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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]

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]

Fly ash fine particles emitted from coal-fired power plants are the primary atmospheric pollutant in China. The pressure, temperature, and velocity distribution of the flow field in a chamber was simulated to evaluate chemical agglomeration. The effect on the removal efficiency of composition, concentration, pH, K + content, and zeta potential of the chemical agglomeration solutions as well as surfactant and flue gas temperature were evaluated. The results suggested that suitable solutions could significantly improve the removal efficiency of fine particles. Among these, kappa-carrageenan performed best and achieved a removal efficiency of 47.1%. Synergism was detected as two different chemical agglomeration solutions were mixed together: a mixture of kappa-carrageenan and konjac glucomannan attained a removal efficiency of 59.3%, higher than their individual values. The efficiency improved initially and then decreased as the solution K + concentration increased. Also surfactants affected agglomeration: cationic and non-ionic surfactants enlarged the removal efficiency by 9.0% and 3.7%, respectively, whereas anionic surfactants lessened average removal efficiency by 5.6%. Zeta potential influenced the removal efficiency as well: it peaked as the zeta potential was around 0 mV. [ABSTRACT FROM AUTHOR]

Abstract: Samples of two high-aluminum coals and an associated fly ash were collected from a coal-fired power plant and a coalfield in Inner Mongolia, China. The mineralogy and physicochemical characteristics of low-temperature ash (LTA), high-temperature ash (HTA), and fly ash from those coals were studied by X-ray diffraction (XRD), X-ray fluorescence (XRF), and field scanning electron microscopy with energy dispersive X-ray spectroscopy (FSEM-EDX). The transformation of typical aluminum-bearing minerals at high temperature was investigated by systematic drop tube furnace (DTF) experiments and thermogravimetric analysis. The results show that the aluminum-bearing minerals in the high-Al coal are mainly boehmite and kaolinite. High temperature treatment transforms the aluminum-rich minerals to gamma alumina (γ-Al2O3), corundum (α-Al2O3), and an amorphous phase. γ-Al2O3 is the main mineral in the HTA (17.4wt.%), while α-Al2O3 and mullite are the main minerals in the fly ash. The high-aluminum fly ash particles are irregular and their shapes are related to their compositions. The degree of irregularity of the high-aluminum fly ash particles is proportional to their aluminum content. The phase transformation of boehmite in the coal during high temperature treatment appears to have involved four stages including: boehmite dehydroxylation, transitional θ-Al2O3 formation, crystal nucleation and α-Al2O3 formation, and growth of α-Al2O3 crystals. The DTF experimental results indicated that the growth of α-Al2O3 crystals has a significant impact on PM emissions. Understanding the mineral transformation mechanism is therefore helpful in reducing PM emissions. [Copyright &y& Elsevier]

Abstract: Ash deposition is one of the major problems encountered in coal-fired power plants. To understand its formation mechanism, six samples of the deposit were collected from different positions of boiler in the Zhuzhou coal-fired power plant in Hunan of China. The mineralogical, chemical compositions, and microstructure of ash samples were analyzed by X-ray diffraction spectrometry (XRD), X-ray fluorescence spectrometry (XRF), optical microscopy, and field scanning electron microscopy equipped with energy dispersive X-ray spectrometry (FSEM-EDX). The results show that the deposits were mainly composed of silica amorphous phases and their chemical compositions of different layers significantly varied. The identified minerals include mullite, cristobalite, hematite, quartz, hercynite, and anorthite. The silica-rich glass phases are derived from volatilization–recondensation of SiO and the interaction between aluminosilicates and other minerals. Several types of crystals were identified in the deposits, including iron-oxide crystals, Fe–Ca-bearing phase, Si-rich phase, and aluminosilicate phase. The deposition of crystals as well as the following melting is the main reason for the porosity structure of deposit. The interaction and eutectic of minerals in coal led to the serious deposition in the coal-fired power plant. [Copyright &y& Elsevier]

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]

Gas pressure changes during the process of coal mine gas drainage and CBM recovery. It is of great importance to understand the influence of sorption pressure on gas diffusion; however, the topic remains controversial in past studies. In this study, four samples with different coal ranks were collected and diffusion experiments were conducted under different pressures through the adsorption and desorption processes. Three widely used models, i.e., the unipore diffusion (UD) model, the bidisperse diffusion (BD) model and the dispersive diffusion (DD) model, were adopted to compare the applicability and to calculate the diffusion coefficients. Results show that for all coal ranks, the BD model and DD model can match the experimental results better than the UD model. Concerning the fast diffusion coefficient Dae of the BD model, three samples display a decreasing trend with increasing gas pressure while the other sample shows a V-type trend. The slow diffusion coefficient Die of BD model increases with gas pressure for all samples, while the ratio β is an intrinsic character of coal and remains constant. For the DD model, the characteristic rate parameter kΦ does not change sharply and the stretching parameter α increases with gas pressure. Both Dae and Die are in proportion to kΦ, which reflect the diffusion rate of gas in the coal. The impacts of pore characteristic on gas diffusion were also analyzed. Although pore size distributions and specific surface areas are different in the four coal samples, correlations are not apparent between pore characteristic and diffusion coefficients. [ABSTRACT FROM AUTHOR]

To clarify the pyrolysis mechanism of different nitrogen functionalities in coal during oxy-fuel combustion (OFC), fast pyrolysis tests of four nitrogen models containing the raw proportion of low-temperature ash were performed under a CO 2 -rich atmosphere in a vertical fixed bed at 1100 °C. The oxidation characteristics of nitrogen functionalities in the investigated coal during fast CO 2 -rich pyrolysis were further studied by comparing CO 2 -rich atmosphere with argon atmosphere. Results show that during conventional pyrolysis pyridinic nitrogen tends to be oxidized to pyridine N-oxide by oxygen functionalities in coal, afterwards high-temperature pyrolysis of the latter may lead to more NO 2 emissions. During CO 2 -rich pyrolysis quaternary nitrogen has a good potential to be oxidized to pyridonic nitrogen by oxidizing species in atmosphere, and further decomposition of the latter could generate NH 3 so as to suppress NO 2 formation. The yield of fuel-N to NO 2 corresponding to CO 2 -rich pyrolysis decreased by roughly three times than that of conventional pyrolysis. The oxidation effect of CO 2 on pyrolysis behaviors of nitrogen functionalities in coal is supposed to be another key factor of low NO x emissions during the OFC process regardless of the reduction effect of CO induced by elevated CO 2 level. [ABSTRACT FROM AUTHOR]

Photocatalytic oxidation is an attractive method for Hg-rich flue gas treatment. In the present study, a novel cerium-based TiO 2 nanofibers was prepared and selected as the catalyst to remove mercury in flue gas. Accordingly, physical/chemical properties of those nanofibers were clarified. The effects of some important parameters, such as calcination temperature, cerium dopant content and different illumination conditions on the removal of Hg 0 using the photocatalysis process were investigated. In addition, the removal mechanism of Hg 0 over cerium-based TiO 2 nanofibers focused on UV irradiation was proposed. The results show that catalyst which was calcined at 400 °C exhibited better performance. The addition of 0.3 wt% Ce into TiO 2 led to the highest removal efficiency at 91% under UV irradiation. As-prepared samples showed promising stability for long-term use in the test. However, the photoluminescence intensity of nanofibers incorporating ceria was significantly lower than TiO 2 , which was attributed to better photoelectron-hole separation. Although UV and O 2 are essential factors, the enhancement of Hg 0 removal is more obviously related to the participation of catalyst. The coexistence of Ce 3+ and Ce 4+ , which leads to the efficient oxidation of Hg 0 , was detected on samples. Hg 2+ is the final product in the reaction of Hg 0 removal. As a consequence, the emissions of Hg 0 from flue gas can be significantly suppressed. These indicate that combining photocatalysis technology with cerium-based TiO 2 nanofibers is a promising strategy for reducing Hg 0 efficiently. [ABSTRACT FROM AUTHOR]

[Display omitted] • Organic polymer can remove SO 3 based on sulfonation reaction. • A 1:1 mass ratio of SO 3 to organic polymers achieves about 90% SO 3 removal. • The SO 3 removal by organic polymers is not interfered by SO 2. • Organic polymer can still achieve a removal rate of about 90% for different SO 3 concentrations coal-fired flue gas. The unconventional pollutant SO 3 generated during coal combustion poses significant risks to equipment and the atmosphere. Currently, alkaline adsorbents are widely studied for SO 3 removal but suffer from high alkali consumption and cost due to the presence of other acidic gases. A new method using organic polymers (XTG) based on sulfonation reactions for SO 3 selective removal is proposed. Experimental investigations were carried out to study the effectiveness of XTG in removing SO 3 at temperatures ranging from 200 to 400˚C. At lower temperatures (200-250˚C), a mass ratio of approximately 3:1 of SO 3 to XTG achieved around 90 % SO 3 removal efficiency. At higher temperatures (250-400˚C), a mass ratio of 3:2 was required to achieve a similar removal efficiency. It was determined that XTG exhibited selective removal of SO 3 and did not react with SO 2. XTG has a low sensitivity to the concentration of SO 3 , as it achieved a removal efficiency of approximately 87 % at 50 mg/m3. The presence of sulfonic acid groups in the reaction products confirmed the occurrence of sulfonation reactions. As an electrophilic reagent, SO 3 tended to attack regions of XTG with high electron density, leading to sulfonation reactions and the formation of sulfonic acid groups along the XTG main chain, ultimately facilitating SO 3 removal. [ABSTRACT FROM AUTHOR]

• The heavy minerals in coal were investigated by the low temperature ashing and the gravity separation experiments. • Chlorite is the most common mineral in the heavy mineral fraction of the high-silicon coals. • It can be generated a considerable proportion of PM 1 particles during the high-silicon coal combustion. • Smaller particles contain a higher content of quartz in the high-silicon fly ash. To understand the mineralogical characteristics and transformation behaviours of silicon-bearing minerals during coal combustion, seven typical high silicon (high-Si) coals and two high-Si fly ashes generated from high-Si coal-fired power plants were chosen. The coals were first treated by a method of low temperature ashing and the float-sink test for heavy minerals separation. Subsequently, low temperature ashes (LTA), light mineral fractions (LM), heavy mineral fractions (HM), and fly ashes from coal-fired power plants were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) combined with energy spectrum analysis (EDX), X-ray fluorescence spectrometry (XRF), and simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC).The results show that The mineral compositions in the LTA and LM are almost the same and majorly composed of quartz, kaolinite, calcite, dolomite, daphnite, chlorite-serpentine, pyrite, and anatase. The mineral compositions identified in the HM are clearly different from those in the LTA and LM. Pyrite, fluorapatite, anatase, siderite, dolomite and a plenty of silicate minerals including quartz, clinochlore, daphnite, chlorite, and chamosite are found in the HM. Chlorite is a quite common mineral in the HM with different shapes, including schistose, long tetragonal prism, cylindrical, block-shaped, and near-spherical, can be identified. The minerals identified in the fly ashes from the high-Si coal-fired power plants include quartz, mullite, and hematite. The mullite in the fly ashes is derived from the transformations of quartz, kaolinite, and chlorite in the coals. The quartz in the fly ash is mainly derived from the unchanged quartz in coal and a secondary origin from the SiO 2 -Al 2 O 3 phase transformation. The high-Si fly ash with the size fraction of 38.5–74 μm contains the highest SiO 2 content. [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]

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]

Fly ash fine particles emitted from flue gas during coal combustion are the primary atmospheric pollutants in China. The purpose of this study was to investigate the characteristics of the zeta potential of fine particle suspensions. The relationship between the zeta potential and the fine particle removal efficiency was also discussed. Batch experiments were conducted to evaluate the zeta potential of fine particle aqueous solutions under various pH, ion concentration, surfactant, polymer, and chemical agglomeration solution conditions. A chemical agglomeration system was designed to simulate the removal process of the fine particles. The test results indicated that the zeta potential absolute value of the solution decreased initially and then increased as the pH increased. As the pH increased from 4 to 12, the zeta potential decreased from Zp  = 9.4 mV to Zp  = −45.4 mV. The isoelectric point (IEP) was 4.3. Also at the IEP, the highest fine particle removal efficiency of 25.9% was achieved. The zeta potential increased as the metal cation concentration of the solutions increased. The trivalent cation Al 3+ exhibited the best performance, which increased Zp from −32.1 mV to −11.2 mV and produced the highest fine particle removal efficiency of 9.2%. Polymers significantly impacted the zeta potential. As the concentration of kappa-carrageenan (CAR) increased from 0.01% to 5%, the zeta potential increased from −30.1 mV to 12.6 mV. The highest fine particle removal efficiency of 41.8% was acquired at a concentration of 0.5%, which had the lowest zeta potential absolute value of 3.5 mV. It can be inferred that the increase in the zeta potential induced the growth of the energy barrier, which prevented particle agglomeration. The suspension with a lower zeta potential exhibited a better fine particle removal efficiency. [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]

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]

Wet flue gas desulfurization (WFGD) systems have several benefits, including SO 2 removal and Hg pollution control. However, the absorbed ionic mercury may be transformed into insoluble elemental mercury because of the chemical interaction with the aqueous scrubbing solution, which causes mercury re-emission and reduces the mercury capture efficiency of the scrubber. This study investigates the effects of operating temperatures, pH, and O 2 and SO 4 2 − concentrations on the reduction of Hg 2 + in the presence of SO 3 2 − in a simulated desulfurization aqueous solution. The results indicate that excess SO 3 2 − inhibits Hg 2 + reduction due to the formation of the stable Hg(SO 3 ) 2 2 − complex, whereas a low SO 3 2 − concentration (< 2 mM) leads to enhanced mercury re-emission due to the formation of more redox-unstable HgSO 3 . The Hg 0 release increases from 18.6% to 59.6% when the operating temperature increases from 45 °C to 55 °C. A pH decrease in the slurry from 5 to 3 causes a significant increase in the Hg 0 emission from 6.9 to 127.9 μg/m 3 in a simulated desulfurization slurry. In addition, O 2 caused a secondary emission of Hg 0 by damaging the stable redox complexes of Hg 2 + and SO 3 2 − . In the presence of oxygen, the Hg 0 emission decreases; subsequently, a HgSO 3 SO 4 2 − complex is formed. Sulfate (HgSO 4 and HgSO 3 SO 4 2 − ) inhibit the emission of Hg 0 . [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]

• The combustion tests of Zhundong coals after washing and adding kaolinite are studied. • The effects of kaolinite additives on sodium release and PM formation are conducted. • The mechanism of different types of sodium release and PM formation is revealed. Zhundong coal causes serious slagging problems and particle matter (PM) pollution due to its high sodium content. In this paper, sodium release and PM formation experiments were carried out in tube and laboratory dropper furnaces using three types of coal in Zhundong. The effects of kaolinite additives on sodium release and PM formation, as well as the mechanism of different types of sodium release and PM formation, were investigated. The results showed that compared with water-soluble sodium, most organic sodium was released after a series of complex complexation reactions, such that kaolinite exhibited a better adsorption effect on water-soluble sodium. Furthermore, the concentration of different types of Na in PM emitted differed as a result of different coals, which would lead to different collision frequencies between particles and kaolinite. The PM 2.5 stemmed from the homogeneous condensation of volatile elements and the fragmentation of minerals in the combustion, while the PM 10 originated from the coalescence of the fine fragments of fly ash. Moreover, the kaolinite additive intensified the heterogeneous condensation reaction with gaseous sodium to form larger particles, due to the reaction effect of kaolinite for water-soluble sodium of PM 2.5 being stronger than organic sodium and the organic sodium of PM 10 being stronger than water-soluble sodium. [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]

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]

• 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]

Highlights: [•] A kinetic model was developed to describe Hg0 oxidation over CeO2/TiO2 catalysts. [•] Without SO2, CeO2 exhibited excellent performance in catalyzing Hg0 oxidation by chlorine. [•] SO2 inhibited reactions between Hg0 and chlorine species over pure CeO2. [•] Combining CeO2 with TiO2 enhanced its resistance to SO2. [•] Important kinetic data were obtained through the comparisons of theoretical model with experimental results. [ABSTRACT FROM AUTHOR]

Abstract: MnO x -CeO2 mixed-oxide supported on TiO2 (Mn-Ce/Ti) was synthesized by an ultrasound-assisted impregnation method and employed to oxidize elemental mercury (Hg0) at 200°C in simulated coal combustion flue gas. Over 90% of Hg0 oxidation was achieved on the Mn-Ce/Ti catalyst at 200°C under simulated flue gas representing those from burning low-rank coals with a high gas hourly space velocity of 60,000h−1. Gas-phase O2 regenerated the lattice oxygen and replenished the chemisorbed oxygen, which facilitated Hg0 oxidation. HCl was the most effective flue gas component responsible for Hg0 oxidation. 10ppm HCl plus 4% O2 resulted in 100% Hg0 oxidation under the experimental conditions. SO2 competed with Hg0 for active sites, thus deactivating the catalyst''s capability in oxidizing Hg0. NO covered the active sites and consumed surface oxygen active for Hg0 oxidation, hence limiting Hg0 oxidation. Water vapor showed prohibitive effect on Hg0 oxidation due to its competition with HCl and Hg0 for active adsorption sites. This study provides information about the promotional or inhibitory effects of individual flue gas components on Hg0 oxidation over a highly effective Mn-Ce/Ti catalyst. Such knowledge is of fundamental importance for industrial applications of the Mn-Ce/Ti catalyst in coal-fired power plants. [Copyright &y& Elsevier]

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: TiO2 supported Mn-Ce mixed oxides (Mn-Ce/Ti) synthesized by an ultrasound-assisted impregnation method were employed to oxidize elemental mercury (Hg0) at low temperatures in simulated low-rank (sub-bituminous and lignite) coal combustion flue gas and corresponding selective catalytic reduction (SCR) flue gas. The catalysts were characterized by BET surface area analysis, X-ray diffraction (XRD) measurement and X-ray photoelectron spectroscopy (XPS) analysis. The combination of MnO x and CeO2 resulted in significant synergy for Hg0 oxidation. The Mn-Ce/Ti catalyst was highly active for Hg0 oxidation at low temperatures (150–250°C) under both simulated flue gas and SCR flue gas. The dominance of Mn4+ and the presence of Ce3+ on the Mn-Ce/Ti catalyst were responsible for its excellent catalytic performance. Hg0 oxidation on the Mn-Ce/Ti catalyst likely followed the Langmuir–Hinshelwood mechanism, where reactive species on catalyst surface react with adjacently adsorbed Hg0 to form Hg2+. NH3 consumed the surface oxygen and limited the adsorption of Hg0, hence inhibiting Hg0 oxidation over Mn-Ce/Ti catalyst. However, once NH3 was cut off, the inhibited mercury oxidation activity could be completely recovered in the presence of O2. This study revealed the possibility of simultaneously oxidizing Hg0 and reducing NO x at low flue gas temperatures. Such knowledge is of fundamental importance in developing effective and economical mercury and NO x control technologies for coal-fired power plants. [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]

[Display omitted] • The organic or inorganic affinities of trace elements are speculated and determined. • The proportions of trace elements going into fly ash are positively correlated with their volatility. • Volatilization of trace elements during laboratory combustion has been divided into three stages. Partitioning behavior of 17 deleterious trace elements in Ge-rich coals during coal combustion was studied in a bench-scale combustion apparatus in a laboratory and in full-scale combustion in a coal-fired power plant. Methods used in this study include spectrophotometry, tube furnace combustion, inductively coupled plasma mass spectrometry (ICP-MS), and statistical evaluation. A comparison of the results obtained at these two scales and of the factors affecting their volatilization behavior during combustion are discussed. These seventeen trace elements tend to be volatilized more completely during combustion in coal-fired power plant than in a laboratory-scale combustion environment due to the differences in operating conditions. The average proportions of elements going into fly ash from feed coals during combustion are positively correlated with the trace element volatilities. Volatilization behavior of trace elements in laboratory-scale combustion involves three stages: initial release (<500 ℃), relative stability (500–1,000 ℃), and secondary release or stability (>1,000 ℃). The seventeen trace elements can be classified into four groups according to their behavior during the above-mentioned stages. Factors affecting behavior of elements in combustion, such as combustion conditions, modes of occurrence, concentrations, and geochemical affinities, are discussed. A new insight into the behavior of potentially deleterious trace elements during combustion is given, which provides further guidance to controlling their emissions. [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]

• High temperature can increase the Si-bearing compounds vaporization and fine particle emission. • Si-bearing compounds vaporization is much higher in the reducing atmosphere than the oxidizing atmosphere. • There is a peak content of SiO 2 in PM 10 , which is in the range of 60–80%. • PM 0.1 formation is influenced by the vaporization-coagulation of SiO 2 and secondary Si-bearing compounds. Pure silica, typical high-silicon coals (Xuanwei area, China) and their low temperature ashes (LTA) were selected to carry out a vaporization experiment in different atmospheres to reveal the release mechanism of silicon. Further, high-silicon coal combustion experiments were conducted using a drop tube furnace (DTF) to investigate the formation behaviors of fine particulate matter (PM) and the distribution of silicon in the different-sized particles. Field emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectroscopy (EDX) and X-ray fluorescence spectrometry (XRF) were used to study the morphology and chemical compositions, respectively. The results show that the high temperature would promote Si-bearing compounds vaporization and fine particle emission. The SiO 2 vaporization rate in the reducing atmosphere (steam and CO 2) is much higher than that in the oxidizing atmosphere (air and CO 2 /O 2). Higher O 2 concentrations in CO 2 /O 2 atmospheres will handicap Si-bearing compounds vaporization; the SiO 2 vaporization rate of Yantang coal decreased from 4.7% to 3.9% as the O 2 concentration increased from 10% to 30% at 1400 °C. A maximum value of the PM 1.0 concentration can be observed at 0.1 μm, and there is a peak content of SiO 2 in PM 10 , which is in the range of 60–80% for different temperatures. The mechanism of PM 0.1 formation is related to the vaporization-coagulation of the refractory SiO 2 and secondary Si-bearing compounds, and the more Si that vaporizes at high temperatures, the more PM 0.1 that is generated during coal combustion. [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]