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

Review on magnetic adsorbents for removal of elemental mercury from coal combustion flue gas

Under the influence of human activities, atmospheric mercury (Hg) concentrations have increased by 450% compared with natural levels. In the context of the Minamata Convention on Mercury, which came into effect in August 2017, it is imperative to strengthen Hg emission controls. Existing Air Pollution Control Devices (APCDs) combined with collaborative control technology can effectively remove Hg2+ and Hgp; however, Hg0 removal is substandard. Compared with the catalytic oxidation method, Hg0 removal through adsorbent injection carries the risk of secondary release and is uneconomical. Magnetic adsorbents exhibit excellent recycling and Hg0 recovery performance and have recently attracted the attention of researchers. This review summarizes the existing magnetic materials for Hg0 adsorption and discusses the removal performances and mechanisms of iron, carbon, mineral-based, and magnetosphere materials. The effects of temperature and different flue gas components, including O2, NO, SO2, H2O, and HCl, on the adsorption performance of Hg0 are also summarized. Finally, different regeneration methods are discussed in detail. Although the research and development of magnetic adsorbents has progressed, significant challenges remain regarding their application. This review provides theoretical guidance for the improvement of existing and development of new magnetic adsorbents.

Self-Constructing 100% Water-Resistant Metal Sulfides through In Situ Acid Etching for Effective Elemental Mercury (Hg0) Capture

Metal sulfides (MSs) can efficiently entrap thiophilic components, such as elemental mercury (Hg0), and realize environmental remediation. However, there is still a critical problem challenging the extensive application of MSs in related areas, i.e., how to self-regulate their water (H2O) resistance without complexing the sorbent preparation procedure. This work for the first time developed an in situ acid-etching method that self-engineered the water affinity of MSs through changing the interfacial interaction between MSs and Hg0/H2O. The introduction of abundant, undercoordinated sulfur onto the sorbent surface was the primary reason accounting for the significantly improved H2O resistance. The high surface coverage of undercoordinated sulfur induced the formation of polysulfur chains (Sx2-) that stabilized Hg0 via a bridging bond and repelled H2O, attributed to the favorable electron configurations. These properties made the surface of MSs highly hydrophobic and increased the adsorption selectivity toward Hg0 over H2O. The MSs exhibited 100% H2O resistance even in the presence of 20% H2O, which is much higher than the H2O concentration under most practical scenarios. From these perspectives, this work for the first time overcame the detrimental effects of H2O on MSs through a self-regulating way that is scalable and negligibly complexes the sorbent preparation pathway. The highly water-resistant and cost-effective MSs as prepared can serve as efficient Hg0 removal from industrial flue gas in the future.

In situ acid etching boosts mercury accommodation capacities of transition metal sulfides

Transition Metal sulfides (TMSs) are effective sorbents for entrapment of highly polluting thiophiles such as elemental mercury (Hg⁰). However, the application of these sorbents for mercury removal is stymied by their low accommodation capacities. Among the transition metal sulfides, only CuS has demonstrated industrially relevant accommodation capacity. The rest of the transition metal sulfides have 100-fold lower capacities than CuS. In this work, we overcome these limitations and develop a simple and scalable process to enhance Hg⁰ accommodation capacities of TMSs. We achieve this by introducing structural motifs in TMSs by in situ etching. We demonstrate that in situ acid etching produces TMSs with defective surface and pore structure. These structural motifs promote Hg⁰ surface adsorption and diffusion across the entire TMSs architecture. The process is highly versatile and the in situ etched transition metal sulfides show over 100-fold enhancement in their Hg⁰ accommodation capacities. The generality and the scalability of the process provides a framework to develop TMSs for a broad range of applications.

[Formula: see text] modified AC for removing gaseous elemental mercury from flue gas

Mercury pollution from coal-fired power plants has always been an environmental concern, and adsorption technology is an effective method for Hg⁰ removal. In this study, copper-iron binary metal sulfide modified activated carbon ([Formula: see text]) adsorbent was synthesized. The performance and mechanism of mercury removal were tested by adsorption experiments and characterization methods. The results showed that the mercury removal efficiency of [Formula: see text] under simulated flue gas (SFG) conditions at 150 °C could reach 91%, which was higher than [Formula: see text] and [Formula: see text]. Compared with [Formula: see text], the introduction of Fe increased the proportion of [Formula: see text], which was usually linked to [Formula: see text], resulting in the generation of more [Formula: see text](Cu^IS^I) species. Meanwhile, the generation of active sulfur sites such as [Formula: see text] was generated, which had a facilitative effect on the oxidation of Hg⁰. Stable [Formula: see text] was the predominant product on the adsorbent surface. The 2% sulfur loadings had significantly improved the sulfur resistance of conventional AC.

Molten salt synthesis of WS2 and MoS2 nanosheets toward efficient gaseous elemental mercury capture

The development of high-efficient adsorbents for Hg⁰ capture in a broad temperature window remains a big challenge. Transition-metal dichalcogenides (TMDs) present great prospects owing to their two-dimensional layered structures and abundant active sulfur species. Here, tungsten disulfide (WS₂) and molybdenum disulfide (MoS₂) nanosheets are easily synthesized via a molten salt route and employed for Hg⁰ sequestration. With the elevation of the annealing temperature, the Hg⁰ capture ability of WS₂ nanosheet gradually enhances, while MoS₂ nanosheet first increases and then decreases. They both display good mercury removal performances in an enlarged temperature range of 60-260 °C. Acidic flue gas components (i.e., SO₂ and NO) subtly interfere the mercury removal process, indicating the prospective application potentials of WS₂ and MoS₂ nanosheets in thermal plants.

Mercury removal from coal combustion flue gas by pyrite-modified fly ash adsorbent

Pyrite and fly ash have certain advantages in adsorption and mercury oxidation. The pyrite-modified fly ash (PY + AC-FA) mercury adsorbent was prepared by mixing pyrite (PY) with acid-modified fly ash (AC-FA), which has better mercury removal effect than AC-FA. The experimental results of mercury adsorption show the following: when the reaction temperature is 50 °C, the best doping proportion of modified fly ash is 20 wt%, the mass proportion of pyrite to acid-modified fly ash is 4:1, and the flue gas flow rate is 1.0 L/min; the adsorbent has the best performance, and the adsorption rate of mercury reaches 91.92%. It was also found that the quasi-second-order kinetic model could describe the entire process of adsorption, and its adsorption process was mainly influenced by chemisorption. XRF, BET, SEM, XRD, and TG-DSG were used to characterize these adsorbents, and the mechanism of mercury removal of pyrite-modified fly ash adsorbent is inferred: Hg⁰ is first adsorbed on the surface of the adsorbent, and then oxidized to HgS by the active component FeS₂ in pyrite-modified fly ash.

Different Crystal Forms of ZnS Nanomaterials for the Adsorption of Elemental Mercury

ZnS is a promising sorbent in recovering Hg⁰ from industrial flue gas due to its excellent Hg⁰ adsorption capacity. However, the internal structure-activity relationship still needs to be further clarified. In this work, ZnS sorbents with different structures were synthesized with the hydrothermal method by tuning the temperature. The samples had significant differences in the crystallinity, morphology, particle size, and sulfur (S) active sites. The results indicated that Hg⁰ removal performance was determined by the specific surface area and S active sites. ZnS synthesized at low temperatures (80-ZnS and 120-ZnS) had a larger surface area, while the S sites on the high-temperature-synthesized sample (160-ZnS) were more active for Hg⁰ adsorption. The 160-ZnS sample exhibited a much higher Hg⁰ adsorption amount per unit surface area. Further characterization revealed that S₂^2- and S_x were the main active sites for Hg⁰ adsorption. S_x existed in the form of long-chain polysulfur (L-S_x) on 80-ZnS and 120-ZnS, while it exhibited in the form of short-chain polysulfur (S-S_x) on 160-ZnS. L-S_x had negligible adsorption ability, while S-S_x had a high affinity for Hg⁰. Hg⁰ can react with S₂^2- and S-S_x, forming α-HgS and β-HgS, respectively. The new insight in this work can provide theoretical guidance for the design and structure optimization of ZnS, facilitating its practical industrial application.

DFT and Experimental Studies on the Mechanism of Mercury Adsorption on O2-/NO-Codoped Porous Carbon

The utilization of O₂ and NO in flue gas to activate the raw porous carbon with auxiliary plasma contributes to an effective mercury (Hg)-removal strategy. The lack of in-depth knowledge on the Hg adsorption mechanism over the O₂-/NO-codoped porous carbon severely limits the development of a more effective Hg removal method and the potential application. Therefore, the generation processes of functional groups on the surface during plasma treatment were investigated and the detailed roles of different groups in Hg adsorption were clarified. The theoretical results suggest that the formation of functional groups is highly exothermic and they preferentially form on a carbon surface, and then affect Hg adsorption. The active groups affect Hg adsorption in a different manner, which depends on their nature. All of these active groups can improve Hg adsorption by enhancing the interaction of Hg with a surface carbon atom. Particularly, the preadsorbed NO₂ and O₃ groups can react directly with Hg by forming HgO. The experimental results confirm that the active groups cocontribute to the high Hg removal efficiency of O₂-/NO-codoped porous carbon. In addition, the mercury temperature-programmed desorption results suggest that there are two forms of mercury present on O₂-/NO-codoped porous carbon, including a carbon-bonded Hg atom and HgO.

Binary mineral sulfides sorbent with wide temperature range for rapid elemental mercury uptake from coal combustion flue gas

Developing efficient sorbents with rapid kinetics is the main challenge encountered for Hg⁰ capture from coal combustion flue gas in a sorbent injection scenario. Binary mineral sulfide-based materials combining copper sulfide (CuS) and zinc sulfide (ZnS) to exert their capabilities for Hg⁰ capture at the low- and high-temperature was for the first time reported for Hg⁰ removal to realize a wide temperature range sorbents. When the molar ratio between CuS and ZnS was 10%, the as-synthesized 10Cu-Zn nanocomposite exhibited excellent Hg⁰ uptake rate at 150°C that could degrade 40 μg/m³ of Hg⁰ to undetectable level at the end of a 60-s experiment with the dosage of only 1 mg. This Hg⁰ uptake rate is folds higher compared to that when bare CuS or ZnS was adopted alone at this specific temperature. The typical flue gas atmospheres had negligible effect on Hg⁰ removal over 10Cu-Zn in a short contact time, which further suggests that the binary sorbents were proper to be injected before the electrostatic precipitator system. Moreover, it is found that, by adjusting the ratio between CuS and ZnS, it is potential to develop binary sorbent suiting any temperature conditions that may achieve an exceedingly high Hg⁰ capture performance. Thus, this work not only justified the candidature of 10Cu-Zn as a promising alternative to traditional activated carbon for Hg⁰ capture from coal combustion flue gas but also guided the future development of multi-component mineral sulfide-based sorbents for Hg⁰ pollution remediation from various industrial flue gases.

Detrimental effects of SO2 on gaseous mercury(II) adsorption and retention by CaO-based sorbent traps: Competition and heterogeneous reduction

Reliable gaseous Hg(II) measurement is crucial to mercury emissions control from coal-fired flue gas, but Hg(II) sampling under SO₂ condition could probably increase the uncertainty of sorbent traps. CaO-AcS synthesized from calcium acetate and porous support were previously demonstrated to be effective for Hg(II) trapping under SO₂-free condition. This work further evaluated SO₂ influence on its Hg(II) retention ability via integrating experimental and DFT computational studies. Increased breakthrough rate of HgCl₂ was found in a two-section CaO-AcS trap under SO₂ conditions. Significant basicity and porosity loss of CaO-AcS were attributed to the formation of agglomerate CaSO₃. Hg⁰ release from CaO-AcS samples suggested potential reactions between Hg(II) and SO₂. The detected HgO and Hg₂SO₄ species by Hg-TPD in CaO-AcS further confirmed this speculation. Moreover, both competition and reduction effects of SO₂ on surface-bound Hg(II) species were substantiated by DFT calculations. SO₂ showed a stronger interaction with CaO than HgCl₂ because SO₂ has a lower LUMO level and can accept electrons easier. Reaction pathways indicated Hg(II) was partially reduced to Hg₂SO₄ under SO₂-deficient condition, or directly reduced to Hg⁰ under SO₂-rich condition. This work fully proposed the SO₂ influence mechanisms and improvement countermeasures for practical gaseous Hg(II) sampling.

Amorphous Molybdenum Selenide Nanosheet as an Efficient Trap for the Permanent Sequestration of Vapor-Phase Elemental Mercury

The key challenge of vapor-phase elemental mercury (Hg0) sequestration is the rational design of a sorbent with abundantly available ligands that exhibit excellent affinity toward Hg0 to simultaneously achieve a high uptake capacity and rapid capture rate. In this work, it is demonstrated how the correct combination of functional ligands and structural properties can form an ideal remediator for permanent Hg0 immobilization. The adsorption capacity of an amorphous molybdenum triselenide (MoSe3) nanosheet greater than 1000 mg g-1 is the highest recorded value compared to previously reported sorbents tested in a fixed-bed reactor. Meanwhile, the uptake rate of 240 µg g-1 min-1 is also the highest recorded rate value. Mercury selenide as formed exhibits extremely low leachability when environmentally exposed. This impressive performance is primarily attributed to the appropriate layer space between the nanosheets that permeated Hg0 and the existence of diselenide (Se2 2-) ligands that exhibit excellent affinity toward Hg0. Thus, this work not only provides a promising trap for permanent Hg0 sequestration from industrial and domestic sources with minimum hazard but also provides a detailed illustration of using structural advantages to obtain an ideal sorbent as well as guidance for the further development of Hg0 decontamination techniques.

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.

Outstanding Performance of Recyclable Amorphous MoS3 Supported on TiO2 for Capturing High Concentrations of Gaseous Elemental Mercury: Mechanism, Kinetics, and Application

Hg⁰ capture by sorbents was a promising technology to control Hg⁰ emission from coal-fired power plants and smelters. However, the design of a high performance sorbent and the predicting of the extent of Hg⁰ adsorption were both extremely limited due to the lack of adsorption kinetics and structure-activity relationship. In this work, the adsorption kinetics of gaseous Hg⁰ onto MoS₃/TiO₂ was investigated and kinetic parameters were obtained by fitting breakthrough curves. According to the kinetic parameters, the removal efficiency, the adsorption rate and the capacity for Hg⁰ capture were accurately predicted. Meanwhile, the structure-activity relationship of metal sulfides for gaseous Hg⁰ adsorption was built. The chemical adsorption rate of gaseous Hg⁰ was found to mainly depend on the amount of surface adsorption sites available for the physical adsorption of Hg⁰, the amount of surface S₂^2- available for Hg⁰ oxidation and gaseous Hg⁰ concentration. As MoS₃/TiO₂ showed a superior performance for capturing high concentrations of Hg⁰ due to the large number of surface adsorption sites for the physical adsorption of gaseous Hg⁰, it has promising applications in recovering Hg⁰ from smelting flue gas.

Role of Sulfur Trioxide (SO3) in Gas-Phase Elemental Mercury Immobilization by Mineral Sulfide

Mineral sulfide based sorbents were superior alternatives to traditional activated carbons for elemental mercury (Hg⁰) immobilization in industrial flue gas. A systematical study concerning the influence of sulfur trioxide (SO₃) on Hg⁰ adsorption over a nanosized copper sulfide (Nano-CuS) was for the first time conducted. SO₃ was found to significantly inhibit the Hg⁰ removal over Nano-CuS partially because SO₃ oxidized the reduced sulfur species (sulfide) with high affinity to mercury to its oxidized sulfur species (sulfate). Moreover, a brand new "oxidation-reduction" mechanism that led to a simultaneous oxidation of sulfide and reduction of mercury on the immobilized mercury sulfide (HgS) was responsible for the inhibitory effect. Even though the released Hg⁰ from the reduction of mercury in HgS could be oxidized by SO₃ into its sulfate form (HgSO₄) and recaptured by the sorbent, the "oxidation-reduction" mechanism still compromised the Hg⁰ capture performance of the Nano-CuS because HgSO₄ deposited on the sorbent surface could be easily leached out when environmentally exposed. These new insights into the role of SO₃ in Hg⁰ capture over Nano-CuS can help to determine possible solutions and facilitate the application of mineral sulfide sorbents as outstanding alternatives to activated carbons for Hg⁰ immobilization in industrial flue gas.

Design of O2/SO2 dual-doped porous carbon as superior sorbent for elemental mercury removal from flue gas

A porous carbon was synthesized via hydrothermal carbonization and CO₂ activation. O₂ and SO₂ were successfully co-doped onto carbon surface by applying non-thermal plasma technique. Porous carbon possessing excellent textural properties is effective to adsorb the radicals generated by plasma. Plasma promotes the adsorption of O₂ and SO₂ on carbon surface with the formation of abundant CO, C-S and C-SO_x (x = 1-3) groups. The O₂/SO₂ dual-doped porous carbon was utilized to adsorb elemental mercury (Hg⁰) from the flue gas of coal combustion. The Hg⁰ adsorption ability of the O₂/SO₂ dual-doped porous carbon is closely related with the concentrations of O₂ and SO₂ for plasma treatment and the treatment time. The optimal O₂/SO₂ dual-doped porous carbon exhibited far greater Hg⁰ adsorption capacity than a commercial brominated activated carbon. Density functional theory was employed to understand the Hg⁰ adsorption mechanism at the molecular level. CO, C-S and C-SO_x (x = 1-3) groups enhanced the interaction of Hg⁰ with surface carbon atom. The activity of them for enhancing Hg⁰ adsorption is in the order of C-SO₂ >  CO > C-S > C-SO > C-SO₃. Porous carbon can be activated by plasma in flue gas containing O₂ and SO₂, and used as superior sorbent for Hg⁰ removal.

Removal of gaseous elemental mercury by modified diatomite

Novel adsorbents with low cost and high efficiency that do not produce secondary pollutants are vital for removing gaseous elemental mercury (Hg⁰) from coal-fired power plants. In this study, eight diatomite-based adsorbents were developed and used to remove Hg⁰ in a bench-scale fixed-bed reactor. The effects of active substances, reaction temperature, and gas components on the Hg⁰ removal performance of diatomite (Dia) and the mechanisms were investigated. After modification, the specific surface area of diatomite increased by 2-to-12 fold, and the Hg⁰ removal performance was greatly improved. The Hg⁰ removal efficiencies of the adsorbents decreased in the following order: I-Dia > Br-Dia > Cl-Dia. The Hg⁰ removal efficiency of CuBr₂-Dia reached 91% in the simulated flue gas at the optimal reaction temperature (140 °C). The simultaneous presence of O₂ and HCl promoted the Hg⁰ removal by CuBr₂-Dia. NO alone also played a significant role in Hg⁰ removal. However, SO₂ exhibited clear inhibitory effect. The average Hg⁰ removal efficiencies of CuBr₂-Dia were 60% under 1200 ppm SO₂, 87% under 1200 ppm SO₂ + 300 ppm NO, and 93% under 4% O₂ + 1200 ppm SO₂ + 300 ppm NO. The changes in the active adsorption sites caused by NO, and those caused by NO + SO₂ were different and irreversible. During the Hg⁰ removal process, Hg⁰ was oxidized to the Hg²⁺ or Hg⁺ species, while Cu²⁺ and Br radicals were reduced to Cu⁺ and Br^-, respectively.

Dual Roles of Nano-Sulfide in Efficient Removal of Elemental Mercury from Coal Combustion Flue Gas within a Wide Temperature Range

Nanostructured zinc sulfide (Nano-ZnS) has been demonstrated to be an efficient adsorbent for removal of elemental mercury (Hg⁰). However, the Hg⁰ removal performance deteriorates once the flue gas temperature deviates from the optimal temperature of 180 °C. In this study, ultraviolet (UV) light, which is generally generated through corona discharge in electrostatic precipitators (ESPs), was adopted to enhance Hg⁰ removal by Nano-ZnS. With the UV irradiation, Nano-ZnS exhibited excellent performance in Hg⁰ removal within a much wide temperature range from room temperature to 240 °C. A Hg⁰ removal efficiency of 99% was achieved at 60 °C even under extremely adverse conditions, that is, gas flow with an extremely high gas hourly space velocity but without hydrogen chloride. At low temperatures, Hg⁰ was mainly oxidized by superoxide radicals (•O₂^-) and hydroxyl radicals (•OH) generated by UV photostimulation to form mercuric oxide (HgO). At high temperatures, most Hg⁰ was immobilized as mercuric sulfide (HgS), as both the enhanced chemisorption and the accelerated transformation of HgO to HgS facilitated the formation of HgS. Compared with commercial activated carbon, injection of Nano-ZnS can utilize the UV in ESPs to warrant a higher Hg⁰ removal efficiency within a much wider temperature range.

Oxygen-Rich Porous Carbon Derived from Biomass for Mercury Removal: An Experimental and Theoretical Study

A porous carbon was synthesized by the combination of freeze-drying and CO₂ activation from starch. Nonthermal plasma was employed to quickly produce oxygen functional groups on a porous carbon surface. The plasma treatment has a negligible effect on the textural properties of the porous carbon. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses suggested that the plasma treatment significantly increased the amount and promoted the evolution of oxygen groups on surface. The unique pore structure of porous carbon was proven favorable to effective oxygen loading. The elemental mercury (Hg⁰) adsorption ability of the oxygen enriched porous carbon was tested. The results indicated that the oxygen-rich porous carbon constitutes an effective sorbent for Hg⁰ removal. The excellent textural properties, surface atomic oxygen concentration, and the type of oxygen group are the three key factors for realizing high Hg⁰ removal performance. Density functional calculations were performed to understand the effect of oxygen groups on Hg⁰ adsorption. Carbonyl and ester groups are beneficial for Hg⁰ adsorption, whereas epoxy, carboxyl, and hydroxyl groups inhibit Hg⁰ adsorption. Plasma treatment enhances Hg⁰ adsorption by increasing the amount of ester and carbonyl groups on surface.

Multiform Sulfur Adsorption Centers and Copper-Terminated Active Sites of Nano-CuS for Efficient Elemental Mercury Capture from Coal Combustion Flue Gas

Nanostructured copper sulfide synthesized with the assistance of surfactant with nanoscale particle size and high Brunauer-Emmett-Teller surface area was for the first time applied for the capture of elemental mercury (Hg⁰) from coal combustion flue gas. The optimal operation temperature of nano-CuS for Hg⁰ adsorption is 75 °C, which indicates that injection of the sorbent between the wet flue gas desulfurization and the wet electrostatic precipitator systems is feasible. This assures that the sorbent is free of the adverse influence of nitrogen oxides. Oxygen (O₂) and sulfur dioxide exerted a slight influence on Hg⁰ adsorption over the nano-CuS. Water vapor was shown to moderately suppress Hg⁰ capture efficiency via competitive adsorption. The simulated adsorption capacities of nano-CuS for Hg⁰ under pure nitrogen (N₂), N₂ + 4% O₂, and simulated flue gas reached 122.40, 112.06, and 89.43 mgHg⁰/g nano-CuS, respectively. Compared to those of traditional commercial activated carbons and metal sulfides, the simulated adsorption capacities of Hg⁰ over the nano-CuS are at least an order of magnitude higher. Moreover, with only 5 mg loaded in a fixed-bed reactor, the Hg⁰ adsorption rate reached 11.93-13.56 μg/g min over nano-CuS. This extremely speedy rate makes nano-CuS promising for a future sorbent injection technique. The anisotropic growth of nano-CuS was confirmed by X-ray diffraction analysis and provided a fundamental aspect for nano-CuS surface reconstruction and polysulfide formation. Further X-ray photoelectron spectroscopy and Hg⁰ temperature-programmed desorption tests showed that the active polysulfide, S-S dimers, and copper-terminated sites contributed primarily to the extremely high Hg⁰ adsorption capacity and rate. With these advantages, nano-CuS appears to be a highly promising alternative to traditional sorbents for Hg⁰ capture from coal combustion flue gas.

Insight into elemental mercury (Hg0) removal from flue gas using UV/H2O2 advanced oxidation processes

Elemental mercury (Hg⁰) emitted from coal-fired power plants and municipal solid waste (MSW) incinerators has caused great harm to the environment and human beings. The strong oxidized ^•OH radicals produced by UV/H₂O₂ advanced oxidation processes were studied to investigate the performance of Hg⁰ removal from simulated flue gases. The results showed that when H₂O₂ concentration was 1.0 mol/L and the solution pH value was 4.1, the UV/H₂O₂ system had the highest Hg⁰ removal efficiency. The optimal reaction temperature was approximately 50 °C and Hg⁰ removal was inhibited when the temperature was higher or lower. The yield of ^•OH radicals during UV/H₂O₂ reaction was studied by electron paramagnetic resonance (EPR) analysis. UV radiation was the determining factor to remove Hg⁰ in UV/H₂O₂ system due to ^•OH generation during H₂O₂ decomposition. SO₂ had little influence on Hg⁰ removal whereas NO had an inhibitory effect on Hg⁰ removal. The detailed findings for Hg⁰ removal reactions over UV/H₂O₂ make it an attractive method for mercury control from flue gases.