Gas-phase Elemental Mercury Removal Research Articles

Gas-phase elemental mercury removal by bamboo charcoal impregnated with KMnO4: mechanism study

Bamboo charcoal is made from biomass with porous structure. The performance of bamboo charcoal (BC) and KMnO4-modified BC was studied with a bench-scale fixed-bed reactor. X-ray photoelectron spectroscopy, X-ray diffraction, elemental analysis and BET surface area analysis were used to determine the physical and chemical property of the sorbents. The results show that the modification increased the oxygen functionalities and π electrons, which facilitate the mercury oxidation on sorbent surface and act as possible active centers for elemental mercury.

Elemental mercury removal by I−-doped Bi2WO6 with remarkable visible-light-driven photocatalytic oxidation

In this work, I–-doped Bi2WO6 composites were synthesized using a one-step hydrothermal method, and the effect of iodine doping on their photocatalytic efficiency in gas-phase elemental mercury removal was evaluated under visible-light irradiation. The results showed that 1.0 wt.% iodine doped Bi2WO6 exhibited the optimal Hg0 removal efficiency of 87.6 % and 97.5 % under N2+O2+CO2 and N2+O2+CO2+SO2+NO conditions, respectively. The improved photocatalytic activity of Bi2WO6 can be ascribed to the reduction in the potential energy of its conduction band and recombination rate of electron-hole pairs, as well as the acceleration of charge transfer. The density functional theory calculations showed that iodine was doped in the (WO4)2– layer and oxidized HgO can be adsorbed on the surface of I– doped Bi2WO6. The OBi site was found to be exhibit weak adsorption with respect to HgO, implying that most conducive to the desorption of HgO. Finally, the photocatalysis mechanisms was elaborated.

Gas-phase elemental mercury removal by nano-ceramic material

The nano-ceramic which is mesoporous silica material was applied to test the removal efficiency of gas-phase Hg0 using a fixed-bed reactor. The physical and chemical properties of nano-ceramic were investigated by various techniques such as BET surface area (BET), X-ray diffraction, fourier transform infrared spectrometer (FTIR), and scanning electron microscope (SEM); then, the sample was tested for mercury adsorption under different conditions. The mercury adsorption tests shown that different Hg0 concentration, adsorption temperature, gas flow rate, and different gas components have significant effects on the mercury removal performance of nano-ceramic, and the adsorption removal rate of nano-ceramic can be 75.58% under the optimal experimental conditions. After fitting the experimental data to the adsorption model, it was found that the theoretical maximum mercury adsorption amount q max of nano-ceramic is 1.61 mg g−1 and there were physical and chemical adsorption at the same time. The adsorption kinetics fitting results shown that the adsorption process of nano-ceramic exhibits multi-segment characteristics of “transmembrane–diffusion–adsorption.”

Inherent thermal regeneration performance of different MnO2 crystallographic structures for mercury removal.

Manganese oxides with different crystallographic structures were investigated for gas-phase elemental mercury removal. The inherent thermal regeneration performance and mechanism of α- and γ-MnO2 were studied. The manganese dioxides were found to possess a mercury removal efficiency of higher than 96% even after 120 min mercury exposure except for β-MnO2 which removed much less mercury than Mn2O3. The α-MnO2 was found to have a higher recyclability of mercury capture and better durability for regeneration than γ-MnO2. During the first 1 h of exposure, α-MnO2 showed an excellent mercury capacity of 128 μg/g over 5 regeneration cycles. While for γ-MnO2, the mercury capacity of the fifth cycle was reduced to 68.74 μg/g, which is much lower than 131.42 μg/g for the first cycle. The microstructure of α-MnO2 was maintained throughout regeneration cycles due to its capability to retain lattice oxygen. In comparison, γ-MnO2 experienced reconstruction and phase transformation induced by oxygen vacancies due to lattice oxygen loss during regeneration process, leading to a degradation in mercury capture. The α-MnO2 oriented composite was found to be better developed into a regenerable catalytic sorbent for mercury removal from flue gases of coal-fired power plants.

Metal oxide nanoparticle-modified graphene oxide for removal of elemental mercury

ABSTRACTMercury is an extremely toxic element that is primarily released by anthropogenic activities and natural sources. Controlling Hg emissions, especially from coal combustion flue gas, is of practical importance in protecting the environment and preventing human health risks. In the present work, three metal oxides (MnO2, CuO, and ZnO) were loaded on graphene oxide (GO) sorbents (designated as MnO2-GO, CuO-GO, and ZnO-GO). All three adsorbents were successfully synthesized and were well characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results indicated that the metal oxide nanoparticles (NPs) successfully decorated the GO. The elemental Hg adsorption capabilities of the three sorbents were subsequently evaluated using an in-house built setup for cold vapour atomic fluorescence spectrophotometry (CVAFS) with argon as the carrier gas for mercury detection. The testing temperature ranged from 50°C to 200°C at intervals of 50°C. MnO2-GO showed an excel lent Hg0 adsorption capacity via chemisorption from 50 to 150°C and a mercury removal efficiency as high as 85% at 200°C, indicating that the MnO2-NP-modified GO is applicable for enhancing gas-phase elemental mercury removal. However, neither CuO-GO nor ZnO-GO performed well. This work provides useful insights into the development of novel sorbent materials for the elemental mercury removal from flue gases.

A systematic review on the efficiency of cerium-impregnated activated carbons for the removal of gas-phase, elemental mercury from flue gas.

In the present systematic review, we aimed to collect and analyze all the relevant evidence on the efficiency of cerium-impregnated versus virgin-activated carbons (ACs) for the removal of gas-phase elemental mercury (Hg0) from the flue gas of coal-fired power plants and to assess the effect of different calcination and operational parameters on their efficiency. A total of eight relevant papers (out of 1193 hits produced by the search) met the eligibility criteria and were included in the study. Results indicated that the Hg0 adsorption capacity of cerium-impregnated ACs is significantly higher than that of virgin ACs, depending highly on the impregnation and operational parameters. It was noticed that although cerium-impregnated ACs possessed smaller surface areas and pore volumes, their Hg0 removal efficiencies were still higher than their virgin counterparts. An increased Hg0 removal efficiency was in general found by increasing the operational adsorption temperature as high as 150-170°C. Studies also indicated that NO, SO2, and HCl have promoting impacts on the Hg0 removal efficiency of Ce-impregnated ACs, while H2O has an inhibitory effect.

Study of Mercury Adsorption by Low-Cost Sorbents Using Kinetic Modeling

In order to make further progress in the field of reducing mercury emissions to the atmosphere, it is necessary to develop efficient and economically viable technologies. Low-cost solid sorbents are a candidate technology for mercury capture. However, kinetic models are required to predict the adsorption mechanism and to optimize the design of the process. In this study, several low-cost materials (biomass chars) were evaluated for the removal of gas-phase elemental mercury and kinetic studies were performed to investigate the mechanism of mercury adsorption. These kinetic studies were also used to predict the behavior of a fixed-bed column. The models applied were pseudo-first-order and pseudo-second-order equations, Fick’s intraparticle diffusion model, and the Yoon–Nelson model. The chars obtained from the gasification of plastic-paper waste demonstrated the best behavior for mercury capture because of their high Brunauer–Emmett–Teller surface area, large total pore volume (mainly micropore volume), an...

Elemental mercury removal by the modified bio-char from medicinal residues

The purpose of this paper is to investigate the bio-char from medicinal residue in gas phase elemental mercury removal. The bio-char was derived from pyrolysis char modified by both physical and chemical modification. Physical activation (microwave and steam) improves pore structure and introduces oxygenic functional groups. Chemical activation (chloride-impregnated) significantly promotes elemental mercury capture capacity. Mercury adsorption by NH4Cl-impregnated bio-char was much better than those by ZnCl2-impregnated and HCl-impregnated bio-chars. A combination kinetic model presents a strong correlation with the adsorption data for the chloride-impregnated bio-chars. The model results reveal the importance of mass transfer during the initial stages of element mercury adsorption for these materials. Furthermore the overall element mercury adsorption process is strongly governed by chemisorption for the chloride-impregnated bio-chars. The studies showed that the modified bio-chars derived from medicinal residue might be cost effective sorbents with high activity, which can be used as an alternate to commercial activated carbons (CACs) or modified CACs in the removal of element mercury.

Mercury removal over the vanadia–titania catalyst in CO2-enriched conditions

The removal of gas-phase elemental mercury was investigated in CO2-enriched flue gas (oxy-fuel combustion) using selective catalytic reduction (SCR) catalysts (V2O5–WO3/TiO2). Experiments were carried out using various concentrations of CO2, O2, NH3, NO and temperatures. The removal of NO and Hg0 in the CO2-enriched flue gas condition increased with the temperature and decreased again, the maximum Hg0 and NO removal was observed at approximately 65% and 85%, respectively at 250–350°C, which indicated that Hg0 and NO could be simultaneously removed over V2O5–WO3/TiO2. The presence of enriched CO2 (80vol.%) assisted the Hg0 removal and inhibited the NO removal, whereas the effect of NO on the Hg0 removal varied according to the NO concentrations. The presence of Hg0 promoted NO removal in CO2-enriched flue gas at low temperature 200–300°C whereas inhibited NO removal greatly at high temperature (>300°C). In the SCR system, the presence of NH3 inhibited the Hg0 removal greatly. The mercury species analysis and catalyst characterization results showed that the removal of Hg0 over V2O5–WO3/TiO2 at 250–350°C was mainly attributed to the oxidation of Hg0. Mechanisms of the oxidation of Hg0 at 250–350°C in the CO2-enriched flue gas condition over the V2O5–WO3/TiO2 catalysts were: (1) the reaction between vanadia oxide and Hg0 to form adsorbed mercuric oxide (HgO(ad)–V2O4); (2) the oxidation of Hg0 by chemisorbed oxygen on the surface of catalyst; (3) the oxidation of Hg0 by function group of CO to form HgO and COC.

Adsorption performance and mechanism of bentonite modified by ammonium bromide for gas-phase elemental mercury removal

Bentonite was modified with ammonium bromide to enhance its adsorption performance for the removal of elemental mercury. The adsorbents were characterized by N2 adsorption/desorption, X-ray diffraction (XRD), elemental analysis, and Fourier transform infrared spectroscopy (FT-IR); the adsorption test was carried out in a laboratory-scale fixed-bed reactor. The results showed that the performance of sodium bentonite in mercury removal is only slightly higher than that of calcium bentonite; however, its performance in mercury removal can be greatly enhanced through the modification with ammonium bromide. The mercury removal efficiency reaches 97.7% over the sodium bentonite modified with ammonium bromide (Br-Ben/Na). High temperature may promote the removal of Hg0 and the mercury removal efficiency remains higher than 90% over the 10% Br-Ben/Na adsorbent for a long time at 140°C, suggesting that chemical adsorption played a dominant role in the adsorption process. Through the modification with ammonium bromide, the sodium ions were replaced with the ammonium ions added to the bentonite layers; the specific surface area of the modified bentonite is decreased, whereas the average pore size is increased. During the calcination activation process, the ammonium ions may combine with bentonite within the layers, forming the adsorption active centers, which promotes the reaction between Br− and Hg0 and then enhance the adsorption performance of bentonite in the removal of mercury.

Gas-phase elemental mercury removal from flue gas by cobalt-modified fly ash at low temperatures

Co modified fly ash (FA) prepared by the wet impregnation method was investigated for gas-phase elemental mercury capture under air at 80°C in this paper. X-ray fluorescence spectrometry, Brunauer–Emmett–Teller, scanning electron micrographs, X-ray diffraction, thermogravimetric (TG) analysis and X-ray photoelectron spectroscopy (XPS) were employed to characterize the samples. Experimental results showed that the optimal Co loading was 9 wt%, which gave a Hg0 removal efficiency of 76% in a laboratory packed-bed reactor at low temperatures in the presence of O2. The high removal efficiency was mainly attributed to oxidation of Hg0 by the enrichment of well-dispersed Co3O4 on the surface of FA. However, higher Co loading resulted in the decrease of removal efficiency due to the decline of surface area and Co3O4 agglomeration. TG and XPS characterization indicated that Hg0 was oxidized by Co3O4 and some of the oxidized mercury formed recombination mercury oxide with Co3O4, which could either exist stably at low temperature or be desorbed from the adsorbents at higher temperature. Finally, the possible adsorption mechanisms were proposed according to the observed phenomena.

Design of sulfur treated activated carbon fibers for gas phase elemental mercury removal

Several methods have been used to introduce sulfur containing groups in glass fiber supported activated carbon fibers (ACFs). The chemical and physical properties of these sulfur treated ACFs have been evaluated to determine their mercury adsorption capacities. Although sulfur impregnations decreased surface area and pore volume of ACFs, Hg uptake capacities increased when compared to raw ACF samples. For our sulfur-treated samples, sulfur atoms were incorporated into the carbon matrix in the form of sulfide and sulfate. The sulfide groups appeared to be more effective for mercury removal than sulfate. A possible mechanism for mercury adsorption, which is likely to involve the oxidation process of Hg°, is also discussed. Besides the effects of chemical structure on mercury adsorption, the effects of pore properties associated with adsorbents have also been studied.

Enhanced capture of elemental mercury by bamboo-based sorbents

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

Gas-phase elemental mercury removal in a simulated combustion flue gas using TiO2 with fluorescent light

A previously proposed technology incorporating TiO2 into common household fluorescent lighting was further tested for its Hg0 removal capability in a simulated flue-gas system. The flue gas is simulated by the addition of O2, SO2, HCl, NO, H2O, and Hg0, which are frequently found in combustion facilities such as waste incinerators and coal-fired power plants. In the O2 + N2 + Hg0 environment, a Hg0 removal efficiency (ηHg) greater than 95% was achieved. Despite the tendency for ηHg to decrease with increasing SO2 and HCl, no significant drop was observed at the tested level (SO2: 5–300 ppmv, HCl: 30–120 ppmv). In terms of NO and moisture, a significant negative effect on ηHg was observed for both factors. NO eliminated the OH radical on the TiO2 surface, whereas water vapor caused either the occupation of active sites available to Hg0 or the reduction of Hg0 by free electron. However, the negative effect of NO was minimized (ηHg > 90%) by increasing the residence time in the photochemical reactor. The moisture effect can be avoided by installing a water trap before the flue gas enters the Hg0 removal system. Implications: This paper reports a novel technology for a removal of gas-phase elemental mercury (Hg0) from a simulated flue gas using TiO2-coated glass beads under a low-cost, easily maintainable household fluorescent light instead of ultraviolet (UV) light. In this study, the effects of individual chemical species (O2, SO2, HCl, NO, and water vapor) on the performance of the proposed technology for Hg0 removal are investigated. The result suggests that the proposed technology can be highly effective, even in real combustion environments such as waste incinerators and coal-fired power plants.

Removal of Gas-Phase Elemental Mercury in Flue Gas by Inorganic Chemically Promoted Natural Mineral Sorbents

A variety of natural mineral sorbents were synthesized and tested on a lab-scale fixed-bed system to evaluate mercury removal efficiencies under a simulated flue gas condition that contains 84% N2, 4% O2, and 12% CO2 in volume fraction. Three types of natural minerals, bentonite (Ben), mordenite (Mor), and attapulgite (Atp), were selected as raw sorbents, and several chemical promoters, such as CuCl2, NaClO3, KBr, and KI, were employed to enhance mercury removal abilities of the raw sorbents. The physical-chemical characteristics of these minerals were analyzed by an X-ray diffractometer (XRD), an accelerated surface area and porosimeter (ASAP) using the N2 isotherm adsorption/desorption method, and X-ray fluorescence (XRF) spectrometry. The mercury concentration was detected continuously using a VM3000 online mercury analyzer. The results showed that CuCl2-impregnated Atp (Cu-Atp) and CuCl2-impregnated Ben (Cu-Ben) presented about 90% average Hg0 removal efficiencies at 120 °C, respectively. In addition, as the temperature increased, the removal efficiencies decreased. Although NaClO3-impregnated Atp showed an average Hg0 removal efficiency more than 90% at 120 °C, its performance was limited by the testing temperature, and that was probably due to the high iron oxide content in Atp. For the KI-impregnated sorbents, high mercury removal efficiencies could be observed, and the efficiencies increased steadily with the temperature increased from 70 to 150 °C. The three natural minerals presented poor adsorption abilities for bromine, which resulted in the disappointing mercury removal efficiencies. Generally, Cu-Atp, Cu-Ben, and KI-impregnated sorbents were promising cost-effective mercury sorbents.

Removal of Gas-Phase Elemental Mercury by Photocatalytic with Liquid Absorption

In order to study the influence of UV irradiation, treat temperature of nano-titanium dioxide and intensity of UV irradiation on the mercury removal performance, experiments were carried out on a photocatalytic oxidization system to find the best experimental conditions. Commercial Degussa P25 was used as a photocatalyst loading on titanium mesh, and the mercury removal efficiency was stable at 8% in the absence of UV irradiation. Under the UV irradiation of 300W mercury lamp, the mercury removal efficiency surged to 100%. With the same light intensity, the same removal time, the mercury removal efficiency of nano-titanium dioxide calcinated at 100°C reached 92.2% after 0.5h while the mercury removal efficiency of nano-titanium dioxide calcinated at 500°C reached 93.6%. Intensity of UV irradiation has a positive impact on the mercury removal performance.

Removal of Gas-Phase Elemental Mercury by Bromine-Impregnated Activated Carbon

Br-impregnated activated carbon for gas-phase elemental mercury adsorption experiments were carried out at a fixed-bed system to get the suitable mass fraction of KBr impregnation solution. Hg removal efficiency of 1% wt KBr-ACs was 69.0%, while that of 10% wt KBr-ACs was 57.9%. Both of them were higher than that of the raw activated carbon, 42.2%. The removal efficiency of Hg0 was not proportional to bromine concentration. Under 80-180°C, Hg removal efficiency of 1% wt KBr-ACs were 68.3%-71.8%, and at 140°C it reached the highest due to the increasing chemical adsorption ability of the functional groups which was on the surfaces of activated carbons by impregnating. At 160°C, Hg removal efficiency was lower than that at 140°C due to desorption making physical adsorption decrease, so that the total adsorption decreased.

Gas-phase elemental mercury removal by novel carbon-based sorbents

To develop cost-effective carbon-based sorbents used in gas-phase elemental mercury removal, the performance of commercial bamboo charcoal (BC) produced from renewable bioresource of bamboo and modified BC was investigated with a bench-scale fixed-bed reactor. The simple impregnation method was used to modify the BC using ZnCl 2, NH 3·H 2O and HNO 3 separately. BET, XPS, elemental analysis and FT-IR were used to determine the pore structure and surface chemistry of the sorbents. The characterization of the physical and chemical properties of sorbents in relation to Hg 0 adsorption capacity provided important information on the Hg 0 adsorption mechanism. This suggested that the modified BCs have excellent adsorption potential for elemental mercury at a relatively higher temperature of 140 °C except for the NH 3·H 2O impregnated BC. The amount of Hg 0 absorbed depends on the concentration of impregnant used. The impregnation has increased the sorbents’ active sites for mercury adsorption and the specific reaction mechanism has been further analyzed.

Gas-Phase Elemental Mercury Removal by CeO2 Impregnated Activated Coke

We have studied gas-phase elemental mercury (Hg0) capture by a CeO2 loaded activated coke (AC) using a laboratory-scale fixed-bed reactor under simulated flue gas conditions. Through systematic inv...

Removal of gas-phase elemental mercury by iodine- and chlorine-impregnated activated carbons

Gas-phase Hg0 adsorption experiments were carried out using iodine (I)- and chorine (Cl)-impregnated granular activated carbons in a laboratory-scale fixed-bed reactor. To verify the effect of chemical loading contents on removal of mercury, different concentrations of chemicals such as KI and HCl were applied. In addition, two types of impregnated activated carbons (ACs) were tested at different temperature conditions. The characteristics of impregnated ACs were analyzed using scanning electron microscopy/energy-dispersive spectroscopy for surface morphology and chemical contents. BET analysis for surface area and X- ray spectroscopy for identification of mercury compounds on the carbon surface were conducted. Hg0 removal efficiency increased with temperature in the case of I-impregnated ACs, while the removal efficiency decreased with temperature for Cl-impregnated ACs. According to increasing chemical content, the surface area decreased and the morphology of carbon became more complicated. Both types of impregnated ACs showed reasonable efficiency for gas-phase Hg0 removal by adsorption.