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Reduction of mercury emission from coal combustion is a serious task for public health and environmental societies. Herein, Ce-doped TiO2 (Ce/TiO2) catalyst coupling with a novel optical fiber monolith reactor was applied to efficiently remove elemental mercury (Hg0) from coal-fired flue gas. Under the optimal operation condition (i.e., 1.5 mW/cm2 UV light, 90 °C), above 95% of Hg0 removal efficiency was attained over the optical fiber monolith reactor coating with 3.40 g/m2 Ce/TiO2 catalyst. The effects of flue gas compositions on Hg0 removal performance were clarified systematically. Gaseous O2 replenished the surface oxygen, hence maintaining the production of free radicals and promoting the removal of Hg0. SO2, HCl, and NO inhibited Hg0 removal in the absence of O2 due to the competitive adsorption and consumption of free radicals. However, SO2 and HCl significantly enhanced Hg0 removal with the participation of O2, while NO exhibited obviously inhibitory effect even with the assistance of O2. H2O also decreased the Hg0 oxidation capacity owing to the competitive adsorption and reduction of HgO. The optical fiber monolith reactor exhibited much superior Hg0 removal capacity than the powder reactor. Utilization of Ce/TiO2 catalyst coupling with an optical fiber monolith reactor provides a cost-effective method for removing Hg0 from coal-fired flue gas. [ABSTRACT FROM AUTHOR]

In this study, a simple method combining sol-gel and impregnation techniques was employed to synthesize magnetic Cu/MnFe 2 O 4. The resulting material demonstrated outstanding efficiency in removing mercury, achieving over 90% at reaction temperatures ranging from 150 °C to 200 °C. Through Cu incorporation, the Hg0 removal performance of Cu 0.15 MnFe was significantly enhanced, leading to a high adsorption capacity of 70.1 mg/g. This surpasses the capabilities of many previously reported adsorbents and holds great potential for enhancing the stability of Hg recovery efficiency. Furthermore, the presence of O 2 , HCl, and NO further improved the Hg0 removal. Conversely, H 2 O had an mild inhibitory effect on Hg0 removal. Additionally, the introduction of Cu noticeably mitigated the inhibitory impact of SO 2 on mercury removal characteristics and alleviated the issue of SO 2 poisoning in adsorbents. The primary active sites responsible for the oxidation of elemental mercury are the redox reaction between Cu2+/Cu+ and Mn3+/Mn2+, and adsorbed oxygen species. Through the oxidation process, Hg0 is primarily converted into various compounds, including HgO, Hg(NO 3) 2 , HgCl 2 , and HgSO 4. As a result, the prepared magnetic recyclable adsorbent, with its high mercury adsorption capacity, exhibits promising prospects for industrial application in the low-temperature removal of Hg0 from coal-fired flue gas. [Display omitted] • Magnetic Cu/MnFe 2 O 4 adsorbent was prepared using a simple method. • Cu/MnFe 2 O 4 owned a large Hg adsorption capacity of 70.1 mg/g. • The introduction of Cu greatly alleviated SO 2 poisoning in adsorbents. • Cu2+, Mn3+ and O* play a crucial role as active sites for Hg0 oxidation. [ABSTRACT FROM AUTHOR]

Trace elements (TEs) in coal result in substantial pollutant emissions and cause serious damage to the ecological environment and human health in China. The emission and control of TEs, especially mercury, during coal combustion are of significant concern, and extensive studies have been performed in China in recent years. This paper reviews the emission characteristics and control strategies of mercury and other TEs during coal combustion in China. The occurrence of TEs in Chinese coals, including the average content of TEs in Chinese coals, the distribution of TEs in Chinese coals from different coal-forming periods, coal ranks, and coal-bearing regions are summarized. The emission characteristics of five specific TEs (Hg, As, F, Se, and Cr) during coal combustion in China are reviewed in detail. Effects of the coal type, combustion temperature, and combustion mode on the partitioning behaviour and emission characteristics of TEs are discussed. The effects of existing air pollution control devices of coal-fired power plants in China on the speciation and emission of TEs are discussed comprehensively. Various sorbents, such as activated carbon, fly ash, calcium-based sorbents, metal oxides, and mineral sorbents, used for TE removal are also summarized. Moreover, the removal performance of different sorbents for capturing certain TEs is compared comprehensively. Finally, future work for TE emission control in China is proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Compare mercury removal performance of biochar pretreated by hydrothermal technique and wet impregnation. • Mercury removal performance for biochar pretreated by hydrothermal technique reached 90%. • Hydrothermal pretreatment enhanced thermolysis reaction intensity of biomass and extended the specific surface area. • Hydrothermal pretreatment could promote the construction of oxygen-containing active sites. To further widen the specific surface area and enrich functional groups of biochar for improving the mercury removal performance, this paper compared the difference between wet impregnation and hydrothermal pretreatment to preload ferric chloride on active sites construction of biochar surface. Through systematically evaluating the physicochemical properties of biochar modified by various methods, the mechanism of mercury removal was analyzed. The results indicated that the hydrothermal pretreatment at 180 °C could widen the specific surface area of the precursor benefiting for modifiers adsorption and render the apparent activation energy reduced to 34.11 kJ/mol, causing more intense thermolysis reaction during carbonization. In this way, the specific surface of biochar reached to 282.4 m2/g and a more abundant porous structure was constructed. Additionally, after hydrothermal pretreatment, the proportion of chemisorbed oxygen and C O bonds on the surface of biochar was significantly promoted, facilitating the formation of HgO. The improvement of both physical structure and chemical properties of biochar together increases the mercury removal efficiency to over 90 % under the N 2 atmosphere. [ABSTRACT FROM AUTHOR]

To understand the interaction of fly ash and mercury, systematic experiments on mercury oxidation in single flue gas composition are conducted on a fixed bed reactor system, the desorption rate and speciation of mercury are valuated. The results indicate that fly ash itself can significantly promote elemental mercury oxidation. A classification of fly ash activated sites is developed according to the speciation of mercury during adsorption-desorption tests, the reaction mechanism of mercury oxidation by fly ash is proposed. Acid gas can promote mercury oxidation and improve the stability of oxidation product. Lattice oxygen is an important oxidant of mercury oxidation. [ABSTRACT FROM AUTHOR]

The abatement of mercury from oxyfuel combustion flue gas should be paid special attention due to the metal embrittlement and aluminum corrosion for CO 2 compression device. The effects of enriched CO 2 and H 2 O in oxyfuel combustion atmosphere on mercury removal over biochar (BC) and magnetic biochar (MBC) was studied. Hg0 was firstly captured by physical adsorption and then oxidized to various mercury compounds. A large amount of organic groups, especially C O group, were formed with the assistance of enriched CO 2. As a result, more Hg0 was oxidized over BC and more organic Hg (Hg-OM) was formed on BC and MBC. However, the content of chemisorbed oxygen on MBC was reduced under oxyfuel combustion atmosphere, hence reducing the formation of HgO on MBC compared with air combustion atmosphere. The enriched H 2 O significantly inhibited the removal of mercury over MBC. Chlorine was demonstrated as the most significant active components for mercury removal, since HgCl 2 was the dominant species on MBC. This work clarified the effects of enriched CO 2 and H 2 O on Hg0 adsorption over BC and MBC, which is essential for further improving the adsorption activity. [ABSTRACT FROM AUTHOR]

The regeneration performance of spent catalyst after mercury removal as well as the involved reaction mechanism was investigated. The effects of restoration with or without O 2 and/or HCl, O 2 and HCl concentration, regeneration temperature, and heating rate on regeneration performance were studied, respectively. The results suggested that two steps were essential in the regeneration process: (1) releasing the sulfur and mercury species adsorbed on the catalyst; (2) restoring the surface chemistry of catalyst by O 2 and HCl. Optimal regeneration performance of spent catalyst was attained after thermal desorption at 400 °C and following by the restoration of O 2 and HCl. The changes in surface chemistry of catalyst revealed that the sulfur and mercury species could be fully released by heating at 400 °C, and the deactivated adsorption sites was exposed. With the assistance of O 2 and HCl, the surface chemistry of Cu and Cl was restored close to original CuCl 2 . Four cycles of mercury adsorption−catalyst regeneration showed that the mercury removal capacity did not vary appreciably with respect to fresh catalyst after multiple regeneration. [ABSTRACT FROM AUTHOR]

[Display omitted] • An efficient mercury adsorption and recovery agent was designed. • The mercury removal efficiency of different forms of Se were compared. • The morphology and particle size of HgSe generation were explored. • Designed a mercury recovery route to improve the purity of HgSe. Mercury, is a highly toxic chemical that poses serious hazards to both humans and the environment to be controlled. In this paper, Different Se forms have great varying performance of gaseous mercury(Hg0) removal. Nano-amorphous red selenium(ar-Se) has an excellent adsorption effect on Hg0 successfully synthesized by one step oxidation reduction. The factors to ar-Se such as flue gas components, temperature, gas flow rate, and pH affecting mercury removal effect were investigated. The results showed that the ar-Se achieved high utilization (>74.9 %) and mercury affinity (>97 %) at room temperature. Mercury removal rate was almost unaffected by gas components at room temperature, and it kept a stable mercury adsorption in long-time gaseous mercury recovery experiments, which responded to the high electron activity on its surface. Long-range periodic structures with no regular atomic arrangement decide ar-Se in an active state having high specific surface area, surface activity, good dispersion. The HgSe nanoparticles(NPs) was formed by the adsorption of gaseous mercury onto ar-Se. For further recycling of mercury, a recovery route for HgSe has been proposed and oxygen was found having a strong influence on the production of HgSe. [ABSTRACT FROM AUTHOR]

• Two-dimensional layered Bi 2 WO 6 nanosheets were prepared using a hydrothermal method. • C 2 /2D-BWO exhibits a photocatalytic mercury removal efficiency of up to 86.3 %. • The effects of SO 2 and NO in flue gas on Hg oxidation were also studied. • The experiments and DFT calculations showed that CQDs improved the photoactivity of 2D-BWO. Photocatalytic technology has the advantages of environmental friendliness, low energy consumption, and fast reaction speed, which can be applied in the field of visible light mercury removal. High stability and narrow bandgap are fundamental factors for ideal semiconductor photocatalysts. A novel method of hydrothermal synthesis of CQDs/2D-BWO composite catalyst to improve the oxidation efficiency of elemental mercury was proposed. The morphology, physicochemical properties, and optical performance of the materials were fully characterized. The experiment of Hg oxidation efficiency under visible light showed that C 2 /2D-BWO exhibited a Hg removal efficiency of was as high as 86.3 % under visible light and adequate cyclic stability. The effects of SO 2 and NO on Hg oxidation were also studied, and the reasons for the improved of photocatalytic activity of CQDs on 2D-BWO were analyzed based on DFT calculations. The reaction mechanism of the catalytic oxidation of Hg by C 2 /2D-BWO was proposed, and C 2 /2D-BWO was found to be an efficient and stable visible light catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • Swirl diffusion strategy boosts Hg removal effectiveness of magnetospheres injector. • A mathematical model was established to predict the Hg removal efficiency from CC-MF. • Particle coverage increased by 51%, with a Hg removal efficiency of up to 88.7%. • The optimal operating parameters of the CC-MF swirl injector device were determined. The emissions of mercury from coal-fired flue gas poses a major threat to public health and ecosystems. Modified magnetospheres (CC-MF) mercury removal technology provides an economical, reusable, and eco-friendly solution, overcoming the drawbacks of conventional activated carbon injection (ACI) techniques. To address the issues of inadequate particle diffusion and uneven injection in traditional mercury removal injectors, this study developed a single-hole swirl injector. Furthermore, a mathematical model for mercury removal was developed and imported in the form of a UDF into Fluent for the evaluation of section coverage rate and mercury removal efficiency. The simulation results demonstrated that the section coverage rate of the swirl injector improved by 51.0%, reaching 81.0% compared to the direct injector. Additionally, the mercury removal efficiency increased by 41.3%, reaching 88.7%. This work identified the optimal operational parameters for the CC-MF mercury removal system, providing valuable insights for its practical application. [ABSTRACT FROM AUTHOR]

Experimental studies on Hg 0 removal by CuCl 2 modified magnetospheres (Cu 6 –MF) injection were performed in an entrained flow reactor system. The factors affecting the Hg 0 removal efficiency were investigated, including the initial Hg 0 concentration, sorbent concentration in flue gas, sorbent particle size, sorbent residence time in flue gas, and flue gas temperature. The results indicated that, as the raise of initial Hg 0 concentration, the Hg 0 removal efficiency increased. The Hg 0 removal efficiency also increased with the increase of sorbent residence time and sorbent concentration in flue gas. When the residence time was 1.61 s and the sorbent concentration was 1.09 g/m 3 , the Hg 0 removal efficiency could reach to 80.6%. However, with the further increase of residence time and sorbent concentration, the Hg 0 removal efficiency did not increase continuously. The smaller particle size was favorable for the Hg 0 removal. In the industrial application, the particle size could be selected as 45–74 μm when comprehensively considering the Hg 0 removal efficiency, the cost of sorbent preparation, and other factors. The acid flue gases have negligible impacts on Hg 0 removal, while moisture plays a slightly negative role in Hg 0 removal under SFG atmosphere. With the superior Hg 0 removal performance, the Cu 6 –MF sorbent may presents great potentials for Hg 0 removal in coal-fired power plants. [ABSTRACT FROM AUTHOR]

The gaseous elemental mercury (Hg0) emitted from coal-fired flue gas is extremely harmful to the atmospheric environment and human health. In this study, a 2D/2D Bi 2 MoO 6 (2 0 0)/g-C 3 N 4 heterojunction photocatalyst was synthesized and exhibited a high visible-light driven Hg0 removal efficiency up to 99.5% in an atmosphere consisting of N 2 , O 2 (6%), CO 2 (12%), NO (100 ppm), SO 2 (800 ppm), and H 2 O (5%). The introduction of surfactant CTAB led to further exposure of the highly active (2 0 0) crystal facet of Bi 2 MoO 6 , with a higher reactive oxygen species ratio than the original mainly exposed (1 3 1) crystal facet, and inhibited the agglomeration of Bi 2 MoO 6 , thereby greatly reducing the micro-thickness and improving the specific surface area. The smaller thickness effectively promoted the separation of photoinduced carriers and the speed of transfer to the interface. Additionally, through EPR characterization and work function calculation, we observed that the change in the exposed crystal facet regulated the Fermi level of Bi 2 MoO 6 nanosheets, altering the direction of the built-in electric field at the interface with g-C 3 N 4. This formation of an S-scheme 2D/2D Bi 2 MoO 6 (2 0 0)/g-C 3 N 4 heterostructure further facilitated the recombination of unintentional carriers and strengthened the separation and catalysis of effective photogenerated carriers. To a certain extent, this work provides a guidance for the research of photocatalysis to achieve efficient and sustainable mercury removal from coal-fired flue gas. [Display omitted] • A S-scheme 2D/2D Bi 2 MoO 6 (2 0 0)/g-C 3 N 4 heterostructure was prepared. • The surface activity was enhanced by CTAB regulation. • Fermi level modulation changed the internal electric field, boosting charge transfer. • Great Hg0 photocatalytic ability of the catalyst under visible light was tested. • The photocatalytic mechanism was verified by DFT calculations. [ABSTRACT FROM AUTHOR]

The Hg 0 removal capacities of magnetospheres from fly ash collected from different power plants were investigated at a wide temperature range of 100–400 °C. The relationship between Hg 0 removal efficiency ( η T ) and iron content/species of magnetospheres was investigated. The magnetospheres attained the optimal Hg 0 removal capacity at 250 °C. The reaction temperature played an important role in Hg 0 adsorption and oxidation behaviors. At low reaction temperature (100 °C and 150 °C), the adsorption of Hg 0 played a predominant role in Hg 0 removal, while the Hg 0 removal mainly depended on the Hg 0 oxidation capacity at high temperature (200–400 °C). The Hg 0 removal capacity increased with the increase of iron content. The percentage of ferrospinel and hematite in magnetospheres is a key factor for determining the Hg 0 removal capacity as well. Hydrogen fluoride (HF) could remove the glass-phase materials on the magnetospheres and the active iron species embedded in the glass phase could be exposed and accessible. After fluorinated by HF, the Hg 0 removal capacity increased in different degree for different magnetospheres, which depended on the content of active iron species in raw magnetospheres. [ABSTRACT FROM AUTHOR]

In this study, manganese oxides supported on titania was prepared by sol-gel method and employed as SCR catalyst for simultaneous NO and mercury removal from coal combustion flue gas. The simultaneous NO and Hg 0 conversion rate on MnO x /TiO 2 was evaluated in different atmospheres, and the interaction between denitration and demercuration was investigated. The results indicated that MnO x /TiO 2 had good activity in simultaneously removing NO and Hg 0 in SCR atmosphere (NH 3 + NO + O 2 + N 2 ). However, both NO conversion and Hg 0 removal efficiency were inhibited in simulated coal combustion flue gas compared to that in SCR atmosphere because of the presence of SO 2 leading to the generation of sulfite and sulfate on the catalyst. H 2 O in simulated coal combustion flue gas had negative effect on the catalytic performance as well. NO conversion in oxy-fuel combustion flue gas was lower than that in air combustion flue gas, while Hg 0 removal efficiency in oxy-fuel combustion flue gas was higher than that in air combustion flue gas. Hg 0 displayed no obvious influence on NO conversion and N 2 selectivity over SCR process. And SCR atmosphere showed almost no inhibition to Hg 0 removal when the temperature was below 300 °C. At the optimal temperature for NO conversion (250 °C), the inhibition of SCR atmosphere on Hg 0 removal became stronger as the space velocity (GHSV) increased, but the inhibitive effect could be ignored when GHSV slowed down to 50,000 h − 1 or less. [ABSTRACT FROM AUTHOR]

The behaviour of mercury is investigated in a 35 MW th large pilot boiler of oxyfuel combustion with dry and wet flue gas recycle (FGR). The mercury species in fly ash particles as well as the involved reaction mechanism are systematically investigated. The results suggest that higher concentration of gas–phase mercury (Hg g ) is contained in oxyfuel combustion flue gas. The conversion of Hg g to particulate associated mercury (Hg p ) is enhanced in oxyfuel combustion. Different mercury species are presented in fly ash collected from air and oxyfuel combustion: trigonal red HgS is the main mercury species in air combustion; mercury bound to organic matter (Hg–OM) and trigonal red HgS are both dominant in the samples from oxyfuel combustion. The prominent difference is the significantly increase of Hg–OM in oxyfuel combustion atmosphere. The oxyfuel combustion atmosphere would favor the formation of oxygen–rich functional groups, especially the C O group, which is responsible for the adsorption of mercury and formation of Hg–OM in fly ash. [ABSTRACT FROM AUTHOR]

[Display omitted] • Basic reference data for Hg migration and control were obtained. • Removal efficiency of HgT by flue gas purification equipment is 92.40%. • CuBr 2 -modified activated carbon exhibits excellent Hg0 removal performance. • Mechanism of CuBr 2 -modified activated carbon for Hg0 removal were revealed. This study evaluated the emission and control characteristics of mercury during hazardous chemical waste incineration. Meanwhile, for the complex flue gas conditions generated by hazardous chemical waste incineration, the commercial activated carbon used in the incineration system was modified with CuBr 2 , and its Hg0 removal performance was tested. The results showed that the major proportion of Hg was in the fly ash, and the content accounted for 74.53 % of the total Hg. The Hg content in the fly ash increased with decreasing fly ash particle size. In the exhaust flue gas, the Hg content was 11.05 % of the total Hg, in which the mass percentages of Hg2+ and Hg0 were 59.08 % and 40.92 %, respectively. The flue gas purification equipment of the incineration system had a removal efficiency of 92.40 % for HgT. The saturated Hg0 removal capacity of the modified activated carbon was improved by 33.51 times. Under simulated incineration flue gas conditions, the modified activated carbon was able to achieve an Hg0 removal efficiency of 92.85 %. The results can contribute to the understanding of Hg emissions from hazardous chemical incineration systems and provide guidance for efficient Hg removal from activated carbon. [ABSTRACT FROM AUTHOR]

• The millimeter-grade Se/SiO 2 adsorbent can be used as a filler in a fixed bed reactor. • The saturated adsorption capacity of mercury is up to 101.04 mg/g. • HgSe is the main product of mercury removal from adsorbent under flue gas conditions. • The carrier of Se/SiO 2 is soluble SiO 2 , and high purity of HgSe can be recovered. Massive Hg emissions from coal-fired units cause serious environmental pollution and result in a substantial waste of Hg resources. In this study, the prepared millimeter-grade Se/SiO 2 adsorbent was applied as a filler to adsorb mercury in a fixed-bed reactor to obtain the high value-added product HgSe, which solved the problem of short contact time and secondary pollution caused by the traditional injection mercury removal adsorbents. Experimental Hg removal showed that the 25 % Se-loaded adsorbent exhibited excellent Hg removal performance at 150 °C, with a saturation adsorption capacity of mercury was as high as 101.04 mg/g, nearly 300 times that of commercial activated carbons. Additionally, the influence of the flue gas composition on the Hg removal performance of Se/SiO 2 was studied. The results showed that O 2 , NO, and HCl increased the efficiency of Hg removal and SO 2 and SO 3 had trivial impact on the Hg removal performance. The Hg temperature-programmed desorption test results showed that the adsorbed Hg appeared predominantly as HgSe on the sample surface. DFT calculations verified that Se loading improved Hg removal performance and defined the adsorption mechanism. Moreover, the prepared Se/SiO 2 adsorbent carrier was soluble SiO 2 , which provided a good condition for the subsequent high-purity collection of HgSe. Finally, the technological process of Hg removal via Se-loaded adsorbents and the recovery of HgSe were proposed, which could offer a new way to achieve the resource utilization of Hg. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hg0 oxidation over the Mn-based catalysts followed L-H mechanism proven by kinetics. • The reaction rate constants showed an advantage over some other catalysts. • The kinetic parameters were further improved with the addition of O 2 into flue gas. • The apparent activation energy was much lower than that of the other approaches. A kinetic approach was adopted to analyze the reaction mechanism of elemental mercury (Hg0) oxidation by HCl over three Mn-based low-temperature SCR catalysts, MnO x /TiO 2 , Fe-MnO x /TiO 2 and CeMnO 3. Experimental results validated that Hg0 oxidation efficiencies of the catalysts were promoted by HCl at different temperatures. The kinetic models for the heterogeneous Hg0 oxidation were established and verified based on the experimental data. The verification results demonstrated that Hg0 oxidation over the Mn-based catalysts follows Langmuir-Hinshelwood mechanism. The kinetic parameters of reaction rate constant and HCl adsorption constant were calculated from the model fitting equations. The reaction rate constant was raised with the increase of temperature, while the HCl adsorption constant presented the opposite trend. The Mn-based catalysts with the reaction rate constant of 84.17–335.77 s−1 showed the advantage over some other catalysts such as commercial V 2 O 5 -(WO 3)/TiO 2 and CeO 2 /TiO 2. The kinetic parameters were further improved in the presence of O 2. The apparent activation energy for Hg0 oxidation over the catalysts that was derived from the kinetic parameters was 4.13–12.53 kJ/mol, which was much lower than that of the other approaches. The advantageous kinetic parameters and apparent activation energy were favorable for the Mn-based catalysts to act as low-temperature SCR catalyst for synergistic Hg0 removal. The kinetic study results were of fundamental significance for designing the reactor according to the known flue gas conditions, used catalyst and required Hg0 oxidation efficiency. [ABSTRACT FROM AUTHOR]

Elemental mercury (Hg0) is a highly hazardous pollutant of coal combustion. The low-temperature SCR catalyst of MnO x /TiO 2 can efficiently remove Hg0 in coal-burning flue gas. Considering its sulfur sensitivity, the effect of SO 3 on the catalytic efficiency of MnO x /TiO 2 and Fe modified MnO x /TiO 2 for Hg0 removal was investigated comprehensively for the first time. Characterizations of Hg-TPD and XPS were conducted to explore the catalytic mechanisms of Hg0 removal processes under different conditions. Hg0 removal efficiency of MnO x /TiO 2 was inhibited irreversibly from 92% to approximately 60% with the addition of 50 ppm SO 3 at 150 ℃, which resulted from the transformation of Mn4+ and chemisorbed oxygen to MnSO 4. The existence of H 2 O would intensify the inhibitory effect. The inhibition almost disappeared and even converted to promotion as the temperature increased to 250 ℃ and above. Fe modification on MnO x /TiO 2 improved the Hg0 removal performance in the presence of SO 3. The addition of SO 3 caused only a slight inhibition of 1.9% on Hg0 removal efficiency of Fe modified MnO x /TiO 2 in simulated coal-fired flue gas, and the efficiency maintained good stability during a 12 h experimental period. This work would be conducive to the future application of MnO x /TiO 2 for synergistic Hg0 removal. [Display omitted] • SO 3 exerted an irreversible influence on Hg0 removal performance of MnO x /TiO 2. • The effect of SO 3 converted from inhibition to promotion as temperature increased. • Fe modification improved Hg0 oxidation efficiency by 4.9%−12.4% at 100–350 ℃. • SO 3 inhibited Hg0 removal efficiency of Fe-MnO x /TiO 2 by 1.9% in simulated flue gas. [ABSTRACT FROM AUTHOR]

Abstract: Nanofibers prepared by an electrospinning method were used to remove elemental mercury (Hg0) from simulated coal combustion flue gas. The nanofibers composed of different metal oxides (MO x ) including CuO, In2O3, V2O5, WO3 and Ag2O supported on TiO2 have been characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersing X-ray (EDX) and UV–vis spectra. The average diameters of these nanofibers were about 200nm. Compared to pure TiO2, the UV–vis absorption intensity for MO x –TiO2 increased significantly and the absorption bandwidth also expanded, especially for Ag2O–TiO2 and V2O5–TiO2. Hg0 oxidation efficiencies over the MO x –TiO2 nanofibers were tested under dark, visible light (vis) irradiation and UV irradiation, respectively. The results showed that WO3 doped TiO2 exhibited the highest Hg0 removal efficiency of 100% under UV irradiation. Doping V2O5 into TiO2 enhanced Hg0 removal efficiency greatly from 6% to 63% under visible light irradiation. Ag2O doped TiO2 showed a steady Hg0 removal efficiency of around 95% without any light due to the formation of silver amalgam. An extended experiment with 8 Hg0 removal cycles showed that the MO x –TiO2 nanofibers were stable for removing Hg0 from flue gas. Factors responsible for the enhanced photocatalytic activities of the MO x –TiO2 nanofibers were also discussed. [Copyright &y& Elsevier]

Abstract: High surface area SiO2–TiO2–V2O5 (STV) catalysts of various titania loadings were synthesized by a sol–gel method. The STV catalysts were tested for oxidation of elemental mercury (Hg0) and its capture in simulated coal combustion flue gas representing those from combustion of low-rank coals (sub-bituminous and lignite). Experiments were conducted in a fixed-bed reactor at temperatures ranging from 26 to 400°C. In simulated flue gas, Hg0 oxidation efficiency over the STV catalysts was found to decrease dramatically from 135 to 300°C. At typical selective catalytic reduction (SCR) operating temperatures, the catalyst''s oxidation activity increased as titania loading of the STV catalysts increased up to 18wt%. The reaction mechanisms over the STV catalysts at SCR operating temperatures were investigated using individual flue gas components (HCl, NO, SO2 and H2O) with O2 balanced in N2. Hg0 oxidation over STV catalysts follows the Eley–Rideal mechanism where active surface species generated from adsorbed flue gas components react with gas-phase or weakly adsorbed Hg0. Fresh STV catalysts had some capability for adsorbing oxidized mercury (Hg2+) at 350°C, and no obvious effect of the adsorbed Hg2+ on subsequent Hg0 oxidation was observed. The presence of HCl with O2 had excellent oxidation and capture efficiency; however, without O2 it remarkably inhibited Hg0 adsorption on the STV catalysts. NO and SO2 promoted Hg0 oxidation and capture in the presence of O2, but their promotional effects were insignificant in the absence of O2. Water vapor showed prohibitive effects on Hg0 oxidation due to its competition with reactive species such as HCl and NO for active adsorption sites. This study demonstrates the feasibility of using STV catalysts for Hg0 removal at typical SCR operating temperatures. The identification of the reaction mechanism provides critical information for developing effective SCR catalysts for Hg0 oxidation in coal combustion flue gas. [Copyright &y& Elsevier]

• Magnetospheres was modified through H 2 S as an efficient sorbent for Hg0. • Elemental sulfur derived from H 2 S oxidation was responsible high-efficient Hg0 adsorption. • Gaseous Hg0 was immobilized as stable HgS with extremely low leaching ratio. • The application route for Hg0 removal by using magnetospheres with suface sulfidation modification was proposed. Reduction of elemental mercury (Hg0) emission from coal-fired power plants is an enormous challenge. In this work, magnetospheres separated from fly ash was modified through H 2 S as an efficient sorbent (i.e., S-MS) for Hg0. Elemental sulfur with high affinity towards Hg0 was formed on the S-MS surface through selective catalytic oxidation of H 2 S. The sulfidation temperature played an important role in Hg0 adsorption over S-MS, ascribing to the variation of sulfur species on S-MS. The S-MS exhibited above 80% Hg0 adsorption efficiency with a sulfidation temperature of 150 °C for 30 min. The optimal Hg0 adsorption performance was obtained at 50 and 75 °C, implying that the S-MS could be adopted by injecting into the duct upstream of wet electrostatic precipitator (WESP) system. The gaseous Hg0 was immobilized by S-MS as stable mercury sulfide (HgS) owing to the presence of abundant sulfur species that is active for binding Hg0. The leaching ratio of mercury from spent S-MS in WESP effluent was as low as 1%, hence minimizing the secondary mercury pollution from the industrial waste. The cost analysis demonstrates that the mercury removal technology on the basis of magnetospheres adsorbents exhibited much superiority in operation cost compared with commercial activated carbon injection technology. Thus, the S-MS, with specific features, such as high Hg0 adsorption performance, minimized environmental hazardous and recyclability, displayed great potential in Hg0 sequestration. [ABSTRACT FROM AUTHOR]

• The Hg0 removal by CuCl 2 -MF technology was applied to large coal-fired units. • The mercury removal performance of CuCl 2 -MF with different conditions were studied. • The optimal magnetosphere injection parameters were assured by the results of tests. • CuCl 2 -MF showed superior Hg0 removal ability and mercury recovery performance. CuCl 2 –MF was a cost–efficient and highly efficient sorbent for Hg removal from flue gas in coal-fired units. In this study, the Hg0 adsorption and oxidation performance of CuCl 2 –MF with different conditions were studied at a 1000 MW commercial scaled coal-fired power plant. Under the optimal conditions, the total removal efficiency of Hg and the Hg recovery rate reached 98.72% and 52.76% using CuCl 2 –MF injection combined with the existing pollutant control device. The magnetosphere particle size of 45 μm–75 μm exhibited the highest mercury removal capacity. Additionally, the final mercury emission concentration was 0.334 μg/m3 and the corresponding relative mercury removal efficiency was 89.81%. The results of this study proved that elemental mercury removal by CuCl 2 –MF was also suitable for large-scale coal-fired units with a high Hg removal efficiency even in the low concentrations of mercury, which provided a reference for the practical application of this technology in other units in the future and supplied valuable experience for other mercury removal technologies. [ABSTRACT FROM AUTHOR]

CuFe 2 O 4 is regarded as a promising candidate of catalyst for Hg0 oxidation in industrial flue gas. However, the microcosmic reaction mechanism governing mercury oxidation on CuFe 2 O 4 remains elusive. Herein, experiments and quantum chemistry calculations were conducted for understanding the chemical reaction mechanism of oxygen-assisted mercury oxidation on CuFe 2 O 4. CuFe 2 O 4 shows the optimal catalytic activity towards mercury oxidation at 150 ºC. The reactivity difference of different lattice oxygen species is associated with its atomic coordination environment. The lattice oxygen coordinating with two octahedral Cu atoms and a tetrahedral Fe atom shows higher catalytic activity towards mercury oxidation than other lattice oxygen atoms. The inverse spinel structure of CuFe 2 O 4 is favorable for O 2 activation due to the Jahn-Teller effect, thereby promoting mercury oxidation. O 2 molecule preferably adsorbs on iron active site and dissociates into active oxygen species. Hg0 oxidation is a three-step reaction process: Hg0 adsorption, Hg(ads) → HgO(ads), and HgO desorption. The energy barrier of mercury oxidation by chemisorbed oxygen is lower than that of mercury oxidation by lattice oxygen. The chemisorbed oxygen preserves higher reactivity towards mercury oxidation than lattice oxygen. Hg(ads) → HgO(ads) is the rate-determining step of mercury oxidation by chemisorbed oxygen because of the higher energy barrier of 116.94 kJ/mol. This work could provide the theoretical guidance for the diversified structure design of highly-efficient catalysts used for elemental mercury oxidation. [Display omitted] • Hg0 oxidation by oxygen species over CuFe 2 O 4 was studied by quantum chemistry. • The reactivity of lattice oxygen is related to its atomic coordination environment. • Hg0 oxidation by chemisorbed oxygen over CuFe 2 O 4 is a three-step reaction process. • Hg0 oxidation shows similar kinetics in the presence and absence of gaseous oxygen. [ABSTRACT FROM AUTHOR]

The elemental mercury was catalytically removed by V 2 O 5 /TiO 2 and Ce doped V 2 O 5 /TiO 2 catalysts under the UV irradiation at 30–160 °C to determine whether the catalysts could simultaneously have both thermo- and photo-catalytic activities. The physicochemical properties of catalysts were characterized by XRD, SEM, EDX, BET, XPS, UV–visible, PER and EIS. The experimental results demonstrated that V 2 O 5 /TiO 2 and Ce-doped catalysts possessed both thermo- and photo-catalytic reactivities. A suitable reaction temperature (120 °C) and UV light had promoting effects on mercury removal efficiency. In addition, owing to the high oxidation capability as well good oxygen storage performance of Ce4+, Ce doping could greatly improve the mercury removal properties of the catalyst, reduce the inhibition of SO 2 and make NO the component with enhanced effect. Ce doping also had the capability of enhancing the light absorption intensity in the UV region as well as the separation rate of photoinduced carriers. Finally, DFT calculations of V-Ti and Ce-V-Ti for Hg0 removal were investigated to further verify the experimental conclusion. • Ce doped V 2 O 5 /TiO 2 displayed excellent thermo- and photo-catalytic properties. • Ce4+ had good oxidation performance and oxygen storage performance in Hg0 capture. • Ce doped V 2 O 5 /TiO 2 presented good resistance to NO and SO 2。. • DFT calculations for Hg0 adsorption were performed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Vo-BWO/CN Z-scheme heterojunction was synthesized. • The synergistic effect of oxygen vacancy and Z-scheme heterojunction promoted molecular oxygen activation. • Vo-BWO/CN showed superior Hg0 photooxidation activity compared with Vo-BWO and CN. • DFT calculations and mechanism for Vo-BWO and Vo-BWO/CN were revealed. Photocatalytic Hg0 oxidation under visible light radiation is an economic and feasible approach to deal with energy and pollution problems. In this paper, the photocatalytic oxidation capability of gaseous elemental mercury by Bi 2 WO 6 under visible light radiation was further improved by introducing oxygen vacancies and forming the Z-scheme heterojunction with g-C 3 N 4. Firstly, the experimental results demonstrate that oxygen vacancies were beneficial to reduce the band gap, with nearly trebling increase in mercury removal efficiency than that before modification (6.5%) under visible light. Secondly, the Vo-Bi 2 WO 6 /g-C 3 N 4 composite with 10 wt% g-C 3 N 4 content exhibited an optimal Hg0 removal efficiency of 87.2% compared with Vo-Bi 2 WO 6 (17.8%) and pure g-C 3 N 4 (12.4%) under the N 2 + 4%O 2 atmosphere. The improved photocatalytic efficiency could be primarily due to the formation of a built-in electric field between g-C 3 N 4 and Vo-Bi 2 WO 6 through the carrier transmission mechanism of Z-scheme heterojunction, enhancing the light absorption intensity in the visible range, facilitating the movement and separation of photoinduced carriers as well as improving the interfacial charge-transfer efficiency. Finally, DFT calculations provides a theoretical basis for the role of oxygen vacancies and the internal electric field generated between two interfaces. [ABSTRACT FROM AUTHOR]

The application of mercury removal technology in coal-fired power plants has attracted much attention. In this paper, performances of CuBr 2 -modified tonstein from coal seams (MTCS) injection at an entrained flow reactor system and a 50-MW coal-fired power plant and their corresponding mechanisms were studied. The results showed that the increase of the injection rate, the reduction of the particle size, the extension of the residence time, and the increase of the initial Hg0 concentration were all conducive to mercury removal. At an entrained flow reactor, SO 2 and H 2 O obviously inhibited mercury removal, but this inhibition could be reduced with the increase of the residence time or the participation of NO and HCl. Specifically, with the participation of 1200 ppm SO 2 , the Hg0 removal efficiency was 56.9% and 82.8% at 0.6 s and 1.2 s, respectively. In the temperature range of 30–150 °C, the Hg0 removal efficiency in the flue gas at the simulated flue exit was approximately 83–93%. In addition, at a 50 - MW coal-fired power plant, the injection of MTCS was beneficial to Hg0 removal. In this process, most Hg0 was converted to Hg2+ by active substances, and then captured using fabric filter (FF) and wet flue gas desulfurization (WFGD) device. Injecting MTCS with a particle size of 300 mesh and concentration of 0.31 g/m3 can result in a relative mercury removal efficiency of up to 82.9% in the flue gas at the WFGD outlet, indicating that the low-cost mineral adsorbent MTCS is a suitable choice for mercury control in coal-fired power plants. Image 1 • MTCS exhibits excellent Hg0 removal performance in injection experiments. • An increased MTCS concentration in the flue gas leads to greater Hg0 removal. • A smaller particle size of MTCS is conducive to Hg0 removal. • Injecting 0.31MTCS300 can remove 82.9% of HgT in the flue gas at the WFGD outlet. [ABSTRACT FROM AUTHOR]

• Doping of I− into Bi 2 WO 6 induced the lattice contraction of Bi 2 WO 6 nanosheets. • doping decreased potential energy of CB edge, reserving good oxidation ability. • doped Bi 2 WO 6 showed superior Hg0 photooxidation activity compared with Bi 2 WO 6. • DFT calculations and mechanism for I− doped Bi 2 WO 6 to oxidized Hg0 were elucidated. In this work, I–-doped Bi 2 WO 6 composites were synthesized using a one-step hydrothermal method, and the effect of iodine doping on their photocatalytic efficiency in gas-phase elemental mercury removal was evaluated under visible-light irradiation. The results showed that 1.0 wt.% iodine doped Bi 2 WO 6 exhibited the optimal Hg0 removal efficiency of 87.6 % and 97.5 % under N 2 +O 2 +CO 2 and N 2 +O 2 +CO 2 +SO 2 +NO conditions, respectively. The improved photocatalytic activity of Bi 2 WO 6 can be ascribed to the reduction in the potential energy of its conduction band and recombination rate of electron-hole pairs, as well as the acceleration of charge transfer. The density functional theory calculations showed that iodine was doped in the (WO 4)2– layer and oxidized HgO can be adsorbed on the surface of I– doped Bi 2 WO 6. The O Bi site was found to be exhibit weak adsorption with respect to HgO, implying that most conducive to the desorption of HgO. Finally, the photocatalysis mechanisms was elaborated. [ABSTRACT FROM AUTHOR]

• Modified tonstein (CuBr 2 -TCS) effectively removed Hg0 from simulated flue gas. • O 2 significantly facilitated Hg0 removal by the spent adsorbent after the cycle. • The adding order of NO and SO 2 had a large effect on the performance of CuBr 2 -TCS. • Both Cu2+ and Br played key roles in the process of Hg0 removal. Tonstein in coal seam (TCS) is a kind of mining solid waste, which was developed to a novel adsorbent (CuBr 2 -TCS) by using copper bromide modification. In this paper, CuBr 2 -TCS was subjected to elemental mercury (Hg0) removal experiment in simulated coal-fired flue gas (SFG). Several characterization methods were used to determine the mineralogical characteristics of TCS and reaction mechanisms. In-depth, the Hg0 removal performances of CuBr 2 -TCS under different flue gas components were explored. The results revealed that CuBr 2 -TCS exhibited 92.1% and 78.3% Hg0 removal efficiency in dry and wet SFG, respectively. HCl and O 2 facilitated Hg0 removal performance of CuBr 2 -TCS by supplementing oxygen atoms and halogens, respectively, accompanying some intermediate transition products such as Cu 2 OBr 2. SO 2 played a serious suppressive role. SO 2 acting alone or NO and SO 2 acting simultaneously caused irreversible changes in the surface functional groups that formed active sites with NO. However, the thermal stability of the adsorbed mercury on the adsorbent which was spent in N 2 + SO 2 + O 2 atmosphere became better. In addition, the spent adsorbent that first went through the Hg0 removal process in N 2 + NO atmosphere, exhibited higher Hg0 removal efficiency in N 2 + SO 2 + NO atmosphere than that first reacted in N 2 + SO 2 atmosphere. CuBr 2 -TCS is a cost-effective adsorbent for the Hg0 abatement from the coal-fired flue gas (CFG). [ABSTRACT FROM AUTHOR]

The environmental problem concerning Hg pollution has received worldwide attention. Coal fired power plants are responsible for large amounts of Hg emission and produce abundant by-products in particular gypsum which is capable of extensive use. In this study, the migration of Hg in the gypsum production process and effluent treatment process in a typical wet flue gas desulfurization (WFGD) system was investigated and the temperature programmed decomposition technique was applied to identified Hg species in these products. Hg concentration in both the solid and liquid fraction of samples obtained in wet flue gas desulfurization system were determined by atomic fluorescence spectroscopy. The results indicated that gypsum accounted for a small proportion (29.9%) of Hg while the majority of Hg was transported to effluent treatment process where over 99.6% Hg was removed. The amount of Hg discharged from WFGD in the drainage, gypsum, and desulfurization sludge were 0.04 t/yr, 13.56 t/yr, and 9.56 t/yr, respectively. Desulfurization environment promoted HgS formation and lead to HgS being dominant in gypsum. The alkaline environment in the effluent treatment process contributed to the formation of HgO which was regarded as the primary Hg compound and accounted for 49.5%, 54.8%, and 78.5% of the total Hg in the neutralization tank, precipitation tank, and flocculation tank, respectively. The occurrence of HgCl 2 in the solid fraction attributed to absorption of solid particles when it precipitated and was enhanced by the addition of chemicals. There was no obvious difference in the proportion of HgSO 4 in the effluent treatment process. Systematic studies on difference in the partitioning of Hg species enables a better understanding on Hg behavior and provides conferences on targeting removal of Hg species in WFGD system. Image 1 • Hg species identification in WFGD system was studied by TPD method. • Hg species evolution was investigated in gypsum production and effluent treatment process. • Hg migration behavior in WFGD system was studied. [ABSTRACT FROM AUTHOR]

The mercury removal performance of a low-cost recyclable CuCl 2 modified magnetospheres (Cu-MF) was investigated at a 50 MWth coal-fired power plant. An increase in the Cu-MF injection rate facilitated the mercury removal and recovery process. With the combination of the existing pollutant control devices and the Cu-MF injection, an overall mercury removal efficiency of 99.3% could be achieved. Under optimal conditions, the mercury emitted from the stack was reduced to 0.10 μg/m3. Most of the mercury in the flue gas migrated to the fly ash with the spent Cu-MF. Subsequently, through magnetic separation, 67.4% of the input mercury could be recovered. The comparison of experimental results showed that Cu-MF was more effective than fly ash in removing and recovering mercury from the flue gas. With the injection of Cu-MF, HgCl 2 was formed on the magnetospheres and was identified by the mercury-temperature-programmed decomposition (Hg-TPD) experiments. The magnetospheres with the lowest particle size showed the highest mercury removal capacity. This work is expected to provide valuable guidance for optimising the mercury removal technology in large scale commercial applications in future. [ABSTRACT FROM AUTHOR]

• This review discusses the development of mineral adsorbents for Hg0 removal. • Species, physicochemical characteristics and modification methods are summarised. • Mercury removal performance, influence factors and mechanisms are also summarised. • Modified mineral adsorbents are low-cost and effective in removing mercury. Mercury emissions from coal-fired power plant flue gas (CFFG 1 1 CFFG is an abbreviation for coal-fired power plant flue gas.) threaten the natural environment and human health, and this has attracted the attention of environmental protection departments and scientific researchers in recent years. Mineral adsorbents perform well at mercury removal and extensive studies on them have been conducted. This review discusses the progress in researching the application of mineral adsorbents to mercury emission control technologies applied to CFFG. The species and physicochemical characteristics of some common mineral adsorbents are briefly introduced and various modification methods, mainly including high temperature activation, acid activation, organic modification, inorganic modification and combinations of modifications, are summarised. As well, the mercury removal performance of various mineral adsorbents is evaluated, and the results indicate that removal performance relates to the actions of the mineral carrier combined with modification methods which are able to improve the physical structure of minerals and/or increase the number of active sites for mercury removal on the mineral surfaces. The effects of the main process parameters, including reaction temperature and flue gas components (O 2 , HCl, SO 2 , NO, H 2 O, Hg0, etc.), on mercury removal by different mineral adsorbents are also systematically reviewed. Moreover, the possible adsorption and oxidation approaches involved in the process of mercury removal by mineral adsorbents are discussed. This review indicates that the chemical active site is the key factor for mercury removal. Our economic evaluation indicates that the cost of mineral adsorbent is much lower than that of activated carbon, showing that mineral adsorbents have promise in terms of industrial applications. Finally, future work necessary for the continued development of mineral adsorbent injection technology for CFFG mercury control is proposed. [ABSTRACT FROM AUTHOR]