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1.
When balancing the element mercury (Hg) two coal-fired power plant units — one with slag tap boilers (ST, 2 × 220 MW) and one with a dry bottom boiler (DB, 475 MW) were compared. Both systems are provided with electrostatic precipitators (ESP), nitrogen oxides removal (DeNOx) and flue gas desulfurization (FGD) systems. The Hg in the flue gas is predominantly in gas phase. Only 15 % of the Hg introduced by the coal leaves the unit with the bottom or fly ash. Depending on the operating mode, 30 to 40 % of the Hg is separated in the FGD systems. The overall separation rate for the total system ranges between 45 to 55 %, the residue is emitted in the form of gaseous Hg species. At full load, the Hg concentration in the cleaned gas is less than 6 μg/m3. In the flue gas path of another dry bottom boiler (DB1, 480 MW) the concentrations of the gaseous species of bivalent mercury (Hg2+), elemental mercury (Hg0), and total mercury content (Σ Hg) were determined. The sum of the concentrations of Hg2+ and Hg0 is in agreement with the measurement of Σ Hg. Directly downstream of the boiler Hg2+ dominates with 77 %, while Hg0 amounts to 23 %. In the high-dust DeNOx system Hg0 is oxidized almost completely to Hg2+ (96 %). Air heater and electrostatic precipitator do not influence the Hg species concentrations. The FGD system eliminates approximately 80 % of the Hg2+. At the same time the quantity of Hg0 increases by the factor 10. In the cleaned gas Hg0 dominates with 76 % as compared to Hg2+ with 24 %. At full load the concentration of Σ Hg in the cleaned gas is also below 6 μg/m3.  相似文献   

2.
This is a preliminary study of the reactions of mercury (Hg) in the human mouth with dental amalgams. It was conducted by analysing saliva samples from subjects with amalgam fillings and control subjects with no amalgams. Samples were collected both prior to and after cleaning the mouth. These samples were analyzed for elemental mercury (Hg0), inorganic mercury (Hg2+) and methylmercury (MeHg). We concluded that the concentrations after cleaning represented the systemic concentrations. Hg2+ and MeHg were found in all systemic samples from both subjects and controls, while Hg0 was found only in the samples from subjects with amalgams. In the control group, the concentrations found before and after cleaning the mouth were equivalent. In the amalgam group, concentrations of Hg2+ found before cleaning the mouth were 10 to 40 times higher than those found after cleaning, suggesting that the oxidation reaction of Hg° into Hg2+ takes place. For MeHg, a similar but less pronounced pattern as Hg2+ was found, supporting methylation in the mouth.  相似文献   

3.
Mercury speciation in contaminated soils by thermal release analysis   总被引：1，自引：0，他引：1  
Thermal release analysis of mercury species in contaminated soils was performed by temperature controlled continuous heating of the samples in a furnace coupled to an Atomic Absorption Spectrophotometer (AAS). It was shown that this method allows the identification of different redox states of Hg-species through their characteristic releasing temperature ranges. The method was applied to Hg-contaminated samples from an inactive chlor-alkali production plant in former East Germany (GER), and from a gold mining area in Poconé, Mato Grosso, Brazil (BRA), as well as synthetic soil samples obtained by spiking pre-heated soil matrices (GER and BRA) with the following mercury species: Hg0, Hg2Cl2, HgCl2, HgO and HgS. The samples GER, in general, frequently showed the presence of Hg2+ probably bound to humic substances, in the case of samples with higher total carbon content. Only in highly contaminated samples (>3000 ppm of mercury) was Hg0 the predominant species. The samples BRA more frequently showed the presence of mercury species in the lower oxidation states, i.e. Hg1+ in combination with Hg0. The method allows observing changes in Hg-speciation in the samples with time, mainly changes among the oxidation states Hg0, Hg1+ and Hg2+. The treated GER matrix showed a stronger tendency to oxidise Hf-species than the BRA treated matrix, in which only added Hg0 is partially oxidised to Hg2+ and Hg1+. In contrast, the BRA matrix showed a pronounced tendency to reduce spiked Hg2+ to Hg1+. This may be the reason for the presence of Hg1+ in the majority of original BRA samples. The method appears to be very useful to study speciation of mercury and its dynamics. It can be used as a tool for monitoring mercury oxidation states and/or reactions of mercury in soils.  相似文献   

4.
An intensive survey of mercury speciation was performed at a site on the Upper St. Lawrence River near Cornwall, Ontario, Canada with a history mercury contamination in sediments. Surface sediments were collected every 1.50 h. Total mercury (Hgtotal), methylmercury (MeHg), organic carbon, inorganic and organic sulphur were determined in the solid fraction. Dissolved Hgtotal, MeHg and dissolved organic carbon (DOC) were measured in pore waters. Concentrations of Hgtotal in the upper layers (first 5 cm) were high, ranging from 1.42 to 25.8 nmol g?1 in solids and from 125 to 449 pM in pore waters. MeHg levels were also high, ranging from 4.34 to 34.1 pmol g?1 in solids and from 40 to 96 pM in pore waters. This amounts to up to 1.4% of Hgtotal present as MeHg in solids and 64% in pore waters. A daily pattern for Hgtotal was observed in the solid fraction. The MeHg distribution in solids and pore waters was not correlated with Hgtotal or DOC, suggesting that the concentrations of MeHg are probably more influenced by the relative rates of methylation/demethylation reactions in the sediment–water interface. Acid volatile sulphide levels and DOC were inversely correlated with organic sulphur (Sorg) levels suggesting that both parameters are involved in the rapid production of Sorg. A positive correlation was also observed between Hgtotal and Sorg in solids (R?=?0.87, p?<?0.01) illustrating the importance of organic sulphur in the retention and distribution of Hg in the solid fraction of the sediments. The results suggest that variations of Hgtotal concentrations in Upper St. Lawrence River surface sediments were strongly influenced by the formation/deposition/retention of organic sulphur compounds in the sediment–water interface.  相似文献   

5.
The Hg concentrations in coal as fired in power plants in the Netherlands are low, 0.2 mg·kg?1 on average. After combustion the Hg is released partly (between 1 and 98%, on average 42%) in a gaseous phase, which is finally emitted into the air. The other part of the Hg, which remains in the ash is separated from the flue gases by electrostatic precipitators. The variation of the vaporisation percentage of Hg is probably caused by the presence of two chemical forms: Hgo and HgCl2. This may be concluded from the observation that relatively high concentrations of HCl in the flue gases (≈150 mg·m?3) give rise to low Hg concentration in the vapor phase. In cases when the concentrations of HCl are relatively low (≈25 mg·m?3) the amount of Hg in the vapor phase is high. The average gas phase concentrations of Hg in the flue gases, based on 33 measurements with no FGD, is 4.1 μg·mfo ?3. In a wet FGD based on the lime/limestone-gypsum process 50 to 70% of the Hg in the flue gases is removed, leaving a residual concentration of 1–2 μg·mfo ?3. The emission factor is then about 0.5 mg·GJ?1 or 5 μg·kWhr?1. In one particular measuring serie the fate of Hg was studied in a FGD-installation with a prescrubber.  相似文献   

6.
Experimental results from a study of the gas and aqueous phase reactions of elemental mercury (Hg0) with methyl iodide (CH3I) and dimethyl sulfide (DMS) are presented. In aqueous phase experiments with CH3I we found no observable increase in methyl mercury (MeHg). A small formation of MeHg, however, was observed in some (but not all) gas phase experiments in sunlight. A loss of Hg0 and a simultaneous formation of oxidized mercury (Hg(II)) was also observed in these experiments. No reaction, neither methylation or oxidation, was found between Hg0 and DMS under any conditions investigated. These experiments suggest that a simple homogeneous gas or aqueous phase methylation of Hg0 by DMS or CH3I in the atmosphere cannot account for the significant levels of MeHg observed in precipitation.  相似文献   

7.
Spectroscopic (XRD, XPS, ICP-MS and AAS) and microscopic (ESEM) techniques have been used in order to study the chemical effects with emphasis on mercury speciation, during thermal treatment of a mercury contaminated soil. In the untreated soil, mercury was found concentrated in spherical particles, which were successively broken down upon thermal treatment. Hg0 and inorganic mercury compounds (presumably HgO(s) and HgSO4(s)) could be detected. No (CH3)2Hg and only traces of CH3Hg+ could be found. The dependence on temperature and heating time indicated that the evaporation of mercury from the soil was partly controlled by diffusion mechanisms. Mercury volatilized in two separate stages during heating; initial elemental vaporization, and subsequent volatilization of the oxide or sulfate phase at higher temperatures (>230°C). By thermal treatment at 470°C and 20 min, a removal of >99% of the mercury could be achieved.  相似文献   

8.
Most technologies used for decontamination presents good results for high concentrations, but limitations for lower ones. The desirable Hg concentration in the water is extremely low because of its toxicity. The aims of this study were to evaluate inorganic mercury (Hg2+) and methylmercury (CH3Hg+) toxicity in Nostoc paludosum, to assess the potential of this cyanobacteria strain to remove these Hg species from aqueous medium and also to investigate Hg methylation by the cyanobacteria. CH3Hg+ determination was performed by gas chromatography-pyrolysis-atomic fluorescence spectrometry in cultures exposed to a concentration of 20 μg L?1 for 30 days. Both Hg species were removed from the supernatant, ranging from 73 to 96% of Hg2+ and from 73 to 95% of CH3Hg+. Ultrastructural Hg2+ effects in the cyanobacteria cells investigated by transmission electron microscopy revealed higher production of glycogen, cyanophycin, and intrathylacoidal spaces than the control group. When Hg was added to the culture in the form of CH3Hg+, a decrease corresponding to approximately 60% of the initial concentration due to Hg volatilization was observed. The production of CH3Hg+ by the cyanobacteria was detected in concentrations near the limit of detection (0.0025%) of the bioaccumulated THg. This is an advantage for biotechnological decontamination applications, as CH3Hg+ is a very toxic specie and can be bioaccumulated and biomagnified. The results demonstrated that cyanobacteria cells are an efficient alternative to retain and/or remove Hg at low concentrations and they constitute a potential tool for a “final cleaning” of contaminated waste water.  相似文献   

9.
The gas phase oxidation of elemental mercury by ozone   总被引：2，自引：0，他引：2  
The gas phase reaction between elemental mercury (Hg0) and ozone (03) has been studied in sunlight, in darkness, at different temperatures, and different surface-to-volume (s/v) ratios. At 03 concentrations above 20 ppm, a loss of Hg0 and a simultaneous formation of oxidized mercury (Hg(II)) was observed. The results suggest a partly heterogeneous reaction, with a gas phase rate constant of 3±2×10?20 cm3 molec.?1 s?1 at 20 °C. This corresponds to an atmospheric Hg half-life of about one year at a mean global 03 concentration of 30 ppb.  相似文献   

10.
As global mercury emissions from coal fire power plants increase with the continuing rise of coal consumption, mercury capture methods are being developed to prevent mercury??s escape into the atmosphere. Titanium dioxide (TiO2) in the presence of ultra violet light (UV-A; ?? max ??360?nm) and oxygen will capture mercury as the solid product HgO(s). Testing the effects of TiO2 in the presence of other pollutants has so far been limited. We have performed kinetic and product studies of mercury adsorption in the presence of the gaseous flue co-pollutant NO2(g). We extensively studied the gas-phase reaction of NO2(g) with Hg (g) 0 . We compared the gas-phase reaction to the same reaction performed in the presence of thin TiO2 particle surfaces from 0 to 100?% relative humidity. The second-order rate constant was measured to be k?=?(3.5?±?0.5)?×?10?35?cm6 molecules?2?s?1, independent of the presence of titania or the total surface area available for adsorption. Exposure of NO2(g) to titania surfaces that were already saturated in captured mercury (HgO(s)) increased total mercury uptake onto the surface. We discuss the implications of this study to the capture of mercury emissions prior to release to the atmosphere.  相似文献   

11.
Total and elemental mercury (Hg) in simulated flue gas was measured on-line by a commercial Semtech® Hg analyzer. This instrument is based on Zeeman modulated Atomic Absorption Spectrometry. Both a wet chemical solution and a dry physical pyrolysis converter were applied to reduce the Hg(II) in the gas before leading it to the detector. Results show that the Semtech® analyzer is suitable for measuring elemental Hg even in the presence of 2500 ppm SO2 and 500 ppm HCl. For the measurement of Hg(II), the wet method is suitable only at SO2 concentrations <50 ppm. The dry thermal converter filled with crushed quartz chips together with a small amount of soda lime converts Hg(II) quantitatively at laboratory scale. This result is promising, since the trace gases delivered to the system, such as SO2, and HCl are similar to those produced in coal burning and waste incineration processes. The limiting factor for such a converter is its comparatively short life time of performance, about 20 hours.  相似文献   

12.
Methodological and experimental studies of the abiotic uptake of gaseous substances by organic soils were performed. The static adsorption method of closed vessels for assessing the interaction of gases with the solid and liquid soil phases and the dynamic method of determining the sorption isotherms of gases by soils were analyzed. The theoretical substantiation of the methods and their practical implementations on the basis of a PGA-7 portable gas analyzer (Russia) were considered. Good agreement between the equilibrium sorption isotherms of the gases and the Langmuir model was revealed; for the real ranges of natural gas concentrations, this model can be reduced to the linear Henry equation. The limit values of the gas sorption (Langmuir monolayer capacity) are typical for dry samples; they vary from 670–4000 g/m3 for methane and oxygen to 20 000–25 000 g/m3 for carbon dioxide. The linear distribution coefficients of gases between the solid and gas phases of organic soils (Henry constants) are 8–18 units for poorly sorbed gases (O2, CH4) and 40–60 units for CO2. The kinetics of the chemicophysical uptake of gases by the soil studied is linear in character and obeys the relaxation kinetic model of the first order with the corresponding relaxation constants, which vary from 1 h ?1 in wet samples to 10 h ?1 in dry samples.  相似文献   

13.
Due to the inherent differences in bioavailability and transport properties of particulate and dissolved mercury (HgP and HgD), it is important to understand the processes by which each is mobilized from soil to stream. Currently, there is a paucity of HgP data in the literature despite the fact that it can be the dominant fraction in some systems. We analyzed HgP in conjunction with volatile solids (VS, an estimate of organic content) and total suspended solids (TSS) and investigated the viability of using turbidity as a surrogate measure of HgP. Samples were collected for flow conditions ranging from 72 to 8,223 L?s?1 during October 2009 through March 2010 in a 10.5-km2 forested headwater catchment. Total Hg concentrations ranged from 0.28 to 49.60 ng L?1, with the relative amount of HgP increasing with discharge from approximately 40% to 97%. Storm dynamics of HgP and HgD were not consistent, indicating unique controls on the export of each fraction. During high-flow events, HgP was consistently higher on the rising limb of the hydrograph compared with the receding limb for a range of discharge events, with this hysteresis contributing to a degraded relationship between HgP and streamflow. Overall, HgP was strongly positively correlated with VS (r 2?=?0.97), confirming the known association with organic carbon. Due to a consistent organic fraction of the suspended solids (34?±?6%), HgP was also well correlated with TSS (r 2?=?0.95), with an average of 0.10 ng of HgP per milligram of TSS in this system. Stream turbidity measured with an in situ sonde also had a strong correlation with TSS (r 2?=?0.91), enabling commutative association with VS (r 2?=?0.86) and HgP (r 2?=?0.76). Turbidity can explain more than twice the temporal variance in HgP concentrations (n?=?50) compared with discharge (r 2?=?0.76 versus 0.36), which leads to improved monitoring of HgP dynamics and quantification of mass fluxes.  相似文献   

14.
Maricou  H.  Pereira  D.  Verschuere  L.  Philips  S.  Verstraete  W. 《Water, air, and soil pollution》1998,107(1-4):423-442
Using an electronic nose, concentration ranges of volatile fatty acids(VFAs), methane and butane, NH3, HCl, SO2 andN2O have been measured to establish the relation between theconcentration in the liquid or the gas sample and the electronic nosereading. A quantitative sensorial odor perception (SOP) was introduced,based on the average reaction of the twelve available sensors of theelectronic nose. The results of the different compounds showed that thesensors reach a saturation level with increasing concentration. In the lowerconcentration ranges, linearity between concentration and signal outputoccurred. This linear interval was situated for the VFAs between thedetection limit in the range of 5 to 15 g dissolved compound per L distilledwater and the upper limit of 60 g L-1. For the gases, thedetection limit varied between 6 and 690 volumes of gas per million ofvolumes air (ppmv). The upper limit of the linear interval ranged from 100–3000 ppmv depending on the compound. For the olfactometry reference product n-butanol, with a reported olfactory lower threshold valueof 0.04 ppmv, the electronic nose was less sensitive and gave a detectionlimit around 975 ppmv. The different compounds could be visualized in radarplots, which had a specific profile for each compound. The higher theconcentration of the volatile compounds in the air, the larger the surfaceof the respective radarplot. A discriminant analysis showed clusters ofcompounds such as the VFAs, the non polar gaseous compounds methane andbutane and the other more polar gaseous compounds.  相似文献   

15.
Since increased Hg-concentrations in fish in lakes and rivers in northern Europe, northern parts of the U.S.A. and Canada were found, environmental Hg research has focused intensively on the factors determining leaching of mercury from soil into water systems. This article presents the results of a leaching experiment with undisturbed soil columns treated with HgCI2 and CH3HgCl using radio-analytical techniques. The columns were irrigated with rain of different acidity, rain volumes and irrigation intensities. The leaching of mercury was traced by detecting the vertical distribution of 203Hg in the soil profiles. Advantages and disadvantages of radioanalytical scanning techniques are discussed. The results of Hg leaching in the soil columns indicate a considerably stronger leaching of monomethyl mercury compared to inorganic mercury. Leaching of the two Hg-species is ruled by competition of H+ induced soil-Hg desorption with DOM-Hg complex formation; both being affected by rain acidity. Rain intensity had no visible effect on leaching of Hg2+ and CH3Hg+. An extended rain duration increased the leaching of CH3Hg+.  相似文献   

16.
Mercury Content of Illinois Soils   总被引：2，自引：0，他引：2  
For a survey of Illinois soils, 101 cores had been collected and analyzed to determine the current and background elemental compositions of Illinois soils. Mercury and other elements were determined in six samples per core, including a surface sample from each core. The mean mercury content in the surface samples was 33 ± 20 g/kg soil, and the background content was 20 ± 9 g/kg. The most probable sources of mercury in these soils were the parent material, and wet and dry deposition of Hg0 and Hg2+ derived from coal-burning power plants, other industrial plants, and medical and municipal waste incinerators. Mercury-bearing sewage sludge or other fertilizers applied to agricultural fields could have been the local sources of mercury. Although the mercury content correlated with organic carbon content or clay content in individual cores, when all the data were considered, there was no strong correlation between mercury and either the organic carbon or the clay-size content.  相似文献   

17.
Chemical speciation of mercury (Hg) in a wide variety of combustion flue gas matrices has been determined using the mercury speciation adsorption (MESA) method. The MESA sampling system for gas phase Hg species employs a series of heated, solid phase adsorbent traps. Flue gas oxidized Hg species (Hg(II) and MMHg) are adsorbed by a potassium chloride (KCl) impregnated soda lime sorbent. Elemental Hg (Hg0) is collected by an iodated carbon sorbent after passing through the KCl/soda lime sorbent. Total Hg (Hgt) is determined by summation of species. In the laboratory, cold vapor atomic fluorescence spectroscopy (CVAFS) is used for detection of Hg collected on the solid sorbents, after appropriate sample digestion and preparation. The MESA method has been evaluated for species stability, matrix effects, breakthrough, artifacts and precision. Based on eight duplicate samples a mean precision of 6.8% 11% and 4.5% (relative percent difference) has been calculated for Hg0, Hg(II) and Hgt respectively. Intercomparison of the MESA method with other methods shows very good agreement for Hgt. Mass balance calculations at 5 sites range from 75 to 140%, with a mean of 97±25%. Overall mean speciation results from 19 separate determinations suggest that Hg(II) has a 1 sigma range of 40 to 94% in coal combustion flue gas at, the inlet to pollution control devices.  相似文献   

18.
It is known that in wetland soils and soils contaminated with mercury (Hg), direct biotic reduction of Hg2+ to Hg0 leads to Hg0 emissions to the atmosphere. In terrestrial soils, numerous factors have been reported that control Hg0 emissions, but it is still unclear if biotic processes are also important. In this study, microbiological activity of Cambisol monoliths from a subalpine grassland with Hg concentrations of approx. 100 ng g–1 were manipulated in laboratory incubation experiments. Elemental Hg emissions were recorded together with CO2 emission rates as proxy for microbiological respiration. Emissions of Hg0 increased from approx. 5 ng m–2 h–1 up to 130 ng m–2 h–1 with stimulated biological activity (glucose addition, increase in temperature) and decreased with inhibited activity (chloroform fumigation, autoclaving, drying). Similar patterns with evasion rates of >90 ng m–2 h–1 were observed after dried soils were remoistened again. Our results indicated that processes leading to Hg0 emissions from uncontaminated terrestrial soils are at least partly controlled by biotic processes. However, it is still uncertain if Hg0 emission is caused directly by biotic reduction of Hg2+ or indirectly by abiotic reduction, induced by products of microbiological degradation, e.g., humic acids.  相似文献   

19.
Mercury fallout was measured 10 m from the selected emission site, the Sulfur Banks fumarole area, Hawaii Volcanoes National Park; at stations on Maui and Oahu, respectively 200 km and 380 km distant from the Sulfur Banks; and at the Hawaii Geothermal Project drill site, only 40 km from source. Sulfur Banks and Oahu measurements were carried out on six occasions between 1972 and 1976, each time within the same 24 h period. Gold foil was used for collection of elemental mercury (Hg°) and copper foil for both oxidized (Hgox) and elemental forms. The rate of deposition at the Sulfur Banks was high ? 800 μm m?2 day?1, or 300 kgkm?2 annually. The same figure applied to the relatively nearby geothermal project site. At both remote stations the fallout rate was approximately 10 fold lower. At four measurement times out of six the ratio HgO/Hgox ranged from 0.195 to 0.463 at the Sulfur Banks source and from 1.80 to 5.15 at the remote stations. On two occasions, heavy rains selectively reduced Hgox at the emission site. Model calculations compared Sulfur Banks fallout with rates of re-emission of Hg by vegetation, and the importance of the biotic factor in determination of mass balances and fluxes was emphasized. Aspects of the geochemistry and toxicology of Hg were considered briefly in relation to emission and deposition, and to the occurrence of Hg°.  相似文献   

20.
Chemical reactions of mercury in combustion flue gases   总被引：2，自引：0，他引：2  
Atmospheric Hg is present in different physical and chemical forms, which determine its atmospheric transformation and transport capacities. The chemistry of Hg in flue gases is thus of importance for the deposition pattern around point source emissions. In order to apply Hg cleaning methods in flue gases its speciation is also of importance. To investigate this under realistic conditions, a 17 kW propane fired flue gas generator was used, while the kinetics of specific Hg reactions were investigated in a continuous flow reactor. Elemental Hg is readily oxidized by Cl2 and HCl both at room and at elevated temperatures (up to 900 °C) but not by NH3, N2O, SO2 or H2S. It reacts with O2 if a catalyst, such as activated carbon, is present. A slow reaction between Hg and NO2 has also been noted.  相似文献   

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