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Coal-fired power plants represent the largest source of mercury emissions worldwide. Using fly ash, a byproduct of these plants, as a sorbent to remove mercury has proven to be difficult. Here, we found that the fresh surface of modified fly ash has good adsorption performance, and it declines obviously with time because of unsaturation characteristics on surface. On the basis of this mechanism, our study provides a method to in situ capture mercury with high surface energy modified fly ash by mechanochemical and bromide treatment. Fresh modified fly ash with active sites is injected into the flue to directly adsorb mercury. A continuous system within a full-scale 300 MWe plant showed that the mercury adsorption performance of the modified fly ash is similar to that of activated carbon, which is the industry benchmark for the treatment of mercury emission in fossil power generation units. This is a breakthrough and indicates that modified fly ash can become an efficient and convenient industrial sorbent for the removal of mercury.

The mercury migration and conversion characteristics of the lignite unit is not clear. The mercury concentration were measured by 30B method at five flue gas sampling points (before and after SCR, before low-temperature economizer, before and after desulfurization) in Inner Mongolia Guohua Hulunbuir Power Generation Co., Ltd. The emission concentration of mercury in the flue gas at the stack is 6.16, 4.53 and 2.98 μg/m3 at 319, 450, 550 MW, respectively. The emission concentration of mercury in flue gas decreases with the increase of unit load. In addition, the pollutant control devices have a synergistic effect on the mercury removal and the co-control efficiency is 31.48%, 29.68% and 66.65% at 319, 450, 550 MW. According to the mercury balance calculation, it can be found that after coal combustion, most of the mercury in the flue gas is discharged into the atmosphere (44.85%-65.27%), followed by fly ash (27.81%-51.15%) and gypsum (3.95%-14.61%). The fly ash test results indicate that the hardness value is between 0.28-7.15 GPa. The study results provide the basic data for further deep removal mercury from flue gas of coal-fired power plant.

The mercury removal capacity of biochar can be improved by plasma modification and the functional group is an important factor affecting the mercury removal. This paper examines factors such as discharge voltages, gas flow rates, chlorine concentrations and discharge times that may affect functional groups on the surface of biochar. The mercury removal performance of the tobacco stem biochar prepared under different Cl2 plasma modification conditions was investigated using a fixed bed reactor. The number of C–Cl bonds and carboxyl increased after modification and decreased in mercury removal. Longer discharge times can destroy the biochar surface and possibly cause a decrease in the number of active sites. Increasing the discharge voltage promotes the formation of C–Cl bonds and carboxyl groups. Excessive gas flow rates cause active chlorine to be carried out of the reactor quickly which reduces the formation of C–Cl. The amount of C–Cl bonds increases with increased chlorine concentration. In the modified biochar, C–Cl and carboxyl take part in the adsorption of mercury to form HgCl2 and HgO, while the unmodified biochar is mainly physically adsorbed Hg0. C–Cl is the main functional group participated in mercury removal and the carboxyl is a secondary functional group. The proportion of HgCl2 is at least 68.2% in the used modified biochar. Under optimum conditions, the initial mercury removal efficiency of modified tobacco biochar was 99.1%, and the efficiency was still 79.1% after 100 min. [ABSTRACT FROM AUTHOR]

Bromide coupled mechanical modified (BMM) fly ash showed good mercury adsorption performance. However, we have no information about the environmental stability after mercury adsorption. In this paper, environmental stability was investigated by desorption method in different temperature and improved continuous extraction experiments. Long-term environmental stability experiments showed that mercury desorption rates of BMM fly ash and activated carbon (AC) were both less than 5 % after placing them in the natural environment for one year. The stability of BMM fly ash after mercury adsorption was similar to that of AC. BMM method not only increased the specific surface area, but also improved the stable binding of bromide modifier on the surface, thereby improving the adsorption performance and stability. After adsorption, mercury in BMM fly ash existed in the form of HgBr 2 , HgS and HgO. Moreover, the improved continuous extraction experiments showed that the residue fraction of mercury in BMM fly ash was highest reaching 28 %, which was higher than that of AC (21 %). DFT calculation also showed that the presence of bromine reduced the adsorption energy of the mercury adsorption process, which proved that the presence of bromine improved the adsorption efficiency and stability of the adsorbent. These results indicate that BMM fly ash has the same environmental stability as AC, thus it has great potential application value for mercury removal from flue gas in coal-fired power plants. • Stability of adsorbents in three simulated natural environments are evaluated. • Mercury residue form is proposed to evaluate the stability of adsorbents. • Bromide coupled mechanical modified fly ash has good stability. [ABSTRACT FROM AUTHOR]

Power plant coal fly ash was modified for mercury adsorption. The fly ash was subjected to mechanochemical ball milling and bromide compounds were added. The results show that mercury capture capacity increased with increasing grinding time, up to 50 min. Grinding over 50 min did not lead to further improvements. Results from the mercury adsorption test show that the mechanochemical processing technique coupled with the addition of bromide compounds improves mercury adsorption performance for fly ash. Both physical and chemical factors contribute to the improvements in capture performance. Increasing the grinding time produced smaller particles with higher surface area. As a result, more unburned carbon was exposed, which resulted in better mercury adsorption. Thermal gravimetric analysis of modified fly ash shows combustion peak temperatures shift towards lower temperatures with increased grinding time. This result indicates that mechanical treatment increased the thermal activity of fly ash. As a result of this study, the first on-line modified fly ash unit was installed on site at a 300 MW coal fired power plant in China. [ABSTRACT FROM AUTHOR]

Using waste fly ash for mercury capture applications is an attractive, low-cost option for power plants. In this paper, the influence of nitric oxide (NO) on the mercury adsorption characteristics of HBr modified fly ash in an entrained-flow reactor was investigated using continuous monitoring and thermal decomposition methods. The results show that the adsorption efficiency of mercury by HBr modified fly ash was significantly enhanced when NO was added to the flue gas. Additionally, the rate of change of mercury concentration in the flue gas was increased due to increasing NO. The mercury adsorbed by HBr modified fly ash, in the entrained-flow reactor, exists primarily in two forms, HgBr 2 and HgO. In the experiments of mercury adsorption with HBr modified fly ash on the entrained-flow reactor, NO mainly augmented the generation of HgBr 2 . [ABSTRACT FROM AUTHOR]

In order to provide better understanding of mercury sorption properties on HBr-modified fly ash, fixed bed experiments using two different bituminous coal fly ashes were designed and conducted under air-simulated flue gas atmosphere. Temperature-programmed desorption method was used to analyze the mercury speciation during the adsorption process in both original and modified fly ashes. Results revealed that fly ash with an evener distribution of bromine-containing compounds on the surface, less competitive cations in the fly ash composition, and more negatively charged site has a better adsorption property for Hg. Even though mercury species in the two original FA are HgCl-HgO and HgS-HgO, respectively, the mercury species adsorbed by HBr-modified fly ash is predominately a FA-Br-Hg complex and HgO compound; the same kind of species accounts for same proportion in each sample. [ABSTRACT FROM AUTHOR]

Activated carbon (AC) is an effective adsorbent that is used in a wide range of applications. This is due to its high adsorption capacity and fast removal rate. This study evaluated processing conditions for synthesizing AC from coal pitch. The objective was to establish what processing conditions produced AC with the best adsorption performance. Factors such as carbonization temperature, activation temperature, steam flow rate and the addition of additives have been studied. A real-time, fixed-bed mercury adsorption system was used to evaluate the AC prepared from coal pitch. Results showed that the temperature and the KOH mixing rate in the carbonization process play an important role in the formation of the functional groups on the surface of the char. Additionally, the temperature and the steam flow rate in the activation process significantly affects AC surface area and pore distribution, important factors relating to mercury adsorption performance. [ABSTRACT FROM AUTHOR]

Coal-fired power plants are significant contributors to the anthropogenic emission of mercury. This study focus on evaluated the methods for modification and preparation of fly ash adsorbent which can be applied to adsorb mercury from power plants. Comparing with isometric impregnation and ion exchange method, it was found that the cost and preparation time of the mechanochemical method significantly reduced. Hg adsorption performances of NHBr-modified fly ashes and subsequent effects of mechanical energy on modifying fly ash were investigated, and the results indicated that increasing mechanical force can make the distribution of bromides to be more uniform and increase the number of surface active sites and groups. Furthermore, Hg removal efficiency improved significantly with the increasing bromine loading at 150 °C. There is a positive correlation between mechanical energy on modifying fly ash and subsequently Hg adsorption performance. TG/MS analysis was utilized to determine the thermal stability and released material of different samples. Results demonstrated the release of ammonia, which from the modified fly ashes with mechanochemical method, most likely enhances the oxidation and subsequent adsorption of mercury in the 150-200 °C temperature range. All results revealed that the mechanochemical application method for adsorbent preparation on site is competitive on economy, practicability, and mercury removal efficiency. [ABSTRACT FROM AUTHOR]

Highlights: [•] Mercury concentration change rate was suggested for evaluating the adsorption rate. [•] Combined Br− with H+, the adsorption ability of HBr-modified fly ash was obvious. [•] Particle size was an important influential factor in fly ash adsorption. [Copyright &y& Elsevier]

• Effect of modified fly ash on TEs emissions in a 1000 MW coal-fired power plant. • Modified fly ash has a significant oxidation effect on the TEs, especially As. • Increasing of smaller particle size and active sites may result in more Pb capture. • Approximately 30%~74% of reduction on TEs' emission in ESP and WFGD by fly ash injection. Modified fly ash injection was installed at the outlet of selective catalytic reduction (SCR) systems in a 1000 MW coal-fired power plant, reaching 94% mercury capture rate. Due to chemical and mechanical treatment of raw fly ash, the modified fly ash has a higher oxidation capability, finer particle size, and more active sites. The co-benefit of the reduction of trace elements (TEs), such as arsenic (As), selenium (Se), and lead (Pb), when using on-line modified fly ash was investigated in this study. The results between with and without modified fly ash indicated that it is between 30% and 74% of reduction on the three TEs' emission in both electrostatic precipitator (ESP) and wet flue gas desulfurization (WFGD) systems with the additional fly ash injection. The finer particle property is the dominant factor to reduce the emission of Se and Pb at such lower temperature (Temp) range. The Se itself also has the higher volatility to make capture more difficult than that of Pb. The strong chemical reaction between As and calcium with the smaller particle size reduced the As in the gas phase. The materials balance including solid, liquid, and gas phase also establish to confirm the sampling and measurement are validated of each value in this study. Above 97% of As and Pb are in the fly ash. Around 67% of the Se was captured in the WFGD unit. The Se had the higher emission in the stack. [ABSTRACT FROM AUTHOR]

A series of biochars were prepared from rice(RI), tobacco(TO), corn(CO), wheat(WH), millet(MI), and black bean straw(BB). These biochars were used to study the mechanism of elemental mercury(Hg 0 ) adsorption by hydrochloric acid modified biochars. The biochars were modified by 1 M hydrochloric acid (HCl) and then used in a fixed-bed Hg 0 adsorption experiment. As would be expected, the results indicated that HCl modification increased the Hg 0 adsorption performance of the six biochars. After modification, the Hg 0 adsorption efficiency of tobacco biochar increased from 8.2% to 100.0%, and the average Hg 0 adsorption capacity of the biochars increased by 61 times. The acid modification dissolved the metal compounds in the biochar, reducing the metal content and increasing the average surface area of the biochar. The average surface area of the raw biochars increased from 29.9 to 110.1 m 2 /g after HCl modification. The extra surface area was mostly created in the micropores, leading to a significant increase in the amount of micropores. These micropores effectively adsorbed the Cl atoms, which acted as active sites for Hg 0 . In the adsorption process, Hg 0 diffused into the interior of modified biochars via mesopores, and finally the adsorbed Cl in the micropores reacted with Hg 0 to form HgCl 2 . [ABSTRACT FROM AUTHOR]

The objective of this study was to develop a high efficiency activated carbon (AC) sorbent for mercury removal. The vapor deposition method was used to modify the raw AC. This method is relatively easy to carry out and uniformly modifies the AC. The results of this study indicate that AC modified by iodine steam vapor deposition has much better Hg capturing capacity than AC modified by bromide deposition under the same experimental conditions. London dispersion forces and exposure of the sorbent surfaces play important roles in elemental mercury (Hg 0 ) adsorption. Adsorption kinetic behavior was also studied under different experiment conditions. Results indicated that the pseudo-second model was the best fit to the actual mercury adsorption behavior onto AC-I 2 sorbent. The effect of adsorbent mass and gas flow rate on adsorption behavior were examined. Results indicated that increasing the sorbent mass led to an increase in Hg adsorption capacity, while increasing the gas flow rate resulted in a significant decrease in Hg adsorption capacity. Decreases in Hg adsorption capacity were likely due to a shorter contact time and lower partial pressure reducing the number of contact opportunities between the Hg atoms and the sorbent surface. Finally, a general dynamic equation was determined that can be used to help predict Hg adsorption curve of AC-I 2 sorbent without completing a real fixed-bed Hg adsorption experiment. [ABSTRACT FROM AUTHOR]

Mercury is harmful to the human body and to the ecological environment. Mercury emission from coal-fired power plants is one of the main sources of anthropogenic mercury emissions. Adsorbents and catalysts are popular materials developed to capture mercury from flue gas. Sulphur oxides (SO 2 , SO 3) are the main components of flue gas; their concentration is more than 3 orders of magnitude higher than that of mercury. Sulphur oxides have a significant effect on mercury adsorption and catalytic processes. However, the effect mechanisms of sulphur oxides on mercury removal by adsorbents/catalysts are not uniform. In this review, the effects of SO 2 and SO 3 on the mercury removal process by adsorbents/catalysts are provided separately, and the suggested influence mechanisms are also summarized. SO 2 has a two-sided effect on the performance of mercury removal by adsorbents and catalysts. Oxidation and activated adjacent sites are considered to be the main reasons for the promotion effect of SO 2. Competitive adsorption, active consumption and sulphate deposition are the main reasons for inhibition of mercury removal by SO 2. O 2 , H 2 O, SO 2 concentration and temperature have an impact on the effect of SO 2 on mercury removal. SO 3 can enhance the mercury removal efficiency of metal oxides-containing materials by increasing mercury oxidation rate. This review aims to promote a basic understanding of the effect of sulphur oxides on the mercury removal process and outline the future research direction of sorbents/catalysts for mercury removal, thereby advancing the research, development and application of materials with high sulphur resistance ability and removal efficiency. Image 1 • The promotion effect of SO 2 is achieved by oxidation and adjacent sites activation. • Inhibition reasons: competitive adsorption, activity consumption, sulphate deposition. • SO 3 can enhance mercury removal efficiency of metal oxide supported material. • Gas components and temperature influence the effect of SO 2 on mercury removal. • Sulphur-resistant and magnetic metals enhance the practicality of adsorbents/catalysts. [ABSTRACT FROM AUTHOR]

• H 2 S treated biochar was used for removing Hg(II) in hydrocarbons. • CaS/MgS, C-S and C = O groups in biochar played a major role on Hg(II) removal. • Biochar adsorbents had little effect on the quality of hydrocarbons. • Life cycle for the usage of biochar was provided for application. Three kinds of biochar, tobacco, rice and wheat, were treated with H 2 S to remove Hg(II) from hydrocarbons. The removal efficiency of the three biochars without H 2 S treatment was less than 12%. The removal efficiency of H 2 S treated tobacco had the best performance, and the removal efficiency increased by more than 87%. The characteristics of H 2 S treated biochar were analysed by FTIR, XPS, and TPD. The inorganic sulphides played a major role through ion exchange with metals. The sulphur-containing functional group C-S in organic sulphides and the carbonyl group C = O played a secondary role in the process of mercury removal through functional group complexation. In addition, the chemical and physical properties of gasoline before and after adsorption were compared to demonstrate that the sorbents had little effect on the heating value and the structure of hydrocarbons. The modified biochar also showed good stability after a life cycle test. [ABSTRACT FROM AUTHOR]

The mercury removal performance of chlorine plasma-modified biochar was tested under NH 3 and NH 3 combined with a NO/SO 2 atmosphere. The addition of NH 3 promotes the mercury removal process of modified biochar, and the mercury removal efficiency can be increased by up to 17.5%. NH 3 can induce the conversion of chloride to C–Cl, making it easier to bind to Hg0. NO also exhibits a promoting effect on mercury removal. This is because Hg0 can be converted to HgO by the oxidation of NO. When the flue gas contains both NH 3 and NO, the mercury removal efficiency is not as good as when the two gases are present alone. It is due to that NO will be consumed with NH 3 at high temperatures and NO 3 − will be generated on the surface of biochar and occupy the active site. SO 2 inhibits mercury removal by modified biochar through competitive adsorption. Sulphates and sulphites are more likely to form on the surface of biochar in the case of the coexistence of NH 3 and SO 2. The deposition of the chemical salt on the surface of the biochar causes the pores to be blocked and the active sites to be occupied, thereby deteriorating the efficiency of mercury removal. Image 1 • NH 3 is beneficial for mercury removal from Cl 2 plasma-modified biochar. • NH 3 promotes the conversion of Cl− to C–Cl to produce more chlorine active sites. • The efficiency of mercury removal will be weakened when NH 3 is added to NO. • Sulphates and sulphites occupy the biochar in coexistence of NH 3 and SO 2. [ABSTRACT FROM AUTHOR]

• H 2 O and SO 2 reversibly deactivate TiO 2 -BiOIO 3 in photocatalytic mercury removal. • SO 2 /SO 3 conversion rate was 0.08% and inhibited as the H 2 O content increased. • Generated Hg2+ and SO 3 detach from the catalyst and re-diffuse into the gas. • Superoxide radicals oxidize Hg0 and SO 2 to Hg2+ and SO 3 without H 2 O. • Hydroxyl radicals served as strong oxidative site in the presence of H 2 O. TiO 2 -BiOIO 3 heterostructures were prepared to study the photocatalytic removal of elemental mercury, sulphur tolerance and SO 2 /SO 3 conversion under UV irradiation. TiO 2 -BiOIO 3 produced excellent photocatalytic performance with highest Hg0 adsorption and oxidation efficiencies of 58.5% and 36.5%. SO 2 exhibited a negative effect on elemental mercury removal, and the oxidation efficiency of Hg0 and SO 2 were also inhibited as H 2 O content increased. The conduction band of BiOIO 3 trapped electrons from that of TiO 2 , the electrons reduced pre-adsorbed oxygen to superoxide radicals (O 2 −), which efficiently oxidize Hg0 and SO 2 , the generated Hg2+ and SO 3 re-diffused into the gas. In the presence of H 2 O, photogenerated electrons flowed from the conduction band of BiOIO 3 to the valence band of TiO 2 , I 3 −/I− acted as an electron transfer medium and prevented recombination of electrons and holes (h+), the gathered h+ reacted with H 2 O to form hydroxyl radicals (OH), which is oxidative species other than the oxidative site. [ABSTRACT FROM AUTHOR]

• The C–S groups generated in the plasma promote the removal of mercury. • The mercury removal efficiency of biochar increased from 26.4% to 95.5% after modification. • Hg0 is adsorbed on the modified sample to form HgS and HgO. • Active S released from broken C–S bonds at high temperature reacts with Hg0 in the gas phase. Six biomasses (rice, tobacco, corn, wheat, millet and black bean straws) were used to prepare biochar. The mercury removal performance of the obtained biochars after H 2 S plasma modification was tested, and characterisation was by FTIR (including in-situ FTIR), XPS and TPD. The mercury removal efficiency of biochar was enhanced after H 2 S plasma modification. The initial efficiency of wheat straw biochar was raised from 26.4% to 95.5% after modification. The number of sulfur-containing and carboxyl functional groups on the surface of the biochar increased through plasma modification. C–S and carboxyl are considered as the main functional groups forming HgS and HgO in mercury removal. The biochar after modification exhibited better mercury removal capacity at low temperatures. Active S is released from the C–S bonds at high temperature and further oxidises Hg0 in the gas phase. The adsorption process of modified samples is controlled by physical and chemical adsorption at 30 °C, while the main part of the reaction at 150 °C takes place in the gas phase. [ABSTRACT FROM AUTHOR]

Flue gas mercury emissions from waste rotary kiln incineration plants in Northern China was sampled using the US Environmental Protection Agency's 30B method and Ontario Hydro (OH) method. The average mercury emissions concentration was 13.38 ± 4.08 μg/Nm3 (based on the 30B method) and 18.66 ± 8.19 μg/Nm3 (based on the OH method). Coincidentally, it was also found that the uncertainty in Hg measurements of the raw feedstock was responsible for the fluctuation in the flue gas Hg data. The Hg emission consisted of Hg0, followed by Hg2+ and Hgp species, accounting for 59–82%, 3–26% and 14.84–16.03% of total Hg, respectively. Mercury was released from the ash to the flue gas after the fabric filter due to the high temperature. Based on the 30B and OH methods, the re-release rates of total Hg were 45.09% and 40.38%, respectively. The scrubbing tower in this type of system can remove most of the Hg2+ from the flue gas, and the total Hg removal efficiencies across the desulfurization units were 59.70% and 92.19%, respectively. 1. Domestic waste ferment pool, 2. Hopper, 3. Rotary kiln, 4. Second combustion chamber, 5. Settling chamber, 6. Heat recovery boiler, 7. Quench tower, 8. Fabric filter, 9. Primary scrubber tower, 10. Secondary scrubber tower, 11. Stack. [Display omitted] • Hg emissions in the waste incineration plants was tested by 30B and OH Methods. • The average mercury emissions concentration was 13.38–18.66μg/Nm3. • The re-release rate of Hg was 40.38–45.09% in the FF. • Most of the Hg in this waste incineration plant was distributed in slag and flue gas. [ABSTRACT FROM AUTHOR]

A novel and efficient adsorbent (TM-MoSe 2 , TM = Fe, Co, Ni) for mercury removal was developed and studied. The adsorption of mercury species (Hg0, HgCl, and HgCl 2) and the oxidation of Hg0 by HCl on TM-MoSe 2 (001) surface were explored at molecular level by density functional theory (DFT). The results shown that the Hg0 adsorption capacity of MoSe 2 was improved by the doping of Fe/Co/Ni, which was also confirmed by experiments. The initial Hg0 removal efficiency of MoSe 2 -based adsorbents reached 96.4–100.0%. In addition, HgCl was mainly adsorbed on TM-MoSe 2 (001) surface in the form of dissociation. The escape of Hg atom from HgCl resulted in the release of Hg0 again. However, HgCl 2 could be fixed well on the surface of adsorbent through molecular adsorption or dissociative adsorption. For the oxidation process of Hg0 by HCl, it abided with the Langmuir–Hinshelwood mechanism. In comparison with direct oxidation (Hg → HgCl 2), two-step pathway (Hg → HgCl → HgCl 2) was an achievable reaction route with lower energy. Furthermore, the Hg → HgCl process was the rate-limiting step of the two-step pathway. The proposed adsorption and oxidation mechanism of mercury species on TM-MoSe 2 (001) provide advanced strategies on the development of adsorbents for industrial mercury removal. [Display omitted] • TM-MoSe 2 (TM = Fe, Co, Ni) was proposed as a novel adsorbent for mercury removal. • The doping of Fe/Co/Ni improved the adsorption capacity of MoSe 2 to Hg0. • The adsorption of HgCl/HgCl 2 on TM-MoSe 2 was in the form of dissociation and molecular. • The oxidation of Hg0 by HCl on TM-MoSe 2 followed the Langmuir–Hinshelwood mechanism. [ABSTRACT FROM AUTHOR]

• A mercury removal system was developed by injecting modified fly ash. • Before ESP, PM increased with more injection of fly ash and higher coal load. • The emission of PM was not significantly changed after passing through PECD. This study examines the impact of adding a mercury removal system which uses modified fly ash on particulate matter (PM) emissions from a coal-fired power plant. The modified fly ash injection technology has been demonstrated and was installed in a commercial power plant and reached 91.9% mercury removal efficiency. An important consideration was that the emission limitation for PM –5 mg/Nm3, should not be exceeded due to the addition of 0.2% (by mass) of modified fly ash to untreated fly ash fed to a coal boiler unit. Thus, the effect of modified fly ash injection on the PM emissions was studied at different locations in the power plant: before and after the Electrostatic Precipitator (ESP), after the Flue Gas Desulphurization (FGD) unit. Measurements were also made at the stack. The results showed that after the modified fly ash was injected into the flue gas stream from the boiler, the mass concentration of particulate matter leaving the particulate emission control device (PECD) was slightly increased. However, the distribution of PM 10 , PM 2.5 , PM 1 and PM 0.2 was not significantly changed due to the addition of 0.2% (by mass) of modified fly ash. The results indicated that the total PM removal efficiency of the PECD was still around 99.1 ~ 99.9% for the case of mass concentration and 98.6 ~ 99.7% for number concentration. The mass emission concentration of PM 10 with modified fly ash injection were 2.46 and 1.96 mg/m3 at 100% and 50% load, respectively. [ABSTRACT FROM AUTHOR]

• The adsorption mechanism between Hg (II) in gasoline and KI-13X was explored. • The Hg (II) adsorption amount of zeolite increased by 18 times after 2% KI loaded. • KI was impregnated into microspores more than on the surface of the sorbent. • There were two main active sites for I atom in the zeolite for mercury capture. Mercury (Hg) removal from natural gas condensates is a hot topic due to its importance in petroleum refineries. Unfortunately, though much attention has been paid to the adsorption efficiency of sorbents in industry, mercury adsorption mechanisms are rarely addressed. This paper studies the adsorption mechanisms of zeolite 13X impregnated with potassium iodide (KI) on ionic mercury (Hg(II)) from gasoline. The effects of different KI loading amounts, initial mercury concentrations, and adsorption times of mercury removal were investigated by adsorption experiments. The adsorption efficiency increased from 15% to 91%, and the adsorption amount increased by 18 times after the addition of pristine zeolite loaded with 2% KI. The preferential adsorption sites of potassium (K), iodine (I), and Hg atoms in zeolite were calculated by the grand-canonical Monte Carlo (GCMC) method. The center of the super cage (center 1) and interface between the super cages (center 2) provided the main I active sites for Hg capture. In addition, the adsorption energies between I and Hg were analyzed by density functional theory (DFT), and partial density of states (PDOS) analysis indicated that Hg interacts strongly with I in the super cage. Hence, during the adsorption process, mesopores served as an entrance for active materials. Hg(II) in gasoline diffused to the micropore channels via mesopores and were captured by I, forming HgI 2. These results cast a new light on the development of novel sorbents for mercury removal. [ABSTRACT FROM AUTHOR]

• Hg0 can be chemically adsorbed on ZnSe (1 1 0) surface and interact with zinc atom. • The presence of SO 2 enhance the activity of adjacent sites for Hg0 adsorption. • SO 2 inhibits Hg0 adsorption by occupying the sites when SO 2 concentration is high. • HCl and H 2 O inhibit Hg0 adsorption by competitive adsorption mechanism. Due to its low cost, rich resource reserve, and high affinity for gas-phase mercury, zinc selenide has been investigated as a promising sorbent to control mercury emission. In order to gain molecular level insights into the adsorption mechanism, density functional theory (DFT) calculations were applied to the process of mercury adsorption on the (1 1 0) surface of ZnSe. Our results indicated that chemical adsorption played a crucial role in the Hg0 adsorption on the ZnSe (1 1 0) surface. Mercury atoms interacted energetically with surface Zn atoms through the interactions between atomic orbitals. The proposed process of transformation of Hg to HgSe can be described in three steps: i.e., Hg0 → Hg (ads) → HgSe (ads) → HgSe. The effects of SO 2 , H 2 O, and HCl on the adsorption of Hg0 on the surface of ZnSe were also investigated. SO 2 , H 2 O, and HCl are able to be chemisorbed on the surface of ZnSe (1 1 0) with the highest binding energies of −43.58 kJ/mol, −72.23 kJ/mol, −52.93 kJ/mol, respectively. Moreover, SO 2 shows a dual effect on Hg0 binding, while H 2 O and HCl may suppress Hg0 adsorption on the ZnSe (1 1 0) surface. Theoretical study suggested that ZnSe sorbent has an excellent potential for the efficient removal of gas-phase mercury. [ABSTRACT FROM AUTHOR]

• The speciation of Hg, As, Pb, Cd, and Cr were studied from different ash hoppers. • The unburned carbon and the particle size of fly ash are major factors to control the speciation. • The arsenic, chromium, and cadmium have the most potential to be leached out. In the power plants, the particle size of fly ash was gradually decreased from the front row to the last row of the hopper. The high mercury captured rate was shown with the high unburned carbon content in the front row of the hopper. 80% of mercury captured in the front hopper was in the residual fraction and the rest was in the oxidizable fraction. The other four trace elements tended to be captured more with the smaller particle size of fly ash in the latter hoppers. Above 90% of lead in fly ash at different hoppers was in the speciation of the residual fraction. This indicated that the lead was the less tendency to be leached out during landfill. The speciation of acid-soluble, reducible, and oxidizable fraction for As, Cr and Cd was significantly increased in the fly ash at different hoppers. This indicated that the combustion technology in each power plant had a significantly impact on the speciation of these trace elements in different hoppers. Thus, the usage of the separation technology method to better understand the behavior of trace elements in the fly ash to avoid fly ash's disposal through increasing the beneficial use of fly ash. [ABSTRACT FROM AUTHOR]

• Biochar adsorbed oxygen and water from the air during storage. • Adsorbed O 2 dominates the generation of oxygen-containing functional group in plasma. • O–C O is only generated on H 2 O adsorbed biochar under non-oxygen plasma. • The generated oxygen-containing functional group oxidises Hg0 to HgO. Biochar was subjected to N 2 -plasma treatment after adsorbing water or oxygen. The mercury removal efficiency of the obtained samples was tested. The results of H 2 O-thermogravimetric and O 2 -temperature programmed desorption show that biochar had adsorption capacity for both water and oxygen during storage. The adsorbed water exhibited an inhibitory effect on mercury removal. However, after plasma treatment, water decomposed into oxygen-containing active radicals and combined with biochar to form oxygen-containing functional groups. The generated functional groups compensated for the inhibition of mercury capture. After the biochar adsorbed oxygen, the biochar was easily sintered under plasma, thereby reducing the mercury removal performance. The oxygen-containing functional groups formed by plasma treatment of oxygen adsorbed biochar also improved the mercury removal efficiency. Hg-temperature programmed desorption revealed that Hg0 could be oxidised by the generated oxygen-containing functional group to form HgO. Correlation analysis showed that the oxygen adsorbed by the biochar from air during storage was the main source of oxygen-containing functional groups generated under a non-oxygen plasma environment. The correlation coefficient was up to 0.999. During normal storage, the oxygen adsorbed by the adsorbent from the air can be converted into oxygen-containing functional groups during the plasma modification process, thereby oxidising Hg0. [ABSTRACT FROM AUTHOR]

• SO 2 inhibited the Hg0 removal, while SO 3 promoted the Hg0 removal. • SO 3 was more easily adsorbed on the surface of the catalyst compared with SO 2. • The adsorbed SO 3 served as a new active site for Hg0 removal. • SO 3 adsorption was promoted at high temperature, improving Hg0 removal. The Cu/ZSM-5 was used to study the effects of SO 3 on mercury removal. The addition of SO 2 decreased the Hg0 removal efficiency but the efficiency increased from 82% to 95% after 21 ppm SO 3 was introduced at 200 °C. The inhibition effect of SO 2 on mercury removal was weakened at 400 °C and the promotion effect of SO 3 on mercury removal was enhanced significantly. HgSO 4 was the main mercury species formed on the catalyst in the presence of SO 3. The in-situ FTIR results showed a large number of S-related peaks were generated on the surface of the catalyst with SO x (SO 2 and SO 3). The peak of adsorbed SO 2 weakened when SO 2 and SO 3 coexisted in the reaction atmosphere. This is due to the SO 3 inhibiting the adsorption of SO 2. The peak of adsorbed SO 3 was the most obvious and was then gradually consumed after Hg0 introduced. Meanwhile, the peak of sulphate appeared on the surface of the catalyst. This indicated SO 3 preferentially adsorbed on the catalyst to form active sites for oxidizing Hg0 to HgSO 4. The adsorption of SO 3 on the catalyst was promoted at 400 °C, compared with 200 °C, which directly contributed to the enhancement of Hg0 removal. [ABSTRACT FROM AUTHOR]

• Ce doping promoted Hg0 oxidation, but inhibited the oxidation of SO 2 to SO 3. • Both lattice oxygen and Mn4+ with high oxidability increased after Ce addition. • The content of HgSO 4 was more than 72% on the catalyst in the presence of SO 2. • NH 3 and H 2 O had a significant inhibitory effect on Hg0 and SO 2 oxidation. A series of Mn-Ce/SAPO-34 catalysts were prepared to study the catalytic oxidisation of elemental mercury (Hg0). Sulphur tolerance and SO 3 formation over the catalyst were studied further. Hg0 was transported by compressed air from PSA Cavkit. NO, SO 2 , and NH 3 are standard gases, and H 2 O is produced by gas carrying. Mn could incorporate into the cerium oxide lattice to form capping oxygen and well-dispersed high valance manganese ions after the addition of Ce, which was conducive to NO removal and Hg0 oxidisation. 9 Mn-9Ce showed the best performance regarding Hg0 conversion, achieving more than 92% Hg0 conversion efficiency at 50–300 °C. The sulphur resistance of the Mn-based catalyst was significantly improved after the addition of cerium due to the high affinity of Ce for SO 2 , and the relative content of HgSO 4 was exceeded 72% on the 9 Mn-9Ce catalyst with SO 2 ; SO 3 formation over the 9 Mn-9Ce decreased by 17% compared with the 9 Mn. H 2 O not only reduced the available active site, but also decreased the oxidation rate of SO 2. The active sites were preferentially occupied by NH 3 rather than Hg0 and SO 2 , generated NH 4 + occupied cation vacancies. Therefore, both H 2 O and NH 3 have inhibitory effects on Hg0 conversion and SO 3 formation. [ABSTRACT FROM AUTHOR]