary causality, such as air and soil temperature and atmospheric humidity. The SEM results provided further evidence for primary and consequent causality as crucial drivers of the GEM flux. This study demonstrates the importance of key primary parameters, such as atmospheric pressure, solar irradiance, and soil moisture content, that can be used to predict mercury release from soils, as well as the importance of consequent parameters, such as air and soil temperature and atmospheric humidity. Monitoring the magnitude of these environmental parameters alone may facilitate the estimation of mercury release from soils and be useful for detailed modelling of soil–air Hg exchange.

Gaseous elemental mercury emissions from informal E-Waste recycling facilities in Pakistan

Detrimental effects of mercury (Hg) on ecosystems and human health have been well-documented. Whereas emissions of gaseous elemental mercury (GEM) from e-waste recycling have been reported in developed countries, much less is known about the situation in the Global South. Using a total of 132 passive air samplers, seasonally resolved concentrations of GEM in air were measured continuously at 32 informal e-waste recycling facilities and background location in Pakistan for a period of one year between September 2020 and December 2021. Annual average GEM concentrations at the studied locations ranged from 1.8 to 92 ng m−3. Among the studied cities, higher concentrations were measured in Karachi (mean ± s.d: 17 ± 22, range: 4.2–92 ng m−3), Lahore (16 ± 4.2, 8.2–22 ng m−3) and Peshawar (15 ± 17, 4.9–80 ng m−3), while lower levels were measured in Hyderabad (6.9 ± 6.2, 3.1–25 ng m−3), consistent with a higher rate of informal recycling activities in metropolitan areas. Seasonally, higher GEM levels occurred during autumn (15 ± 16: 3.3–92 ng m−3) and summer (13 ± 8.7: 1.8–80 ng m−3) than in winter (12 ± 8.4: 2.5–49 ng m−3) and spring (9.2 ± 7.3: 1.8–80 ng m−3), possibly reflecting enhanced volatilization at higher temperatures and/or varying magnitude of recycling operations in different seasons. Policies and strict regulations related to e-waste management should be developed and implemented urgently in the country.

Chemical-Physical Model of Gaseous Mercury Emissions from the Demolition Waste of an Abandoned Mercury Metallurgical Plant

Soils from decommissioned Hg mine sites usually exhibit high levels of total mercury concentration. This work examines the behavior of mercury in the atmosphere on samples of contaminated debris of a demolished metallurgical plant present in La Soterraña mine, Asturias (Spain). Previously, a strong dependence of the Hg gas concentration Cmax (ng/m3) with the temperature T (K) was determined empirically. Hg gas concentration varied between 6500 ng/m3 at low temperatures, 278 K (5 °C), and up to almost 60,000 ng/m3 when the temperature reaches 303 K (30 °C). Then, two different models were proposed to explain the behavior of the mercury emitted from this source. The first model is based on Arrhenius theory. The gas flux per unit area perpendicular to the flow F (g/sm2) is an exponential function of the apparent activation energy Ea (J/mol): F = cf exp(-Ea/RT). The values of cf = 1.04·107 and Ea = 48.56 kJ/mol allows the model to fit well with the field measurements. The second model is based on Fick’s laws, and the flux F (g/sm2) can be estimated by F = (K′ MHg pv)/RT where K′ = 8.49·10−7, MHg = 200.56 g/mol and the partial vapor pressure of gaseous mercury pv (Pa) can be estimated from the saturation vapor pressure of gaseous mercury pv = 0.00196·ps and the August’s law log(ps) = 10.184–3210.29/T. This method is also validated with results measured in situ. Both methods are accurate enough to explain and predict emission rate G (g/s), gas flux F (g/sm2) and maximum Hg gas concentration over the debris Cmax (ng/m3) as a function the temperature T (K).

Chemodynamics of Mercury (Hg) in a Southern Reservoir Lake (Cane Creek Lake, Cookeville, TN, USA): I—Estimation of the Kinetics of Photochemical Reduction of Aquatic Hg(II) Using Field-Measured Data of Hg Water/Air Exchange and Dissolved Gaseous Hg

An alternative, independent estimation of the kinetics of aquatic Hg(II) photochemical reduction featuring dissolved gaseous mercury (DGM) emission from water in consideration was obtained by using a mass balance box model. An interactive Excel spreadsheet was constructed to implement the model equations to yield the rate constants and the rates of the Hg(II) photoreduction. The model calculations used field-measured data of DGM paired with its emission flux coupled with the corresponding field sampling times. This data set came from a previous, separate, year-long field study conducted at a southern reservoir lake (Cane Creek Lake, Cookeville, Putnam County, TN). The mean value of the model-calculated rate constants (kDGM) of the Hg(II) photoreduction for the warm season (June–August) (4.5 fM h−1/pg L−1) is higher than that for the cold season (October–January) (2.2 fM h−1/pg L−1). The rate constants were found to be the highest (22.5 fM h−1/pg L−1) in August whereas the lowest (0.03 fM h−1/pg L−1) in January. The model-calculated rate constants are clearly higher in value than but comparable in order of magnitude to the published kinetic data. The model-calculated rates (rDGM) of the Hg(II) photoreduction are significantly higher, by one order of magnitude (102 vs. 101) than the apparent rates calculated using the same field DGM data without consideration of the Hg emission from the water. A sensitivity analysis of the model parameters points to a high sensitivity of Hg emission flux to the rate constant under modeled realistic environmental conditions. The initial Hg(II) concentration is also a sensitive model parameter under certain conditions. The results of our model study support the conclusion that DGM emission from water has a strong impact on the kinetics of aquatic Hg(II) photoreduction and the model calculation can provide an independent, valuable approach for estimating the kinetics of aquatic Hg(II) photoreduction.

Empirical Model of Gaseous Mercury Emissions for the Analysis of Working Conditions in Outdoor Highly Contaminated Sites

The project SUBproducts4LIFE is a LIFE-funded research project that aims to demonstrate innovative circular economy concepts by repurposing industrial subproducts/waste (coal ash and gypsum from coal power plants, blast furnace slag, and steelmaking slag from steel factories) for the remediation of contaminated soils and brownfield areas associated with Hg mining on a large scale. Within the project, one of the objectives is related to worker safety by developing protocols and elaborating a guide of good practices to work under in these highly contaminated areas. The present research aims to assess the working conditions in an abandoned mine facility in terms of gaseous mercury in the environment, evaluating the main areas of the mine to ensure the health and safety of all workers and visitors. The study developed an empirical model for estimating the gaseous mercury concentration at any temperature with the target of scheduling the work to avoid occupational hazards. The research concluded that working without restrictions for temperatures under 15 °C in all the mine’s facilities is possible.

Hg in the hydrothermal fluids and gases in Baia di Levante, Vulcano, Italy

The importance of fluid and gaseous mercury (Hg) emissions from hydrothermal systems in the shallow, coastal ocean is poorly constrained. However, there are indicators that they could be a significant natural Hg source. We evaluated the hydrothermal Hg emissions around Vulcano Island, Aeolian Arc, Italy, which is host to a marine shallow-water hydrothermal system (MSWHS) in Baia di Levante. Fluids were collected with porewater probes, and gases were collected into Tedlar© bags. Total Hg (THg) concentrations in the hydrothermal fluids ranged from 2.9 to 2888 pM. The concentrations of volatile Hg were below 8 pM and trended positively with increasing temperature. Monomethyl Hg (MMHg) was not detected. Total Hg in the gases ranged from 0.03 to 1.82 μmol/m3.High concentrations of THg were associated with low Cl-concentrations, low pH-values, and high K/Cl and Mg/Cl ratios. Concentrations of THg in the hydrothermal fluids resulted from mixing between meteoric water, seawater, condensed fumarolic vapor, and a deep hydrothermal fluid. However, not all low-Cl fluids were high THg samples. Samples taken along the coast of the La Fossa crater contained substantially less THg (2.9 to 29.4 pM), despite similar hydrothermal indicators as those in the Baia di Levante samples. These data support subsurface circulation models, which discuss the downslope flow of condensed La Fossa crater gases to the coast. In the hydrothermally active area of Baia di Levante, concentrations of THg were elevated relative to background surface seawater, ranging from 40 to 5110 pM. In comparison, the remainder of the bay ranged from 0.8 to 2.4 pM.The flux of Hg to the atmosphere from surface waters was calculated through dissolved Hg concentrations. The flux at each sampled site ranged from 0 to 19.6 pmol/m2/hr. The highest flux rates were determined for those areas with visible hydrothermal activity, particularly those with high gaseous emission rates. Surface water concentrations declined rapidly away from point sources, indicating atmospheric emission, dilution through mixing, or scavenging and sedimentation. In hydrothermally active areas, Baia di Levante sediments contained THg concentrations of 2.42 nmol/g and 49.52 nmol/g, which were significantly above background (0.03 nmol/g).The largest gaseous point source, Bambino, released >2 L of gas per second. Although, Hg concentrations in the gas were low (113 to 122 nmol/m3) relative to other measured point sources near the beach (1768 to 1817 nmol/m3), due to the volume of discharge, surface water concentrations were elevated (131 pM).The Hg present in the hydrothermal system of Vulcano contributes Hg to the atmosphere and local seawater as a natural source.

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.

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.

Temporal and spatial assessment of gaseous elemental mercury concentrations and emissions at contaminated sites using active and passive measurements

Gaseous elemental mercury (GEM) concentrations and emissions at legacy contaminated sites represent poorly characterised components of global mercury (Hg) inventories. Here we apply both active (Tekran 2537A) and passive (MerPAS) sampling methods to comprehensively assess GEM concentrations and emissions across four dimensions (three spatial, one temporal) at a legacy contaminated site with elevated soil Hg. Concentrations are measured up to 37.4 (active) and 10.8 (passive) ng m−3, which represents enhancements of 23× and 7× above background (1.62 ng m−3), respectively. Temporal resolution of the sampling methods defines this difference (active: 5-min; passive: 44 days). Diurnal (active) GEM concentration patterns were highest in contaminated areas at night when low wind speeds compress the boundary layer. Passive sampling substantially improves the spatial characterisation of GEM concentrations both horizontally (highest GEM concentration in areas with elevated soil Hg) and vertically (improved vertical concentration gradient using telescopic sampling towers). Passive sampler deployments were used to generate a GEM emissions estimate (landfill-to-atmosphere) of 1.2 ± 0.6 kg yr−1 (or 310 ± 150 ng m−2 h−1). This study demonstrates how combining active (strength: temporal assessment) and passive (strength: spatial assessments) sampling improves the evaluation of GEM concentrations and emissions to the atmosphere at Hg contaminated sites across four dimensions.

Effect of flue gas purification facilities of coal-fired power plant on mercury emission

The types and concentration of mercury in flue gas of nine coal-fired units were measured by OH method and the mercury content in desulfuration wastewater, slag, fly ash and gypsum were also measured. The influences of conventional pollutant removal facilities such as SCR denitration facility, dust removal facility, and wet flue gas desulfurization facilities on mercury type and concentration were studied. The results indicate that mercury emission type is mostly gaseous mercury and mercury emission in nine units all meets the standard requirement. SCR denitrification facilities have a great effect on mercury type, promoting oxidation of elemental mercury into oxidized mercury which is easily removed by downstream dust removal facilities and wet desulfurization facilities. Particulate mercury is synergistically removed in dust removal facilities, with mercury removal ratio between 13.5% and 80.6% which depends on particulate mercury proportion. The oxidized mercury is synergistically removed in wet desulfurization facilities, with mercury removal ratio between 9.0% and 72.9%. Mercury is transferred from coal to fly ash and desulfuration gypsum, and mercury stability in the solid by-products needs to be studied.

β-FeOOH/C nanocomposite for elemental mercury removal as a new approach to environmental and natural gas processes

β-FeOOH/C nanocomposite was successfully prepared by self-assembled method of iron oxyhydroxide on carbonized sample from date stone. The phases, morphology and structure of the prepared β-FeOOH/C sample were characterized by XRD, FT-IR, BET and TEM, then compared to both parent amorphous carbon and FeOOH. The three samples are tested for their adsorptive properties toward elemental mercury removal in fixed-bed adsorption at different temperatures (25, 40, 55 and 70 °C). The data indicate high dispersion of β-FeOOH nanorods, of ≈ 5-25 nm in length and ≈ 1-2 nm in diameter, within the porous carbon structure. The maximum adsorption capacity was 1405.1 μg/g for β-FeOOH/C at a flow rate 250 mL/min, temperature 25 °C and 50 μg/Nm3 as Hg° initial concentration. The operating life of FeOOH/C is detrimined from breakthrough curve. The breakthrough time (tb) at Cout/Cin=0.05‒0.1 and equilibrium time (te) at Cout/Cin = 0.9‒1.0 were found to be 11 hours and 27 days, respectively. The adsorption mechanisms follow pseudo‒first‒order kinetics. Yoon‒ Nelson and Thomas models good described the experimental Hg° breakthrough curve model. The findings reveal the feasibility of FeOOH/C composite to be used as a potential and low-cost adsorbent for removing Hg° from natural gas, by not only reducing the environmental problems associated with gaseous mercury emissions but also by making the process more economical and simple.

Diffuse emission and transport of gaseous elemental mercury (GEM) in the Mapamyum geothermal system, Western Tibet (China)

Mercury (Hg) is a widely spread pollutant, owing to its high mobility in the nature. The rising input of Hg into the atmosphere has resulted in enhanced Hg pollution in both terrestrial and aquatic ecosystems. The Tibetan plateau, which is known as the roof of the world, is considered as a Hg-sensitive ecosystem. The Himalayan-Tibetan geothermal belt, which is formed due to the collision between India and Eurasia, is an important potential source of Hg to the atmosphere. However, previous studies to the emission and transport of geological Hg in the Tibetan Plateau are still rare. Understanding emission and transport of Hg in the Tibetan Plateau can provide important constraints on global Hg budget and its pollution transport. Diffuse emission and transport of gaseous elemental mercury (GEM or Hg0) in the Mapamyum geothermal system (MGF) of western Tibet was investigated and simulated by the closed-chamber method and the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) dispersion model. The estimated annual output of GEM in the MGF, calculated over an area of 41,615 m2, was in the order of 6.1 × 10−4 ton. He-C isotope ratios of the geothermal samples were all within the range of typical crustal domain. Combing with the hydrothermal analysis, it could deduce the Hg0 in the MGF might derive from both deep lithosphere and the upper crust. The GEM diffused from the source region was mainly dispersed to the NW direction. The maximum concentration of GEM is mainly distributed around the MGF, which is also the region with the largest deposition rate. The simulated results of the HYSPLIT dispersion model suggest that the GEM emitted from the MGF would not significantly enhance the atmospheric Hg concentration, whereas the deposition and accumulation of GEM around the source region is not negligible.

Assortment of herbaceous plants for remediation of soils contaminated with oil products and heavy metals

Biological remediation is the final stage of soil remediation. It is carried out to reduce and prevent the effects of technological disturbances. Plants can uptake and transform heavy metals, inorganic anions, oil products and pesticides. Recommendations were based on the practice experience and scientific researches. The quantitative chemical analysis of the soil pollutants demonstrated the presence of cations of heavy metals and oil products, and a rather high content of chlorides and sulfates was also detected. Such soils should be considered as saline. Therefore, plants for remediation should: a) correspond to the natural and climatic zone; b) show resistance to pollutants; c) plants must be salt tolerant. The composition consists of the following herbs. Medicago x varia Martyn is promising for areas with extreme environmental conditions. Agropyron tenerum Vasey is a good plant for phytoremediation of oil-sludge-contaminated soil. Festuca pratensis is well in universal, road, construction, sports lawns, and for special purposed lawns. Dactylis glomerata decreases gaseous mercury emission to the atmosphere and mercury mobility in soils. Phleum pratense have high phytostabilization potential in polluted soils and adaptation to soil pollution by this metals. That mixture is resistant for contaminated soils.

Dactylis glomerata L. cultivation on mercury contaminated soil and its physiological response to granular sulphur aided phytostabilization

Most mercury (Hg) deposition in the environment results from anthropogenic inputs, Chlor-Alkali Plants (CAPs) particularly had a significant Hg impact on the environment at a regional scale. Exposure to mercury compounds resulting in various toxic effects for living organisms. The aim of this study was to investigate the capacity of granular sulphur (S) soil amendment and cultivation of Dactylis glomerata to decrease gaseous mercury emission to the atmosphere and mercury mobility in soils affected by CAP activity in the past. The effect of this approach on D. glomerata physiological status was also assessed (Hg concentration in biomass, chlorophyll a fluorescence, pigment contents and oxidative stress). Stabilization of mercury in soil and reduction of root and shoot concentration did not influence biomass production. Despite similar yields, photosynthetic efficiency was higher for plants grown in sulphur amended soil compared to unamended soil, particularly observed in phenomenological energy fluxes. Relative chlorophyll content was 30% lower for amended soil plants, however based on chlorophyll fluorescence data those were in high portion ineffective. Oxidative stress products and catalase activity did not differ significantly between experimental treatments. Sulphur amendment was a key factor for reduction of Hg mobility in soil (reduced by about 30%) while plant cover was significant for the reduction of Hg atmospheric emission (emissions were 2-times higher in sulphur amended soil without plant cover). Due to the very high concentration of Hg in soil (798.2 ± 7.3 mg kg−1), growth inhibition was consistent regardless of treatment, demonstrated in the overload Reactive Oxygen Species scavenging mechanism and similar biomass yields. This leads to the conclusion that Hg may have greater impact on Calvin-Benson cycle associated enzymes than on the light-dependent photosynthesis phase. Despite these limitations this approach may still decrease environmental risks by reducing Hg emission to the atmosphere and reducing groundwater contamination.

Mercury emission from industrially contaminated soils in relation to chemical, microbial, and meteorological factors

The Minamata Convention entered into force in 2017 with the aim to phase-out the use of mercury (Hg) in manufacturing processes such as the chlor-alkali or vinyl chloride monomer production. However, past industrial use of Hg had already resulted in extensive soil pollution, which poses a potential environmental threat. We investigated the emission of gaseous elemental mercury (Hg0) from Hg polluted soils in settlement areas in the canton of Valais, Switzerland, and its impact on local air Hg concentrations. Most soil Hg was found as soil matrix-bound divalent Hg (HgII). Elemental mercury (Hg0) was undetectable in soils, yet we observed substantial Hg0 emission (20–1392 ng m−2 h−1) from 27 soil plots contaminated with Hg (0.2–390 mg Hg kg−1). The emissions of Hg0 were calculated for 1274 parcels covering an area of 8.6 km2 of which 12% exceeded the Swiss soil remediation threshold of 2 mg Hg kg−1. The annual Hg0 emission from this area was approximately 6 kg a−1, which is almost 1% of the total atmospheric Hg emissions in Switzerland based on emission inventory estimates. Our results show a higher abundance of Hg resistance genes (merA) in soil microbial communities with increasing soil Hg concentrations, indicating that biotic reduction of HgII is likely an important pathway to form volatile Hg0 in these soils. The total soil Hg pool in the top 20 cm of the investigated area was 4288 kg; hence, if not remediated, these contaminated soils remain a long-term source of atmospheric Hg, which is prone to long-range atmospheric transport.

Effect of wet flue gas desulfurization facilities of coal-fired power plants on mercury emission

The speciation and content of mercury in flue gas were measured before and after WFGD of eight coal-fired units by Ontario Hydro method and the effect of WFGD on mercury species distribution and concentration was investigated. The results show that mercury is mainly composed of gaseous form and mercury emission concentration after WFGD in different units has very large difference. The effect of WFGD on mercury emission is embodied on synergistic removal of gaseous mercury with average mercury removal efficiency of 36.8%. Mercury is transferred from flue gas to desulfurization gypsum in WFGD. The mercury stability in desulfurization gypsum and the second mercury pollution are worthy of attention.

Investigation of mercury emissions from burning of Australian eucalypt forest surface fuels using a combustion wind tunnel and field observations

Environmental cycling of the toxic metal mercury (Hg) is ubiquitous, and still not completely understood. Volatilisation and emission of mercury from vegetation, litter and soil during burning represents a significant return pathway for previously-deposited atmospheric mercury. Rates of such emission vary widely across ecosystems as they are dependent on species-specific uptake of atmospheric mercury as well as fire return frequencies. Wildfire burning in Australia is currently thought to contribute between 1 and 5% of the global total of mercury emissions, yet no modelling efforts to date have utilised local mercury emission factors (mass of emitted mercury per mass of dry fuel) or local mercury emission ratios (ratio of emitted mercury to another emitted species, typically carbon monoxide). Here we present laboratory and field investigations into mercury emission from burning of surface fuels in dry sclerophyll forests, native to the temperate south-eastern region of Australia. From laboratory data we found that fire behaviour — in particular combustion phase — has a large influence on mercury emission and hence emission ratios. Further, emission of mercury was predominantly in gaseous form with particulate-bound mercury representing <1% of total mercury emission. Importantly, emission factors and emission ratios with respect to carbon monoxide and carbon dioxide, from both laboratory and field data all show that gaseous mercury emission from biomass burning in Australian dry sclerophyll forests is currently overestimated by around 60%. Based on these results, we recommend a mercury emission factor of 28.7 ± 8.1 μg Hg kg−1 dry fuel, and emission ratio of gaseous elemental mercury relative to carbon monoxide of 0.58 ± 0.01 × 10−7, for estimation of mercury release from the combustion of Australian dry sclerophyll litter.

Carbon-based sorbents impregnated with iron oxides for removing mercury in energy generation processes

Gaseous phase mercury emissions into the atmosphere from fossil fuel combustion processes for energy production are a matter of serious environmental concern. Several technologies have been studied and proposed to address this problem, but none of them is mature enough from a commercial point of view. This study aims to provide new insights into the interaction between mercury and iron oxides in order to enable the design of cost-effective mercury capture technology based on regenerable sorbents. Different iron oxides supported on an activated carbon were prepared and tested for the removal of elemental mercury (Hg0). It was found that 1) maghemite promoted the removal of mercury to a greater extent than goetite/hematite achieving 100% efficiencies and 2) the mercury-sorbent interaction is determined by the oxygen vacancies present in the iron oxide. The mercury retention efficiency is maintained after the sorbent is regenerated and it is not deactivated by the presence of acid gases. The results obtained with the sorbent loaded with maghemite open new perspectives for the retention of gaseous Hg0, combining high efficiency, good regenerability and lower price in comparison with sorbents developed to date. Once the regeneration capacity is assessed, the adsorption process will be scaled.

Alginate-pyrolyzed porous carbon as efficient gas phase elemental mercury scavenger

The present research work demonstrates the potential of porous carbon (PC) fabricated through facile one-step method from calcium alginate biomass as a low cost and efficient scavenger for gas phase elemental mercury (Hg°) from natural gas. Performance of the prepared PC at different temperatures (500, 700 and 900 °C) using fixed-bed setup mimicking the plant conditions revealed that PC-900 demonstrated to be a promising adsorbent for removing Hg°. The excellent sorption performance of PC-900 could be attributed to its BET surface area and large pore volume which rendered easy sorption of Hg° into the porous network. The equilibrium adsorption results further confirmed that sorption capacity decreased from 1236 to 1089 μg/g with increase in temperature from 30 to 50 °C, indicating exothermic nature of adsorption. The sorption isotherms well fitted the Langmuir model, with maximum adsorption capacity of 1236 μg/g at 30 °C. A comparison of the sorption capability of bio-derived PC-900 with sulfur impregnated carbon (SIC) at 50 °C affirmed that the uptake capacity of PC-900 (1089.6 μg/g) was much higher than SIC (887.2 μg/g). These results reveal the promising solutions offered by alginate pyrolyzed PC for scavenging Hg° from natural gas, by not only reducing the environmental problems associated with gaseous mercury emissions but also by making the process more economical.

Mitigation of gaseous mercury emissions from waste-to-energy facilities: Homogeneous and heterogeneous Hg-oxidation pathways in presence of fly ashes

This study describes the main mechanisms that take part in the mercury homogeneous oxidation pathway in presence of some of the main reactive compounds formed during waste incineration processes (O2, HCl, SO2 and NO). Series of model, synthetic dry flue gases were used to elucidate the effects of HCl, SO2, NO and their proportions in the gas on mercury behaviour. Three samples of fly ash collected from a MSWI facility were characterized and evaluated both for Hg heterogeneous oxidation and Hg removal in a laboratory scale device. The results obtained in this study showed that homogeneous mercury oxidation in the models MSWI and coal combustion flue gas atmospheres was 52 ± 5% and 25%, respectively. SO2, NO and HCl have a synergetic effect in Hg oxidation in presence of oxygen, but the main differences found are mainly caused by the strong influence of HCl and the likely inhibitory oxidation effects of SO2. Surface area together with carbon and chloride content of the fly ashes were correlated with their capacity for Hg-heterogeneous oxidation and adsorption. The sample of fly ash with relatively high content of unburnt carbon and chlorine, and with BET surface (2.42 m2/g) was able to remove up to 100% of Hg0 (g) during 300 min. The results obtained in this study provide a complete overview of the behaviour of mercury during MSWI processes and may help to clarify the fate/behaviour of mercury in a filter (e.g. electrostatic precipitator) providing a deeper knowledge about the impacts of fly ash properties on mercury fate in waste incineration.