Gaseous Elemental Mercury Removal Research Articles

Experimental and theoretical study on recovered nano amorphous selenium as efficient adsorbents for mercury capture from flue gas

The cost-effective removal of gaseous elemental mercury from coal-fired flue gas is crucial for environmental protection. In this study, nano amorphous selenium (nano-a-Se) adsorbent was recovered from desulfurization wastewater to remove Hg0 in flue gas. The results indicate that nano-a-Se has a high efficiency in the amorphous form with a saturated adsorption capacity of 2034.32 mg g−1. The Se utilization ratio of nano-a-Se reached 80% of the theoretical limit. Meanwhile, nano-a-Se exhibited high resistance to NO and SO2 poisoning. Moreover, the Hg0 removal mechanism of nano-a-Se was analyzed by experimental analysis and density functional theory (DFT) calculations. The results demonstrate that nano-a-Se can convert Hg0 into stable mercury selenide, a high-value by-product with little risk of mercury re-release. Therefore, nano-a-Se is expected to be a novel adsorbent with high efficiency in capturing Hg0, which can help realize the resource utilization of toxic elements from the environment.

The design of high-entropy metal sulfides promising high-performance gaseous elemental mercury removal

Regulating the surface coordination environment and improving the formation of active species represent the key factor in designing high-performance metal sulfide-based sorbents for gaseous Hg0 capture. This paper reported the Hg0 adsorption by high entropy metal sulfides for the first time, and clarified the mechanisms involved in the evolutions of active species as well as the Hg0 adsorption. The multiple metal components of the high entropy metal sulfides have great significance in improving the surface chemistry. The addition of Ce helps not only the formation of chemically homogeneous structure, but also the generation of high valence state metal cations and unsaturated sulfur species, thereby improving obviously the Hg0 removal ability. The synthesized CeNiCoMnCuSx has a high Hg0 adsorption capacity of 10.52 mg·g−1 at 80 %-breakthrough, and a Hg0 adsorption rate of 4.31 μg·g−1·min−1. The high valence state metal cations (Ni3+, Co3+, Mn4+, Cu2+ and Ce4+) and unsaturated Sx2− and S22− species can directly oxidize Hg0 and convert it into HgS. In comparison, the quaternary sulfide counterpart (NiCoMnCuSx) cannot form a main phase structure, and has obviously lower percentages of high valence state metal cations and unsaturated sulfur species. This work provides a new space for developing metal sulfides for Hg0 adsorption.

Copper selenide anchored on Ti3C2 MXene via Lewis acidic etching route for efficient removal of gaseous elemental mercury

A fundamental obstacle that restricts the use of metal selenides for gaseous elemental mercury (Hg0) immobilization is the failure to take both the optimization of intrinsic structure favorable for Hg0 diffusion and adequate exposure of metal selenide towards Hg0 into consideration. In this work, a Ti3C2 MXene/Cu2Se sorbent for Hg0 sequestration was synthesized via a Lewis acid etching route combined with room-temperature selenization pathway. During this strategy, copper chloride plays a dual role, i.e., an etching agent for the Ti3C2 MXene synthesis and a precursor for Cu0 decoration. Cu2Se precursors (Cu0) were dispersedly and firmly pre-anchored on the substrate, effectively avoiding the agglomeration and warranting excellent dispersion of Cu2Se. Compared with pristine Cu2Se, Ti3C2 MXene/Cu2Se exhibits advantageous structural characteristics fully boosting Hg0 diffusion kinetics. Meanwhile, the enhanced dispersion of Cu2Se from the prefixation of Cu0 largely enhances the exposure and utilization of selenide. Consequently, Ti3C2 MXene/Cu2Se shows a Hg0 adsorption capacity of 147.64 mg g−1, which is much higher than those of Cu2Se and most other metal selenides. Impressively, its uptake rate of 688.99 μg g−1 min−1 is the highest record rate in metal selenides. Moreover, Ti3C2 MXene/Cu2Se still maintained outstanding Hg0 adsorption performance under relatively high reaction temperature with the shelter of Ti3C2 MXene. Typical fuel gas situations including coal combustion flue gas, smelting flue gas, natural gas have negligible influences on its Hg0 adsorption performance, indicating its extensive applicability and flexibility for actual industrial situations. This work also provides valuable hints for the trade-off of structural properties and ligands exposure to design Hg0 sorbents with satisfactory Hg0 sequestration performances.

Clean Modification of Carbon-Based Materials Using Hydroxyl Radicals and Preliminary Study on Gaseous Elemental Mercury Removal

Clean Modification of Carbon-Based Materials Using Hydroxyl Radicals and Preliminary Study on Gaseous Elemental Mercury Removal

Removal of gaseous elemental mercury using corn stalk biochars modified by a green oxidation technology

Straw biochars are the widely used carbon materials for adsorbing gaseous Hg0 due to developed porous structure. However, its application is restricted by scarcity of active sites on carbon surface. Existing modification methods such as acids, halides, sulfides, metal oxides, etc. have problem of secondary pollution. In this work, a corn stalk biochar modified with UV/H2O2 green modification technology was prepared to capture gaseous Hg0 for the first time. The physicochemical properties of the adsorbent and the effect of several key parameters containing H2O2 concentration, adsorption temperatures and common gas components on gaseous Hg0 capture were studied. The kinetic process and mechanisms of gaseous Hg0 adsorption were also expounded. Research indicated that through producing ·OH free radicals with high activity, UV/H2O2 green modification technology could not only improve pore structure of corn stalk biochar, but also make containing-O functional group more abundant on carbon surface, promoting gaseous Hg0 adsorption. Optimal H2O2 modification concentration and adsorption temperature are 3 wt% and 120 °C, respectively. The capture process of gaseous Hg0 accorded with quasi second-order kinetic equation. Chemisorbed oxygen (O*) and CO functional group show pivotal roles in the capture processes of gaseous Hg0.

Engineering of Defect-Rich Cu2WS4 Nano-homojunctions Anchored on Covalent Organic Frameworks for Enhanced Gaseous Elemental Mercury Removal.

Fabricating two-dimensional transition-metal dichalcogenide (TMD)-based unique composites is an effective way to boost the overall physical and chemical properties, which will be helpful for the efficient and fast capture of elemental mercury (Hg0) over a wide temperature range. Herein, we constructed a defect-rich Cu2WS4 nano-homojunction decorated on covalent organic frameworks (COFs) with abundant S vacancies. Highly well-dispersed and uniform Cu2WS4 nanoparticles were immobilized on COFs strongly via an ion pre-anchored strategy, consequently exhibiting enhanced Hg0 removal performance. The saturation adsorption capacity of Cu2WS4@COF composites (21.60 mg·g-1) was 9 times larger than that of Cu2WS4 crystals, which may be ascribed to more active S sites exposed in hybrid interfaces formed in the Cu2WS4 nano-homojunction and between Cu2WS4 nanoparticles and COFs. More importantly, such hybrid materials reduced adsorption deactivation at high temperatures, having a wide operating temperature range (from 40 to 200 °C) owing to the thermostability of active S species immobilized by both physical confined and chemical interactions in COFs. Accordingly, this work not only provides an effective method to construct uniform TMD-based sorbents for mercury capture but also opens a new realm of advanced COF hybrid materials with designed functionalities.

Development of copper sulfide functionalized CeO2 nanoparticle for strengthened removal of gaseous elemental mercury from flue gas

The development of effective sorbents is of great significance for realizing the immobilization of gaseous elemental mercury from coal-fired flue gas. Herein, CuS/CeO2 composite sorbent was synthesized by a simple precipitation method for the removal of elemental mercury from flue gas. The ability of CuS/CeO2 to capture mercury at different temperatures and different flue gas components (HCl, SO2, O2 and NO) were tested. It indicates that CuS/CeO2 exhibits excellent Hg0 removal performance both at 60–150 °C and in different flue gas components. Moreover, the equilibrium adsorption capacity of CuS/CeO2 was 32.304 mg g−1 at 120 °C, which was 59.8 times that of CuS/GCN and 190 times that of ZnS modified activated carbon. Density functional theory (DFT) calculations further verified that the synergistic relationship between defect oxygen and unsaturated sulfur sites on the surface promotes the Hg0 removal performance of CuS/CeO2. By virtue of these advantages, CuS/CeO2 is a prodigious candidate for the effective mercury removal from various types of industrial flue gases. This work may open-up new approaches for the development of heavy metal sorbents through the inter-doping of metal sulfides with transition metal oxides to enhance surface active sites to tune the adsorption capacity.

Preparation of nano α-Fe2O3 and γ-Fe2O3 and used for elemental mercury removal

The rod-shaped nano α-Fe2O3 and γ-Fe2O3 were prepared by a hydrothermal method. And the crystal phase structure, particle size, morphology and surface area of the synthesized nano α-Fe2O3 and γ-Fe2O3 were characterized by XRD and BET analysis. The removal of gaseous elemental mercury by nano α-Fe2O3 and γ-Fe2O3 was carried out on a fixed bed reactor. The effects of oxygen, bed temperature, particle size and acid flue gas components have been discussed. The results show that elemental mercury could be oxidized by nano α-Fe2O3 and γ-Fe2O3 with the presence of oxygen.

Bimetallic Fe–Cu-Based Metal–Organic Frameworks as Efficient Adsorbents for Gaseous Elemental Mercury Removal

The bimetallic iron–copper based metal–organic frameworks (FeCu-MOFs) with rich chlorine were synthesized and used to remove gaseous elemental mercury (Hg0). The mercury removal performance on the ...

The coupling use of electro-chemical and advanced oxidation to enhance the gaseous elemental mercury removal in flue gas

A novel diffusion electro-chemical combined advanced oxidation reactor offers potential for elemental mercury (Hg0) removal in flue gas and shown excellent performance. This study introduced an ultraviolet light into the electric catalytic system to form an UV-electric oxidation system to strengthen Hg0 removal. Hg0 removal efficiency in the combined UV-electric oxidation system reached up to 65%. Hg0 is excited by UV lamp with a wavelength of 253.7 nm, and a very small amount of oxygen contained in high-purity nitrogen can still participate in Hg0 oxidation reaction. In addition, the Fenton method has also been introduced into the simple electrolysis system. Both the above combined system can improve the efficiency of Hg0 removal. The electro-chemical GDE was characterized by SEM, BET, and contact angle and gas permeability. The electro-chemical and advanced oxidation process (Fenton method and UV illumination) combined within a system or individually in series were explored the different influencing factors. The gaseous elemental mercury removal mechanism of the combined electro-chemical and advanced oxidation was investigated via combining the experimental data and theoretical reasoning. Electrochemical coupling with other advanced oxidation technologies is a promising technology.

Nanoscale CuFe2O4 monodispersedly anchored on reduced graphene oxide as excellent peroxydisulfate catalyst for removal of gaseous elemental mercury

This paper synthesized a magnetic and robust catalyst, CuFe2O4@rGO, by hydrothermal method and evaluated its catalytic activity towards peroxydisulfate (PDS) for removal of gaseous Hg0. The structure–function relationship of the prepared catalysts was revealed according to the characterization results of XRD, SEM-EDS, TEM, BET, FTIR and XPS. By incorporating into rGO, the catalytic activity of CuFe2O4 was greatly improved because the introduced rGO increased the large specific surface area and enlarged the pore volume, making the CuFe2O4 nanocrystals mono-dispersedly anchoring on the surface of rGO, increasing the accessible reactive sites. The carbon-based groups owing to rGO also acted as the auxiliary catalyst to facilitate PDS activation. CuFe2O4@rGO0.25 was determined as the best catalyst. The influences of key reaction conditions on Hg0 removal were assessed, such as catalyst dosage, PDS concentration, reaction temperature, solution pH, and the concentrations of SO2 and NO. The Hg0 removal efficiency was > 98% under the best conditions. The CuFe2O4@rGO0.25 hybrid catalyst possessed good magnetism, thus was easily separated by applying an external magnetic field, and also kept good catalytic activity after successively used for 10 h, with tiny Cu leaching (0.69%). According to the results of XPS, XRD, FTIR, ESR and radical quenching experiments, the reactivity order of the oxidizing species towards Hg0 removal was concluded as SO4•-> •OH > PDS. The redox reactions including ≡Cu(II)/≡Cu(I), ≡Cu(II)/≡Cu(III) and ≡Fe(II)/≡Fe(III) contributed to the PDS activation, with O2•-/S2O8•− as the reductants. This study gives a new insight into the method of SO4•--induced oxidation for effective removal of gaseous Hg0.

Electrochemical removal of gaseous elemental mercury in liquid phase with a novel foam titanium-based DSA anode

The dimensional stable Ti/Sb-SnO2/PbO2 electrode was prepared by the impregnation method. To remove gaseous elemental mercury (Hg0) from coal combustion, the study of Hg0 oxidation was performed in a gas diffusion electrochemical reactor with the stainless steel mesh cathode and the Ti/Sb-SnO2/PbO2 anode. Hg0 is oxidized into highly water-soluble oxidation states of mercury as a result of the loss of electrons on the anode, which can be removed later utilizing WFGD and other devices. By investigating the effects of applied voltage, the concentration and pH of the electrolyte, reaction temperature, flue gas flow and initial Hg0 concentration on removal, the appropriate conditions for the experiment were obtained. At the pH of 3, the removal efficiency can reach over 90%, which is about 1.7 times the removal of a single foam Ti under the same conditions.

Molybdenum trioxide impregnated carbon aerogel for gaseous elemental mercury removal

A novel gaseous elemental mercury (Hg0) removal agent was successfully synthesized via impregnation method, by using molybdenum trioxide (MoO3) as the active component and carbon aerogel (CA) as the carrier. The as-prepared samples maintained a large specific surface area and excellent pore structure of the pure carbon aerogel, so that MoO3 was better dispersed to obtain enhanced Hg0 removal performance. The maximum efficiency of elemental mercury removal was about 74%, achieved by Mo/C500 sample at 300 °C, while it still had good ability (nearly 60%) in the range of 500–700 °C. The mechanism of mercury oxidation removal was also verified by DFT calculation. This work should help in developing suitable materials for thermocatalytic oxidation of elemental mercury, and also provide some theoretical basis and data support for full-scale application of heavy metal mercury pollution control in coalfired power plants.

Removal of Gaseous Elemental Mercury in a Diffusion Electrochemical Reactor Based on a Three-Dimensional Electrode.

A novel three dimensional electrochemical reactor with nickel foam and carbon paper used as the anode and stainless steel mesh used as the cathodewas studied in this research. Oxidation mercury removal is performed in a self-made diffusion reactor. The influence of the electrolysis voltage, pH, gas flow, and other factors on mercury removal is discussed, as well as the mechanism of anodization mercury removal is explored. The experimental results show that nickel foam has a significant effect on the removal of Hg0, and 80–85% removal can be achieved under optimal conditions. Meanwhile, nickel foam has stable performance at high temperatures (60 °C) and in strong alkaline electrolytes, which also play an effective role in anodized oxidation. Although carbon paper is more stable than nickel foam and less affected by experimental factors, it is sensitive to reaction temperature and can only work in the neutral electrolyte at low temperatures. In contrast, electrochemical catalytic oxidation technology using the nickel foam is more promising for Hg0 removal.

Removal of gaseous elemental mercury using thermally catalytic chlorite-persulfate complex

We developed a novel oxidation method, thermally catalytic chlorite-persulfate (NaClO2-Na2S2O8, shorten as CP), to remove gaseous Hg0. Chlorite and persulfate exhibited an outstanding performance in Hg0 removal as compared to using chlorite or persulfate alone. The cost for using CP is 3–69 USD/lb-Hg0 which is far lower than using Na2S2O8 (1739–2552 USD/lb-Hg0) and NaClO2 (37–1299 USD/lb-Hg0). Kinetics analysis indicated that the rate constant of the reaction between CP and Hg0 is 5250 times and 11.7 times higher than that of using Na2S2O8 and NaClO2 alone. The impacts of CP concentration, thermal catalytic temperature, flue gas residence time and presence of other gases in the flue gas on the Hg0 removal were evaluated. SO2 and NO were found to be the inhibitor and promoter, respectively, for Hg0 removal. Mercury distribution under different atmospheric conditions was determined by using atomic fluorescence spectrometry (AFS). The active oxidizing species produced in the thermal catalysis of CP were determined to be ClO2, SO4− and HO using ultraviolet–visible spectrophotometry (UV–Vis) and electron spin resonance (ESR). HgCl2 and HgSO4 were the main mercury forms in the byproduct according to the X-ray photoelectron spectroscopy (XPS) result. The mechanism of Hg0 removal with using CP was proposed.

SO2 promoted ultrafine nano-sulfur dispersion for efficient and stable removal of gaseous elemental mercury

Development of a low-cost, stable and high-efficiency method is a vital challenge for elemental mercury (Hg0) decontamination from nonferrous smelting flue gas. The ultrafine size (<10 nm) and homodisperse nanometer sulfur (Nano-sulfur) was synthesized from alkali desulfurization solution by using a facile method. The as-synthesized Nano-sulfur exhibited excellent Hg0 removal performance over the bulk sulfur and commercial sublimed sulfur. Sulfur dioxide was surprisingly proved as a promoter for Nano-sulfur to enhance the Hg0 removal in this study. Nano-sulfur dispersion showed higher than 92% removal efficiency for 119 h under high-concentration SO2 atmosphere. The Hg0 adsorption capacity and rate of Nano-sulfur reached 242.1 mg/g and 24.6 μg/(g·min) respectively, which were both higher than other traditional adsorbents like sulfur-containing activated carbon and metal sulfides. Snew was proved as the main active substance to remove Hg0, which could be continuously generated from Nano-sulfur by the reversible reaction under effect of SO2. The gaseous Hg0 was largely transformed to colloidal phase (87.47%) and precipitated phase (10.53%) in the HgS form after wet scrubbing. This work offers a new path towards the design of nonferrous smelting flue gas Hg0 purification method by adding Nano-sulfur dispersion into the wet scrubber of existing air pollution control devices, i.e., flue gas scrubber and wet flue gas desulfurization.

Experimental Study on Mercury Removal and Regeneration of SO2 Modified Activated Carbon

Gaseous elemental mercury removal by activated carbon impregnated with SO2 was studied under simulated flue gas conditions. Brunauer–Emmett–Teller (BET) measurements and X-ray photoelectron spectro...

Removal of gaseous elemental mercury by hydrogen chloride non-thermal plasma modified biochar.

Hydrogen chloride (HCl) non-thermal plasma was applied to introduce Cl active sites on biochar prepared from sorghum straw in this study. Surface modified biochar was then placed in flue gas with typical components to investigate its elemental mercury (Hg0) capture ability. To elucidate the adsorption mechanism & binding properties, samples were characterized by N2 adsorption, scanning electron microscopy with energy dispersive spectrometer (SEM-EDS) and X-ray absorption near edge structure (XANES) analysis of Hg LIII-edge, Cl K-edge and S K-edge. Experimental results showed that HCl plasma modification successfully increased Cl active sites on biochar and greatly increased its mercury removal efficiency. Both HCl treatments (w/without plasma involvement) altered biochar's surface structure and layered structure generated. XANES spectra revealed that adsorbed-Hg on HCl-treated biochars mainly in the form of Hg+. Gaseous Hg0 was believed to heterogeneously react with chlorinated sites through electron-transfer and formed Hg2Cl2 compounds. With the presence of NO or SO2 in the system, adsorbed mercury existed on biochar mainly as Hg+. SO2 competed and inhibited the adsorption of Hg0; while NO promoted Hg0 removal capacity by increasing the active sites and enhancing the adsorption kinetics of adjacent Cl-containing sites.

Removal of Vapor-phase Elemental Mercury over a CuO/PG Catalyst

The removal of gaseous elemental mercury (Hg0) on the palygorskite (PG) supported CuO catalyst (CuO/PG) was studied under N2+O2 atmosphere. This paper describes the effect of CuO loading, reaction temperature, Hg0 concentration and space velocity on Hg0 removal over CuO/PG. The experimental results showed that CuO/PG had a higher Hg0 removal ability than PG, which could be attributed to the oxidation activity of CuO. As CuO loading increased (0-5 wt.%), the ability of CuO/PG to remove Hg0 increased. In the temperature range of 120-210 °C, the highest Hg0 removal ability was at about 180 °C, which might be due to the combined effect of adsorption and oxidation. As the Hg0 concentration and space velocity decreased, the Hg0 removal efficiency increased.

Gaseous elemental mercury removal using VUV and heat coactivation of Oxone/H2O/O2 in a VUV-spraying reactor

A novel process on gaseous elemental mercury removal using vacuum ultraviolet light (VUV) and heat coactivation of Oxone/H2O/O2 (i.e., VUV/heat/Oxone/H2O/O2 system) in a VUV-spraying reactor was investigated for the first time. Experiments were carried out to evaluate the effects of several operating parameters (e.g, VUV wavelength, Oxone concentration, VUV radiation intensity, activation temperature, solution pH and O2 concentration) on Hg0 removal. Mechanism and kinetic law of Hg0 removal were also revealed. The results demonstrated that 185 nm wavelength showed the best performance. Hg0 removal was promoted by increasing VUV radiation intensity, Oxone concentration and O2 concentration, and was weakened by increasing solution pH and SO2 concentration. Activation temperature exhibited dual influence on Hg0 removal. Hg0 was removed by six pathways: (1) oxidized by SO4− and OH that are produced from VUV activation of Oxone; (2) oxidized by O3 and O that are produced from VUV photolysis of O2; (3) oxidized by OH that is produced from VUV photolysis of H2O; (4) removed by light-water excitation reaction; (5) oxidized by SO4− and OH that are produced from heat activation of Oxone; (6) oxidized directly by Oxone. Hg0 removal process followed a fast reaction in VUV/heat/Oxone/H2O/O2 system (i.e., presence of VUV) and a medium speed reaction in heat/Oxone/H2O/O2 system (i.e., absence of VUV).