Mercury Adsorption Efficiency Research Articles

Development of mesoporous silica-based active coatings for methylmercury removal: Towards enhanced active packaging

Active coatings capable of selectively removing pollutants are an innovative approach against human exposure to pollutants via food. This study aimed to develop an active coating capable of removing methylmercury from liquid food media. Thiolation of mesoporous silica particles modified via (3-Mercaptopropyl)trimethoxysilane increased their mercury adsorption capacity to 100 mg/g. The particles were successfully integrated into industrial, epoxy and polyurethane coatings but the induced mercury adsorption efficiency in the coatings was dependent on their type of binder. Scanning electron microscopy and energy-dispersive X-ray results revealed that the silica particles were entrapped within the coatings but remained more accessible to the external media in the industrial and polyurethane coatings. Thermogravimetric analysis confirmed the successful integration of the components. The kinetics of adsorption showed that the adsorption of methylmercury was achieved within a time range of 20-240 min, depending on the binder used in the coating. The methylmercury adsorption ability of the coatings was preserved in different food simulants and in the presence of competitive ions and in an environment comprising cysteine. In vitro biosafety assays on different cell lines showed no negative effect from the silica modification on the safety of the coatings.

Molecular Structure Analysis and Mercury Adsorption Mechanism of Iron-Based Modified Biochar

The elemental composition, molecular skeleton vibration mode, and carbon-chain structure of iron-based modified biochar demercuration materials were studied on a microscopic scale using a variety of characterization methods. A three-dimensional molecular structure monomer model of iron-based modified biochar with defective carbon rings doped with high-valence metals was constructed. The reaction path of Hg0 adsorption on the surface of iron-based modified biochar was studied. The activation energy barrier and the rate-determining step of Hg0 adsorption on the surface of iron-based modified biochar were determined. Then, two reaction mechanisms and the corresponding bonding mechanism of Hg0 adsorption on modified biochar were proposed. In addition, the feasibility of regenerating biochar with different load ratios was verified and the regeneration reaction mechanism of inactivated biochar at different adsorption sites was revealed. The results show that the molecular structure of iron-based modified biochar is dominated by polycyclic aromatic carbon, and its molecular formula is C45H24O12NFe. Adsorption sites on iron-based modified biochar surface are not unique. A heterogeneous oxidation reaction occurs between Hg0, a Lewis base, and modified biochar, a Lewis acid. Hg-O-Fe-Ox–1 and the complex Hg-OM are the main products of Hg0 oxidation. Oxygen vacancies with electrons are the chemical adsorption sites, and Fe3+, lattice oxygen, and chemisorbed oxygen are the main oxidation sites on the modified biochar. The coupling of these four constituents enables the adsorption and oxidation of Hg0. Inactivated biochar can be regenerated by supplementing the lost lattice oxygen or chemisorbed oxygen with more oxygen. The maximum mercury adsorption efficiency decreased to 90% of the primary mercury adsorption efficiency. This study quantitatively revealed the mercury adsorption mechanism of iron-based modified biochar and the regeneration mechanism of inactivated biochar, laying a foundation for further improvements in the mercury adsorption efficiency of metal-modified biochar.

Enhancement of Hg0 adsorption performance at high temperature using Cu-Zn bimetallic sulfide with elevated thermal stability

In this work, a series of Cu-Zn bimetallic sulfides were synthesized to improve the mercury adsorption performance at high temperatures. Results showed that the adsorption performance of Cu-Zn bimetallic sulfides are much better than CuS and ZnS at high temperature. Compared with the pure CuS, the mercury adsorption efficiency greatly increased from 40% to 88% at 220 °C for the optimal Cu0.95Zn0.05S. XRD results showed that Zn can enter into the lattice structure of CuS, which significantly promoted the thermal stability of CuS. TG analysis indicated that the weight loss for the Cu-Zn bimetallic sulfides was only 14%-19%, while the weight loss for CuS is as high as 42%. Moreover, the adding of Zn can significantly inhibit the formation of inactive SO42- during the synthesis process, enabling more Sx and S22- sites exposed on the surface. Raman spectra indicated that the Sx sites mainly existed in the form of long-chain Sx (L- Sx) or ring Sx on the pure CuS, while existed as short-chain Sx (S-Sx) on Cu0.95Zn0.05S. The S-Sx sites are more active in mercury adsorption, resulting in the better performance of Cu-Zn bimetallic sulfides.

Mercury Adsorption Characteristics of Carbon Sorbent with Low Surface Area

ABSTRACT Several studies have been conducted to decrease the cost of sorbents used for the control of mercury emissions. Thus far, several sorbents with low surface areas have been reported to exhibit promising mercury removal capacities. However, based on the results reported, it is difficult to understand the mechanisms of adsorption and oxidization of elemental mercury on sorbents with low surface areas compared to those with higher surface areas. Three types of materials with different surface areas were evaluated herein for use as carbon sorbents for the adsorption of elemental mercury: (1) coal, (2) sewage sludge, and (3) unburned carbon. The respective raw sorbents and FeCl3-impreganted congeners were evaluated. Each sorbent was tested in a fixed-bed reactor system under two simulated flue gas conditions (1) without and (2) with 20 ppm hydrogen chloride (HCl). The injection of HCl increased the mercury adsorption efficiency of all tested sorbents by decreasing the emission of elemental mercury. Doping the sorbent with FeCl3 increased the mercury adsorption efficiency during the earlier test period under both simulated flue gas conditions (without and with HCl). FeCl3-impregnated activated carbon and FeCl3-impregnated unburned carbon emitted large amounts of oxidized mercury during the later test periods.

Mercury adsorption characteristics of Cl-impregnated activated carbons in simulated flue gases

Activated carbon injection upstream of a particulate matter control device is a general method to control mercury in a coal-fired flue gas. Nitrogen oxides (NOx) and hydrogen chloride (HCl) in flue gas have been reported to increase the efficiency of activated carbon for mercury removal. In a coal-fired power plant, a NOx control device is generally located upstream of a particulate matter control device. In addition, if coal with a low chloride (Cl) content is burned, the concentrations of NOx and HCl may be low in the flue gas upstream of a particulate matter control device. Under these conditions, chemically promoted activated carbon is necessary to effectively control mercury. This study was designed to suggest the best chloride compound impregnated on activated carbon depending on the flue gas composition. HCl, ferric chloride (FeCl3) and cupric chloride (CuCl2) were impregnated with an identical concentration of Cl on activated carbon. Then, each sorbent was tested using a fixed-bed reactor system at 140 °C. CuCl2-impregnated activated carbon (CuCl2-AC) was tolerant of SO2 gas. The mercury adsorption efficiency was higher in the order of CuCl2-AC, FeCl3-impregnated activated carbon (FeCl3-AC) and HCl-impregnated activated carbon (HCl-AC) with 1% Cl for all three sorbents for the tests with a simulated flue gas of 12% CO2, 5% O2, 7% H2O, 60–70 µg/m3 Hg0, 500 ppm SO2, 20 ppm NO and N2 balance gas. However, the mercury adsorption efficiencies among the Cl-impregnated activated carbon sorbents became more similar with the increase in Cl concentration on activated carbon.

배기가스 조성에 따른 활성탄의 수은 흡착 특성

Activated carbon injection upstream of a particulate matter control device is a widely applied method for the control of mercury emission from the coal-fired plant and waste incinerator. Performance of activated carbon in mercury control depends on various factors such as flue gas composition, physical and chemical properties of fly ash and activated carbon, etc. This study was designed to investigate the effect of flue gas composition on the mercury adsorption efficiency of activated carbon. Commercial activated carbon was obtained, and a fixed-bed reactor system was used for the tests of its mercury adsorption at various simulated flue gas conditions. A baseline gas consists of 12% carbon dioxide (CO₂), 5% oxygen (O₂), 7% water vapor (H₂O), 60∼70 μg mercury (Hg)/m³ and balance nitrogen (N₂). Each of acidic gases such as sulfur dioxide (SO₂), nitrogen monoxide (NO) and hydrogen chloride (HCl) was added to the baseline gas and injected for the test to investigate the effect of each acidic gas on the mercury adsorption efficiency of activated carbon. In addition, the mercury adsorption efficiency of activated carbon was examined at the conditions of simulated flue gas (1) before air pollution control (2) after desulfurization and (3) after nitrogen oxides (NOx) control.

Solvent-Free Synthesis of Phosphonic Graphene Derivative and Its Application in Mercury Ions Adsorption.

Functionalized graphene was efficiently prepared through ball-milling of graphite in the presence of dry ice. In this way, oxygen functional groups were introduced into material. The material was further chemically functionalized to produce graphene derivative with phosphonic groups. The obtained materials were characterized by spectroscopic and microscopic methods, along with thermogravimetric analysis. The newly developed material was used as an efficient mercury adsorbent, showing high adsorption efficiency. The adsorption isotherms were fitted using Freundlich and Langmuir models. The adsorption kinetics were fitted with pseudo-first order and pseudo-second order models. Adsorption selectivity was determined in the presence of cadmium ions and nickel ions. The presence of mentioned bivalent ions in the solution did not affect mercury adsorption efficiency.

Sulfur abundant S/FeS2 for efficient removal of mercury from coal-fired power plants

Sulfur abundant S/FeS2 prepared by a hydrothermal method was employed for removing elemental mercury (Hg0) from coal-fired flue gas at low temperature. The S/FeS2 exhibited optimal Hg0 adsorption performance at 80 °C, which matched the temperature window between the flue gas desulfurization (FGD) and wet electrostatic precipitator (WESP) systems. The adverse effects of H2O and SO2 on Hg0 adsorption were slight. The Hg0 adsorption capacity of S/FeS2 was up to 2732 μg/g when achieved 50% breakthrough threshold. Both elemental sulfur (S) and FeS2 in the S/FeS2 contributed to the excellent Hg0 adsorption capacity. The mercury leaching tests show that only 0.00076% mercury adsorbed on the S/FeS2 was leached out. The mercury concentration in leachate was 0.694 μg·L−1, which was much lower than that for a commercial AC (1.214 μg·L−1). Furthermore, the S/FeS2 presented about 95% oxidized mercury (Hg2+) adsorption efficiency from WESP effluent. The Hg2+ concentration could decreased rapidly from 50 μg·L−1 to below 2.5 μg·L−1 in 30 min, which was much lower than the World Health Organization (WHO) guideline (6 μg·L−1). With these advantages, S/FeS2 appears to be a promising material for co-beneficial gaseous Hg0 and aqueous Hg2+ removal from power plants by injecting upstream of a WESP system.

Adsorption of mercury by activated carbon prepared from dried sewage sludge in simulated flue gas

ABSTRACTConversion of sewage sludge to activated carbon is attractive as an alternative method to ocean dumping for the disposal of sewage sludge. Injection of activated carbon upstream of particulate matter control devices has been suggested as a method to remove elemental mercury from flue gas. Activated carbon was prepared using various activation temperatures and times and was tested for their mercury adsorption efficiency using lab-scale systems. To understand the effect of the physical property of the activated carbon, its mercury adsorption efficiency was investigated as a function of its Brunauer–Emmett–Teller (BET) surface area. Two simulated flue gas conditions, (1) without hydrogen chloride (HCl) and (2) with 20 ppm HCl, were used to investigate the effect of flue gas composition on the mercury adsorption capacity of activated carbon. Despite very low BET surface area of the prepared sewage sludge activated carbons, their mercury adsorption efficiencies were comparable under both simulated flue gas conditions to those of pinewood and coal activated carbons. After injecting HCl into the simulated flue gas, all sewage sludge activated carbons demonstrated high adsorption efficiencies, that is, more than 87%, regardless of their BET surface area.Implications: We tested activated carbons prepared from dried sewage sludge to investigate the effect of their physical properties on their mercury adsorption efficiency. Using two simulated flue gas conditions, we conducted mercury speciation for the outlet gas. We found that the sewage sludge activated carbon had mercury adsorption efficiency comparable to pinewood and coal activated carbons, and the presence of HCl minimized the effect of physical property of the activated carbon on its mercury adsorption efficiency.

Inhibitory effects of water vapor on elemental mercury removal performance over cerium-oxide-modified semi-coke

A fixed-bed reactor was used to study the effect of water vapor on the efficiency of Hg0 removal over CeO2-modified semi-coke. Adsorption experiments showed that the oxidation activity, and therefore, the mercury adsorption efficiency decreased with increasing water vapor concentrations. Hydrogen temperature-programmed reduction (H2-TPR) indicated that the oxidation activity of CeO2 decreased after water vapor treatment. Fourier-transform infrared (FT-IR) studies revealed that CeO2-H2O showed new bending vibration peaks at 1110cm−1 ascribed to Ce–OH groups. X-ray photoelectron spectroscopy (XPS) results showed that the content of Ce–OH increased from 20.85% to 39.99%, while the lattice oxygen content decreased from 68.21% to 45.83% after water vapor treatment. Density functional theory (DFT) calculations revealed that H2O can be dissociated on clean and oxygen-defective CeO2(111) surfaces to form H atoms and OH fragments. The H atoms associated with the adjacent oxygen atoms of CeO2, and the OH fragments were bound directly with Ce atoms to form Ce–OH for the clean CeO2 surface; or occupied the oxygen vacancies and were surrounded by three Ce atoms via van der Waals forces, without additional bond formation for the oxygen-defective CeO2 surface. Thus, the formation of Ce–OH groups and the consumption of lattice oxygens reduced the Hg0 removal efficiency.

Plasma-induced adsorption of elemental mercury on TiO2 supported metal oxide catalyst at low temperatures

A plasma–catalyst reactor was used for the adsorption of elemental mercury at low temperatures. SiO2, TiO2 and SiO2 or TiO2 supported transition metal oxide catalysts were packed in the plasma discharge zone for adsorption enhancement. The results indicated that non-thermal plasma could induce the adsorption of elemental mercury effectively by catalysts. TiO2 displays much higher adsorption efficiency than SiO2 does. The adsorption efficiency is greatly improved by loading transition metal oxides on TiO2. Mn/TiO2 is the most efficient catalyst, and ~99% of Hg0 adsorption efficiency can be obtained under a SED of 2.3±0.3JL−1. The interaction between the plasma and catalyst was also investigated. The chemical properties of the catalyst, such as the active sites and electron transfer capacity, are key factors that affect adsorption efficiency. The mercury adsorption in plasma–catalyst reactor results primarily from the interaction between weakly adsorbed mercury and activated oxygen on catalyst surface induced by plasma. In addition, the effect of the O2 concentration and HCl on mercury adsorption efficiency was investigated. The adsorption efficiency has a logarithmic correlation with O2 concentration in the gas flow.

Experimental and kinetic studies of gas-phase mercury adsorption by raw and bromine modified activated carbon

Gas-phase mercury capture performance of raw activated carbon (R-AC) and bromine modified activated carbon (AC–Br) was evaluated in a fixed-bed reactor. Effect of flue gas temperature on mercury adsorption efficiency was explored. Sorbent characterization was conducted to feature their morphologies correlated to mercury adsorption efficiency. Adsorption kinetic and thermodynamic analysis of fixed-bed experimental results was also carried out to explore the different mercury adsorption mechanisms of R-AC and AC–Br. The results show that vapor mercury adsorption capacity of AC–Br increases with temperature, but R-AC demonstrates opposite results. The bromine ion (Br−) remains in the mesopore and the surface of R-AC in the form of amorphous during modification process, leading to the reduction of mesopore volume and the increase of micropore volume. The increase of active site (Br−) on activated carbon improves chemisorption of vapor mercury on AC–Br at 150°C and 200°C. The kinetic analysis shows that mercury adsorption on active sites is the adsorption rate controlling step, in which it can be divided into two steps: surface adsorption and intraparticle diffusion adsorption. Vapor mercury adsorption on AC–Br needs more activated energy due to the enhancement of chemisorption. The initial mercury adsorption rate of AC–Br increases with temperature, which is different from that of R-AC. The thermodynamic analysis shows that the adsorption of gas-phase mercury on both R-AC and AC–Br is spontaneous, endothermic and mainly physical in nature enhanced by chemisorption. The bromine modification enhances chemisorption of vapor mercury on AC–Br leading to the increase of complexity degree of mercury adsorption process.

Effects of modified fly ash on mercury adsorption ability in an entrained-flow reactor

This study investigated the effectiveness of fly ash modified with halogenated material in absorbing mercury in an entrained-flow reactor. Two different types of fly ash from coal-fired power plants were treated with varying amounts of CaCl2, CaBr2 and HBr. The first derivative of the Hg removal concentration was explored to help quantify the effectiveness of adsorbents. Characterization studies of the fly ash using SEM and BET indicate that the surface structure of the modified fly ash was altered, and the specific surface area, average pore size and pore volume were all slightly increased. Compared to the unmodified fly ash, both the mercury adsorption efficiency and the mercury concentration change rate in the flue gas improved significantly. The fly ash oxidized by HBr showed the greatest adsorption ability among the three additives. The improvement in the characteristics of the modified fly ash was due to both physical and chemical adsorption. The study also showed that particle size of the fly ash is a significant factor in the removal of mercury from the flue gas. Under experimental conditions, the adsorption efficiencies for the two HBr-modified fly ash (A and B) were 2.4 and 6.7 times greater for>200 mesh than for 80–200 mesh.

Factors affecting Hg(II) adsorption on hybrid nanostructured silicas: influence of the synthesis conditions

This paper reports the synthesis, characterization and mercury adsorption behaviour of new organic–inorganic hybrid nanostructured silicas obtained by co-condensation, molecular imprinting and post-synthesis routes. N2 adsorption–desorption measurements, XRD, FT-IR, MAS NMR, SEM, TEM and elemental analysis were used to characterize the physico-chemical properties of the hybrid nanostructured materials. The materials were studied for Hg(II) adsorption in aqueous medium at pH 3 and compared with unmodified nanostructured silica. Mercury adsorption was higher in the hybrid material prepared by the co-condensation method that reached a mercury uptake of 134 mg Hg/g. The best mercury adsorption efficiency was observed for the hybrid material prepared by molecular imprinting route. The synthetic route employed clearly affects the textural properties of the silica, the amount of organic ligand attached onto the support and mercury adsorption behaviour.

Mercury oxidation and adsorption characteristics of potassium permanganate modified lignite semi-coke

The adsorption characteristics of virgin and potassium permanganate modified lignite semi-coke (SC) for gaseous Hg0 were investigated in an attempt to produce more effective and lower price adsorbents for the control of elemental mercury emission. Brunauer-Emmett-Teller (BET) measurements, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to analyze the surface physical and chemical properties of SC, Mn-SC and Mn-H-SC before and after mercury adsorption. The results indicated that potassium permanganate modification had significant influence on the properties of semi-coke, such as the specific surface area, pore structure and surface chemical functional groups. The mercury adsorption efficiency of modified semi-coke was lower than that of SC at low temperature, but much higher at high temperature. Amorphous Mn7+, Mn6+ and Mn4+ on the surface of Mn-SC and Mn-H-SC were the active sites for oxidation and adsorption of gaseous Hg0, which oxidized the elemental mercury into Hg2+ and captured it. Thermal treatment reduced the average oxidation degree of Mnx+ on the surface of Mn-SC from 3.80 to 3.46. However, due to the formation of amorphous MnOx, the surface oxidation active sites for gaseous Hg0 increased, which gave Mn-H-SC higher mercury adsorption efficiency than that of Mn-SC at high temperature.

Adsorption of Hg2+from aqueous solution on functionalized MCM-41

Mesoporous MCM-41 has been functionalized using 3-aminopropyltriethoxysilane (KH550) and 3-(2-aminoethylamino)propyldimethoxymethylsilane (KH602). The adsorption behavior of Hg2+ on functionalized MCM-41 was investigated systematically. The adsorption rates were very fast and agreed well with pseudo second-order kinetics. The adsorption isotherms fitted the Langmuir model well. The modified MCM-41 adsorbent functionalized using KH602 (NM2) displayed the greatest mercury adsorption efficiency and residual concentration of Hg2+ was able to achieve drinking water standards. The regeneration capacity maintained 99.75% performance when the initial solution concentration was 4 mg L−1 (4000 ppb) at the tenth cycle, meeting the safe regulatory discharge standard for the first time. Meanwhile, regeneration by washing only with deionized water to remove residual surface Hg2+ can cut down the cost of traditional desorption agents and reduce damage to the structure of the adsorbent. Therefore, the adsorbent NM2 has potential and promising application in the field of water pollution control.

Sorption of mercury by activated carbon in the presence of flue gas components

The purpose of the current study is to evaluate the mercury removal ability of F400 and Norit FGD activated carbons, through fixed bed adsorption tests at inert atmosphere (Hg° + N 2). Additionally, adsorption tests were realized on F400 activated carbon, in the presence of HCl, O 2, SO 2 and CO 2 in nitrogen flow. The obtained results, revealed that F400 activated carbon, with a high-developed micropore structure and increased BET area, exhibit larger Hg° adsorptive capacity compared to Norit. HCl and O 2, can strongly affect mercury adsorption, owing to heterogeneous oxidation and chemisorption reactions, which is in accordance with the assumptions of some researchers. Additionally, SO 2 presence enhances mercury adsorption, in contrast with the conclusions evaluated in other studies. The above result could be attributed to the possible formation of sulphur spaces on activated carbon surface and consist of a clarification for the role of SO 2 on mercury adsorption. On the contrary, the mercury adsorption efficiency of F400 activated carbon showed a decrease at about 25%, with increasing CO 2 concentration from 0 to 12%.

Simulation of mercury capture by sorbent injection using a simplified model

Mercury pollution by fossil fuel combustion or solid waste incineration is becoming the worldwide environmental concern. As an effective control technology, powdered sorbent injection (PSI) has been successfully used for mercury capture from flue gas with advantages of low cost and easy operation. In order to predict the mercury capture efficiency for PSI more conveniently, a simplified model, which is based on the theory of mass transfer, isothermal adsorption and mass balance, is developed in this paper. The comparisons between theoretical results of this model and experimental results by Meserole et al. [F.B. Meserole, R. Chang, T.R. Carrey, J. Machac, C.F.J. Richardson, Modeling mercury removal by sorbent injection, J. Air Waste Manage. Assoc. 49 (1999) 694–704] demonstrate that the simplified model is able to provide good predictive accuracy. Moreover, the effects of key parameters including the mass transfer coefficient, sorbent concentration, sorbent physical property and sorbent adsorption capacity on mercury adsorption efficiency are compared and evaluated. Finally, the sensitive analysis of impact factor indicates that the injected sorbent concentration plays most important role for mercury capture efficiency.

Mesoporous silica functionalized with 2-mercaptopyridine: Synthesis, characterization and employment for Hg(II) adsorption

Mesoporous silicas (SBA-15 and MCM-41) have been functionalized by two different methods. Using the heterogeneous route the silylating agent, 3-chloropropyltriethoxysilane, was initially immobilized onto the mesoporous silica surface to give the chlorinated mesoporous silica Cl-SBA-15 or Cl-MCM-41. In a second reaction a multifunctionalized N, S donor compound (2-mercaptopyridine, MP) was incorporated to obtain the functionalized silicas denoted as MP-SBA-15-Het or MP-MCM-41-Het. Using the homogeneous route, the functionalization was achieved via the one step reaction of the mesoporous silica with an organic ligand containing the chelating functions, to give the modified mesoporous silicas denoted as MP-SBA-15-Hom or MP-MCM-41-Hom. When the functionalized mesoporous silicas were employed as adsorbents for the regeneration of aqueous solutions contaminated with Hg(II), mercury adsorption was higher in the mesoporus silicas prepared by the homogeneous method. The modified mesoporous silica MP-SBA-15-Hom displayed the best mercury adsorption efficiency.