Mercury Adsorption Performance Research Articles

Mercury Adsorption and Oxidation Performance of an Iron-Based Oxygen Carrier during Coal Chemical Looping Process.

During chemical looping combustion (CLC) and chemical looping gasification (CLG) of coal, the release, migration, and speciation of mercury in coal are significantly influenced by oxygen-carrier materials; however, the underlying mechanism remains inadequately addressed. In this work, the effect of a typical iron-based oxygen carrier on the release behavior of mercury from a bituminous coal and a lignite was investigated based on the Ontario-Hydro method. It is found that the effect of the iron-based oxygen carrier is attributed to three aspects: the enhanced release rate of mercury from coal, the adsorption of the released mercury, and the oxidization of gaseous Hg0 into Hg2+. With the increasing temperature, the adsorbance of mercury by the iron-based oxygen carrier decreases, while the oxidation of mercury enhances. Even at 900 °C, the adsorbance of mercury by the oxygen carrier remained at 0.1687 g/g, with a relative content of Hg2+ at 22.55%. Additionally, it was observed that iron-based oxygen carriers can physically absorb both Hg0 and Hg2+, while chemisorption refers to complex-compound formation between the iron-based oxygen carrier and mercury.

Rational construction of MoSx via defect engineering for efficient removal of mercury ions from aqueous solution

Mercury ions (Hg2+) are one of the most physiologically toxic heavy metal ions in water. Developing adsorbents for separating and removing mercury ions from aquatic systems has important environmental and social significance. Owing to the hard-soft-acid-base interaction between mercury and sulfur (S) atoms, two-dimensional layered MoS2 holds great promise in capture physiologically toxic Hg2+ from water, but most S atoms are located inside the bulk MoS2, hindering the effective contact with mercury. Defects engineering is considered as an effective way to adjust the structure and achieve superior performance of MoS2. However, reasonable and fine defect modulation to enhance the mercury adsorption performance remains a challenging task. Herein, we reported that molybdenum sulfide with Mo-vacancy structure (MV-MoSx) was fabricated via hydrothermal method and employed to uptake Hg2+. The results showed that this defect type significantly increased the concentration of Mo stripping defects, exposed more active S atoms, and provided MoSx with excellent adsorption performance in adsorption capacity, adsorption kinetics, distribution coefficient, selectivity and so on. In particular, MV-MoSx demonstrates a substantial actual adsorption capacity for mercury, reaching as high as 3723.3 mg/g, which is in close proximity to its theoretical adsorption capacity of 3945.95 mg/g. More importantly, a functionalized composite aerogel system based on MV-MoSx was constructed, which successfully reduced the concentration of Hg2+ solution below the concentration permitted by drinking water standards. Our study not only provide a theoretical basis for the design of novel defect engineering, but also expand the application of transition metal sulfides in the enrichment and separation of heavy metal ions.

Study on mercury adsorption mechanism of iron-modified biomass char in coal-fired flue gas based on density functional theory

As a new type of porous adsorbent, iron-modified biomass char (Fe10%-BC) may efficiently remove Hg0 from flue gas. However, the lack of in-depth research on the mercury adsorption mechanism of biomass char limits the development of this technology. The reaction path of mercury adsorption was quantitatively revealed by DFT (Density Functional Theory). The effects of oxygen-containing groups and adsorption atmosphere on Hg0 adsorption were analyzed. The results show that Hg0 adsorption by Fe10%-BC includes two stages, that is adsorption and oxidation. The modified biochar utilized the strong oxygen release/storage capacity of iron oxides, reacting with Hg0 by Lewis acid-base reaction. Oxygen-containing groups regulated molecular orbital energy level and surface charge distribution of iron-modified biomass char, affecting the adsorption capacity of Fe10%-BC. Aldehyde, ketone and carboxyl group promoted Hg0 adsorption performance of Fe10%-BC, and the effect from strong to weak was aldehyde group > ketone group > carboxyl group. Hydroxyl group inhibited mercury adsorption by Fe%10-BC. The adsorption atmosphere CO2，O2 and HCl promoted the mercury adsorption performance of the iron-based modified biomass char by forming new adsorption sites with the modified biomass char. SO2 consumed the high valence metal and lattice oxygen, forming competitive adsorption with Hg0. Hg0 adsorption efficiency of the modified biomass char decreased to 58%.

Long-term environmental stability of bromide coupled mechanical modified fly ash after mercury adsorption

Bromide coupled mechanical modified (BMM) fly ash showed good mercury adsorption performance. However, we have no information about the environmental stability after mercury adsorption. In this paper, environmental stability was investigated by desorption method in different temperature and improved continuous extraction experiments. Long-term environmental stability experiments showed that mercury desorption rates of BMM fly ash and activated carbon (AC) were both less than 5 % after placing them in the natural environment for one year. The stability of BMM fly ash after mercury adsorption was similar to that of AC. BMM method not only increased the specific surface area, but also improved the stable binding of bromide modifier on the surface, thereby improving the adsorption performance and stability. After adsorption, mercury in BMM fly ash existed in the form of HgBr2, HgS and HgO. Moreover, the improved continuous extraction experiments showed that the residue fraction of mercury in BMM fly ash was highest reaching 28 %, which was higher than that of AC (21 %). DFT calculation also showed that the presence of bromine reduced the adsorption energy of the mercury adsorption process, which proved that the presence of bromine improved the adsorption efficiency and stability of the adsorbent. These results indicate that BMM fly ash has the same environmental stability as AC, thus it has great potential application value for mercury removal from flue gas in coal-fired power plants.

Novel pyrite-type RuS2 adsorbent for elemental mercury capture in a wide temperature range

Metal sulfides have attracted increasing attention in mercury emission control due to their high adsorption capacity and superior sulfur resistance. Nevertheless, the performances of most metal sulfides are still unsatisfactory due to their narrow working temperature window. Here, a novel pyrite-type RuS2 adsorbent is attained using a simple salt melt approach and used for capturing elemental mercury in simulated flue gas. RuS2 exhibits excellent mercury adsorption performance in a wide temperature range of 100–300 °C with mercury removing efficiency all above 78%. Hg0 capture performances of RuS2 can be distinctly influenced by annealing temperatures. RuS2-400 prepared at 400 °C displays the optimal mercury removal performance. Nitric oxide shows a negligible influence on Hg0 removal performance likely due to physical adsorption. Sulfur dioxide presents a subtle negative impact on Hg0 capture efficiency, which is irreversible.

Novel applications of vacuum distillation for heavy metals removal from wastewater, copper nitrate hydroxide recovery, and copper sulfide impregnated activated carbon synthesis for gaseous mercury adsorption

Hydrometallurgical processing of electronic waste produces copper (Cu)-containing wastewater. Recycling of Cu is thus crucial, as it reduces the Cu impact on the environment, and increases Cu sustainability in industry. Vacuum distillation provides excellent performance in both metals removal from aqueous solution, metal recovery, and metal impregnation to porous material. Thus, this work aimed to both utilize a vacuum distillation to remove heavy metals (Cu, Na, Ni, Zn and Fe) and recover copper nitrate hydroxide (Cu2NO3(OH)3) from Cu-containing wastewater in industrial applications (e.g., mordant agent in dyeing and pigment for glass), as well as prepare copper sulfide (CuS) impregnated activated carbon for mercury (Hg0) adsorption.The experimental results indicated a vacuum distillation metals removal efficiency of over 99.99 % at 60 °C and −72 cm Hg. Additionally, the copper nitrate hydroxide (Cu2NO3(OH)3) crystalline solid derived from the vacuum distillation process achieved 77 % purity, and the copper sulfide impregnated activated carbon (CuSAC) adsorbents were prepared by adding activated carbon (AC) during the vacuum distillation process. In adsorption tests, 50 % CuSAC exhibited the greatest gaseous mercury (Hg0) adsorption performance, and it was noted that a high adsorption temperature of 175 °C negatively impacted Hg0 adsorption of 50 % CuSAC due to mercury sulfide (HgS) decomposition. Furthermore, in a simulated flue gas (SFG) environment, Hg0 capture by CuSAC was shown to be slightly obstructed. In addition, mercury temperature-programmed desorption (Hg-TPD) identified that HgS was the dominant species among adsorbed Hg species of Hg-laden 50 % CuSAC, indicating that Hg0 capture of CuSAC was mainly facilitated by sulfur active sites.As such, the vacuum distillation technique proved to efficiently remove metals and leads to successful preparation of adsorbent for Hg. Therefore, the process is an effective treatment method for Cu-containing wastewater, and can be practically applied to capture or recycle Cu in the industry in the future.

Removing mercury from flue gas by sulfur-doped zeolite-templated carbon: Synthesize and adsorption mechanism

Elemental mercury is harmful to humanity and the ecological environment. It is a simple and feasible method to capture elemental mercury by carbon-based adsorbents. The purpose of this work is to develop zeolite-templated carbon with and without sulfur (ZTC and S-doped ZTC) and to explore their mercury adsorption performance. ZTC and S-doped ZTC were synthesized by chemical vapor deposition (CVD) method and their mercury adsorption performance were tested at 30 and 150 °C. Among all ZTC samples, BEA-ZTC-HS exhibited highest mercury removal efficiency (MRE) whose initial value was 99.99% (150 °C) and 97.39% (30 °C) and decreased to 96.63% and 89.15% after one hour mercury adsorption. The physical and chemical properties of the ZTC samples were characterized by various methods to explain the high MRE of BEA-ZTC-HS. The experimental results shown that BEA-ZTC-HS replicated the crystal structure of BEA zeolite faithfully and exhibited regular microporous structure and doesn’t have obvious elemental sulfur whose existence could block the micropores in ZTC. This was helpful to the mass transfer of Hg0 in ZTC. Moreover, the chemical properties of BEA-ZTC-HS shown that the introduced sulfur were mainly bonded to the carbon framework of ZTC in the form of thiophene, sulfone, sulfoxide and sulfonic acid. Those sulfur-containing functional groups provided main active sites for mercury capture and exhibited higher activity at 150 °C. Finally, Density Functional Theory (DFT) was used to reveal the adsorption mechanism of ZTC and S-doped ZTC on Hg0. Due to its good properties of regeneration, higher MRE, good thermal stability and low cost, BEA-ZTC-HS has a wide prospect for industrial application in the wide temperature ranges compared to the activated carbon injection technology.

Study on adsorption mechanism of mercury on Ce-Cu modified iron-based biochar

Combined with sol-gel method and co-precipitation method, Ce-Cu is used to modify iron-based biochar, and the mercury adsorption performance of modified biochar is investigated with a fixed bed adsorption device. The mercury adsorption capacity and regeneration capacity of iron-based modified biochar under different Ce-Cu loading are explored. Pore structure and surface element valence of Ce-Cu modified iron-based biochar are investigated by BET and XPS. H2-TPR and N2-TPD are used to study the reaction path of metal active substances on the surface of modified biochar and the form of mercury on the biochar surface. The microscopic morphology of the biochar is explored by scanning electron microscope (SEM). At the same time, KOH and concentrated hydrochloric acid are used to study the effects of physical adsorption and chemical adsorption on mercury adsorption. The experimental results show that 4 % Ce2 % Cu-FeBC sample has the best mercury removal performance. The cumulative mercury adsorption per unit is 18025 ng•g−1 in 3 hours, and the mercury removal efficiency remains above 90 %. The Ce-Cu modified biochar is mainly mesoporous, and the types of surface-active metals are abundant, which is conducive to the adsorption and oxidation of elemental mercury.11Corresponding author: Yongqiang Zhang. E-mail addresses: 18810927758@163.com The main valence states of mercury on biochar surface are Hg2+, Hg-OM, HgCl2 and HgO are the main forms of existence. The regeneration performance of Ce-Cu modified iron-based biochar is superior, and the mercury removal performance does not decrease after regenerations twice. The rate-controlling step of mercury adsorption on biochar is chemical adsorption.

Enhancement of Hg0 adsorption performance at high temperature using Cu-Zn bimetallic sulfide with elevated thermal stability

In this work, a series of Cu-Zn bimetallic sulfides were synthesized to improve the mercury adsorption performance at high temperatures. Results showed that the adsorption performance of Cu-Zn bimetallic sulfides are much better than CuS and ZnS at high temperature. Compared with the pure CuS, the mercury adsorption efficiency greatly increased from 40% to 88% at 220 °C for the optimal Cu0.95Zn0.05S. XRD results showed that Zn can enter into the lattice structure of CuS, which significantly promoted the thermal stability of CuS. TG analysis indicated that the weight loss for the Cu-Zn bimetallic sulfides was only 14%-19%, while the weight loss for CuS is as high as 42%. Moreover, the adding of Zn can significantly inhibit the formation of inactive SO42- during the synthesis process, enabling more Sx and S22- sites exposed on the surface. Raman spectra indicated that the Sx sites mainly existed in the form of long-chain Sx (L- Sx) or ring Sx on the pure CuS, while existed as short-chain Sx (S-Sx) on Cu0.95Zn0.05S. The S-Sx sites are more active in mercury adsorption, resulting in the better performance of Cu-Zn bimetallic sulfides.

Acceleration of the reaction of H2S and SO2 by non-thermal plasma to improve the mercury adsorption performance of activated carbon

Activated carbon (AC) loading sulfur can improve mercury adsorption performance. Fine sulfur clusters can be generated by the H2S and SO2 reaction, but the reaction is extremely slow at ambient temperatures. This study proposes a cost-effective and efficient method for non-thermal plasma (NTP) to accelerate the reactions between H2S and SO2 on AC to improve elemental mercury (Hg0) removal performance. The NTP treatment experiment was carried out on a laboratory-scale dielectric barrier discharge system. The Hg0 adsorption experiment was conducted via the Tekran Hg CEMS online monitoring device. The results showed that NTP treatment accelerated the reaction of H2S and SO2. The specific surface area and surface morphology of the AC had no significant changes after NTP treatment. However, the surface of AC was enriched with more sulfur in a very short time. H2S and SO2 presented an optimum mixing ratio of 2:1. NTP exhibited an optimum treatment time and voltage of 1 min and 3 kV, respectively. The Hg0 removal efficiency was increased by approximately 70% as compared to AC. In addition, the effects of the adsorption temperature and individual flue gas composition were explored. Further X-ray photoelectron spectroscopy analysis and temperature programmed desorption were also performed. Hg0 adsorption was mainly controlled by chemisorption, wherein the elemental sulfur loaded on AC was the main active site for Hg0 conversion to mercuric sulfide (HgS).

Shell-thickness-induced spontaneous inward migration of mercury in porous ZnO@CuS for gaseous mercury immobilization

• Porous structure of ZnO@CuS are beneficial for mercury capture. • The mercury bonding stability depended largely on CuS shell thickness. • ZnO@CuS [4:3] could adapt to a wider temperature window. • Gaseous mercury tended to migrate inward the ZnO@CuS for firmer combination. Inducing gaseous substances to migrate inward into a solid material is one of the effective methods to improve the interfacial adsorption stability. However, the gaseous mercury (Hg 0 ) adsorption on bulk material, especially mineral sulfides, generally occurred on the outer surface owing to their compact structure, resulting in the low bonding stability. This study prepared porous ZnO@CuS with different shell thickness to investigate mercury adsorption performance and bonding stability. The porous shell structure enabled Hg 0 to migrate inward into ZnO@CuS. Such an inducing effect, on one hand, improved the mercury adsorption performance due to the increase of active sites with the thickened shell. On the other hand, the mercury bonding stability was enhanced along with the increase of shell thickness. The initial mercury desorption temperature gradually increased from 50 to higher than 100 °C, and meanwhile, the desorption peak temperature increased from 150 to 275 °C. The improved bonding stability also enlarged its adaption to a wider temperature window (50–150 °C). Moreover, the optimal ZnO@CuS has a saturated adsorption capacity of 60.53 mg/g, and it has high resistance against O 2 , SO 2, and H 2 O. This work thus offers a promising thickness-induced method to enhance the mercury bonding stability on sulfides.

Utilization of Ag nanoparticles anchored in covalent organic frameworks for mercury removal from acidic waste water

Metal nanoparticles (NPs) have high reaction rate and atom utilization with respect to pollutants in aqueous environments. However, the aggregation and instability in acidic solution limit their practical applications. Mercury removed from acidic solution are still a big problem. In this study, we used a tunable porous covalent organic framework (COF) material as a support for in situ growth of Ag NPs via a one-step solution infiltration method, to enhance the spatial dispersion of NPs and their stability in acidic solution, and for the first time studying the mercury adsorption performance. More importantly, the Ag NPs@COF composite exhibited high removal rate (99 %), ultrahigh Ag atom utilization (150 %), high selectivity and stability, and reusability for Hg(II) removal from acidic aqueous solutions. Meantime, through common characterizations and density functional theory calculations verifying the microscopic adsorption process, we found COF material played an important role in the entire purification process because it provided some electrons to Hg(II) ions via Ag NPs, finally generating an amalgam. Therefore, the present work not only provides a COF-supported Ag NPs material for Hg(II) ions removal from acidic waste water but also opens a new field of design of functionalized COFs material for applications in environmental pollutions control.

Study of the Effect of Adsorption Temperature on Elemental Mercury Removal Performance of Iron-Based Modified Biochar

An iron-based modified biochar was prepared by the coprecipitation method, including single iron-based modified biochar with FeCl3 and iron-based biochar doped with Cu and Mn from CuSO4 and KMnO4. Combined with the physicochemical properties of sorbents, the effect of flue gas temperature on the mercury adsorption performance of the sorbents was explored within the temperature range of 50–350 °C. The adsorption mechanism was further explored by adsorption kinetics, thermodynamics, and temperature-programmed desorption (TPD) analyses. The results showed that the mercury adsorption capacity of unmodified biochar decreased monotonously with temperature, but the adsorption capacities of Fe/BC, FeCu/BC, and FeMn/BC all enhanced first and then weakened, with 200 °C being the optimum adsorption temperature. FeCu/BC had the strongest adsorption capacity, while Fe/BC had the worst one. C═O and COOH, metal oxides and ions, lattice oxygen, chemisorbed oxygen, and Cl ions were all active sites for oxidative adsorption of Hg0, among which Fe2O3 and CuO or CuFe2O4 exerted a synergistic effect. Excessive temperature caused destruction to the porous structure and deactivation of the active centers, leading to the reduction of physisorption and chemisorption. Mercury adsorption on sorbents needs more activated energy due to the enhancement of chemisorption, and the moderate increase of temperature contributed to the adsorption properties of the sorbents. The Hg0 adsorption on modified biochar was spontaneous and endothermic, and the complexity degree of the adsorption process was promoted. TPD results showed that at 200 °C the removal of Hg0 by modified biochar was mainly strong chemisorption and that HgO was mainly formed.

In-Situ Capture of Mercury in Coal-Fired Power Plants Using High Surface Energy Fly Ash.

Coal-fired power plants represent the largest source of mercury emissions worldwide. Using fly ash, a byproduct of these plants, as a sorbent to remove mercury has proven to be difficult. Here, we found that the fresh surface of modified fly ash has good adsorption performance, and it declines obviously with time because of unsaturation characteristics on surface. On the basis of this mechanism, our study provides a method to in situ capture mercury with high surface energy modified fly ash by mechanochemical and bromide treatment. Fresh modified fly ash with active sites is injected into the flue to directly adsorb mercury. A continuous system within a full-scale 300 MWe plant showed that the mercury adsorption performance of the modified fly ash is similar to that of activated carbon, which is the industry benchmark for the treatment of mercury emission in fossil power generation units. This is a breakthrough and indicates that modified fly ash can become an efficient and convenient industrial sorbent for the removal of mercury.

Optimized methods for preparing activated carbon from rock asphalt using orthogonal experimental design

This work evaluated three activation methods, physical activation, chemical activation and combined physical–chemical activation, for preparing activated carbon (AC) from rock asphalt. A high carbon content and the low cost of rock asphalt makes it a good possible raw material for the preparation of activated carbon. The objective of this research was to establish what preparation conditions resulted in the AC with the best performance. Orthogonal experimental design was used to optimize preparation conditions. The criteria for evaluating the AC preparation methods were yield, surface area and mercury adsorption performance of the AC samples prepared with each technique. The optimum experimental conditions for AC preparation using the chemical activation method are: a carbonization heating rate of 12 °C min−1, a carbonization temperature of 400 °C, a carbonization time of 60 min, an activation temperature of 850 °C, an activation time of 120 min and a KOH/asphaltene mix rate of 3 (w/w). The potassium hydroxide added in the chemical activation method reduced the formation of volatiles during the carbonization process. The KOH/asphaltene mix rate and the carbonization temperature play a decisive role on the specific surface area and Hg adsorption capacity of AC. The optimum experimental conditions for AC preparation using the combined physical–chemical activation method are: a carbonization temperature of 450 °C, a carbonization time of 40 min, an activation temperature of 800 °C, an activation time of 60 min, a KOH/asphaltene mix rate of 1 and a steam flow rate of 8 g h−1. In the combined physical–chemical activation method, the KOH/C mix rate, activation temperature and steam flow rate are the primary factors affecting the surface area and Hg adsorption capacity. The surface areas of the AC samples prepared under the optimum experimental conditions in the chemical activation method and the combined physical–chemical activation methods were 2834.3 m2 g−1 and 2102.2 m2 g−1, respectively. The physical activation method was not suitable for preparing AC from rock asphalt due to low char yields.

Experimental Study on Mercury Adsorption and Adsorbent Regeneration of Sulfur-Loaded Activated Carbon

A kind of commercial sulfur-loaded activated carbon (SAC) was experimentally studied on the mercury adsorption and adsorbent regeneration performance. Mercury adsorption experiments were carried out on a bench-scale fixed-bed experimental device. The physicochemical properties of the original and used SAC were characterized and discussed on the basis of the surface area and porosity (Brunauer–Emmett–Teller measurements) and X-ray photoelectron spectroscopy analysis. The results showed that the specific surface areas and the content of oxygen functional groups as well as non-oxidized sulfur on the surface decreased after mercury adsorption. The used samples were regenerated via the co-pyrolysis with elemental sulfur. The regenerated adsorbent showed an average mercury removal efficiency up to 95% in 2 h under the conditions of the co-pyrolysis temperature at 600 °C, 1 h heating time, and sulfur–carbon ratio of 1:1. The regenerated sample was found to be structurally stable and sustainably reactive on the H...

Synthetic calcium-based adsorbents for gaseous mercury(II) adsorption from flue gas and study on their mercury adsorption mechanism

calcium-based sorbents are the potential materials for mercury chloride (HgCl2) adsorption while inert to elemental mercury (Hg0) due to their basic property. A series of calcium-based sorbents were chosen to evaluate the selective adsorption performance of mercury, these sorbents included a calcium oxide adsorbent, a KCl-doped calcium oxide adsorbent and a K2CO3-doped calcium oxide adsorbent which all supported by the mesoporous silica (C-SiO2, CKL-SiO2 and CKO-SiO2) and were synthesized by an impregnation method. All sorbents were firstly characterized by Powder X-ray Diffraction (XRD), Brunauer-Emmett-Teller (BET) and Scanning Electron Microscope (SEM). Characterization results show that C-SiO2 has the best surface structure while the doped KCl would evidently reduce the specific surface area and micropores volume of the sorbent, the doped K2CO3 also has an adverse effect on the surface structure of CaO sorbent but it can significantly improve the basicity of sorbent. Mercury adsorption performance of the sorbents was then evaluated in fixed bed apparatus, the results indicated that all sorbents exhibited a complete breakthrough for gaseous Hg0. Due to the modification of K2CO3 to the CaO sorbent, HgCl2 was fully adsorbed by CKO-SiO2 no matter the SO2 presented or not. CO2-TPD combined with HgCl2-TPD confirmed that diverse basic sites exist on the calcium-based sorbent surfaces and three HgCl2 adsorption behaviors occurred during the adsorption process. Three HgCl2 adsorption configurations were introduced to represent the different adsorption behaviors and the binding intensity of these configurations are in the successive order: monodentate < tridentate < bidentate. The monodentate adsorption configuration is the main HgCl2 adsorption manner on the CaO surface while the bidentate adsorption configuration occurs on the defect surface of sorbent.

Mercury emissions monitoring in a coal-fired power plant by using the EPA method 30B based on a calcium-based sorbent trap

A novel calcium-based sorbent was synthesized from calcium acetate and mesoporous silica through chemical impregnation method. The Brunauer-Emmett-Teller (BET) and scanning electron microscope (SEM) analysis revealed that the sorbent possessed a good surface structure as the calcium salt decomposed to calcium oxide (CaO) through multiple calcination steps. The mercury adsorption performance of the sorbent was investigated in a fixed bed system, the results showed that the sorbent has an obvious penetration behavior for gaseous element mercury (Hg0(g)) while completely adsorbed reactive gaseous mercury (Hg2+(g)) under the pure nitrogen and simulated flue gas atmosphere. On-site sampling test of the calcium-based sorbent traps was ultimately conducted on a 600 MW coal-fired power plant. The Ontario Hydra Method (OHM) was chosen as the reference method to evaluate the accuracy of the sorbent traps sampling results. The measured data obtained by sorbent traps was well consistent with OHM under the selected operational load and all the sorbent traps passed the QA/QC criteria, show that the sorbent traps performed with almost the same accuracy as OHM. The mercury emission and removal characteristics across the existing air pollution control devices (APCDs) were reported based on the sorbent traps sampling results. With the help of SCR for the Hg0 oxidation, ESP for the removal of Hg2+ and Hgp, and the good water solubility of Hg2+ in WFGD, the combination of SCR + ESP + WFGD achieved an excellent mercury removal efficiency with the value of 88.54%. The final mercury emissions from the exhaust were 3.75 μg/m3 and meet the emission requirements of China.

Effect of Nitrogen Oxides on Elemental Mercury Removal by Nanosized Mineral Sulfide.

Because of its large surface area, nanosized zinc sulfide (Nano-ZnS) has been demonstrated in a previous study to be efficient for removal of elemental mercury (Hg0) from coal combustion flue gas. The excellent mercury adsorption performance of Nano-ZnS was found to be insusceptible to water vapor, sulfur dioxide, and hydrogen chloride. However, nitrogen oxides (NOX) apparently inhibited mercury removal by Nano-ZnS; this finding was unlike those of many studies on the promotional effect of NOX on Hg0 removal by other sorbents. The negative effect of NOX on Hg0 adsorption over Nano-ZnS was systematically investigated in this study. Two mechanisms were identified as primarily responsible for the inhibitive effect of NOX on Hg0 adsorption over Nano-ZnS: (1) active sulfur sites on Nano-ZnS were oxidized to inactive sulfate by NOX; and (2) the chemisorbed mercury, i.e., HgS, was reduced to Hg0 by NOX. This new insight into the role of NOX in Hg0 adsorption over Nano-ZnS can help to optimize operating conditions, maximize Hg0 adsorption, and facilitate the application of Nano-ZnS as a superior alternative to activated carbon for Hg0 removal using existing particulate matter control devices in power plants.

Study on the mercury captured by mechanochemical and bromide surface modification of coal fly ash

Power plant coal fly ash was modified for mercury adsorption. The fly ash was subjected to mechanochemical ball milling and bromide compounds were added. The results show that mercury capture capacity increased with increasing grinding time, up to 50min. Grinding over 50min did not lead to further improvements. Results from the mercury adsorption test show that the mechanochemical processing technique coupled with the addition of bromide compounds improves mercury adsorption performance for fly ash. Both physical and chemical factors contribute to the improvements in capture performance. Increasing the grinding time produced smaller particles with higher surface area. As a result, more unburned carbon was exposed, which resulted in better mercury adsorption. Thermal gravimetric analysis of modified fly ash shows combustion peak temperatures shift towards lower temperatures with increased grinding time. This result indicates that mechanical treatment increased the thermal activity of fly ash. As a result of this study, the first on-line modified fly ash unit was installed on site at a 300MW coal fired power plant in China.