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Decontamination of Hg0 from coal-fired flue gas remains an enormous challenge. It is an imperative pursuit to design adsorbents bearing an abundance of accessible chelating sites with a high affinity toward mercury, thus achieving both rapid uptake and high capacity for Hg0. Herein, an electrostatically directed assembly strategy was designed to construct Cu 2 Se decorated commercial polyurethane sponge (Cu 2 Se/PUS) as an efficient Hg0 trap. The surface coverage of Cu 2 Se on the Cu 2 Se/PUS can be rationally adjusted by turning the charge density of Cu 2 Se and PUS. The saturated Hg0 adsorption capacity of Cu 2 Se/PUS was achieved at 217.04 mg g−1 (normalized to the Cu 2 Se coating amount), which was much higher than that of powdery Cu 2 Se (43.66 mg g−1). Multiform selenium active sites (Se- and Se2-) and copper-terminated active centers of Cu 2 Se/PUS co-participated in Hg0 adsorption, instead of the individual role of Se- over powdery Cu 2 Se. The macroporous skeleton structure and the highly dispersed Cu 2 Se boosted the diffusion of mercury to the active sites for immobilization, thus accelerating the consumption of multiple active sites on the Cu 2 Se/PUS. This work not only provided an efficient Hg0 trap but also showed great inspiration for the potential of electrostatically directed assembly methods in constructing adsorbents for diverse environmental remediations. [Display omitted] • Integrated macroporous skeleton molding material as an efficient Hg0 trap. • Electrostatically directed assembly strategy was designed to construct Cu 2 Se/PUS. • The Hg0 adsorption capacity of Cu 2 Se/PUS was as high as 217.04 mg g−1. • Se-, Se2- and Cu-terminated centers of Cu 2 Se/PUS co-participated in Hg0 adsorption. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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]

Highlights • The La 0.8 Ce 0.2 MnO 3 catalyst was highly active for Hg0 oxidation under SFG condition. • NO and HCl promoted Hg0 oxidation by forming active surface species. • H 2 O changed the catalyst surface chemistry and consumed active chlorine, which weakened the Hg0 oxidation. • NH 3 consumed surface oxygen and induced HgO reduction, hence limiting the Hg0 conversion. Abstract La 0.8 Ce 0.2 MnO 3 perovskite catalyst was employed for elemental mercury (Hg0) oxidation in coal combustion flue gas. The effects of flue gas components, including O 2 , NO, SO 2 , HCl, H 2 O as well as the selective catalytic reduction (SCR) reductant (NH 3), on Hg0 oxidation were investigated systematically. Above 90% Hg0 oxidation was obtained at 200 °C under simulated flue gas (SFG) and SCR atmosphere with a gas hourly space velocity of 60,000 h−1. Gaseous O 2 regenerated and replenished surface oxygen, hence promoting the oxidation of Hg0. NO promoted the Hg0 oxidation because of the formation of active surface species like NO 2. HCl facilitated the Hg0 oxidation, and 98.8% Hg0 oxidation was obtained under the atmosphere containing 10 ppm HCl in the co-presence of O 2. SO 2 inhibited Hg0 oxidation because of the irreversible damage on catalytic activity by reacting with the active species on the catalyst·H 2 O also inhibited Hg0 oxidation due to the change of catalyst surface chemistry as well as the consumption of active surface chlorine species (Cl∗). NH 3 competed active sites with Hg0 and induced oxidized mercury reduction, hence limiting the Hg0 conversion. However, the inhibitive effect of NH 3 could be partly offset by the promotional effect of NO. This work clarified the effects of flue gas compositions on Hg0 oxidation over a novel La 0.8 Ce 0.2 MnO 3 perovskite catalyst, which is essential for further improving the catalyst activity. [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]

Samples of magnetic iron–manganese binary oxide supported on activated carbon fiber (Fe 3−x Mn x O 4 /CNF) were prepared for Hg 0 removal from flue gas. The results showed that the Hg 0 removal performance of Fe 3−x Mn x O 4 /CNF was significantly promoted with the increase of Mn incorporating content into Fe 3 O 4 spinel structure. The optimal sample of Fe 2 MnO 4 /CNF, at the optimal reaction temperature of 150–200 °C, attained above 90% of Hg 0 removal efficiency (E a ). CNF played an important role in Hg 0 removal by Fe 3−x Mn x O 4 /CNF due to the disperation of Fe 3−x Mn x O 4 particles and the enhancement for electron transfer process. O 2 enhanced the Hg 0 removal via the Mars-Maessen mechanism, and NO improved the Hg 0 removal performance slightly because of the formation of NO 2 . SO 2 and H 2 O played an inhibitive role in Hg 0 removal due to the competition of active sites for Hg 0 adsorption. A mechanism of Hg 0 removal over Fe 3−x Mn x O 4 /CNF is proposed, in which both Mn cations and lattice/chemisorbed oxygen were thought to the active sites for Hg 0 adsorption/oxidation. Further, the spent Fe 3−x Mn x O 4 /CNF could be regenerated with no obvious decrease of Hg 0 removal performance by water washing followed by thermal treatment at 450 °C in N 2 and calcination at 200 °C in air. [ABSTRACT FROM AUTHOR]

Several modified adsorbents were developed by impregnating palygorskite (Pal) with the active substances CuCl 2 , CuBr 2 , NaBr, sulfur (S), MnO 2 and Co 3 O 4 , which were used to conduct experiments via a bench-scale fixed-bed reactor system in simulated flue gas for evaluating their elemental mercury removal capacity. In addition, a variety of characterization methods were applied to understand the physicochemical properties of these adsorbents. Furthermore, adsorbents, namely, CuCl 2 /CuBr 2 -impregnated Pal (Cu-Pal), were chosen for deep exploration under various gas conditions. The results showed that the mercury removal capability of Pal was greatly improved after impregnation. At 120 °C in pure N 2 , the mercury removal efficiency of the adsorbents modified by CuCl 2 and CuBr 2 could reach 90.9% and 95.2%, respectively, while it could be > 80% for the adsorbents modified by the others. The overall trend showed that O 2 and HCl were beneficial to increasing the mercury removal efficiency of Cu-Pal. To be specific, for CuCl 2 -Pal and CuBr 2 -Pal, when adding in 8% O 2 , their efficiencies could be increased by 6.6% and 1.9% respectively, while 50 ppm HCl increased their efficiencies by 2.8% and 2.1%, respectively. Different from O 2 and HCl, SO 2 and NO had negative effects. The removal efficiencies could be reduced by 6.5% for CuCl 2 -Pal and 4.7% for CuBr 2 -Pal with 1200 ppm SO 2 , while they could be reduced by 4.2% and 2.6% with 300 ppm NO. Compared with CuCl 2 -Pal, CuBr 2 -Pal performed better. Combined with the characterization results, Cu 2 + was reduced to Cu + and halogen migrated into new compounds on the surface of Cu-Pal after reaction. Eventually, the mercury removal mechanism of Cu-Pal was analysed and proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A cyclic Hg0 capture strategy from was proposed for Hg0 removal and recovery. • LCMO-MC pellets were synthesized via a extrusion-spheronization method. • The pellets exhibited high Hg0 removal capacity and excellent cyclic durability. • The pore-creating template improved the microstructures of pellets. Circulating adsorbents in a fluidized bed integrating elemental mercury (Hg0) adsorption and oxidized mercury decomposition/desorption processes could simultaneously achieve adsorbents recycling and mercury recovery during the flue gas mercury removal. The granulation of adsorbent powder is essential to reduce elutriation the looping system. Herein, powdery La 0.8 Ce 0.2 MnO 3 perovskite adsorbent, which has been demonstrated to be highly efficient for Hg0 removal, was moulded into 0.8–1 mm pellets by an extrusion-spheronization method. Meanwhile, microcrystalline cellulose (MC) was used as pore-creating template to constructing porous pellets. The results show that the La 0.8 Ce 0.2 MnO 3 pellets with 20 % MC added during the pelleting process (LCMO-MC) exhibited 90 % Hg0 removal efficiency under a gaseous hourly space velocity (GHSV) of 380,000 h−1, which was comparable to that over the corresponding powdery adsorbent. The LCMO-MC performed well in Hg0 removal at a wide temperature window from 50 to 200 °C. SO 2 and H 2 O displayed slight interference in Hg0 removal, while O 2 and NO enhanced Hg0 removal over LCMO-MC. During six adsorption-decomposition/desorption cycles, the LCMO-MC presented outstanding cyclic durability and about 97 % Hg0 removal efficiency was achieved with a GHSV of 50,000 h−1. The excellent Hg0 removal capacity of LCMO-MC was ascribed to the existence of abundant pore channels for Hg0 diffusion, which in-situ retained during the burning of pore-creating templates at high temperature and newly formed accompanying with the burning gas release. These results demonstrate that the template (i.e., MC) assisted extrusion-spheronization approach is promising to mould adsorbent pellets for Hg0 removal in a fluidized-bed system, which could simultaneously realize adsorbent recycling and mercury recovery. [ABSTRACT FROM AUTHOR]

Uranium is one of the typical naturally occurring radioactive materials in coal. The release and speciation transformation of uranium was investigated at various combustion temperatures, and the thermodynamic modelling was performed to complement the experimental work. The results showed that the uranium release ratio did not increase consistently with the combustion temperature increasing, where the highest release ratio occurred at 500 °C. At the temperature range of 500–900 °C, the uranium release ratio obviously decreased, which could be attributed to the formation of uranate with the interaction of alkaline/alkaline-earth metal compounds in coal. However, some of the thermal unstable uranate was decomposed and released at the temperature above 1000 °C, while part of them remains stable in the combustion product even when the sample was heated at 1200 °C. Further, the interaction mechanism of uranium and alkaline/alkaline-earth metals during coal combustion was proposed based on the experimental and modelling results. This study will provide valuable information for understanding the primary factors and processes that affect the release of uranium during coal combustion. [ABSTRACT FROM AUTHOR]

• Charge distribution modulation and morphology controlling of Cu 2 Se was conducted for enhancing Hg0 adsorption activity. • The Hg0 adsorption capacity and rate of CTAB-Cu 2 Se was high up to 80.2 mg·g−1 and 9.99 mg·g−1·h−1. • The Cu 2 Se-CTAB showed superior Hg0 adsorption performance at wide temperature range. • The flue gas components played insignificant roles in Hg0 removal over Cu 2 Se-CTAB. The abatement of elemental mercury (Hg0) emissions from industrial flue gases remains an enormous challenge. Metal selenides have been demonstrated to be promising Hg0 remediators, and the electron-transfer ability of selenide ligands is one of the key factors that determining the uptake capacity and adsorption rate of Hg0. Herein, a charge distribution modulation strategy was developed to generate desired selenide ligands. The selenide ligands on a tutorial sample, copper selenide (Cu 2 Se), was artificially modulated to −1 valances (Se1-) via electrostatic adsorption of positively charged head groups of cetyltrimethylammonium bromide (CTAB). Unlike other selenide ligand such as Se2-, the Se1- directly acted as an electron acceptor for Hg0 and realize one-step immobilization of Hg0 as environmentally stable mercury selenide (HgSe). Besides, CTAB was beneficial to construct nanosheets with thinner and larger plates, hence facilitated a sufficient exposure of active sites for binding Hg0. Profiting from the above advantages, the Hg0 adsorption capacity of CTAB modulated Cu 2 Se (Cu 2 Se-CTAB) was up to 80.2 mg·g−1, about two times higher than that of bare Cu 2 Se. Meanwhile, the average Hg0 adsorption rate of Cu 2 Se-CTAB before achieving saturation was 9.99 mg·g−1·h−1, much faster comparing with 6.90 mg·g−1·h−1 for regular Cu 2 Se. The Cu 2 Se-CTAB showed superior Hg0 adsorption performance at 40–80 °C and excellent resistance to flue gas interference, which are crucial for real-world applications. This newly designed method not only provides an excellent Hg0 remediator but also offers a tutorial example for a rational modulation of metal selenides for diverse environmental remediations. [ABSTRACT FROM AUTHOR]

The emission of mercury from coal combustion has caused consequential hazards to the ecosystem. The key challenge to abating the mercury emission is to explore highly efficient adsorbents. Herein, sulfur-functionalized carbon (S-C) was synthesized by using a molten-salt pyrolysis strategy and employed for the removal of elemental mercury from coal-combustion flue gas. An ideal pore structure, which was favorable for the internal diffusion of the Hg0 molecule in carbon, was obtained by using a SiO2 hard template and adjusting the HF etching time. The as-prepared S-C with an HF etching time of 10 h possessed a saturation Hg0 adsorption capacity of 89.90 mg·g−1, far exceeding that of the commercial sulfur-loaded activated carbons (S/C). The S-C can be applied at a wide temperature range of 25–125 °C, far exceeding that of commercial S/C. The influence of flue gas components, such as SO2, NO, and H2O, on the Hg0 adsorption performance of S-C was insignificant, indicating a good applicability in real-world applications. The mechanism of the Hg0 removal by S-C was proposed, i.e., the reduced components, including sulfur thiophene, sulfoxide, and C-S, displayed a high affinity toward Hg0, which could guarantee the stable immobilization of Hg0 as HgS in the adsorbent. Thus, the molten-salt pyrolysis strategy has a broad prospect in the application of one-pot carbonization and functionalization sulfur-containing organic precursors as efficient adsorbents for Hg0. [ABSTRACT FROM AUTHOR]

Porous carbons derived from one-pot carbonization and activation of wood sawdust in a molten salt (LiCl-KCl) medium were employed for Hg0 removal. The carbons derived from molten salt carbonization (MSC) displayed much superior Hg0 removal performance comparing with the carbons derived from N 2 pyrolysis method (NC). The best molar ratio of LiCl-KCl was 59:41, the optimal molten salt temperature was 700 °C, and the best mass ratio of wood sawdust to molten salt was 1:10. The MSC displayed good applicability at 50–125 °C. The saturation Hg0 adsorption capacity of MSC was about 7828.39 μg·g−1, far exceeding those for carbonaceous adsorbents reported in literatures. A Hg0 removal mechanism over MSC was proposed, i.e., the hierarchical porous structure accelerated mass transfer of Hg0, and the C O groups served as electron acceptors from Hg0 atoms to form organic matter bonded mercury (Hg-OM). The molten salt could be easily separated from the mixture of MSC for recycling multiple times. Thus, molten salt carbonization method appears to be promising in one-pot carbonization and activation of biomass as efficient adsorbents for gaseous Hg0. [Display omitted] • Porous carbon was prepared by one-pot carbonization and activation of biomass in molten salt. • The Hg0 adsorption capacity of porous carbon reached about 7828.39 µg·g−1. • The porous carbon can be adopted in a wide temperature range of 50–125 °C. • The spent molten salt can be effectively seperated with carbon for reusing. [ABSTRACT FROM AUTHOR]

• CuFeS 2 was adopted as an efficient and recyclable trap for Hg0 sequestration. • The adsorption capacity and rate was high as 37.24 mg·g−1 and 63.40 μg·g−1·min−1. • The flue gas components played insignificant roles in Hg0 removal over CuFeS 2. • The spent CuFeS 2 could be effectively replenished and regenerated for reusing. The development of cost-effective and high-efficient technologies for degrading Hg0 pollution from coal combustion flue gas remains a tremendous challenge. In this work, an earth-abundant mineral, i.e., chalcopyrite (CuFeS 2), was adopted as an efficient trap for Hg0 sequestration. The CuFeS 2 exhibited approximately excellent Hg0 removal performances in a wide temperature ranging from 40 to 100 °C. Typical flue gas components including oxygen (O 2), sulfur dioxide (SO 2), nitrogen monoxide (NO), and water vapor (H 2 O) negligibly interfered the Hg0 adsorption ability, which further solidify the application potential of CuFeS 2 in coal-fired power plant. The Hg0 adsorption capacity and uptake rate was 37.24 mg·g−1 and 63.40 μg·g−1·min−1, respectively, significantly suppressing those of commercial activated carbons. The superior performance of CuFeS 2 were primarily attributed that the disulfide ligands (S 2 2−) could oxidize Hg0 into Hg2+ and subsequently immobilize Hg2+ into mercury sulfide (HgS). The spent CuFeS 2 sorbent could be replenished and regenerated by a thermal decomposition method, which pronouncedly save the operation cost. Therefore, the CuFeS 2 is a potential trap for cost-effective and efficient Hg0 remediation from coal combustion flue gas. [ABSTRACT FROM AUTHOR]

Sulfur abundant S/FeS 2 prepared by a hydrothermal method was employed for removing elemental mercury (Hg 0 ) from coal-fired flue gas at low temperature. The S/FeS 2 exhibited optimal Hg 0 adsorption performance at 80 °C, which matched the temperature window between the flue gas desulfurization (FGD) and wet electrostatic precipitator (WESP) systems. The adverse effects of H 2 O and SO 2 on Hg 0 adsorption were slight. The Hg 0 adsorption capacity of S/FeS 2 was up to 2732 μg/g when achieved 50% breakthrough threshold. Both elemental sulfur (S) and FeS 2 in the S/FeS 2 contributed to the excellent Hg 0 adsorption capacity. The mercury leaching tests show that only 0.00076% mercury adsorbed on the S/FeS 2 was leached out. The mercury concentration in leachate was 0.694 μg·L −1 , which was much lower than that for a commercial AC (1.214 μg·L −1 ). Furthermore, the S/FeS 2 presented about 95% oxidized mercury (Hg 2+ ) adsorption efficiency from WESP effluent. The Hg 2+ concentration could decreased rapidly from 50 μg·L −1 to below 2.5 μg·L −1 in 30 min, which was much lower than the World Health Organization (WHO) guideline (6 μg·L −1 ). With these advantages, S/FeS 2 appears to be a promising material for co-beneficial gaseous Hg 0 and aqueous Hg 2+ removal from power plants by injecting upstream of a WESP system. [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]

[Display omitted] • The Hg2+ reduction process over SCR catalysts were reviewed for the first time. • The effects of typical flue gases on Hg2+ reduction were presented. • The involved reaction mechanisms for Hg2+ reduction were discussed in details. • Suggestions to alleviate the reduction of Hg2+ over SCR catalysts were proposed. The control of mercury emission from flue gas has long been a serious task for the global environment and human health. Utilization of selective catalytic reduction (SCR) catalysts to oxidize Hg0 to form Hg2+ and subsequent capture the Hg2+ through a wet flue gas desulfurization (WFGD) scrubber is an efficient and economical technology for Hg0 removal in coal-fired power plants. Extensive studies have been conducted with regard to Hg0 oxidation over SCR catalysts. However, recent studies found that the reduction of Hg2+, an inverse process to Hg0 oxidation, also occurred even predominated under some SCR conditions. This new observation overturns the general knowledge that SCR catalysts always enhance Hg0 oxidation. To avoid the neglect of Hg2+ reduction and overcome the shortages of existing studies, a critical review of Hg2+ reduction over SCR catalysts was undertaken. The Hg2+ reduction behaviors under various SCR conditions were summarized and the effects of typical flue gas components like hydrogen chloride (HCl), sulfur dioxide (SO 2), water vapor (H 2 O), volatile organic compounds (VOCs), and carbon monoxide (CO) on Hg2+ reduction were also presented. The involved reaction mechanisms for Hg2+ reduction were discussed in details. Moreover, feasible measures to suppress the reduction of Hg2+ in the SCR system were proposed. We expect to clearly explore the mechanism of the Hg0 redox process on SCR catalysts in this review to avoid the neglect of Hg2+ reduction, hence providing guidance for the design of SCR catalysts to achieve an efficient Hg0 oxidation. [ABSTRACT FROM AUTHOR]

• Ti 3 C 2 MXene/Cu 2 Se sorbent was prepared via a Lewis acid etching route. • The Hg0 removal ability of Ti 3 C 2 MXene/Cu 2 Se excelled other metal selenides. • Ti 3 C 2 MXene/Cu 2 Se showed favorable Hg0 removal performance over 100 °C. • Industrial flue gas exerted no effects on Hg0 capture of Ti 3 C 2 MXene/Cu 2 Se. A fundamental obstacle that restricts the use of metal selenides for gaseous elemental mercury (Hg0) immobilization is the failure to take both the optimization of intrinsic structure favorable for Hg0 diffusion and adequate exposure of metal selenide towards Hg0 into consideration. In this work, a Ti 3 C 2 MXene/Cu 2 Se sorbent for Hg0 sequestration was synthesized via a Lewis acid etching route combined with room-temperature selenization pathway. During this strategy, copper chloride plays a dual role, i.e., an etching agent for the Ti 3 C 2 MXene synthesis and a precursor for Cu0 decoration. Cu 2 Se precursors (Cu0) were dispersedly and firmly pre-anchored on the substrate, effectively avoiding the agglomeration and warranting excellent dispersion of Cu 2 Se. Compared with pristine Cu 2 Se, Ti 3 C 2 MXene/Cu 2 Se exhibits advantageous structural characteristics fully boosting Hg0 diffusion kinetics. Meanwhile, the enhanced dispersion of Cu 2 Se from the prefixation of Cu0 largely enhances the exposure and utilization of selenide. Consequently, Ti 3 C 2 MXene/Cu 2 Se shows a Hg0 adsorption capacity of 147.64 mg g−1, which is much higher than those of Cu 2 Se and most other metal selenides. Impressively, its uptake rate of 688.99 μg g−1 min−1 is the highest record rate in metal selenides. Moreover, Ti 3 C 2 MXene/Cu 2 Se still maintained outstanding Hg0 adsorption performance under relatively high reaction temperature with the shelter of Ti 3 C 2 MXene. Typical fuel gas situations including coal combustion flue gas, smelting flue gas, natural gas have negligible influences on its Hg0 adsorption performance, indicating its extensive applicability and flexibility for actual industrial situations. This work also provides valuable hints for the trade-off of structural properties and ligands exposure to design Hg0 sorbents with satisfactory Hg0 sequestration performances. [ABSTRACT FROM AUTHOR]

[Display omitted] • Perovskite pellets shows favorable Hg0 adsorption capacity and mechanical strengths. • Agar powder and silica sol work as a hardener and pore-former, a binder in the granulation. • The Hg0 adsorption performances maintained identical after five adsorption–desorption cycles. • This wet-chemistry granulation strategy can also be extended to other powdery sorbents. Perovskite-based sorbents have received extensive attention in the field of mercury abatement. However, the excellent Hg0 adsorption performance on the lab scale hardly transforms into industrial-scale utilization because of the elutriation and microcrystalline nature of powdery perovskite sorbent. Hence, the granulation of perovskite into pellets is a strongly solicited and urgent demand. In this work, a universal granulation strategy is exploited for fabricating perovskite sorbent pellets for Hg0 capture from coal combustion flue gas (CCFG) based on a facile wet-chemistry method. This route takes advantages of the unique thermal sensitivity and thermal decomposition characteristics of agar powder and surface tension of medium to simultaneously trade off the molding, pore creation, and mechanical property of perovskite-based sorbent pellets. Besides, silica sol was also added to further enhance the physical strengths of sorbent pellets. The obtained perovskite sorbent pellet (i.e., LCMO-A-Z-2) with a favorable BET surface area of 113.16 m2 g−1 and pore diameter of 8.81 nm, largely facilitating Hg0 diffusion and capture over sorbent pellets. LCMO-A-Z-2 was further employed to Hg0 adsorption experiment under simulated CCFG, which exhibited satisfactory Hg0 adsorption capacity of 2.07 mg g−1 and nearly identical Hg0 adsorption performance after 5 cycles. The weight loss was approximately 13 % after 1000 rotations in the anti-attrition ability experiment suggesting its outstanding mechanical strength. It is reasonable to deduce this granulation method can be readily extended to other powdery sorbents. This work makes first step towards the application of sorbent pellets under application-relevant conditions and support the ultimate implementation of traditional sorbents in various large-scale industrial scenarios. [ABSTRACT FROM AUTHOR]

[Display omitted] • A facile chemical bath deposition strategy was developed to fabricate Cu 7 S 4 /Copper Foam sorbent. • Cu 7 S 4 /Copper Foam sorbent is characterized by well-dispersed nanosheet and high permeability. • Cu 7 S 4 /Copper Foam showed much higher Hg0 adsorption capacity and uptake rate compared with those of granular activated carbon. • A versatile pathway to functionalize metal skeleton for Hg0 immobilization was also illustrated. The major challenge to use metal sulfide for elemental mercury (Hg0) immobilization from coal-fired flue gas is exploiting a facile and feasible pathway to achieve its fixed-bed application. In this work, copper sulfide (Cu 7 S 4) nanosheet arrays anchored on copper skeleton as an efficient Hg0 trap with outstanding Hg0 sequestration performance was rapidly fabricated via a facile room-temperature chemical bath deposition method. After being impregnated in the polysulfide solution, the surface of copper foam was quickly oxidized and then converted into Cu 7 S 4 nanosheet, which tightly adhered to the macro-porous copper foam. Benefitted from well arrayed Cu 7 S 4 nanosheet, high-permeability structure, and uniform dispersion of active sites, the as-obtained Cu 7 S 4 /Copper foam favors for its application in Hg0 immobilization under a fixed-bed circumstance. These superiorities contribute to its outstanding Hg0 removal capacity of 38.32 mg g-1and adsorption rate of 6.06 μg g−1 min−1, far transcending that of commercial granular S impregnated activated carbon by magnitudes. This study not only developed an efficient Hg0 sorbent used in fix-bed scenarios but also illustrated a versatile strategy to rapidly functionalize metal skeletons with metal sulfides for vapor Hg0 immobilization from coal-fired flue gas. [ABSTRACT FROM AUTHOR]

[Display omitted] • An activation approach was provided to modify natural sulfide mineral for Hg0 immobilization. • Mechanochemical activation introduced hetero-ligands and generated active copper sulfide. • The Hg0 adsorption capacity of CuCl 2 @Fe 7 S 8 was high up to 283.3 mg g−1. • A schematic was proposed for the preparation, application and regeneration of CuCl 2 @Fe 7 S 8. Man-made metal sulfides (MSs) have been proven to be effective traps for permanent elemental mercury (Hg0) immobilization from anthropogenic sources. However, the fabrication of MSs generally involves complex steps and adopts hazardous precursors, hence compromising its cost-effectiveness and environmental-friendliness. The earth-abundant natural MS minerals might be optimal alternatives to the synthetic MSs, while most of them suffer from limited Hg0 adsorption capacity. Herein, a mild mechanochemical approach under a solid state with the aid of cupric chloride (CuCl 2) was developed to modify pyrrhotite (Fe 7 S 8) from calcination of natural pyrite for Hg0 capture from flue gas. After the CuCl 2 aided mechanical milling, the Hg0 adsorption capacity and uptake rate of the CuCl 2 modified pyrrhotite (CuCl 2 @Fe 7 S 8) reached as high as 283.3 mg g−1 and 188.75 μg g−1 min−1, approximately 400 folds higher than that of raw pyrrhotite. The characterization and density functional theory calculation results reveal that the superior performance of CuCl 2 @Fe 7 S 8 was primarily attributed to the mechanochemical approach which not only introduced hetero-ligands (i.e., Cl) to the adsorbent to combine with Hg0 but also generated extremely active copper sulfide for binding Hg0. The excellent resistance to temperature fluctuation and flue gas interference and its magnetic separation recyclability warrant the application of CuCl 2 @Fe 7 S 8 in real-world conditions. Integrated Hg0 removal technologies based on the performance-enhanced recyclable CuCl 2 @Fe 7 S 8 were also proposed for potential applications in different industrial scenarios including coal combustion flue gas. [ABSTRACT FROM AUTHOR]

CuO loaded MnO x /TiO 2 mixed oxide (CuMnTi) synthesized by an ultrasonic-assisted impregnation method was for the first time employed for simultaneous nitrogen monoxide (NO) reduction and elemental mercury (Hg 0 ) oxidation under selective catalytic reduction (SCR) atmosphere with the presence of NH 3 . The CuMnTi catalyst exhibited a wide temperature window from 150 to 250 °C for both NO reduction and Hg 0 oxidation. At the optimal temperature of 175 °C, CuMnTi reduced 96.4% of the inlet NO and oxidized 100% of the inlet Hg 0 at a very high gas hourly space velocity (GHSV) of 40,000 h −1 . O 2 , HCl and NO significantly promoted Hg 0 oxidation and offset the adverse effect of detrimental flue gas components such as water vapor, SO 2 and NH 3 . The protection effect of CuO over MnO x reserved enough active sites of CuMnTi for Hg 0 oxidation in the presence of NH 3 or SO 2 . Compared with MnO x /TiO 2 (MnTi), the superior redox property, enlarged Hg 0 adsorption capacity and decent SO 2 resistance of CuMnTi ternary system were evidenced to account for its improved catalytic activity. This study indicated future potential for applying CuMnTi catalyst in simultaneous NO reduction and Hg 0 oxidation in low-temperature (150–250 °C) and low-rank (sub-bituminous and lignite) coal combustion flue gases. [ABSTRACT FROM AUTHOR]

The distribution, enrichment, and environmental influence of trace elements and mineral matter in fly ash (FA), bottom ash (BA), and flue gas desulfurization gypsum (FGDG) from a high arsenic coal-fired power plant in Inner Mongolia, China were studied by X-ray diffraction spectrometry (XRD), X-ray fluorescence spectrometry (XRF), field scanning electron microscopy equipped with energy dispersive X-ray spectrometry (FSEM-EDX), atomic fluorescence spectroscopy (AFS), and inductively coupled plasma-mass spectrometry (ICP-MS). The results showed that mineral matter in FA included quartz, mullite, and gypsum, and that in BA included quartz, enstatite, magnetite, and hematite. The arsenic content in the lignites reached 44.4 μg/g, which was much higher than the global average content of lignite. Most of the trace elements in lignite, except for Mo, Sb, and W, had enrichment trends in the fine grade samples. Arsenic is a toxic element enriched in FA compared with the world lignite ash, while there are several elements of environmental concern are depleted elements (Mo, Cd, Ba, and U). The Cs and Hf are also enriched elements in FA, where Hf showed a significant enrichment. The contents of most trace elements in the smaller particles of FA were higher than those in the larger particles, except for Y and Re. The arsenic content in BA was evidently lower than that in FA, which was 24.4 μg/g, and the trace elements enriched in the smaller particles of BA included Li, Zn, Ga, Rb, Mo, Cd, In, Sb, Cs, Nd, Tl, Pb, Bi, and Th. With the exceptions of As, Sr, Cd, and Sb, the amount of trace elements in flue gas desulfurization gypsum was much lower than that in average Chinese soil. Because the fly ash was stacked for a long time, arsenic and several other trace elements leached into soil surrounding the fly ash dump. As a results the elemental content of old fly ash is less than those collected in this study, which indicates the soil in vicinity need to be monitored continuously for their possible environmental effect. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel ball-milling strategy was designed to prepare CuS sorbent for Hg0 capture. • The obtained CuS showed well-structured nanosheets with under-coordinated sulfur. • CuS nanosheet exhibited superior Hg0 removal performance than Nano-CuS. • This facile synthesis logic holds up-scale potential for industrial application. Among various metal sulfides, copper sulfide (CuS) was found to be the most efficient one for the abatement of elemental mercury (Hg0) pollution in coal combustion flue gas because of the enrichment of under-coordinated sulfur along the 〈0 0 1〉 direction. Unlike saturated sulfur, the under-coordinated sulfur exhibits a dual role in oxidizing and immobilizing Hg0, but how to effectively synthesize (0 0 1) surface exposed CuS through a facile method has long been challenging in the Hg0 controlling community. In this work, a feasible synthesis strategy based on mechanical ball-milling procedure was proposed to synthesize (0 0 1) surface exposed CuS under mild conditions. Owing to the controllable nucleus formation and favorable crystalline growth manner under mechanochemical condition, the as-obtained CuS-based sorbent via ball-milling was primarily consisted of well-structured nanosheet containing abundant under-coordinated sulfur ligands, ensuring the adequate exposure of active sites. Consequently, the CuS as obtained exhibited the Hg0 adsorption capacity and uptake rate as high as 86.22 mg g−1 and 112.04 μg g−1 min−1, far surpassing those benchmark metal sulfides as reported in previous studies. Notably, the Hg0 uptake rate of the CuS nanosheet surpasses that of CuS nanoparticle with irregular agglomeration by approximate ten folds. The under-coordinated sulfur, especially polysulfide (S x 2-), was demonstrated to be the primary ligand accounting for the oxidation and sequestration of Hg0 over the surface of CuS nanosheet. This facile synthesis logic with scale-up potential may also be applicable in the preparation of other metal sulfides in addition to CuS, marking an effective attempt stepping towards the industrial application of metal sulfides for Hg0 immobilization from coal combustion flue gas. [ABSTRACT FROM AUTHOR]

[Display omitted] • A one-step facile method was developed to functionalize macroporous skeletons with nanosized mineral sulfides. • The preparation method could homogeneously decorate nanosized mineral sulfides over the macroporous skeleton. • The copper sulfide decorated polyurethane foam showed an excellent performance for elemental mercury capture. • The macroporous sorbent as obtained fits the applicability in a fixed-bed scenario. The critical challenge to achieve cost-effective elemental mercury (Hg0) capture from coal combustion flue gas by using mineral sulfides lies in developing a facile method to realize their fixed-bed application, which hence exhausts the adsorption capacity of mineral sulfides and optimize their economic-sustainability. In this work, a feasible and facile synthesis procedure based on a one-step cetyltrimethylammonium bromide (CTAB) assisted precipitation procedure was proposed to overcome this challenge. During this process, the CTAB played a crucial role to effectively confine the particle size of copper sulfide (CuS) in nanoscale and stably anchor it over the macroporous polyurethane foam (PUF) skeleton. The macropore-enriched CuS/PUF as synthesized was merited for its high throughput morphology, nanoscale particle size of CuS, homogeneous distribution of active components, and multiform surface sulfur ligands, which is promising to be used in a fixed-bed scenario to achieve efficient Hg0 sequestration. These benefits co-derived an excellent Hg0 sorbent with extremely high uptake capacity and adsorption rate (265.6 mg g−1 and 2.16 mg g−1 min−1), exceeding those of other mineral sulfides and traditional activated carbons as reported in previous studies by folds, even by magnitudes. With such an outstanding Hg0 sequestration performance and a macroporous structure, it can be reasonably concluded that the CuS/PUF will be a potential sorbent to be adopted in a fixed-bed scenario, which optimizes the cost-effectiveness of mineral sulfide based sorbents and extend their application flexibility for the Hg0 adsorption from coal combustion flue gas. [ABSTRACT FROM AUTHOR]

• A comprehensive review of mercury abatement by mineral chalcogenides was conducted. • Mercury removal performances of mineral chalcogenides and the primary influence factors were comprehensively summarized. • The involved mechanisms for mercury removal by mineral chalcogenides were discussed. • The restrictions and future perspectives for mercury adsorption by mineral chalcogenide were presented. Mercury contamination has attracted global attentions in the past decades, which posed great threats to the whole ecosystem and human health because of its cumulative hypertoxicity, persistence and migration in the atmosphere. Due to the inferior mercury capture performances and tedious modification procedures of carbon-based sorbents, mineral chalcogenides were regarded as the preferable candidates for gaseous elemental mercury (Hg0) immobilization from industrial flue gas. Mineral chalcogenides exhibit several advantages, such as simple preparation, excellent capture performance, and less secondary pollution in Hg0 adsorption. This review focuses on the latest research advances in Hg0 abatement by mineral chalcogenides. At the beginning, the research status of different typical sorbents for Hg0 removal was overviewed. Then, the performances and application conditions of most mineral chalcogenides for Hg0 removal were introduced in detail. The Hg0 adsorption performance comparison of various mineral chalcogenides was also conducted. Moreover, the influential factors, i.e. reaction temperature, flue gas components, and involved mechanisms for Hg0 removal over different mineral chalcogenides were discussed comprehensively. The objective of this review was to strengthen the comprehension of the developing field and generalize the research directions in the future. [ABSTRACT FROM AUTHOR]

• Amalgam plays an important role in the Hg0 immobilization process by CuS. • Light irradiation excited electron transfer on the Cu-terminated sites of CuS. • Light irradiation inhibited the formation of Cu amalgam and subsequent Hg0 capture. • Light irradiation in ESPs may limit Hg0 removal by mineral sulfide sorbents. An applicable way of mineral sulfide based remediators such as copper sulfide (CuS) for effective abatement of elemental mercury (Hg0) from coal-fired flue gas is to inject them prior to electrostatic precipitators (ESPs), in which light irradiation widely exists because of the corona discharge. A systematical investigation of Hg0 removal by CuS sorbent under light irradiation was conducted for the first time. The results show that light irradiation significantly inhibited the Hg0 removal efficiency of the CuS sorbent. The normalized Hg0 concentration at the reactor outlet even quickly increased from 0 to 0.45 once a lamp was turned on. Light irradiation excited a transfer of electrons on the Cu-terminated sites from inner Cu 3d orbit to outer Cu 4s orbit, and hence inhibited the formation of copper amalgam, which was supposed to be a key step in Hg0 immobilization by the CuS sorbent. Moreover, light irradiation accelerated the decomposition of copper amalgam to Hg0 which re-emitted to the gas flow. With these novel insights into the role of light irradiation concerning Hg0 removal over mineral sulfides, this work can provide guidance for selecting and adopting proper mineral sulfides in real-world coal combustion conditions to replace traditional activated carbons. [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]

• Inactive natural mineral sulfides were functionalized to be highly efficient mercury adsorbents. • Selenizing the natural mineral sulfide decreased the mercury diffusion barrier and hence greatly improve the adsorption rate. • The captured mercury was primarily converted into the most stable mercuric compound, i.e., HgS. • The selenizing method can be used to tailoring different mineral sulfides for abatement of mercury pollution. Directly using earth-abundant natural mineral sulfides (MSs) for elemental mercury (Hg0) removal from coal combustion flue gas remains a challenge because extremely low surface areas of natural MSs largely suppressed their capabilities in Hg0 immobilization. In this work, a new mindset was proposed for the activation of natural MSs by introducing surface selenide (Se2−) ligands to achieve an efficient and rapid Hg0 uptake from coal combustion flue gas. The Se2− loaded pyrrhotite (x Se-FeS) exhibited four folds higher Hg0 uptake rate compared to bare pyrrhotite. The immobilized mercury over the x Se-FeS surface was primarily converted into mercury sulfide (HgS), a mercury species known for its extreme stability when environmentally exposed. The superiority of x Se-FeS was ascribed to that Hg0 bound more weakly with active selenide sites than sulfide sites, and the lower binding energy decreased the diffusion barrier of mercury and improve the reaction rate. The same mindset was proven to be also applicable in tailoring other natural MSs into efficient Hg0 sorbents. From these advantageous perspectives, this work provides a highly promising way for efficiently utilizing naturally enriched MSs as economically feasible and scientifically sound sorbents for Hg0 removal from coal combustion flue gas. [ABSTRACT FROM AUTHOR]

• ·A brand new Fe 3 O 4−x Se y sorbent was purposefully designed for Hg0 immobilization. • ·The Fe 3 O 4−x Se y exhibited excellent Hg0 capture capacity and rate. • ·The Fe 3 O 4−x Se y transferred Hg0 into extremely stable HgSe. • ·A scheme was proposed for the applications and recycling of Fe 3 O 4−x Se y. Abatement of elemental mercury (Hg0) pollution in coal combustion flue gas remains a challenging task especially for the optimal trade-off among effectiveness, environmental-friendliness and cost. In this work, magnetite (Fe 3 O 4) was simply selenized (Fe 3 O 4−x Se y) as an efficient and recyclable sorbent for Hg0 sequestration from coal combustion flue gas. The Fe 3 O 4−x Se y as obtained exhibited an advantageous core-shell like spherical structure, in which the interior Fe 3 O 4 core kept unchanged during the selenization process and warranted the recyclability of Fe 3 O 4−x Se y , while the exterior part exposed to Hg0 was selenized into iron diselenide (FeSe 2) that has high affinity towards Hg0. Moreover, the selenization process introduced more mesopores that were favorable for Hg0 migration and accommodation. Co-benefitted from these perspectives, the Fe 3 O 4−x Se y exhibited a Hg0 adsorption capacity and uptake rate as high as 8.8 mg g−1 and 3.7 μg g−1 min−1, respectively, far exceeding the capacity and rate of bare Fe 3 O 4 and traditional Hg0 remediators. The Hg0 stably immobilized by Fe 3 O 4−x Se y primarily as mercury selenide (HgSe) indicates the Hg-laden Fe 3 O 4−x Se y has negligible mercury re-emission concerns when it is dumped and landfilled. The spent Fe 3 O 4−x Se y can also be effectively retrieved and regenerated for reusing purpose with mercury recovery simultaneously, which could dramatically save the operation costs. Thus, the Fe 3 O 4−x Se y can be expected to be a promising alternative to traditional sorbents for Hg0 sequestration from coal combustion flue gas considering its high efficiency, negligible environmental risk and decent recyclability and reusability. [ABSTRACT FROM AUTHOR]