An electrochemical system for removing and recovering elemental mercury from a gas stream

Efficient mercury removal from aqueous solutions using carboxylated Ti3C2Tx MXene

Water supplies contaminated with heavy metals are a worldwide concern. MXenes have properties that make them attractive for the removal of metal ions from water. This work presents a simple one-step method of Ti₃C₂T_x carboxylation that involves the use of a chelating agent with a linear structure, providing strong carboxylic acid groups with high mobility. The carboxylation decreases the zeta-potential of Ti₃C₂T_x by ~16 to ~18 mV over a pH range of 2.0-8.5 and improves Ti₃C₂T_x stability in the presence of molecular oxygen. pH in the range of 2-6 has a negligible effect on the adsorption capacity of Ti₃C₂T_x and COOH-Ti₃C₂T_x. Compared to Ti₃C₂T_x, COOH-Ti₃C₂T_x has a slightly higher and much faster mercury uptake, and the concentration of mercury ions leached out from COOH-Ti₃C₂T_x is lower. For both Ti₃C₂T_x and COOH-Ti₃C₂T_x, the leached mercury ion concentration is far below the U.S.-EPA maximum level. At an initial Hg²⁺ concentration of 50 ppm and pH of 6, COOH-Ti₃C₂T_x has the equilibrium adsorption capacity of 499.7 mg/g and removes 95% of Hg²⁺ in less than 1 min. Moreover, it has an equilibrium time of 5 min, which is significantly shorter than that of Ti₃C₂T_x (~ 60 min). Finally, its mercury-ion uptake capacity is higher than commercially available adsorbents reported in the literature. Its mercury removal is mainly via chemisorption and monolayer adsorption.

Hollow Multiple Noble Metallic Nanoalloys by Mercury-Assisted Galvanic Replacement Reaction for Hydrogen Evolution

Hollow multimetallic noble nanoalloys with high surface area/volume ratio, abundant active sites, and relatively effective catalytic activity have attracted considerable research interest. Traditional noble nanoalloys fabricated by hydro-/solvothermal methods usually involve harsh synthetic conditions such as high temperatures and intricate processing. We proposed a simple and mild strategy to synthesize platinum- and palladium-decorated hollow gold-based nanoalloys by the galvanic replacement reaction (GRR) at room temperature using hollow gold nanoparticles as templates and mercury as an intermediate. The hollow gold nanoparticles were essential for increasing the number of surface-active sites of the obtained multimetallic nanoalloys, and the introduction of mercury can eliminate the influence of the electrochemical potential of Pt/Pd with Au in the GRRs, increase alloying degrees, and maintain the nanoalloys that exhibit the hollow nanostructures. The structural characterizations of the hollow nanoalloys were studied by means of high-angle annular dark-field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. On the basis of the electrochemical catalytic measurements, the platinum-exposed nanoalloys were found to have excellent electrocatalytic activities. Especially in the presence of palladium, owing to the synergistic effect, the quaternary AuHgPdPt hollow nanoalloy displayed a low overpotential of 38 mV at 10 mA cm^-2 with a small Tafel slope of 56.23 mV dec^-1 for the alkaline hydrogen evolution reaction. In addition, this approach not only expands the application range of the galvanic replacement reaction but also provides new ideas for the preparation of multialloys and even high-entropy alloys at room temperature.

Structural defects in 2D MoS2 nanosheets and their roles in the adsorption of airborne elemental mercury

In this research, ab initio calculations and experimental approach were adopted to reveal the mechanism of Hg⁰ adsorption on MoS₂ nanosheets that contain various types of defects. The ab initio calculation showed that, among different structural defects, S vacancies (Vs) in the MoS₂ nanosheets exhibited outstanding potential to strongly adsorb Hg⁰. The MoS₂ material was then prepared in a controlled manner under conditions, such as temperature, concentration of precursors, etc., that were determined by adopting the new method developed in this study. Characterisation confirmed that the MoS₂ material is of graphene-like layered structure with abundant structural defects. The integrated dynamic and steady state (IDSS) testing demonstrated that the Vs-rich nanosheets showed excellent Hg⁰ adsorption capability. In addition, ab initial calculation on charge density difference, PDOS, and adsorption pathways revealed that the adsorption of Hg⁰ on the Vs-rich MoS₂ surface is non-activated chemisorption.

Insight into elemental mercury (Hg0) removal from flue gas using UV/H2O2 advanced oxidation processes

Elemental mercury (Hg⁰) emitted from coal-fired power plants and municipal solid waste (MSW) incinerators has caused great harm to the environment and human beings. The strong oxidized ^•OH radicals produced by UV/H₂O₂ advanced oxidation processes were studied to investigate the performance of Hg⁰ removal from simulated flue gases. The results showed that when H₂O₂ concentration was 1.0 mol/L and the solution pH value was 4.1, the UV/H₂O₂ system had the highest Hg⁰ removal efficiency. The optimal reaction temperature was approximately 50 °C and Hg⁰ removal was inhibited when the temperature was higher or lower. The yield of ^•OH radicals during UV/H₂O₂ reaction was studied by electron paramagnetic resonance (EPR) analysis. UV radiation was the determining factor to remove Hg⁰ in UV/H₂O₂ system due to ^•OH generation during H₂O₂ decomposition. SO₂ had little influence on Hg⁰ removal whereas NO had an inhibitory effect on Hg⁰ removal. The detailed findings for Hg⁰ removal reactions over UV/H₂O₂ make it an attractive method for mercury control from flue gases.

Cleaning of lead smelting flue gas scrubber sludge and recovery of lead, selenium and mercury by the hydrometallurgical route

The expansion of the nonferrous metal smelting industry in the recent two decades has resulted in the generation of massive quantities of flue gas scrubber sludge containing hazardous heavy metals, such as cadmium, lead, arsenic, selenium and mercury (Hg), posing a potential environmental threat. In this work, lead smelting flue gas scrubber sludge was treated by a hydrometallurgical process to achieve sludge cleaning and economic recovery of metal values lead, selenium and mercury. The sludge was preliminarily leached by sodium chloride solution to extract lead. Under the optimum conditions, 99.8% of lead was selectively leached into the solution and subsequently precipitated by calcium oxide while almost the entire selenium and mercury remained in residue. Ninety-eight percent of selenium and 99.8% of mercury were further leached by hydrochloric acid solution with sodium chlorate. 99.3% of mercury was precipitated as red mercuric oxide from the Se-Hg leach liquor by adding sodium hydroxide. After the mercury was removed from the solution, 97.5% of selenium was reduced and precipitated as crude selenium by reduction with sodium sulfite. Recovery yields of lead, mercury and selenium by this process were 99.6%, 98.9% and 95.5%, respectively.

Fe3-xCuxO4 as highly active heterogeneous Fenton-like catalysts toward elemental mercury removal

A series of novel spinel Fe3-xCuxO4 (0<x<0.71) composites, synthesized by chemical co-precipitation method, are proposed synthesized to use as highly active heterogeneous Fenton-like catalysts to remove elemental mercury (Hg0) from the simulated flue gases. Inductively coupled plasma-Atomic emission spectrometry (ICP-AES), X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area, and X-ray photoelectron spectrometer (XPS) were used to characterize the catalysts. The catalysts were confirmed the presence of the redox pairs Fesurf2+/Fesurf3+ and Cusurf+/Cusurf2+ on the surface of the cubic structure. The performance of heterogeneous Fenton-like reactions for Hg0 removal was evaluated in a lab-scale bubbling reactor at the solution temperature of 50°C. The systematic studies on the effects of different catalysts, H2O2 concentration and solution pH values on Hg0 removal efficiencies were performed. The recycling of the Fe3-xCuxO4 catalysts in Fenton-like solution is stable and Hg0 removal efficiency remain above 90% after 3 cycles. The active hydroxyl radical (OH) generated during heterogeneous Fenton-like reactions was confirmed through electron spin resonance (ESR) spin-trapping technique. The Hg0 removal mechanism has been discussed based on the experimental and analytical results.

Mercury removal from water streams through the ion exchange membrane bioreactor concept

Mercury is a highly toxic heavy metal that causes human health problems and environmental contamination. In this study, an ion exchange membrane bioreactor (IEMB) process was developed to achieve Hg(II) removal from drinking water and industrial effluents. Hg(II) transport through a cation exchange membrane was coupled with its bioreduction to Hg(0) in order to achieve Hg removal from concentrated streams, with minimal production of contaminated by-products observed. This study involves (1) membrane selection, (2) demonstration of process effectiveness for removing Hg from drinking water to below the 1ppb recommended limit, and (3) process application for treatment of concentrated water streams, where >98% of the Hg was removed, and the throughput of contaminated water was optimised through membrane pre-treatment. The IEMB process represents a novel mercury treatment technology with minimal generation of contaminated waste, thereby reducing the overall environmental impact of the process.

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 Mn(x+) 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.

Removal and recovery of gas-phase element mercury by metal oxide-loaded activated carbon

The reusability of Co(3)O(4) (AC-Co), MnO(2) (AC-Mn) and CuCoO(4) (AC-CC) loaded activated carbon (AC) and their element mercury removal efficiency had been studied using a laboratory-scale fixed-bed reactor under simulated flue gas conditions. Tests showed that spent AC-Co could be regenerated through heating at 673 K under N(2) atmosphere and the enrichment regenerated Hg(0) could be collected to eliminate the secondary pollution. Regenerated AC-Mn and AC-CC's Hg(0) removal efficiency decreased greatly due to AC's decomposition and MnO(2)'s crystal structure variation. Compared with AC and metal oxides, metal oxide-loaded AC had higher Hg(0) capture ability and capacity due to AC huge surface areas and lots of function groups. TGA analysis results showed that AC-Co and AC-Mn's HgO adsorptive capacity at 523 K reached 19.8 mg g(-1) and 5.21 mg g(-1), respectively. High loading values and adsorption temperatures were beneficial to AC-Co's Hg(0) removal efficiency. However, CuCoO(4) and MnO(2)'s AC decomposition ability had negative effect on AC-CC and AC-Mn's performance, respectively, especially at high adsorption temperatures and loading values. SO(2) tests showed that AC-CC had higher anti SO(2)-poisoning ability than AC-Co and AC-Mn.