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In this article, pyrolyzed bio-chars derived from a kind of macroalgae, sargassum, were modified by ammonium chloride (NH4Cl) impregnation, and were applied to remove Hg0 from flue gas. The characteristics of sorbents were investigated by the Brunauer–Emmett–Teller, X-ray photoelectron spectroscopy, scanning electron microscopy and ultimate and proximate analysis. The key parameters (e.g. loading value, reaction temperature and concentration of O2, NO, SO2 and water vapor), kinetics analysis and reaction mechanism of Hg0 removal were investigated. The results show that increasing loading value, reaction temperature, O2 concentration and NO concentration enhance Hg0 removal. The increase in SO2 concentration or water vapor concentration has a dual effect on Hg0 removal. The C–Cl groups and C=O groups play an important role in the process of Hg0 removal. The Hg0 removal process of modified samples meets the pseudo-second-order kinetic model. [ABSTRACT FROM AUTHOR]

Abstract Elemental mercury (Hg0) is predominant constituent of flue gas emitted from coal-fired power plants. Adsorption has been considered the best available technology for removal of Hg0 from flue gas. However, adsorbent injection increases the amount of ash generated. In the present study, powdered activated carbon (PAC) was coated on polytetrafluoroethylene/glass fiber filters to increase Hg0 removal while concurrently reducing the amount of ash generated. The optimal PAC coating rate was determined in laboratory experiments to ensure better Hg0 removal with low pressure drop. When PAC of particle size less than 45 μm was used, and the areal density was 50 g/m2, the pressure drop remained under 30 Pa while the Hg0 removal efficiency increased to 15.8% from 4.3%. The Hg0 removal efficiency also increased with decrease in filtration velocity. The optimal PAC coating rate was applied on a hybrid filter (HF), which was combined with a bag filter and an electrostatic precipitator in a single chamber. Originally designed to remove fine particulates matter, it was retrofitted to the flue gas control device for simultaneous Hg0 removal. By employing the PAC coating, the Hg removal efficiency of the HF increased to 79.79% from 66.35%. Also, a temporary reduction in Hg removal was seen but this was resolved following a cleaning cycle in which the dust layer was removed. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Hierarchical Ag-SiO 2 @Fe 3 O 4 magnetic composites were selected for elemental mercury (Hg0) removal from non-ferrous metal smelting flue gas in this study. Results showed that the hierarchical Ag-SiO 2 @Fe 3 O 4 magnetic composites had favorable Hg0 removal ability at low temperature. Moreover, the adsorption capacity of hierarchical magnetic composite is much larger than that of pure Fe 3 O 4 and SiO 2 @Fe 3 O 4. The Hg0 removal efficiency reached the highest value as approximately 92% under the reaction temperature of 150°C, while the removal efficiency sharply reduced in the absence of O 2. The characterization results indicated that Ag nanoparticles grew on the surface of SiO 2 @Fe 3 O 4 support. The large surface area of SiO 2 supplied efficient reaction room for Hg and Ag atoms. Ag–Hg amalgam is generated on the surface of the composites. In addition, this magnetic material could be easily separated from fly ashes when adopted for treating real flue gas, and the spent materials could be regenerated using a simple thermal-desorption method. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Cobalt sulfide sorbent was synthesized for the mercury removal from nonferrous metal smelting flue gas. • The mercury adsorption capacity of sorbent was about 43.03 mg/g with 50% breakthrough threshold. • SO 2 had negligible impact on mercury adsorption of sorbents. • Adsorbed mercury by sorbent could be recycled easily through heating treatment. • The used sorbent could be regenerated and reutilized. Abstract In order to remove and recycle elemental mercury from nonferrous smelting flue gas, cobalt sulfide sorbents were synthesized and tested. The mercury adsorption capacity of sorbent at 100 °C was 43.03 mg/g with 50% breakthrough threshold. The influences of the flue gas components and reaction temperature on the mercury adsorption capacity were investigated, respectively. The results shown that SO 2 , H 2 O, NO and O 2 had negligible impact on mercury adsorption of sorbents. Transmission electron microscopy (TEM), X-ray diffractometer (XRD), mercury programmed desorption (Hg-TPD) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the sorbents. The mercury desorption activation energy from the sorbent was calculated based on a model built by the mercury temperature-programmed desorption data. Additionally, the used cobalt sulfide sorbent was regenerated. The results showed that the cobalt sulfide sorbent could maintain good adsorption performance after regeneration during several cycling tests. Therefore, cobalt sulfide is a suitable sorbent for the mercury removal and recycling from nonferrous metal smelting flue gas. [ABSTRACT FROM AUTHOR]

Highlights • O 2 and SO 2 were co-doped on porous carbon surface by non-thermal plasma. • O 2 /SO 2 co-doped PC exhibits far greater Hg0 adsorption capacity than Br-AC. • Hg0 adsorption mechanism was clarified by experimental data and DFT calculation. Abstract A porous carbon was synthesized via hydrothermal carbonization and CO 2 activation. O 2 and SO 2 were successfully co-doped onto carbon surface by applying non-thermal plasma technique. Porous carbon possessing excellent textural properties is effective to adsorb the radicals generated by plasma. Plasma promotes the adsorption of O 2 and SO 2 on carbon surface with the formation of abundant C O, C–S and C–SO x (x = 1–3) groups. The O 2 /SO 2 dual-doped porous carbon was utilized to adsorb elemental mercury (Hg0) from the flue gas of coal combustion. The Hg0 adsorption ability of the O 2 /SO 2 dual-doped porous carbon is closely related with the concentrations of O 2 and SO 2 for plasma treatment and the treatment time. The optimal O 2 /SO 2 dual-doped porous carbon exhibited far greater Hg0 adsorption capacity than a commercial brominated activated carbon. Density functional theory was employed to understand the Hg0 adsorption mechanism at the molecular level. C O, C–S and C–SO x (x = 1–3) groups enhanced the interaction of Hg0 with surface carbon atom. The activity of them for enhancing Hg0 adsorption is in the order of C–SO 2 > C O > C–S > C–SO > C–SO 3. Porous carbon can be activated by plasma in flue gas containing O 2 and SO 2 , and used as superior sorbent for Hg0 removal. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Hg0 removal efficiency of TiO 2 nanorods-supported MnO x -FeO x -CrO x was evaluated. • Unique dispersion of MnO x , FeO x , and CrO x on TiO 2 resulted in higher Hg0 removal efficiency (∼83%). • O 2 and NO promoted Hg0 oxidation while NH 3 had an inhibitive effect. • Increased Mn4+ and surface adsorbed oxygen (O B) helped for superior performance of MnO x -FeO x -CrO x /TiO 2. Abstract TiO 2 nanorods-supported MnO x , FeO x , CrO x , and MnO x -FeO x -CrO x catalysts have been prepared by a deposition-precipitation method, with the aim of investigating the combination of ternary metal oxides effect on elemental mercury (Hg0) removal. The TiO 2 nanorods-supported MnO x -FeO x -CrO x catalyst manifested the superior Hg0 removal efficiency (∼80-83%) at low temperatures (100–200 °C) in the presence of O 2. The addition of NO promoted the Hg0 removal efficiency under the same reaction conditions. Further, SEM, HRTEM, XRD, BET surface area, and XPS characterization were carried out to explore the physicochemical properties of the catalysts. It was found that the integration of three active metal oxides contributed to the enrichment of active sites and the surface adsorbed oxygen species, thereby improving the catalytic activity. Additionally, both the large surface area and high crystallization of the obtained TiO 2 nanorods resulted in uniform dispersion of the manganese-iron-chromium mixed metal oxide nanoparticles and a high activity. Further, XPS data of spent MnO x -FeO x -CrO x /TiO 2 catalyst indicated that the presence of Mn4+, Cr6+, and Fe3+ could promote Hg0 oxidation due to the strong synergistic interaction between the TiO 2 nanorods-incorporated MnO x , FeO x , and CrO x nanoparticles. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Magnetic Fe-Cl/biochars are synthesized via a simple one-step pyrolysis procedure. • The pore structure and surface functional groups are improved under Fe catalysis. • Fe-Cl/biochars exhibit far better Hg0 removal performance compared to Cl/biochars. • T7Fe5 is superior in adsorption capacity/rate to a commercial activated carbon. • Fe 3 O 4 , C Cl and C O groups serve as active sites for Hg0 removal. Abstract Chlorinated biochars (Cl/biochars) prepared by co-pyrolysis of biomass and polyvinyl chloride (PVC) waste were demonstrated as cost-effective sorbents for elemental mercury (Hg0) removal in our previous study. But the decrease in specific surface area of Cl/biochars caused by PVC melting inhibits the further increase of Hg0 removal performance. Moreover, the difficulty in separating the used Cl/biochars from fly ash restricts the utilization of fly ash as a cement additive. To solve these problems, magnetic chlorinated biochars (Fe-Cl/biochars) are synthesized through one-step pyrolysis of Fe(NO 3) 3 -laden wood/PVC mixtures in this study. The sample characterization showed that magnetic Fe 3 O 4 was introduced into the Fe-Cl/biochars. Besides the magnetism, both increased specific surface area and more C O groups were obtained under Fe catalysis. The Fe-Cl/biochars showed far better Hg0 removal performance compared to the Cl/biochars over a broad reaction temperature range (25–220 °C). O 2 , HCl and NO promoted Hg0 removal whereas SO 2 had little effect on Hg0 removal H 2 O slightly suppressed Hg0 removal. Compared to the commercial activated carbon manufactured specifically for Hg0 removal, Fe-Cl/biochars was superior in both Hg0 adsorption capacity and adsorption rate at 140 °C. The mechanism of Hg0 removal over Fe-Cl/biochars was chemisorption reaction, where Fe 3 O 4 , C Cl and C O provided active sites for Hg0 removal. [ABSTRACT FROM AUTHOR]

Abstract Ag nano-particles (NPs) with high dispersion possess the capacity for elemental mercury (Hg0) removal in low temperature. To further enhance its thermo-stability and electron transfer ability, Ag-Fe 3 O 4 @rGO ternary magnetic composite was synthesized for gaseous Hg0 capture. Results indicated that such composite has a Hg0 removal performance with higher than 92% removal efficiency at 100 °C. The ternary composite has a higher Hg0 removal performance than that of pure rGO and Fe 3 O 4 @rGO. The physical-chemical characterization results indicated that Ag nano-particles in-situ grow on the surface of Fe 3 O 4 @rGO support. The large surface area of rGO supply efficient reaction room for Hg and Ag atoms. Ag-Hg amalgam is ascribed to the mercury uptake mechanism. The spent materials can be regenerated by a simple thermal-desorption method. In addition, this magnetic material provide an opportunity that can be separated from fly ashes when used in real flue gas. [ABSTRACT FROM AUTHOR]

Highlights • The corn cob activated carbons was prepared by chemical activation using ZnCl 2. • The prepared sorbent was applied to remove Hg0 in flue gas with high efficiency. • ZnCl 2 played a key role in mercury removal process. Abstract It is a big challenge to effectively remove elemental mercury (Hg0) from coal fired flue gas with affordable adsorbents. To explore new adsorbents with low cost and high capacity for mercury removal is urgently demanded. On the other hand, it will be a good way to reduce the environmental burden by beneficially utilizing agricultural waste. In this study, one kind of agricultural waste, corn cob, was beneficially used for Hg0 control. The corn cob activated carbon (CCAC) with large surface area was prepared by chemical activation using ZnCl 2 and was employed to remove elemental mercury (Hg0) from simulated flue gas (SFG) for the first time. The results demonstrated that the corn cob activated carbon performed high mercury removal efficiency up to 91.4% at 150 °C. The effects of activator, reaction temperature and main flue gas components were studied. Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX) were used to characterize the physicochemical properties of the adsorbents. The possible mechanism of mercury removal was discussed based on XPS analysis and characterization. The results indicated that ZnCl 2 could not only activate microporous structures of carbon but also played an important role for removal of elemental mercury. The produced AC can be used as an effective adsorbent with low cost for mercury pollution control in flue gas. [ABSTRACT FROM AUTHOR]

Highlights • Porous carbon-supported CuCl 2 was synthesized to remove Hg0 from syngas. • CuCl 2 -PC exhibited superior Hg0 adsorption ability at 200 °C. • Effects of syngas components on Hg0 adsorption were clarified. • XPS analyses were applied to identify the Hg0 adsorption mechanism. Abstract A series of sorbents based on biomass-derived porous carbon-supported CuCl 2 (CuCl 2 -PC) were synthesized and employed for elemental mercury (Hg0) removal from the syngas. The CuCl 2 -PC sorbent with a Cu mass content of 5.6 wt% exhibited superior Hg0 adsorption ability (98.5%) at 200 °C. The meso-/micropores structure of porous carbon is favorable for the well-dispersing of CuCl 2 in the inner pores with the formations of abundant Cu and Cl active sites, and beneficial for Hg0 fast transfer among pores, thereby enhancing the effective collision of Hg0 with active sites. Hg-Cu compound and mercury chlorides could be formed by the reactions of Hg0 with Cu and Cl species. The effects of syngas components on Hg0 adsorption ability of sorbent were investigated. HCl improved Hg0 adsorption by increasing the Cl concentration on sorbent surface. CO, H 2 S and H 2 O did not exhibit notable effects on Hg0 adsorption. Although H 2 could not affect the surface chemistry of sorbent, it could occupy the inner pores of sorbent, thereby making the interactions of Hg0 with active sites difficult. The amount of Cu2+ on sorbent surface decreased after Hg0 adsorption, indicating that the oxidation state of copper changed from Cu2+ to Cu+ under syngas atmosphere. [ABSTRACT FROM AUTHOR]

This study focused on the occurrence of mercury in coal and the effectiveness of mercury and ash removal by an air dense medium fluidized bed (ADMFB). Results of the study revealed that there was a linear correlation between the mercury content, ash content and density of coal. This was attributed to the fact that mercury mainly exists in high density minerals containing elements with a certain affinity for mercury such as silicon, aluminum, iron, titanium, potassium, sodium, chloride, zinc, and magnesium. There is therefore a good correlation between the separation efficiency of ADMFB and the quality of the clean coal, as well as the overall removal of mercury. By optimizing the operating conditions based on the fitting models, clean coal with a mercury content of 0.0841 ppm and a separation efficiency exceeding 99.8% was obtained. The desirability of the separation effect optimized by fitting models was 0.999. Based on these results, it was concluded that ADMFB is an effective way to remove mercury from coal and reduce its ash content. [ABSTRACT FROM AUTHOR]

Highlights • Novel Mn-Ce@rGO binary metal oxides was synthesized for Hg0 removal. • Mn-Ce@rGO composite had an excellent Hg0 removal performance at a wide temperature window. • CeO 2 enhanced the oxygen capture performance of the composite. Abstract Graphene was used for the enhancement of gaseous elemental mercury (Hg0) catalytic oxidation and adsorption over Mn-based oxides. A series of graphene modified Mn-based and Ce-Mn-based oxides were prepared via a hydrothermal method. Experimental results indicated that Mn-Ce@rGO composite has a Hg0 removal efficiency of 91% at 250 °C which was higher than that or pure MnOx and MnOx@rGO under the same reaction conditions. Hg0 removal efficiency decreased in the absence of O 2. The higher SO 2 concentration and space velocity resulted in lower Hg0 removal efficiencies. The mechanism study indicated that high valances of Mn4+ and Mn3+ benefit the Hg0 oxidation and the surface oxygen participated in the Hg0 oxidation process. CeO 2 supplies sufficient oxygen for mercury surface adsorption. During these processes, graphene-enhanced the catalytic oxidation and adsorption processes through supporting more reaction space, facilitating electron transfer and binding sites. Moreover, the spent materials can be regenerated using a simple thermal-desorption method. Mn-Ce@rGO composite was proved to be a prospective adsorbent for Hg0 removal from coal-fired flue gas. [ABSTRACT FROM AUTHOR]

Desulfurization wastewater evaporation technology is used to enhance the removal of gaseous mercury (Hg) in conventional air pollution control devices (APCDs) for coal-fired power plants. Studies have affirmed that gaseous Hg is oxidized and removed by selective catalytic reduction (SCR), an electrostatic precipitator (ESP) and wet flue gas desulfurization (WFGD) in a coal-fired thermal experiment platform with WFGD wastewater evaporation. Effects of desulfurization wastewater evaporation position, evaporation temperature and chlorine ion concentration on Hg oxidation were studied as well. The Hg0 oxidation efficiency was increased ranging from 30% to 60%, and the gaseous Hg removal efficiency was 62.16% in APCDs when wastewater evaporated before SCR. However, the Hg0 oxidation efficiency was 18.99% and the gaseous Hg removal efficiency was 40.19% in APCDs when wastewater evaporated before ESP. The results show that WFGD wastewater evaporation before SCR is beneficial to improve the efficiency of Hg oxidized and removed in APCDs. Because Hg2+ can be easily removed in ACPDs and WFGD wastewater in power plants is enriched with chlorine ions, this method realizes WFGD wastewater zero discharge and simultaneously enhances Hg removal in APCDs. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • ZnO is simultaneously laden on activated carbon during the ZnCl 2 -activation. • Physisorption is not significant and only accounts for about 7% in 130 °C. • Mercury adsorption by ZnO and carbonyl accounts for more than 70%. • ZnO catalyses the Hg0 into HgS with the presence of H 2 S. • The C O group of carbonyl acts as an oxidation site. Abstract In this work, activated carbon with ZnO laden on the surface was prepared by ZnCl 2 -one-step activation of different types of biomass (corn straw, bamboo powder and sawdust) and employed for mercury removal in the coal gas. During the activation, a part of ZnCl 2 is converted into ZnO and laden on activated carbon, which greatly promotes the mercury removal performance with the presence of H 2 S. The ZnO content varies greatly with the content of SiO 2 in the biomass due to its inactivation of ZnO and formation of Zn 2 SiO 4. Carbonyl, which is important to mercury removal is largely retained after the activation at 500 °C and the amount of carbonyl seems to be positively correlated with the specific surface area (related to the lignin content). The temperature programmed desorption method was applied to further analyse the mercury adsorption in the coal gas. The results showed that ZnO and carbonyl play an important role in mercury removal, while the physisorption is not significant and only accounts for approximately 7% at 130 °C. The mechanism study showed that ZnO serves as a catalytic active site and catalyses the Hg0 into HgS with the presence of H 2 S. While the C O group of carbonyl acts as adsorption sites and turns into C O after the adsorption. This study provided a promising preparation method of mercury sorbents in the coal gas, and the influence of surface functional groups was also investigated in detail. [ABSTRACT FROM AUTHOR]

Several novel oxidation removal processes of elemental mercury (Hg0) from flue gas using combined Fe2+/Mn2+ and heat activated peroxymonosulfate (PMS)/H2O2 solutions in a bubbling reactor were proposed. The operating parameters (e.g., PMS/H2O2 concentration, Fe2+/Mn2+ concentration, solution pH, activation temperature, and Hg0/NO/SO2/O2/CO2 concentration), mechanism and mass transfer‐reaction kinetics of Hg0 removal were investigated. The results show that heat and Fe2+/Mn2+ have significant synergistic effect for activating PMS and PMS/H2O2 to produce free radicals to oxidize Hg0. Hg0 removal is strongly affected by PMS/H2O2 concentration, Fe2+/Mn2+ concentration, activation temperature, and solution pH. SO4−· and ·OH produced from combined heat and Fe2+/Mn2+ activated PMS/H2O2 play a leading role in Hg0 removal. Under optimized experimental conditions, Hg0 removal efficiencies reach 100, 94.9, 66.9, and 58.9% in heat/Fe2+/PMS/H2O2, heat/Mn2+/PMS/H2O2, heat/Fe2+/PMS, and heat/Mn2+/PMS systems, respectively. Hg0 removal processes in four systems belong to fast reaction and were controlled by mass transfer under optimized experimental conditions. © 2018 American Institute of Chemical Engineers AIChE J, 65: 161–174, 2019 [ABSTRACT FROM AUTHOR]

A novel method using one-step pyrolysis of waste biomass and brominated flame retarded (BFR) plastic was proposed to prepare brominated biochars (Br-biochars) for elemental mercury (Hg 0 ) removal from coal-fired flue gas. This method could simultaneously realize the disposal of municipal solid waste and the preparation of mercury sorbents. The sample characterization showed that an interaction effect between BFR plastic and biomass occurred during the co-pyrolysis process. The addition of BFR plastic would deteriorate the pore structure of sorbents because the melted plastic residues were aggregated on their surface. But Br emitted from BFR plastic was fixed into the co-pyrolyzed chars in the form of Br – and C–Br group. Br-biochars exhibited far better Hg 0 removal performance compared to virgin biochar. The optimum pyrolysis temperature and plastic/biomass mass ratio were 600 °C and 1:1, respectively. The effects of gas hourly space velocity, adsorption temperature and individual flue gas on Hg 0 removal performance were also explored. The Hg 0 adsorption capacity of Br-sorbents was close to those of commercial activated carbons. Both the experimental data and kinetic model showed that the Hg 0 adsorption over Br-biochars was mainly controlled by chemisorption, where C–Br bonds were the active sites for oxidizing Hg 0 into HgBr 2 . This was confirmed using mercury temperature programmed desorption experiments. [ABSTRACT FROM AUTHOR]

Mercury is an important pollutant emitted from coal-fired power plants. Elemental mercury (Hg 0 ) is harder to be removed than oxidized mercury (Hg 2+ ) and particulate bound mercury (Hg p ) in the flue gas at back-end of furnace. In this study, a method based on computational intelligence was proposed to enhance Hg 0 removal efficiency. It was realized by improving the transformation efficiency of Hg 0 into Hg 2+ and Hg p and then removing them by air pollution control devices. First, relationships between Hg 0 concentrations at the stack and variables like open values of secondary air, open values of over fire air, oxygen at the exit of economizer, load, coal qualities and so on were modeled with aid of tuned PCA-support vector machine. Then, manipulated variables and regulated variables were optimized by particle swarm optimization algorithm to enhance transformation efficiency of Hg 0 . A field thermal adjustment test was carried out on some 600 MW unit and the proposed method was applied to that unit and compared with ACO. Results showed that removal efficiencies were enhanced greatly in general. The increment of removal efficiency can reach up to 14.71%. Besides, optimal strategies can be found in few iterations, making it suitable for online applications. [ABSTRACT FROM AUTHOR]

To avoid the dangerous operational conditions, shorten the preparation time, and improve the adsorption performance of amino-functionalized nanomagnetic materials with a core-shell structure, a magnetic nanocomposite of CoFe2O4@SiO2 was successfully functionalized with amino group (-NH2) through a mild and facile hydrothermal method without the use of any toxic or harmful solvents at a relatively low temperature. The preparation time of the key steps of amino functionalization was shortened from 30 h to about 10 h. The core-shell structure and successful grafting were confirmed by various means. The amino-functionalized CoFe2O4@SiO2 was used for the removal mercury (Hg(II)), a heavy metal, and exhibited excellent magnetic properties and a high Langmuir adsorption capacity of 149.3 mg Hg(II)/g. The adsorption of Hg(II) onto CoFe2O4@SiO2-NH2 followed the pseudo-second-order kinetic equation and Langmuir model. The thermodynamic data showed that the Hg(II) adsorption process was achieved through spontaneous exothermic and monolayer adsorption with electrostatic adsorption and chemisorption. In addition, the as-prepared CoFe2O4@SiO2-NH2 nanoparticles had a good reusable value, good application performance and stability, and can provide a mild and facile way to remove heavy metals from aqueous solution. [ABSTRACT FROM AUTHOR]

The mercury emission from coal-fired flue gas has drawn lots of attention worldwide. To achieve more efficient catalytic oxidation of Hg 0 in both high and low temperature, the RuO 2 modified Ce-Zr solid solution catalysts were prepared and evaluated at various conditions. It was found the polyvinylpyrrolidone (PVP) promoted RuO 2 /Ce 0.6 Zr 0.4 O 2 catalyst displayed higher significant catalytic activity for Hg 0 oxidation. The mechanism of Hg 0 oxidation over RuO 2 /Ce 0.6 Zr 0.4 O 2 (PVP) was studied through various techniques, and Hg 0 oxidation approaches were found to consist of two steps: chemisorption process and regeneration process. The adsorbed Hg 0 was first oxidized with surface chemisorbed oxygen species to form HgO, which could desorb from the surface of catalysts by itself in absence of HCl. Also, the HgO could reacts with Cl − in catalyst or adsorbed HCl to form HgCl 2 , which could desorb into gas phase more readily. O 2 is indispensable for the chemisorption process. And the doping RuO 2 might have a synergistic effect with supporter, which could facilitate chemisorption process. Furthermore, SeO 2 poisoning of catalyst was investigated for the first time and found the existence of SeO 2 could slightly inhibit Hg 0 chemical adsorption process on the surface of the catalyst, while the regeneration process did not significantly affect. [ABSTRACT FROM AUTHOR]

Highlights • Efficient removal of Hg from Mt. Amiata ground waters by microencapsulated TOMAC. • Hg removal close to 100 and 99% can be achieved for pH = 1 and natural, respectively. • A novel mathematical model considering the mercury speciation in natural waters. • Ion exchange equilibrium constants independent on pH and chloride concentration. • Up to 48.84 m3 of a water with 8.36 μg L−1 of Hg can be treated per kg of MC-TOMAC. Abstract An innovative approach to remove mercury from Hg-rich ground-waters of the Abbadia San Salvatore Hg-mining area (Italy) using microcapsules containing trioctyl-methyl-ammonium-chloride (MC-TOMAC) is presented. Waters from three selected locations with mercury concentrations between 1.43 and 256.8 μg L−1 were studied. MC-TOMAC demonstrated high selectivity for mercury, being able to remove it entirely from ground waters in presence of relatively high concentrations of another anions in only one contact step. Besides, MC-TOMAC were able to satisfactorily remove the total mercury from ground waters when the mass ratio of mercury to MC-TOMAC was lower than 0.102 mgHg gMC-TOMAC−1 at pH 1, while up to 99.0 ± 2.0% of mercury was removed at natural pH. The relationship between the liquid and solid that can be treated in one contact step and a countercurrent contact in order to agree with the Council Directive 98/83/EC were stablished for one of the studied ground waters (S2). Additionally, a mathematical model based on the ideal mass action law in the solid phase and considering the metal speciation and their equilibriums in the liquid phase depending on the pH and chloride concentration was developed. Experimental extraction results were successfully fitted with the model, obtaining a value of the two unknown parameters, K { IE 1 } and K { IE 2 } , of 13622.5 and 2269.9 kg L−1; which represent the ion exchange equilibrium constants for the mercury uptake by MC-TOMAC for the species HgCl 3 - and HgCl 4 2 - , respectively. Besides, this model allowed to simulate the solid-liquid equilibrium curves at different pH values and chloride concentrations, indicating the suitable conditions to achieve the process. [ABSTRACT FROM AUTHOR]

Two kinds of bio-chars derived from seaweed, such as sargassum and enteromorpha, are modified by halides impregnation. The modified bio-chars are used to capture Hg 0 from simulated flue gas. The physical and chemical properties of the samples are investigated by various characterization technologies, including proximate and ultimate analysis, Brunauer-Emmett-Teller (BET), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The effects of different types of halides impregnation, halide loading values, individual flue gas component and adsorption temperature on removal of Hg 0 over adsorbents were studied. The mechanism and kinetics of Hg 0 removal were also studied. The results show that potassium iodide modified bio-chars have better Hg 0 adsorption performance than bio-chars modified by potassium chloride and potassium bromide. The optimal potassium iodide loading value is 3 wt%. As the reaction temperature increases, Hg 0 removal efficiency significantly increases. O 2 promotes the Hg 0 removal. Addition of SO 2 inhibits Hg 0 removal over enteromorpha-chars, and shows a double impact on Hg 0 removal over sargassum-chars. Low concentrations of NO and H 2 O are beneficial to Hg 0 removal, whereas high concentrations of NO and H 2 O inhibit Hg 0 removal. Chemisorption is found to be the main control factor for Hg 0 adsorption at 120 °C and 160 °C based on kinetic simulation analysis. The covalent groups (C-I) and the chemisorbed oxygen and/or weakly bonded oxygen species participate in the Hg 0 removal process and are the dominant chemical adsorption sites on the suface of the iodide modified seaweed bio-chars. [ABSTRACT FROM AUTHOR]

The zirconium metal-organic framework material UiO-66 was doped with Ag nanoparticles and investigated for the removal of elemental mercury (Hg 0 ) in flue gas. Physical and chemical characterization of the adsorbents showed that adding Ag did not change the crystal structure and morphology of the UiO-66. Ag doping can improve the redox activity of UiO-66, and the adsorbent exhibited high thermal stability and surface area. Hg 0 removal experiments indicated that UiO-66 exhibited the higher performance compared with P25 and activated carbon, and the addition of Ag exhibited a significant synergistic effect with the UiO-66, which had highest Hg 0 adsorption capacity (3.7 mg/g) at 50 °C. Furthermore, the Hg 0 removal mechanism was investigated, revealing that Hg 0 is removed by the formation of an Ag amalgam and channel adsorption at low temperature, and through Ag-activated oxygen oxidation and channel capture at high temperature. [ABSTRACT FROM AUTHOR]

The effect of CoO x addition on the performance and structure of V 2 O 5 /ZrO 2 –CeO 2 catalyst for simultaneous removal of NO and Hg 0 in simulated flue gas was investigated by various methods including SEM, BET, XRD, XPS, H 2 –TPR and FT–IR. It was found that the introduction of CoO x not only greatly enhanced the redox properties of catalysts, but also increased the catalytic performance for simultaneous removal of NO and Hg 0 . The CoO x –modified V 2 O 5 /ZrO 2 –CeO 2 catalyst displayed excellent catalytic activity for NO conversion (89.6%) and Hg 0 oxidation (88.9%) at 250 °C under SCR atmosphere. The synergistic effect among vanadium, cobalt, and the ZrCe support could induce oxygen vacancies formation and promote oxygen mobility via charge transfer. Besides, CoO x could assist vanadium species in rapidly changing the valence by the redox cycle of V 5+ + Co 2+ ↔ V 4+ + Co 3+ . All the above features contribute to the excellent catalytic performance through CoO x addition. [ABSTRACT FROM AUTHOR]

CeO 2 modified V 2 O 5 /AC catalysts (V-Ce/AC) were synthesized by an ultrasound-assisted impregnation method, and were employed to remove elemental mercury (Hg 0 ) from simulated coal combustion flue gas at low temperature (100–200 °C). The effects of several operation conditions, including the loading of CeO 2 , reaction temperature, the role of O 2 and stability of the catalysts were all investigated, respectively. The results showed that 1 V-8Ce/AC catalysts had the highest catalytic activity with 98.3% Hg 0 removal efficiency at 150 °C. There was synergistic effect on Hg 0 oxidation when V 2 O 5 and CeO 2 combined. Characterization by XPS, we found that both lattice oxygen (O α ) and chemisorption oxygen (O β ) contribute to Hg 0 oxidation. Besides, the possible mechanism of Hg 0 removal over the catalysts was proposed, in which the critical steps were the adsorption of Hg 0 and the oxidation of Hg 0 to Hg 2+ by the active oxygen on catalysts surface. [ABSTRACT FROM AUTHOR]

Cu-BTC, as one of the metal organic frameworks (MOFs), was prepared and employed for the capture of elemental mercury (Hg 0 ) in sintering gas. The material was characterized using TGA, XPS, XRD, BET surface measurement and TEM. Results showed that Cu-BTC had good microscopic morphologies, large BET surface area and high thermal stability, which make it suitable for sintering gas. The Hg 0 removal performance was investigated under different conditions. Cu-BTC had limited Hg 0 removal ability without HCl, but exhibited an excellent Hg 0 removal efficiency when 15 ppm HCl was added. HCl and O 2 played an important role for the Hg 0 removal efficiency when they were at low concentration. According to the results of Hg 0 removal performance and physiochemical characterization, the mechanism of Hg 0 capture was speculated with and without HCl. Furthermore, the influence of SO 2 , NO and H 2 O were studied. SO 2 has inhibition effect on the removal of Hg 0 , while NO can promote the Hg 0 removal. As for H 2 O, it has nearly no effect on mercury removal. When HCl and O 2 were at high concentration, the influence of SO 2 , NO and H 2 O are not significant. [ABSTRACT FROM AUTHOR]

To increase elemental mercury removal efficiency of CuO without HCl gas, the Mn-modified CuO samples were proposed. In this work, four doping ratios of Mn to CuO were fabricated by a hydrothermal synthesis method. The surface morphologies, crystalline structures and chemical states of as-prepared sorbents were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), respectively. The results showed that all the Mn-modified samples contained the CuMnO 2 phase with different contents. The Hg 0 removal experimental results indicated that the Mn-modified CuO sorbents had the higher elemental mercury removal efficiency than pure CuO. The pseudo-first-order kinetic model fitted well to the adsorption experimental data. The CuMnO 2 content in sorbents had a positive effect on mercury capture. We speculated that CuMnO 2 acted as a dominant factor for the mercury removal capacity of Mn-modified CuO sorbents. The high valance Mn oxidized the elemental mercury to oxidized mercury. Moreover, CuO can re-oxidize the low valance Mn to the high valance, resulting in the further increase in Hg 0 removal efficiency. [ABSTRACT FROM AUTHOR]

To remove elemental mercury (Hg 0 ) in chlorine-free coal combustion flue gas efficiently, CuCl 2 loaded CeO 2 -ZrO 2 sorbents (denoted as CC/CZ) were developed. In this way, the abundant Cl and affluent active chemical adsorbed oxygen (O∗) on the surface of the sorbent would be combined and made full use for Hg 0 removal. XRD, XPS, SEM, Raman, TG, and N 2 adsorption/desorption were employed to characterize the sorbents. Hg 0 removal behaviors over CC/CZ were studied using a lab-scale fixed-bed reactor. The sorbent with optimal loading 6% CuCl 2 exhibited superior and stable performances (89.6–97.1%) within a much wider applicable temperature range (100–300 °C) in the absence of HCl. The results also indicated that 6%CC/CZ exhibit very good performance at lower temperature (100–200 °C). The interaction between Cl and chemical adsorbed oxygen was observed and probably responsible for its superior Hg 0 removal performance. XPS results of the fresh, thermal-treated, and spent 6% CuCl 2 /CZ may explain the Hg 0 oxidation process. Hg 0 was mainly oxidized by the generated active chlorine species and the main reaction product was HgCl 2 . The active chlorine species were formed due to the interaction between chlorine and chemical adsorbed oxygen species. [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]

Ocean contains huge biomass resources. Actively developing marine biomass resources has great significance to human development. In this work, a kind of seaweed, sargassum, is used to prepare chars by pyrolysis. The sargassum chars are modified by NH 4 Br reagents using a simple impregnation method, and are applied to capture Hg 0 from flue gas. The physicochemical properties of the samples are investigated using scanning electron microscopy (SEM), proximate and ultimate analysis, X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET), respectively. The effects of pyrolysis temperature, reaction temperatures, loading values and the components of flue gas such as O 2 , water vapor, NO and SO 2 on mercury removal efficiency are studied. Mercury removal mechanism, kinetics and thermodynamics are also investigated. The results show that increasing pyrolysis temperature, reaction temperature, loading value, O 2 concentration and NO concentration enhances mercury removal. Low concentrations of SO 2 and H 2 O are beneficial to mercury removal, and high concentrations of SO 2 and H 2 O inhibit mercury removal. C-Br and C=O covalent groups are the major chemisorption sites for Hg 0 removal. Finally, the kinetic and thermodynamic parameters of mercury removal are also obtained. [ABSTRACT FROM AUTHOR]

Utilization of impregnated carbons (silver/sulfur/iodide) for mercury removal is common, however with limitations in adsorption capacity and application. Continued efforts to develop porous sorbents with better mercury adsorption capacity and kinetics are evident from open literature with the recent focus being on metal sulfide based impregnated porous carbons. However reports on application of metal sulfide based porous carbon adsorbents for gas phase mercury removal are not available in open literature. Towards this objective, the present work attempts to synthesis three different metal sulfide based porous carbons identified as C/CuS, C/ZnS and C/FeS utilizing ultrasound induced wet impregnation method. The adsorbents were subjected to characterization utilizing BET, XRD, FTIR and SEM and were tested for its mercury adsorption capacity. The adsorption capacity of the metal sulfide porous carbons increased nearly three to four fold times with increase in adsorption temperature from 50 to 100 C attributed to the predominance of the chemisorption. Among the three metal sulfide based porous carbons C/CuS was found to exhibit highest adsorption capacity of 23 mg/g at 100 ° C. [ABSTRACT FROM AUTHOR]

Removal of gas-phase mercury is vital in gas processing industries. Herein, we report the preparation of porous sulphur copolymers for capturing elemental mercury (Hg(0)) in the gas phase. Porous sulphur copolymers were prepared using porogen and an inverse-vulcanisation technique. Sulphur powder was mixed with a water-soluble porogen (NaCl) and cross-linked with divinyl benzene (DVB) at 165 °C, and the porous structure was later obtained by dissolving the porogen in water. The porosity of the copolymer was controlled by varying the amount of salt and cross-linker. The effect of pore volume and temperature on the adsorption of mercury from gas phase has been estimated. Samples with larger pore volumes showed a significant increase in adsorption capacity, reaching approximately 151 µg/g at 60 °C. High sulphur content and the porous structure enhanced the adsorption capacity. Furthermore, the thermal conductivities of the porous copolymers were studied at a range temperature. Copolymers with relatively high cross-link densities showed the very low thermal conductivity of approximately 0.048 W/m K at 25 °C, which is much lower than that of pristine sulphur. Abundant availability of sulphur and a simple method of preparation could make porous sulphur copolymers potential candidates for mercury capture and thermal insulation. [ABSTRACT FROM AUTHOR]

Mercury is a toxic heavy metal that, once emitted or released, persists in the environment and circulates between air, water, sediments, soil and living creatures. Therefore, international governments and other authorities are taking measures to control mercury emissions from various sources. Despite many efforts, mercury remains a problematic pollutant in coal-fired installations in regards to differentiation of existing forms and their behavior in flue gas stream and purification units. Scientists try to understand its behavior in the flue gas and to capture it in one place, employing processes of adsorption, absorption, membranes or different catalysis. At the same time, researchers are also developing efficient and economically feasible technologies for mercury control. One such technology involves the capture of mercury in flue gases via gas-cleaning units through co-benefit application. Examples include, for instance, carbon injection in ESP, catalytic conversion in SCR unit, and absorption in a wet desulfurization scrubber. This paper outlines a mercury capture method developed in American and Polish laboratories and will present the pilot-scale research with emphasize on the mercury behavior in the slurry with and without any added reagents. [ABSTRACT FROM AUTHOR]

This study was devoted to the valorization of a plant waste (olive stones): that is widely available in Mediterranean countries in order to remove mercury from natural gas. The raw material from olive stones was prepared by pyrolysis, chemical activation with phosphoric acid, and physical activation under steam. Two olive stone-based granular activated carbons were prepared: one with the virgin stones, while the other was impregnated with sulphur. After treatment, the adsorbents obtained were characterized by determining the iodine number, the methylene blue index, and by estimating the porous properties by N2 adsorption at 77 K. Thermogravimetric analysis and infrared spectroscopy analysis were carried out to determine the functional groups before and after mercury adsorption. An experimental study of vapour-phase mercury adsorption by the activated carbons (virgin and sulphur-impregnated) and a comparison with a commercial material (HGR) were performed. The comparison, made by analyzing the adsorption in a continuous mode, showed that the proportion of sulphur and the porosity were important for the removal of mercury. In the conditions used, the mercury adsorption on the ACs studied follows a physisorption mechanism. The results showed that granular activated carbon-based olive stones (sulphur-impregnated) are very efficient to remove mercury (with 2864 μg/g) and also less expensive than commercial activated carbon due to their local availability. [ABSTRACT FROM AUTHOR]

A series of experiments were conducted in a bubble column reactor to investigate the effects of key influencing factors such as the diperiodatoargentate (III) concentration, the reaction temperature, the solution pH, O2 concentration, SO2 concentration and NO concentration on the Hg0 removal. The results indicated that the average removal efficiency of 77.5 % was reached under the optimal conditions in which the DPA concentration was 1.03mmol/L, the reaction temperature was 40 °C and the solution pH was 8.5; SO2 inhibited Hg0 oxidation due to its competition for the limited oxidant; when NO was in a low concentration, it was found to be a promotion for Hg0 oxidation. The spent solution was analyzed by the CVAFS, The results illustrated that Hg0 was oxidized into Hg2+ by DPA then DPA was converted into Ag+, from which, the reaction mechanism was speculated accordingly. [ABSTRACT FROM AUTHOR]

TiO 2 nanotube (TNT) photocatalysts were synthesized through a facile one-step hydrothermal method using Degussa P-25 as precursor. The resulting TNTs were subsequently washed with deionized water and 0.1–1.0 M HCl to possess a variety of physicochemical properties. Anatase was the major crystalline phase for the resulting TNTs. The Brunauer-Emmett-Teller surface area of TNTs was 307–392 m 2 g −1 . Hydroxyl groups and oxygen vacancies were shown to be generated on the surface of all TNTs. Photocatalytic activity of TNTs for Congo red and crystal violet dye decomposition was strongly determined by their pre-adsorption abilities, which are greatly affected by solution pH. Hg 0 removal by the TNTs was enhanced with increased HCl concentration and the presence of O 2 in the test environment; however, the presence of water vapor reduced the Hg 0 capture due to competitive adsorption of H 2 O. The Cl functionality formed on the surface of TNTs due to HCl treatment appeared to act as one of the adsorption sites and enhance Hg 0 removal, as well as helping in against the competition from water molecules. Nevertheless, the unwashed HCl residues also obstructed other active sites on TNT surface, such as oxygenated groups that also play important role in Hg 0 oxidation and adsorption. [ABSTRACT FROM AUTHOR]

The environmental implications of mercury do not correspond only to the emissions to the atmosphere; the quality of the captured CO 2 to be transported and sequestered has been subject of research, concerning trace quantities of heavy metals participating in mineralization and precipitation reactions in sequestration conditions. For oxycoal combustion, mercury is not an environmental issue alone but also an operational issue, particularly about where mercury could accumulate within the CO 2 processing unit. Therefore, Hg removal is necessary to prevent its attack on the aluminium heat exchangers. In this work, a regenerable sorbent based on carbon supported Au nanoparticles (0.1%wt) has been used for Hg capture under oxycoal combustion atmosphere. The influence of the presence of O 2 , NO, SO 2 and HCl in a gas containing Hg and CO 2 on the sorbent as well as on the Hg oxidation (Au can act as an oxidation catalyst) has been evaluated under a simulated flue gas. The presence of either NO or HCl in the simulated flue gas led to mercury oxidation, with oxidized mercury not evolving in the gas, indicating that it is retained on the sorbent; the oxidized mercury is well stabilized on Au surfaces of the sorbent and favours the Hg-Au amalgam formation. This sorbent has been also evaluated in 3 kWth oxycoal bubbling fluidized bed combustor. A lignite with high sulphur content was burned in presence of limestone. Despite high SO 2 concentration that reached the Au/C sorbent, high capture efficiency was achieved and breakthrough occurred after 3.5 h and 10% breakthrough is not reached during the experiments. Bearing in mind that regeneration time can be adjusted near 1 h, two swing sorbent beds could be used to control mercury emissions under oxycoal combustion conditions. [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 present study reports on the development of a method using ultrasound-assisted extraction (UAE) during the purification of taurine from Porphyra yezoensis . The Box–Behnken design, which is a widely used form of response surface methodology, was used to investigate the effects of parameters on the UAE process. Three independent variables of taurine purification using UAE were studied including: extraction time, temperature, and ultrasonic power. The results showed that the highest taurine yield of 13.0 mg/g was obtained with an extraction time of 38.3 min, the use of 300.0 W ultrasonic power, and an extraction temperature of 40.5 °C. A comparative study of taurine extraction was also conducted using either ultrasonication or mechanical agitation. The results indicated that the ultrasonic process required 9 times less time at 40 °C to obtain taurine with a similar yield as compared to the conventional extraction method. Therefore, UAE can used as an alternative to the conventional extraction method used during the recovery of taurine from P. yezoensis . The UAE method has several advantages, including that it uses lower extraction temperatures and has a shorter extraction time. The taurine present in the extract supernatant was efficiently separated and purified using a combination of 732 cation exchange chromatography and crystallization. The yield of purified taurine using this process was 1.1%. The structure of the purified taurine was confirmed by FTIR, MS, and NMR. Our findings suggest that P. yezoensis can be used as a taurine-rich food or food material. [ABSTRACT FROM AUTHOR]

Highlights: [•] The proposed model for Hg fixation involves adsorption, diffusion and chemical reaction. [•] Experimental data are obtained for low concentration in the gaseous stream. [•] Chemical fixation of mercury inside the solid matrix leads to an increase of mercury removal capacity. [•] Chemical fixation minimizes the risks of mercury re-emission to environment. [Copyright &y& Elsevier]

Abstract: Current approaches for mercury removal have been focusing on injection of powdered activated carbon sorbents into the flue gas stream. In particular, brominated activated carbon has been proven at pilot scale and plant trials to be effective at removing mercury from flue gases of coal-fired power plants. However, activated carbon is a costly source material. Using an industrial solid waste from biomass combustion as an alternative source material to produce sorbents for mercury emission control is an attractive option. This paper describes a novel chemical–mechanical bromination process for production of mercury sorbent from a biomass combustion ash, which is normally considered a solid waste. The chemical–mechanical brominated ash was characterized and tested for mercury capture and release at high temperatures. The brominated biomass ash was found to effectively capture mercury up to 390°C in lab scale tests. The tests of the new brominated sorbent in a 375MW coal fired power plant showed promising performance. [Copyright &y& Elsevier]

Elemental mercury in flue gases from coal combustion is difficult to control. However, oxidized mercury species are soluble in water and can be removed with a high degree of efficiency in wet flue gas desulphurization (WFGD) systems operating in coal combustion plants, provided that no re-emissions occur. In this article the mechanisms affecting the re-emission of oxidized mercury species in WFGD conditions via sulphite ions are discussed. The parameters studied include the operating temperature, the pH, the redox potential, the concentrations of mercury and oxygen in the flue gas and the concentration of reductive ions in the solution. The results show that temperature, pH and the concentration of mercury at the inlet of the WFGD systems are the most important factors affecting oxidized mercury removal. The results indicate that sulphite ions, not only contribute to the reduction of Hg2+, but that they may also stabilize the mercury in the liquid fraction of the WFGD limestone slurry. Consequently, factors that increase the sulphite content in the slurry such as a low oxygen concentration promote the co-capture of mercury with sulphur. [Copyright &y& Elsevier]

Abstract: The combined removals of Hg0 and NO over zeolite (HZSM-5 was chosen to use) modified by copper (Cu/HZSM-5) catalysts were studied under different simulated flue gas conditions. Compared with HZSM-5, Cu/HZSM-5 showed higher activity and performed a synergetic effect for the Hg0 and NO removal at 250°C. But the excess of copper could cause destruction of the thin pore walls and blocking of internal porosity of the catalyst leading to decrease of the activity. A comparison between Cu/HZSM-5 of different silica to alumina ratios (SiO2/Al2O3 ratio) was also performed. The highest NO and Hg0 conversions were observed over the lowest SiO2/Al2O3 ratio. In addition, the experimental results indicated that there was a synergetic effect between HZSM-5 and copper for the removal of NO and Hg0 by accelerating the intermediate formation (NO2) and by strengthening the adsorption NO and Hg0 on the catalyst surface under the reaction conditions. Moreover, the effects of individual flue gas components on the removals of Hg0 and NO were examined. O2 in the flue gas had a positive effect on both Hg0 and NO removals. However, the presence of H2O and SO2 inhibited both Hg0 and NO removals. [Copyright &y& Elsevier]

Non-ferrous metal smelting takes up a large proportion of the anthropogenic mercury emission inventory in China. Zinc, lead and copper smelting are three leading sources. Onsite measurements of mercury emissions were conducted for six smelters. The mercury emission factors were 0.09–2.98 g Hg/t metal produced. Acid plants with the double-conversion double-absorption process had mercury removal efficiency of over 99%. In the flue gas after acid plants, 45–88% was oxidized mercury which can be easily scavenged in the flue gas scrubber. 70–97% of the mercury was removed from the flue gas to the waste water and 1–17% to the sulfuric acid product. Totally 0.3–13.5% of the mercury in the metal concentrate was emitted to the atmosphere. Therefore, acid plants in non-ferrous metal smelters have significant co-benefit on mercury removal, and the mercury emission factors from Chinese non-ferrous metal smelters were probably overestimated in previous studies. [Copyright &y& Elsevier]

Abstract: To develop cost-effective sorbent for gas-phase elemental mercury removal, the bamboo charcoal (BC) produced from renewable bamboo and KI modified BC (BC-I) were used for elemental mercury removal. The effect of NO, SO2 on gas-phase Hg0 adsorption by KI modified BC was evaluated on a fixed bed reactor using an online mercury analyzer. BET surface area analysis, temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) were used to determine the pore structure and surface chemistry of the sorbents. The results show that KI impregnation reduced the sorbents’ BET surface area and total pore volume compared with that of the original BC. But the BC-I has excellent adsorption capacity for elemental mercury at a relatively higher temperature of 140°C and 180°C. The presence of NO or SO2 could inhibit Hg0 capture, but BC-I has strong anti-poisoning ability. The specific reaction mechanism has been further analyzed. [Copyright &y& Elsevier]

Abstract: Gas-phase elemental mercury (Hg0) removal by activated coke impregnated with cerium chloride (AICC) was studied under simulated flue gas conditions. Brunauer–Emmett–Teller (BET), X-ray diffractogram (XRD), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX) and X-ray photoelectron spectroscopy (XPS) analyses were used to characterize the samples. The effects of CeCl3 loading values, reaction temperatures and individual flue gas components including O2, NO, SO2 and H2O (g) on Hg0 removal efficiency of AICC samples were investigated. Results showed that Hg0 removal efficiency of AC was significantly enhanced by CeCl3. The optimal CeCl3 loading value and reaction temperature was around 6% and 170°C, respectively. Additionally, the experiment results of effects of flue gas components on Hg0 removal efficiencies showed that when O2 was present in the flue gas, NO and SO2 were observed to promote Hg0 oxidation. However, in the absence of O2, SO2 showed an insignificant inhibition on Hg0 removal. Furthermore, when H2O was added into the flue gas, the Hg0 removal capacity had a slight declination. The analyses of XRD and XPS showed that Ce x O y and C–Cl were generated on the surface of AICC and those active elements had remarkably positive effects on the Hg0 removal. The reaction mechanism indicated that Hg0 oxidation was achieved through two pathways: one was that Hg0 bond with CeO2 and was converted by the catalytic oxidation of valence variable cerium; the other was that Hg0 reacted with C–Cl on the sample and was oxidized favored by chloride presence. And according to Hg 4f XPS analysis, the mercury on the surface of AICC was mainly in the form of mercuric oxide (HgO) and mercuric chloride (HgCl2). [Copyright &y& Elsevier]

Abstract: Mercury is a pollutant of concern and mercury emissions from cement plants are under environmental regulation. After coal-fired power plants, mercury emissions from cement and mineral production are the second largest anthropogenic sources. Compared to fuels, cement raw materials are the major sources of mercury in the cement kiln flue gas. Cement plants are quite different from power plants and waste incinerators regarding the flue gas composition, temperature, residence time, and material circulation. Cement kiln systems have some inherent ability to retain mercury in the solid materials due to the adsorption of mercury on the solids in the cold zone. However, recirculation of the kiln dust to the kiln will cause release of the captured mercury. The mercury chemistry in cement kiln systems is complicated and knowledge obtained from power plants and incinerators cannot be directly applied in cement kilns. Among the mercury control technologies, sorbent injection upstream of a particulate control device has shown the most promise. Due to material recirculation, and high moisture level in the cement kiln flue gas the application of sorbent injection to cement plants will be more challenging. The sorbent injection system should be installed downstream of the main kiln filter and upstream of a new added polishing fabric filter to avoid the cement kiln dust recycling and disposal issues. To reduce the sorbent cost and possible disposal expense, non-carbon based sorbents that could be added to cement or regenerated in-situ are desired and should be developed. Various mathematical models have been developed to simulate mercury removal in fixed-bed reactors and by sorbent injection upstream of a fabric filter. The fabric filter adsorption models use the adsorption isotherms coupled with diffusion in the sorbent particle and the parameters are obtained by fitting the model to experimental data. Verification of the models by full-scale or pilot-scale data is very limited. [Copyright &y& Elsevier]

Abstract: The wet FGD system is widely recognized as the co-effective removal system for oxidized Hg vapor species and SO2. In this study, a purpose-built device was designed for this experiment and several factors potentially affecting the Hg0 removal efficiency were systematic investigated, including different types of oxidants, pHs and concentrations of potassium permanganate, reaction temperatures, Hg0 inlet concentrations, O2, SO2 and NO concentrations, and different types of absorption solutions. Results indicate that pHs and KMnO4 concentrations, reaction temperatures, SO2 and NO concentrations all have a strong influence on the removal of Hg0, and the inlet concentrations of Hg0 and O2 contribute little to the removal of Hg0. SO2 could significantly inhibit the removal of Hg0, the negative effect is serious especially at lower SO2 concentration, and SO2 could lead to the re-emission of Hg0. Hg0 could be removed effectively by using CaCO3 +KMnO4 solution, when the KMnO4 concentration in the CaCO3 +KMnO4 solution was 1.5mmol/L, the removal efficiencies of SO2, NO and Hg0 were 100%, 40.69% and 90.58%, respectively. So, considering the application to the practical engineering, adding 1.5–2mmol/L KMnO4 into limestone–gypsum flue gas desulfurization systems is necessary. This technology is a promising method for the simultaneous removal of NO, SO2 and Hg0. [Copyright &y& Elsevier]

This work addresses the discrepancy in the literature regarding the effects of sulfuric acid (H2SO4) on elemental Hg uptake by activated carbon (AC). H2SO4 in AC substantially increased Hg uptake by absorption particularly in the presence of oxygen. Hg uptake increased with acid amount and temperature exceeding 500 mg-Hg/g-AC after 3 days at 200 °C with AC treated with 20% H2SO4. In the absence of other strong oxidizers, oxygen was able to oxidize Hg. Upon oxidation, Hg was more readily soluble in the acid, greatly enhancing its uptake by acid-treated AC. Without O2, S(VI) in H2SO4 was able to oxidize Hg, thus making it soluble in H2SO4. Consequently, the presence of a bulk H2SO4 phase within AC pores resulted in an orders of magnitude increase in Hg uptake capacity. However, the bulk H2SO4 phase lowered the AC pore volume and could block the access to the active surface sites and potentially hinder Hg uptake kinetics. AC treated with SO2 at 700 °C exhibited a much faster rate of Hg uptake attributed to sulfur functional groups enhancing adsorption kinetics. SO2-treated carbon maintained its fast uptake kinetics even after impregnation by 20% H2SO4. [ABSTRACT FROM AUTHOR]

Calcium-based scrubbers designed to absorb HCl and SO2 from flue gases can also remove oxidized mercury. Dissolved mercury halides may have an appreciable partial vapor pressure. Chemical reduction of the dissolved mercury may increase the Hg emission, thereby limiting the coremoval of mercury in the wet scrubbing process. In this paper we evaluate the effects of the pH level, different gypsum qualities, and iron in flue gas desulfurization (FGD) scrubber suspensions. The impact of these parameters on mercury vapor pressure was studied under controlled laboratory conditions in model scrubber suspensions. A major influence is exerted by pH values above 7, considerably amplifying the mercury concentration in the vapor phase above the FGD scrubber suspension. Gypsum also increases the mercury re-emission. Fe(III) decreases and Fe(II) increases the vapor pressure significantly. The consequences of the findings for a reliable coremoval of mercury in FGD scrubbers are discussed. It is shown that there is an increased risk of poor mercury capture in lime-based FGD scrubbers in comparison to limestone FGD scrubbers. [ABSTRACT FROM AUTHOR]