A review on removal of mercury from flue gas utilizing existing air pollutant control devices (APCDs)

Mercury removal mechanism of brominated high-sulfur petroleum coke: Experimental and DFT study

Reaction interface structures of mechanochemical bromine modified high-sulfur petroleum coke (HSPC) as amorphous carbon are critical for Hg0 removal with SO2. This study first found low concentrations of SO2 promote mercury removal while high concentrations do not inhibit it. To distinguish benzene ring skeleton and epitaxial active edges, according to XPS analysis, two new edge models with thiophene were proposed, followed by corresponding defective structures. The calculation of density function theory (DFT) reveals that spatial adsorption of bromine, SO2, and Hg0 is a more universal configuration. The defective armchair-S significantly lowers the energy barrier of Hg0 oxidation while the defective zigzag configurations are more stable. The armchair-Br-1SO2-2 added one negative extreme point near C-Br and broadened the activity region. Further, a new promotion pathway of SO2 is proposed that SO2 pulls Hg0 forming strong physisorption. However, excess SO2 molecules do not compete with mercury for adsorption. Although the adsorption energy of mercury is higher on intact structures, the oxidation energy barrier is lower on defective structures with SO2, and even direct mercury oxidation on zigzag-S with two SO2 molecules. This study can provide a theoretical basis for functionalized carbon-based adsorbents removing Hg0 in actual flue gas.

A reliable model to predict mercury solubility in natural gas components: A robust machine learning framework and data assessment

Mercury contamination in natural gas poses serious risks to production, processing, and transportation, leading to equipment corrosion, worker safety hazards, environmental pollution, and economic losses. Accurately predicting mercury solubility in methane, ethane, and multicomponent systems is essential for effective mitigation and regulatory compliance. This study employs advanced machine learning (ML) approaches, namely multilayer perceptron (MLP), generalized regression neural network (GRNN), and extra trees (ET), to estimate mercury solubility under varying pressure and temperature conditions. A high-quality dataset was used to train and validate these models, ensuring accuracy and reliability. The MLP model demonstrated the highest predictive performance with a determination coefficient of 0.9998, and a root mean square error of 1.7430 ppb. Besides, the MLP model effectively captured solubility trends, while feature importance analysis identified temperature as the dominant factor. The Leverage approach confirmed dataset reliability, with 96.5 % of data points within the trust region. This pioneering ML-based framework, the first of its kind for mercury solubility estimation, holds great industrial potential. It enables real-time monitoring, minimizes risks of equipment failure and human exposure, and supports environmental protection by reducing mercury emissions. By integrating this intelligent approach, operators can enhance safety, efficiency, and sustainability in natural gas operations.

Preparation and Hg0 Removal Performance of MIL-101(Cr)-Derived Carbon Matrix Composites

The temperature at which pollutants are treated varies across different industrial processes. To address the high cost of raw materials for MOFs and the low efficiency of Hg0 removal in low-temperature environments, a series of MIL-101(Cr)-derived carbon matrix composite materials were prepared by combining MIL-101(Cr) with biomass and multiple metals. These materials were synthesized through a sol-gel method followed by carbonization. This study investigates the effects of composite ratios and adsorption temperatures on Hg0 removal, utilizing XRD, BET, and other characterization techniques to elucidate the mercury-removal mechanism of the PDC-MIL composite materials. The results indicate that MIL101(Cr) significantly influences the formation of the gel skeleton. When the composite ratio of MIL-101(Cr) to biomass is 1:1, the material exhibits an optimal pore structure, leading to high Hg0 removal efficiency over a wide temperature range. The removal of Hg0 by these composite materials involves both physical adsorption and chemisorption. Low temperatures favor physical adsorption, while high temperatures promote chemisorption. The sol-gel composite method facilitates cross-linking polymerization between MOFs and SiO2, enabling better pore structure connectivity with biomass and MOFs, thereby optimizing the poor pore structure observed after pyrolysis. Consequently, the improved pore structure enhances physical adsorption at low temperatures, mitigates desorption at high temperatures, and increases the contact probability of Hg0 with active sites within the pores, significantly improving the mercury-removal ability of the material across a broad temperature range.

Porous carbon adsorbent from cellulose acetate for efficient Hg0 adsorption from coal-fired flue gas

The elemental mercury emitted from coal flue gas has caused serious harm to the ecological environment, and the development of high efficiency Hg0 adsorbents has been a research hotspot. In this study, cellulose acetate derived carbon adsorbent was prepared by the combination of soft template and activation method, which realized the efficient removal of Hg0 from coal flue gas. The mechanism of adsorption process was studied by FTIR, Hg-TPD and kinetic simulation. The results show that the soft template agent mainly constructed mesopores in the adsorbent, and the activator mainly constructed micropores. The synergistic effect of the two significantly enhanced the physical adsorption of Hg0 by the adsorbent. In addition, cellulose acetate with high O/C (0.93) was used as a carbon source to promote the formation of a large number of C = O functional groups on the surface of the adsorbent, which is the main chemisorption site of Hg0. The adsorbent has a high mercury adsorption capacity, reached 3,800 μg/g.

Synergistic removal of Hg0, HCl, and SO2 from flue gas in municipal solid waste incineration by mechanically modified fly ash

The emissions of flue gas components (such as Hg0, SO2, HCl) and the generation of hazardous waste fly ash from municipal waste incineration pose a significant threat to environmental integrity. In this study, a mechanochemical method combined with a modifier is innovatively proposed for the modification of fly ash to remove Hg0. In the fixed bed adsorption experiment, the removal efficiency of up to 60 percent can be achieved by ball milling (700rap,30min) alone. The modification of fly ash by mechanical force coupling with pyrite can achieve Hg0 removal efficiency is increased to more than 90 percent. By taking advantage of the excellent adsorption capacity of modified fly ash for acidic gases, the enhancement of S and Cl∗ active sites on the surface of modified fly ash strengthened the removal efficiency of modified fly ash for Hg0. DFT simulations evidenced that the defective S sites caused by the ball milling process could enhance the adsorption capacity of pyrite for Hg0. The fly ash was modified with mechanically coupled pyrite and alkalis and was able to have good adsorption capacity for acidic gases, the highest removal effect reached 93.1% and 96.7% for SO2 and HCl, respectively. The adsorbed acid gases increased the S and Cl∗ active sites, which led to the removal of Hg0 from the modified fly ash to more than 94.4%, achieving the synergistic removal of acid gases and Hg0. This method can realize the integrated technical route of "Fly ash collection - Online modification - Timely injection". A novel investigation was conducted on the elimination of flue gas contaminants and the reutilization of perilous fly ash.

Spatial distribution and risk assessment of heavy metal pollution from enterprises in China

Heavy metal pollution (HMP) directly affects the safety of agricultural products, thereby impacting human health. Industrial emissions, as the main source of soil HMP in China, require in-depth research on their pollution risks. Based on national heavy metal (HM) enterprise data, this paper analyzes the spatial distribution characteristics of key enterprises involved in the HMP across the country. It constructs the risk assessment index system of enterprise HMP based on the "source-pathway-receptor" (SPR) process of the HMP, evaluates and partitions the risk of the HMP from enterprises nationwide. The results show that: (1) Enterprises and pollutant discharge outlets are mainly distributed in the eastern and southeastern coastal regions. Jiangxi, Yunnan, Guangdong, and Hunan Province are the main distribution regions of smelting enterprises, with the most types of HM pollutants. The hazard of pollution sources shows a spatial distribution pattern of higher risk in the southwest and north, and lower risk in the central region. Counties with high-risk pollution sources are mainly distributed in Yunnan, Hunan, Guangdong, Inner Mongolia, and Jiangxi Province. (2) The hazard of pollutant transmission pathways shows a spatial distribution pattern of higher risk in the southeast and lower risk in the central region. About 31.5 % of counties are at extremely high risk, mainly distributed in the southeastern coastal regions of Guangdong, Jiangsu, Zhejiang, Jiangxi, Shandong, and Fujian Province. (3) The vulnerability of the receptors shows significant clustering characteristics in the northeast and central regions. About 3.3 % of counties have a receptor vulnerability level of "extremely high," mainly distributed in Inner Mongolia, Jilin, Heilongjiang, Liaoning Province in the northeast, as well as Hubei and Jiangsu Province. (4) About 1.55 % of counties nationwide have a comprehensive risk level of the HMP classified as "extremely high," mainly distributed in Guangdong Province and Inner Mongolia. Additionally, some counties in Yunnan, Hunan, Jiangsu, Jiangxi, and Zhejiang Province have a risk of exceeding pollution standards, requiring further preventive measures to reduce pollution risks in the future. This paper can provide a scientific basis for the prevention and control (P&C) of the HMP in China.

Solid-Phase Microextraction Mediated Solid-Phase Dielectric Barrier Discharge Vapor Generation-Atomic Fluorescence Spectrometry for Sensitive Determination of Mercury in Seawater

A novel method coupling solid-phase microextraction (SPME) to solid-phase dielectric barrier discharge (SPDBD) vapor generation was proposed and used for the sensitive detection of trace mercury (Hg) in seawater with atomic fluorescence spectrometry (AFS) in this work. The method proposed herein offers the unique advantages of integrating desorption and chemical vapor generation into one step, eliminating the use of elution reagents, and reducing the analysis time. SPME with multiwalled carbon nanotubes (MWCNTs) coated on the glass tube was used to extract Hg2+ in seawater. The Hg2+ was then desorbed and reduced to Hg0 vapor by SPDBD, which was detected by cold vapor AFS. The parameters affecting Hg2+ extraction, desorption, and vapor generation were studied. The detection limit of Hg2+ was 0.0003 μg L-1, and the relative standard deviation at a Hg2+ concentration of 0.05 μg L-1 was 4.4%. This method also has excellent antimatrix interference ability for Hg2+ determination with recoveries between 91.8% and 101.1% in the presence of extremely high concentrations (two million times excess) of coexisting ions. The practicality of this method was also evaluated by analyzing two different certified reference materials of Hg2+ in water and several seawater samples with good spike recoveries (94.0%-107.4%). Compared with solid-phase photothermo-induced vapor generation, this method has higher extraction efficiency and higher desorption efficiency without the assistance of heating as well as a lower detection limit of Hg2+, which is capable of performing trace Hg analysis in seawater.

Comparative study of the sequential extraction methodologies for fractionation analysis of mercury in coal of Thar coalfield

The primary objective of this study was to evaluate the bound fractions of mercury (Hg), physicochemical parameters, and mineral composition of coal. Coal samples were collected from various depths within Block-VII of the Thar coalfield in Pakistan. The Hg associated with different chemical fractions of coal was extracted using a sequential extraction scheme as per the community bureau of reference (BCR) protocol. This study utilized both the BCR-sequential extraction method (BCR-SEM) and a single-step sequential extraction based on an ultrasonic-assisted method (SSE-UAM) for the fractionation analysis of Hg in coal. The extraction methodologies, BCR-SEM and SSE-UAM, were specifically designed for analyzing Hg fractionation in coal samples. The SSE-UAM offers an operational advantage, requiring only 2 h compared to the 51 h needed for BCR-SEM. The analyses were validated using standard reference material (SRM-1635a) and the spiking addition method, achieving a recovery percentage of 97.1% for total Hg concentrations using the pseudo-extraction method in SRM-1635A. Total Hg content in the coal samples ranged from 0.60 to 2.34 µg g-1 across four different coal seams from Block-VII of the Thar coalfield. Additionally, Hg concentration was observed to decrease with increasing depth, attributed to changes in mineralogical composition. The highest concentration of Hg was detected at a depth of 200-203 m, while the lowest concentration was at a depth of 152-154 m. The concentration of Hg in various fractions was 32-60% in the acid-soluble fraction, 1.72-4.92% in the reducible fraction, and 9.58-50.8% in the oxidizable fractions. The coal sample characteristics were analyzed using an elemental analyzer and scanning electron microscopy with energy-dispersive spectroscopy. Cold vapor atomic absorption spectrometry (CV-AAS) was used to measure the extracted fractional concentration of Hg in coal.

An assessment of inorganic components in condensable particulate matter as a function of surface aggregation, spatial suspension state and particle size

Experimental studies assessed the removal efficiency and fine-size distribution of CPM coupled with compositional analysis across air pollution control device systems (APCDs) at an ultra-low emission (ULE) power plant. The findings indicated total CPM emissions were reduced to a minimum of 0.418 mg/m3 at the Wet Electrostatic Precipitator (WESP). The Wet Flue Gas Desulfurization (WFGD) showed the highest removal efficiency (98%) across all particle sizes, notably in the ultra-micron range. Selective Catalytic Reduction (SCR) demonstrated a mere 34% overall efficiency, with a negative removal rate in the ultra-fine particle range. The WESP effectively removed CPM only in sub-micron and ultra-micron sizes, but significantly increased water-soluble ions formation in ultra-fine spatially suspended CPM (CPMspa), leading to overall negative efficiency. Thus, the removal efficiency of the ultra-fine particle range was most affected among the three particle size ranges when the flue gas went through the APCDs. Major metal elements and water-soluble ions were more readily removed by APCDs due to their surface aggregation, while the removal of trace elements like Hg and Se was limited. Reducing SO42-/NH4+ formation in SCR, and optimizing WESP spray system operations based on flue gas components are essential steps in controlling CPM concentration in ULE power plants.

An Innovative Approach for Elemental Mercury Adsorption Using X-ray Irradiation and Electrospun Nylon/Chitosan Nanofibers

A novel approach was proposed, utilizing an electrical field and X-ray irradiation to oxidize elemental mercury (Hg0) and encapsulate it within a nanofibrous mat made of Polyamide 6/Chitosan. The X-rays contributed significantly to the conversion of Hg0 into Hg+ by producing electrons through the photoionization of gas molecules. The positive and negative pole electrodes generated an electric field that exerted a magnetic force, resulting in the redirection of oxidized elemental mercury towards the negative pole electrode, which was coupled with a Polyamide 6/Chitosan nanofiber mat. The evaluation of the Polyamide 6/Chitosan nanofibers exposed to oxidized mercury showed that the mercury, found in the steam of a specially designed filtration device, was captured in two different forms. Firstly, it was chemically bonded with concentrations ranging from 0.2 to 10 ng of Hg in total. Secondly, it was retained on the surface of the Polyamide 6/Chitosan nanofibers with a concentration of 10 microg/m3 of Hg per minute. Nevertheless, a concentration of 10 microg/m3 of mercury is considered significant, given that the emission levels of mercury from each coal power plant typically vary from approximately 4.72 to 44.07 microg/m3. Thus, this research presents a viable approach to reducing mercury emissions from coal-fired power plants, which could result in lower operational expenses and less secondary environmental effects.

Mercury abatement in the environment: Insights from industrial emissions and fates in the environment

Mercury's neurotoxic effects have prompted the development of advanced control and remediation methods to meet stringent measures for industries with high-mercury feedstocks. Industries with significant Hg emissions, including artisanal and small-scale gold mining (ASGM)-789.2 Mg year-1, coal combustion-564.1 Mg year-1, waste combustion-316.1 Mg year-1, cement production-224.5 Mg year-1, and non-ferrous metals smelting-204.1 Mg year-1, use oxidants and adsorbents capture Hg from waste streams. Oxidizing agents such as O3, Cl2, HCl, CaBr2, CaCl2, and NH4Cl oxidize Hg0 to Hg2+ for easier adsorption. To functionalize adsorbents, carbonaceous ones use S, SO2, and Na2S, metal-based adsorbents use dimercaprol, and polymer-based adsorbents are grafted with acrylonitrile and hydroxylamine hydrochloride. Adsorption capacities span 0.2-85.6 mg g-1 for carbonaceous, 0.5-14.8 mg g-1 for metal-based, and 168.1-1216 mg g-1 for polymer-based adsorbents. Assessing Hg contamination in soils and sediments uses bioindicators and stable isotopes. Remediation approaches include heat treatment, chemical stabilization and immobilization, and phytoremediation techniques when contamination exceeds thresholds. Achieving a substantially Hg-free ecosystem remains a formidable challenge, chiefly due to the ASGM industry, policy gaps, and Hg persistence. Nevertheless, improvements in adsorbent technologies hold potential.

Bibliometric analysis on mercury emissions from coal-fired power plants: a systematic review and future prospect

Coal-fired power plants (CFPPs) are one of the most significant sources of mercury (Hg) emissions certified by the Minamata Convention, which has attracted much attention in recent years. In this study, we used the Web of Science and CiteSpace to analyze the knowledge structure of this field from 2000 to 2022 and then reviewed it systematically. The field of Hg emissions from coal-fired power plants has developed steadily. The research hotspots can be divided into three categories: (1) emission characterization research focused on speciation changes and emission calculations; (2) emission control research focused on control technologies; (3) environmental impact research focused on environmental pollution and health risk. In conclusion, using an oxygen-rich atmosphere for combustion and installing high-efficiency air pollution control devices (APCDs) helped to reduce the formation of Hg0. The average Hg removal rates of APCDs and modified adsorbents after ultra-low emission retrofit were distributed in the range of 82-93% and 41-100%, respectively. The risk level of Hg in combustion by-products was highest in desulfurization sludge (RAC > 10%) followed by fly ash (10% < RAC < 30%) and desulfurization gypsum (1% < RAC < 10%). Additionally, we found that the implementation of pollution and carbon reduction policies in China had reduced Hg emissions from CFPPs by 45% from 2007 to 2015, increased the efficiency of Hg removal from APCDs to a maximum of 96%, and reduced global transport and health risk of atmospheric Hg. The results conjunctively achieved by CiteSpace, and the literature review will enhance understanding of CFPP Hg emission research and provide new perspectives for future research.

Biomimetic mercury immobilization by selenium functionalized polyphenylene sulfide fabric

Highly efficient decontamination of elemental mercury (Hg0) remains an enormous challenge for public health and ecosystem protection. The artificial conversion of Hg0 into mercury chalcogenides could achieve Hg0 detoxification and close the global mercury cycle. Herein, taking inspiration from the bio-detoxification of mercury, in which selenium preferentially converts mercury from sulfoproteins to HgSe, we propose a biomimetic approach to enhance the conversion of Hg0 into mercury chalcogenides. In this proof-of-concept design, we use sulfur-rich polyphenylene sulfide (PPS) as the Hg0 transporter. The relatively stable, sulfur-linked aromatic rings result in weak adsorption of Hg0 on the PPS rather than the formation of metastable HgS. The weakly adsorbed mercury subsequently migrates to the adjacent selenium sites for permanent immobilization. The sulfur-selenium pair affords an unprecedented Hg0 adsorption capacity and uptake rate of 1621.9 mg g-1 and 1005.6 μg g-1 min-1, respectively, which are the highest recorded values among various benchmark materials. This work presents an intriguing concept for preparing Hg0 adsorbents and could pave the way for the biomimetic remediation of diverse pollutants.

Plasma-catalyzed combined dynamic wave scrubbing: A novel method for highly efficient removal of multiple pollutants from flue gas at low temperatures

In this study, we developed a novel approach combining a non-thermal plasma system with M(Ce, Cu)-Mn/13X oxidation and post-dynamic wave wet scrubbing technologies, for effectively removing multiple pollutants from flue gases. Experimental results demonstrated that the plasma coupled with post-dynamic wave wet scrubbing achieved impressive synergistic removal efficiencies of 98% for SO2, 50.9% for NO, and 51.3% for Hg0 in flue gas. Through the use of M(Ce, Cu)-Mn/13X catalysts synthesized via the co-precipitation, the oxidation efficiency of the system is significantly enhanced, with synergistic removal efficiencies reaching up to 100% for SO2, 98.7% for NO, and 96% for Hg0. Notably, (Ce-Mn)/13X exhibited superior catalytic activity, the results are supported by comprehensive sample characterization, DFT mechanistic analysis, and experimental validation. Additionally, we elucidated the plasma oxidation mechanism and the working principles of the M(Ce, Cu)-Mn/13X loaded catalysts. This innovative technology not only facilitates pollutant oxidation but also ensures their complete removal from flue gas, providing a high-efficiency, cost-effective, and environmentally friendly solution for the treatment of multi-pollutants in flue gases.

Integrated high-gravity process for HCl removal and CO2 capture using carbide slag slurry in a rotor-stator reactor: Experimental and modeling studies

The treatment of flue gas containing HCl and CO2 has garnered significant attention. This study proposes an integrated high-gravity process based on a rotor-stator reactor (RSR) for HCl removal and CO2 capture through mineralization using carbide slag slurry (CSS), an industrial waste. Experimental and modeling studies were conducted to investigate the absorption performance and mass-transfer mechanism. Considering the properties of CSS, Ca(OH)2 slurry was used to simulate CSS for HCl and CO2 absorption in the RSR. The influences of solid content, rotational speed, gas flow rate, and liquid flow rate were investigated, resulting in HCl and CO2 absorption efficiencies of 87.3%-98.9% and 33.8%-65.7%, respectively. Two mechanistic mass-transfer models were established based on surface renewal theory and penetration theory, respectively, to depict the process. The predicted values aligned well with the experimental results, with deviations generally less than 25%. The study further explored the absorption of HCl and CO2 using an actual CSS operated in recycle in the RSR and investigated the characteristics of the solids in fresh and carbonated CSS using XRD, TGA, and SEM. The results indicated that the actual CSS had excellent absorption performance, generally consistent with Ca(OH)2 slurry, and that Ca(OH)2 in CSS was almost completely converted to CaCO3 (calcite).

Impact of Glasgow Climate Pact and Updated Nationally Determined Contribution on Mercury Mitigation Abiding by the Minamata Convention in India

India is one of the largest emitters of atmospheric anthropogenic mercury (Hg) and the third-largest emitter of greenhouse gases in the world. In the past decade, India has been committed to the Minamata Convention (2017) in addition to the Paris Climate Change Agreement (2015) and the Glasgow Pact (2021). More than 70% to 80% of India's mercury and carbon dioxide emissions occur because of anthropogenic activities from coal usage. This study explores nine policy scenarios, the nationally determined contribution (NDC) scenario, and two deep decarbonization pathways (DDP) with and without mercury control technologies in the energy and carbon-intensive sectors using a bottom-up, techno-economic model, AIM/Enduse India. It is estimated that NDC scenarios reduce mercury emissions by 4%-10% by 2070; while coal intensive (DDP-CCS) pathways and focus on renewables (DDP-R) reduce emissions by 10%-54% and 15%-59%, respectively. Increase in the renewables share (power sector) can result in a significant reduction in the costs of additional pollution-abating technologies in the DDP-R scenario when compared with the coal intensive DDP-CCS scenario. However, the industry sector, especially iron and steel and metal production, will require stringent policies to encourage installation of pollution-abating technologies to mitigate mercury emissions under all the scenarios.

To be support or promoter: the mode of introducing ceria into commercial V2O5/TiO2 catalyst for enhanced Hg0 oxidation

Ce-modified commercial vanadium-based catalysts are still in a rapid development stage in terms of optimizing Hg⁰ oxidation performance. Due to the universal property of ceria, it can act as either support or promoter to supported vanadium-based catalysts. However, the introduction mode of Ce on the Hg⁰ oxidation is still unclarified. Herein, introducing Ce to vanadium-based catalysts as a promoter (VCe/Ti) plays a more effective role in the Hg⁰ oxidation than only doping Ce into TiO₂ support (V/CeTi). It is revealed that the strong interaction between V and Ce increases the orbital hybridization, and reduces the lowest unoccupied molecular orbital (LUMO) of V, which is conducive to adsorbing and activating HCl. The excellent performance of the VCe/Ti catalyst can be ascribed to its superior redox ability, stronger HCl adsorption capacity, abundant surface oxygen vacancies, and the redox equilibrium (Ce³⁺ + V⁵⁺ ↔ Ce⁴⁺ + V⁴⁺), which improves electron transfer, and thus the catalytic activity. This work provides the potential application of Ce-modified V-based catalysts for the simultaneous control of NO_x and Hg⁰ in stationary sources.

Effecting pattern study of SO2 on Hg0 removal over α-MnO2 in-situ supported magnetic composite

α-MnO₂ was in-situ supported onto silica coated magnetite nanoparticles (MagS-Mn) to study the adsorption and oxidation of Hg⁰ as well as the effecting patterns of SO₂ and O₂ on Hg⁰ removal. MagS-Mn showed Hg⁰ removal capacity of 1122.6 μg/g at 150 °C with the presence of SO₂. Hg⁰ adsorption and oxidation efficiencies were 2.4% and 90.6%, respectively. Hg⁰ removal capability deteriorated at elevated temperatures. Surface oxygen and manganese chemistry analysis indicated that SO₂ inhibited the Hg⁰ removal through consumption of adsorbed oxygen and reduction of high valence manganese. This inhibiting effect was observed to be counteracted by O₂ at lower temperatures. O₂ tended to compete with SO₂ for active sites and further create additional adsorbed oxygen sites for Hg⁰ surface reaction via surface dissociative adsorption rather than replenish the active sites consumed by SO₂. The high valence manganese was also preserved by O₂ which was essential to Hg⁰ oxidation. The intervention of O₂ in the inhibition of SO₂ on Hg⁰ removal was weakened at temperatures higher than 250 °C. Aa a result, Hg⁰ tends to be catalytic oxidized in the condition of low reaction temperatures and with the presence of O₂ over α-MnO₂ oriented composites.

Heavy metals accumulation in bivalve mollusks collected from coastal areas of southeast China

The distribution of six heavy metal and metalloids (As, Cd, Cr, Hg, Ni and Pb) was analyzed in 597 bivalve mollusks (8 species) collected from coastal areas of southeast China. Target hazard quotient, total hazard index, and target cancer risk were calculated to evaluate potential human health risks from bivalve consumption. The mean concentrations of As, Cd, Cr, Hg, Ni and Pb were 1.83, 0.581, 0.111, 0.0117, 0.268 and 0.137 mg kg^-1 wet weight in bivalves. The average estimated daily intakes for As, Cd, Cr, Hg, Ni and Pb were 1.156, 0.367, 0.07, 0.007, 0.167 and 0.087 μg kg^-1 body weight/day. Health risk assessment showed that there was no non-carcinogenic health risk to general residents to these metals from consumption of bivalves. Cd intake through mollusks posed a potential cancer risk. Accordingly, regular monitoring for heavy metals, especially Cd is recommended with respect to potential contaminant on marine ecosystems.

Distribution, chemical fractionation, and potential environmental risks of Hg, Cr, Cd, Pb, and As in wastes from ultra-low emission coal-fired industrial boilers in China

This study conducted a comprehensive investigation of the distribution, chemical fractionation, and potential environmental risks of Hg, Cd, Cr, Pb, and As in waste based on new data from five ultra-low emission (ULE) coal-fired industrial boilers (CFIBs). The results showed that fly ash was enriched with Cd, Pb, As, and Hg, while its Cr contents were not invariably higher than those of slag. Fly ash was the predominant output flow for Hg, Cd, Cr, Pb, and As in the tested ULE boilers, with higher proportions of HTEs in the fly ash and lower proportions of HTEs in the flue gas than in the non-ULE boilers. The average proportions of residual Hg, Cd, Cr, Pb, and As in wastes revealed the following order: slag > fly ash > flue gas desulfurization (FGD) by-products. The potential environmental risks of Hg, Cd, Cr, Pb, and As in the fly ash, slag, and FGD by-products of CFIBs at the county level in the Beijing-Tianjin-Hebei Air Pollution Transmission Channel Cities ("2 +26 cities") region showed spatial heterogeneity. It is predicted that the potential release of Pb, Cr, and Cd in the fly ash would increase and that of the FGD by-products would decrease after the implementation of the ULE retrofitting of all CFIBs.

Mercury removal from flue gas by a MoS2/H2O heterogeneous system based on its absorption kinetics

An enhanced MoS₂/C₁₀TAB/H₂O system was built and investigated for Hg⁰ removal based on strengthening the Hg⁰ gas-liquid mass transfer. The results showed that adding 7 mg/L C₁₀TAB can improve the Hg⁰ removal efficiency from 76.5 to 88.7% as decrease of the solution surface tension. Keeping 2000 rpm of stirring rate accelerated the renewal rate of gas-liquid interface, thereby enhancing Hg⁰ removal. SO₂ slightly promoted the Hg⁰ removal efficiency to 91% because of the absorption of SO₂ causing a decrease in the solution pH from 6.9 to 4.3. NO participated in Hg⁰ removal reactions but not removed in this system which visibly enhanced the Hg⁰ removal efficiency to 94%. The Hg mass transfer kinetics were analyzed to determine how C₁₀TAB promoted Hg⁰ removal. The Hg-TPD, Hg fate, and species results revealed that Hg⁰ was first oxidized to Hg²⁺, then bonded with S to generate HgS and enrich on the MoS₂. Therefore, improving the Hg⁰ gas-liquid mass transfer can enhance Hg⁰ removal in MoS₂/H₂O system, which can provide reference for purification of other insoluble pollutants in absorption system.

Regeneration mechanism of a novel high-performance biochar mercury adsorbent directionally modified by multimetal multilayer loading

Biochar that is directly obtained by pyrolysis exhibits a low adsorption efficiency; furthermore, the process of recycling adsorbents is ineffective. To solve these problems, conventional chemical coprecipitation, sol-gel, multimetal multilayer loading and biomass pyrolysis coking processes have been integrated. After selecting specific components for structural design, a novel high-performance biochar adsorbent was obtained. The effects of the O₂ concentration and temperature on the regeneration characteristics were explored. An isothermal regeneration method to repair the deactivated adsorbent in a specific atmosphere was proposed, and the optimal regeneration mode and conditions were determined. The microscopic characteristics of the regenerated samples were revealed along with the mechanism of Hg⁰ removal and regeneration by using temperature-programmed desorption technology and adsorption kinetics. The results show that doping multiple metals can reduce the pyrolysis reaction barrier of the modified biomass. On the modified surface of the sample, the doped metals formed aggregated oxides, and the resulting synergistic effect enhanced the oxidative activity of the biochar carriers and the threshold effect of Ce oxide. The optimal regeneration conditions (5% O₂ and 600 °C) effectively coordinated the competitive relationship between the deep carbonization process and the adsorption/oxidation site repair process; in addition, these conditions provided outstanding structure-effect connections between the physico-chemical properties and Hg⁰ removal efficiency of the regenerated samples. Hg⁰ adsorption by the regenerated samples is a multilayer mass transfer process that involves the coupling of physical and chemical effects, and the surface adsorption sites play a leading role.

S,N-rich luminous covalent organic frameworks for Hg2+ detection and removal

The challenge for simultaneous detection and removal of Hg²⁺ is the design of bifunctional materials bearing abundant accessible chelating sites with high affinity. Covalent-organic frameworks (COFs) are attracting more and more attention as potential bifunctional materials for Hg²⁺ detection due to their large specific surface area, ordered pores, and abundant chelating sites. Here, a new luminous S,N-rich COF_BTT-AMPD based on hydrophilic block unit of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AMPD) was constructed, which improved the solubility and affinity for Hg²⁺ greatly. Another S-rich fused-ring unit of benzotrithiophene tricarbalaldehyde (BTT) enhanced the conjugation of COF_BTT-AMPD, and the methyl-rich chains block unit of AMPD effectively suppressed the aggregation-caused quenching. Thus, the COF_BTT-AMPD emitted strong fluorescence at 546 nm in liquid and solid as well as different solvent with a wide pH range, which was used for the visual detection and removal of Hg²⁺ (detection limit: 2.6 nM, linear range: 8.6 × 10^-3-20 μM, monolayer adsorption capacity: 476.19 mg g^-1) successfully. COF_BTT-AMPD-based fabric and light-emitting diode coatings were further constructed to realize the visual detection of Hg²⁺ vapor. The results reveal the potential of S,N-rich luminous COF_BTT-AMPD for Hg²⁺ detection and remediation in the environment.

Structure-Directing Role of Support on Hg0 Oxidation over V2O5/TiO2 Catalyst Revealed for NOx and Hg0 Simultaneous Control in an SCR Reactor

The crystal structure of TiO₂ strongly influences the physiochemical properties of supported active sites and thus the catalytic performance of the as-synthesized catalyst. Herein, we synthesized TiO₂ with different crystal forms (R = rutile, A = anatase, and B = brookite), which were used as supports to prepare vanadium-based catalysts for Hg⁰ oxidation. The Hg⁰ oxidation efficiency over V₂O₅/TiO₂-B was the best, followed by V₂O₅/TiO₂-A and V₂O₅/TiO₂-R. Further experimental and theoretical results indicate that gaseous Hg⁰ reacts with surface-active chlorine species produced by the adsorbed HCl and the reaction orders of Hg⁰ oxidation over V₂O₅/TiO₂ catalyst with respect to HCl and Hg⁰ concentration were approximately 0 and 1, respectively. The excellent Hg⁰ oxidation efficiency over V₂O₅/TiO₂-B can be attributed to lower redox temperature, larger HCl adsorption capacity, and more oxygen vacancies. This work suggests that to achieve the best simultaneous removal of NO_x and Hg⁰ on state-of-the-art V₂O₅/TiO₂ catalyst, a combination of anatase and brookite TiO₂-supported vanadyl tandem catalysts is supposed to be employed in the SCR reactor, and the brookite-type catalyst should be on the downstream of the anatase-based catalyst due to the inhibition of NH₃ on Hg⁰ oxidation.

The Effects of Physical-Chemical Evolution of High-Sulfur Petroleum Coke on Hg0 Removal from Coal-Fired Flue Gas and Exploration of Its Micro-Scale Mechanism

As the solid waste by-product from the delayed coking process, high-sulfur petroleum coke (HSPC), which is hardly used for green utilization, becomes a promising raw material for Hg⁰ removal from coal-fired flue gas. The effects of the physical-chemical evolution of HSPC on Hg⁰ removal are discussed. The improved micropores created by pyrolysis and KOH activation could lead to over 50% of Hg⁰ removal efficiency with the loss of inherent sulfur. Additional S-containing and Br-containing additives are usually introduced to enhance active surface functional groups for Hg⁰ oxidation, where the main product are HgS, HgBr, and HgBr₂. The chemical-mechanical activation method can make additives well loaded on the surface for Hg⁰ removal. The DFT method is used to sufficiently explain the micro-scale reaction mechanism of Hg⁰ oxidation on the surface of revised-HSPC. ReaxFF is usually employed for the simulation of the pyrolysis of HSPC. However, the developed mesoporous structure would be a better choice for Hg⁰ removal in that the coupled influence of pore structure and functional groups plays a comprehensive role in both adsorption and oxidation of Hg⁰. Thus, the optimal porous structure should be further explored. On the other hand, both internal and surface sulfur in HSPC should be enhanced to be exposed to saving sulfur additives or obtaining higher Hg⁰ removal capacity. For it, controllable pyrolysis with different pyrolysis parameters and the chemical-mechanical activation method is recommended to both improve pore structure and increase functional groups for Hg⁰ removal. For simulation methods, ReaxFF and DFT theory are expected to explain the micro-scale mechanisms of controllable pyrolysis, the chemical-mechanical activation of HSPC, and further Hg⁰ removal. This review work aims to provide both experimental and simulational guidance to promote the development of industrial application of Hg⁰ adsorbent based on HSPC.