Hg0 Removal Efficiency Research Articles

Rapid and solvent-free construction of S-rich covalent organic polymer for efficient removal of mercury

Mercury (Hg(Ⅱ)) is an extremely hazardous heavy metal ubiquitously discovered in the global environment. Covalent organic polymers (COPs) have been recognized as promising adsorbents due to their exceptional properties tailored for Hg(II) sequestration. Nevertheless, the synthesis of the majority of COPs requires rigorous experimental conditions. Herein, a sulfur (S)-rich COP denoted as TpTU was successfully constructed using a solvent-free approach. Compared to TpUrea without S, TpTU exhibited superior Hg(Ⅱ) capture performance. The experimental results demonstrated splendid adsorption performance for Hg(Ⅱ) (187 mg·g−1), and the adsorption isotherm was well-fitted to the Freundlich model (R2 > 0.98). Meanwhile, adsorption equilibrium was achieved within 5 min, and thermodynamic analyses indicate that the adsorption process is endothermic in nature. In addition, TpTU exhibited exceptional selectivity for Hg(II) even in the presence of competing ions. The mechanism investment revealed that the incorporation of heteroatoms, particularly S and nitrogen (N), plays a critical role in enhancing the affinity of COP toward Hg(Ⅱ). Moreover, no significant loss is observed for its capacity even after eighth adsorption–desorption cycles, demonstrating remarkable reusability of TpTU. Furthermore, TpTU also achieved Hg(Ⅱ) removal efficiency of over 98.9 % in actual water samples. These results prove the practical potential of TpTU for the purification of Hg(II) polluted water, offering a promising avenue towards cleaner and safer water resources.

Fabrication of recoverable Bi2O2S/Bi5O7I/ZA hydrogel beads for enhanced photocatalytic Hg0 removal in the presence of H2O2

The effective removal of elemental mercury (Hg0) is a global challenge due to its toxicity and bioaccumulation threat to public health and ecosystems. Photocatalytic technology by visible light-driven photocatalysts is promising for Hg0 removal. However, effective separation of photocatalyst powders from reaction solution limits its widespread use. To solve the problem, we report for the first time the successful fabrication of recoverable Bi2O2S/Bi5O7I/ZA hydrogel beads for enhanced photocatalytic Hg0 removal in the presence of H2O2. Characterization techniques such as XRD, TEM, EDS, XPS, UV–vis DRS, PL, etc. are employed to understand the physicochemical properties and photoelectric performance of the photocatalysts. The serial BOSI photocatalysts all outperform the single component, which is attributed to the formation of a heterojunction between Bi5O7I and Bi2O2S. The coupling of 2-BOSI-ZA beads with H2O2 shows favorable synergistic effect, with Hg0 removal efficiency in the following order: H2O2 + 2-BOSI-ZA < 2-BOSI-ZA + FSL < H2O2 + 2-BOSI-ZA + FSL. TPC, EIS, and PL tests confirm that the introduction of Bi2O2S effectively suppresses charge carrier recombination. ESR and free radicals capture experiments demonstrate that the main species responsible for removal of Hg0 are •O2– and •OH. Density functional theory calculations exhibit that the internal electric field (IEF) between Bi5O7I and Bi2O2S contributes to the spatial charge separation of the heterojunction. The IEF leads to an S-scheme carrier transfer mechanism at the Bi2O2S/Bi5O7I interface that benefits the carrier separation on Bi5O7I, resulting in an enhanced photocatalytic performance. This work can provide further inspiration for designing hydrogel photocatalysts with an excellent activity in conjunction with oxidants in the field of mercury pollution control.

Mechanistic investigations into the removal of Hg0 over Pt-based sorbents by warm syngas cleanup

Commercial sorbents for Hg0 removal from syngas operate at low temperatures (<120 ºC), which impacts the thermal efficiency of integrated gasification and chemical production processes. For the first time, supported Pt-based sorbents with different supports, viz., Pt/SBA-15, Pt/S-40, Pt/ZrO2, Pt/CeO2, and Pt/TiO2 are synthesized for high-temperature (≥200 ºC) Hg0 removal. Pt/SBA-15 shows the highest cumulative Hg0 removal efficiency (>99 %) at 270 ºC in N2, which is retained for much higher durations (>20 h) compared to the best-reported Pd-based and metal oxide sorbents. Besides amalgam formation, Hg0 removal on Pt/ZrO2 and Pt/CeO2 occurs via oxidation at high temperatures (> 270 ºC), which explains the reduced negative effect of high temperature over these sorbents. In contrast to other supports, the removal efficiency over Pt/SBA-15 is above 99 % even in the presence of H2, H2O, and CO2, and is attributed to the hydrophobic mesoporous silica support. DRIFTS studies indicate CO adsorption on the active Pt sites over all sorbents. Based on the inferences obtained, a kinetic model is developed and integrated into a reactor-scale model which effectively simulates the spatio-temporal features of Hg0 sorption over Pt/SBA-15.

Synergistic effects of multi-walled carbon nanotubes and Mn0.4Cu0.6Fe2O4 on mercury removal with high efficiency and sulfur resistance

Although ferrite-based adsorbents are the potential mercury removal materials for the high thermal stability, they usually suffer from a low efficiency in flue gas environment, especially under SO2 condition. In the present paper, the multi-walled carbon nanotubes (MWCNTs) are utilized to improve the adsorption capacity of the Mn0.4Cu0.6Fe2O4 adsorbents as well as inhibit the influence of flue gas composition. The influences of temperature, adsorbent type and the flue gas composition on Hg0 removal efficiency are evaluated by experiments. The physical adsorption property of MWCNTs provides a platform for Hg0 oxidation by Mn0.4Cu0.6Fe2O4. The synergistic effect between MWCNTs and Mn0.4Cu0.6Fe2O4 enhances the mercury removal efficiency as well we the sulfur resistance. The results find that the adsorbent of Mn0.4Cu0.6Fe2O4 containing 14 % MWCNTs has a high mercury removal efficiency of 95.6 % at 120 °C even under 1000 ppm SO2 concentration. The kinetic behaviors of adsorbent adsorption are analyzed by theoretical models. The mechanisms of porous carbon-containing modifier to improve the mercury removal performance of Mn0.4Cu0.6Fe2O4 are explored carefully. The present ferrite-based adsorbent exhibits promising prospects for the practical industrial applications of the low temperature mercury removal from coal-fired flue gas.

Online in-situ modification of biochar for the efficient removal of elemental mercury and co-benefit of SO2/NO removal

In this study, non-thermal plasma discharge was proposed for online in-situ modification of biochar injected into coal-biomass co-combustion flue gas, aiming to achieve the combined removal of elemental mercury (Hg0), NO, and SO2 from flue gas. After plasma discharge, the pore structure of biochar was slightly improved whereas the surface morphology of biochar was almost unchanged. After plasma discharge under O2, SO2, and HCl atmospheres, the oxygen, sulfur, and chlorine contents of biochar were obviously increased. More exactly, additional functional groups were formed on the modified biochar surface, such as CO, C(O)OC, CS, and CCl. Compared with raw biochar, the biochar modified under HCl, SO2, O2, H2O and CO2 atmospheres exhibited higher Hg0 removal efficiency, and longer modification time resulted in better Hg0 removal performance. The optimal modification atmosphere and reaction temperature were the simulated flue gas (SO2 + HCl + CO2 + O2 + H2O + NO + N2) and 20 ℃-100 ℃, respectively. The modified biochar exhibited excellent resistance to SO2 and H2O. The addition of HCl, CO2, NO, and O2 contributed to Hg0 removal. The removal efficiency of NO and SO2 attained a maximum of 100 %. The Hg0 removal mechanism was further revealed, where CO, C(O)OC, CS, and CCl served as active components.

Salts-activated synthesis of Cu/Co co-doped biochar for efficient removal of elemental mercury from coal combustion flue gas

Mercury immobilization from coal combustion flue gas remains challenging due to the shortage of cost-effective sorbents. In this study, Cu/Co co-doped biochar (CuxCoyBCT) was synthesized through one-step pyrolysis of wood loaded with Cu and Co salts, which was applied to remove elemental mercury (Hg0) from the simulated flue gas. The BET surface area and pore volume of CuxCoyBC650 were vastly higher compared with CuBC650 because of the catalytic effect of cobalt. The synergistic effects between Cu and Co facilitated the transformation of Cu2O into CuO during pyrolysis. The doping of Co resulted in a more uniform dispersion of CuOx and highly dispersed CoOx was also observed in CuxCoyBCT. For this reason, the Hg0 removal performance of CuxCoyBCT was obviously improved after Co doping. The optimal Cu/Co molar ratio and pyrolysis temperature were 1:1 and 650 °C, respectively. The sample of Cu1Co1BC650 showed satisfactory Hg0 removal efficiency (>88 %) over a broad temperature range (100 °C–180 °C). It was remarkable that SO2 facilitated Hg0 removal and H2O had negligible effect on Hg0 removal over CuxCoyBCT. The presence of O2 and NO was conductive to Hg0 removal. The mechanism of Hg0 removal over CuxCoyBCT was further revealed. The results indicated that the heterogeneous adsorption and catalytic oxidation of Hg0 occurred simultaneously, where chemisorbed oxygen, CuO, and Co3O4 served as active components.

One-step utilizing of waste acidic Cu-containing etching solution to prepare hierarchical Cu-ZSM-5 for efficient flue gas Hg0 removal

Developing mercury adsorbents could mitigate environmental risk of mercury pollution. In this study, waste acidic Cu-containing etching solution from PCBs etching industry was utilized for the simultaneous porosity etching and Cu/Cl sites loading to prepare WA-ZSM for Hg0 removal via a one-step method. WA-ZSM synthesized with different waste acid concentrations exhibited over 94 % Hg0 removal efficiency within 60 min. The long-term stability of 5WA-ZSM under 110 μg/m3 Hg0 within 300 min was higher than 90 %. The dealumination process significantly affected the formation of micropores and Cu loading into the pore structure. The EFAl-Al3+ and “Si-O-Cu” structures formed by dealumination greatly enhanced the strong acid sites and the Cu sites improved the medium strong acidity. Isolated [Cu-OH]+ sites and [Cu–O-Cu]2+ sites are the main active sites in Hg0 removal. This method successfully synthesizes low-cost, high-efficiency Hg0 adsorbents using hazardous wastes, presenting a significant advancement in sustainable waste utilization and mercury pollution control.

Decoupling the influence of NOx in flue gas on the application of nano-amorphous selenium for mercury removal

Nitrogen oxides are inevitable hazardous components in coal-fired flue gas. This study designed a series of experiments and combined theoretical calculations to systematically investigate the effect of NOx on the removal of element mercury (Hg0) by nano-amorphous selenium (nano-a-Se). It was found that the impact of NOx on the removal of Hg0 by nano-a-Se primarily involves two mechanisms: competitive adsorption between NOx and Hg0, and the induced reduction effect of NOx on chemisorbed mercury (HgSe). NO inhibits the removal of Hg0 by nano-a-Se, and competitive adsorption is identified as the main influencing factor. Whereas the inhibitory effect of NO2 on the adsorption of Hg0 by nano a-Se can be counteracted due to its oxidizing effect on Hg0. Therefore, although NO2 presents stronger competitiveness than NO in the competitive adsorption with Hg0, it still shows a promoting effect on Hg0 removal, with 50 ppm NO2 restoring 5.7 % of the Hg0 removal efficiency. Additionally, the mechanism of NOx-induced reduction of HgSe was investigated in detail. NO2 is more capable of inducing the reduction of Hg(II) from HgSe to Hg0. This study presents new insights into the underlying influence mechanism, which could provide valuable references for the application of other selenium-based adsorbents.

H2S induced in-situ formation of recyclable metal sulfide-based sorbent for elemental mercury sequestration in natural gas

Enlightened by the phenomenon that hydrogen sulfide (H2S) can readily decompose on metal oxides to generate sulfide species and the obtained metal sulfides are generally adopted as Hg-affine ligands for Hg0 capture, a urea modified copper oxide (U-CuO) was prepared via high-temperature calcination of the mixture of urea and copper nitrate for Hg0 removal in natural gas containing H2S. Benefitted from the decomposition of urea and the release of gaseous decomposition products, the as-synthesized U-CuO was enriched with abundant base sites and lattice oxygen, and characterized with developed textural features, which facilitates the diffusion and adsorption of H2S and subsequent sequestration of Hg0. The Hg0 adsorption capacity and uptake rate of U-CuO under simulated natural gas (N2 + 500 ppm H2S+8% H2O) reached as high as 134.06 mg g−1 and 58.32 μg g−1 min−1, respectively, which largely surpassed those of most CuS-based sorbents for Hg0 immobilization. Besides, U-CuO sorbent also exhibited satisfactory recyclability only through simple thermal treatment, the Hg0 removal efficiency of U-CuO maintained above 97 % even after ten adsorption-regeneration rounds. This preparation strategy not only provides valuable hints to guide the design and synthesis of Hg0 sorbents used for natural gas containing H2S but also inspires further investigation for the cost-effective performance enhancement of Hg0 sorbents.

Iodide- and electrochemical assisted removal of mercury by Cirsium arvense from gold tailings in the Amansie West District, Ghana

Mercury (Hg) pollution in Ghana through mining has become a serious environmental challenge. This study investigates the potential of Cirsium arvense to photostabilize Hg using electrokinetic current with or without an iodide solution in gold mine tailings heavily contaminated through mining activities in southern Ghana. An initial Hg concentration of 9.60 mg/kg using cold vapor atomic absorption spectrometry (CVAAS) was determined. The biological absorption coefficient, bioconcentration factor, and translocation factor of Hg have been presented. Cirsium arvense therefore had a higher bioconcentration factor (BCF) of 2.6–5.15 mg/kg, and a transfer factor (TF) of 0.24–0.36 indicating a higher efficiency for phytostabilization. Both the rate and time of extractions of Hg from the tailings by Cirsium arvense are efficiently improved in the combined electric current and iodide treatment. Plant and electric current combined treatment and plant and iodide combined treatment had only 60 and 50% phytostabilization rates, respectively. The combined plant, iodide, and electric current treatment has proven to be superior with about >90% Hg removal rate. Therefore, the combined plant, iodide, and electric current treatment resulted in a higher Hg removal efficiency by Cirsium arvense in a shorter period due to higher solubilization rate and electromigration effects on Hg species.

Hollow tubular MnOx prepared by flame annealing with cotton fiber as sacrificial template and its applications for Hg0 adsorption in flue gas

The mass discharge of mercury from coal-fired power plant has caused great harm, abating mercury emissions is of preoccupation for protecting public environmental safety and human health. Metal oxides are often used for Hg0 removal in the flue gas. In this paper, a hollow tubular MnOx(MnCot) was successfully prepared by rapid flame annealing using cotton fiber as a sacrificial template. The MnCot were then well characterized and tested for its capability for Hg0 removal in flue gas. The results indicate that the flame assisted synthesis method for rapidly prototyping metal oxides with typical structures is achievable. The hollow tubular structure of the cotton fiber is well reprinted with good crystallization of Mn3O4. The inner diameter of the hollow tubular MnCot is about 10 μm, and the thickness of the tube is about 1 μm. The Hg0 removal efficiency on MnCot can be maintained as high as 90 % under simulated flue gas atmosphere below 240°C. O2 and NO have a positive effect on the Hg0 removal, which can act as the fresh active sits thus enhancing its capability for Hg0 removal. However, the presence of SO2 will result in the surface sulfation on MnCot, thus deteriorating its capability for Hg0 removal. Further, the competitive adsorption between SO2 and Hg0 on the material will also weaken its capability for Hg0 removal. The hollow tubular MnOx rapidly prepared by one-step flame annealing has a good industrial application potential for Hg0 removal in coal-fired flue gas.

Industrial grade calcium sulfide modified by selenium for elemental mercury removal from flue gas

Metallic sulfides (MS) adsorption is considered as an effective method to remove Hg0 from coal-fire flue gas. Se modification can significantly improve Hg0 removal process on MS due to the high affinity constant between Se and Hg0. CaS as a production from wet flue gas desulfurization has potential Hg0 removal ability. Therefore, in the present work, Se modified industrial grade CaS was prepared to remove Hg0 and the effect of the ratio of CaS to Se on Hg0 removal process was studied. Characterization results show that Ca1-Se1.7 had the richest porous structure and largest surface area resulting in more available surface active sites. In addition, Ca1-Se1.7 has the highest content of Se−, who can remove Hg0 via Hg0(ad)+Se22-→HgSe+Se2-. As a result, Ca1-Se1.7 has the highest Hg0 removal efficiency of nearly 100 % from 60 ℃ to 100 ℃, and it reaches 85 % even in the presence of 500 ppm SO2. The Hg0 adsorption kinetic was well defined by the pseudo-first-order kinetic model and internal diffusion model, so that Hg0 diffusion especially internal diffusion is the primary controlling step.

Optimizing removal of elemental mercury from flue gas using halide‐impregnated red mud

AbstractMercury (Hg0) emission from coal‐fired industrial plants poses severe threats to ecosystem sustainability and human health, urging the development of novel and cost‐effective adsorbents to treat industrial flue gas. Herein, the modification of industrial residual red mud (RM) through the impregnation of hydrogen halides (HH) and its adsorption characteristics for removing elemental mercury from combustion flue gas was reported. Experimental investigation of HH‐modified RM reveals that the hydrogen iodide (HI)‐modified RM with a concentration of 1.5 M had a maximum Hg0 removal efficiency of 98%, whereas hydrogen bromide (HBr) 1.5 M modified RM had a maximum Hg0 removal efficiency of 90%. The effect of various parameters, such as reaction temperature and halide concentrations, were also found to be influential for the adsorption efficiency of the modified RM. Moreover, it is important to highlight the chemisorption characteristics of HI‐modified RM, which significantly enhances the efficiency of the removal process. The Hg0 removal efficiency increases with the increase in HI concentration (1.5 M @ 93%) with an optimal reaction temperature of 140°C. Furthermore, the maximum Hg0 removal attained with a change in NO concentration was 98% at 200 ppm. However, increasing the SO2 concentration reduces the efficiency of RM for removing Hg0 in simulated coal combustion flue gas. The pseudo‐second‐order model (R2 = 0.98) accurately describes the adsorption of in kinetic investigations, indicating a chemisorption mechanism. This analysis of the chemisorption mechanism highlights the efficiency of halide‐modified industrial solid waste, which has the potential to be used in the design of economical and innovative adsorbents for reducing environmental pollution. The present study employed specific reaction parameters such as reaction temperature, halide loading contents, and different flue gas compositions, which had not been extensively explored.

Elemental mercury removal by copper-containing brominated pyrolytic chars derived from waste printed circuit boards

Waste printed circuit boards (WPCBs) containing brominated flame retardants (BFRs) would result in serious environmental pollution without pertinent treatments. However, bromine-containing materials have been proven highly efficient for elemental mercury removal (Hg0). This work proposes a win–win strategy of a cost-effective Hg0 removal method and a highly efficient utilization of WPCB-derived chars. Diverse copper-containing brominated pyrolytic chars of WPCBs were prepared in a fixed bed reactor at 500–700 °C tailored for Hg0 removal from coal-fired flue gas. The resulting copper-containing pyrolytic chars were proven to have a high Hg0 removal efficiency. Various characterizations and adsorption curves insights into the impacts of copper, sorbent weights, pyrolysis and adsorption temperatures, on Hg0 removal efficiency of WPCB-derived chars. The results indicate that copper in WPCBs enhances the fixation of the bromine elements in pyrolytic chars, resulting in improved Hg0 removal performance. The optimal pyrolysis and adsorption temperatures for pyrolytic chars are 600 °C and 140 °C, respectively. Under optimized conditions, a Hg0 removal efficiency exceeding 90 % is realized after 30 min of adsorption. Notably, the results indicating the Hg0 adsorption capacity of WPCB-derived chars rivals that of commercial activated carbons and significantly surpasses that of biochar. Both adsorption kinetics and characterizations affirm that chemisorption is the predominant adsorption method. The C-Br bond and CuO emerge as crucial active sites facilitating the oxidation of Hg0.

Cysteamine-Anchored MOF through Post-Synthetic Modification Strategy for the Effective Removal of Mercury from Water.

The introduction of cysteamine functionality, referred to as Q-ZIF-67-SH, was successfully achieved through postsynthetic modification while maintaining the structural and thermal stability of the quasi metal-organic framework Q-ZIF-67. By subjecting ZIF-67 to controlled partial deligandation at 310 °C under an air atmosphere, a substantial number of unsaturated cobalt sites were generated within the quasi ZIF-67 (Q-ZIF-67) structure. These unsaturated cobalt sites facilitated effective coordination with cysteamine, resulting in the development of the thiol-functionalized framework Q-ZIF-67-SH. The potential of these metal-organic frameworks (MOFs) for the adsorptive removal of hazardous Hg(II) was investigated. Various factors, such as the type of sorbent, pH, adsorbent dosage, initial concentration of Hg(II), and presence of coexisting ions, were thoroughly examined and comprehensively explained. Thiol-anchored MOF significantly enhanced the efficiency of Hg(II) removal, achieving an impressive removal rate of up to 99.2%. Furthermore, it demonstrated a maximum adsorption capacity of 994 mg g-1 and a distribution coefficient of 2.5 × 106 mL g-1. A good correspondence with pseudo-second-order kinetics and the Langmuir model was observed through the fitting of adsorption kinetics and the isotherm model. The thermodynamic data strongly indicate that the adsorptive removal of Hg(II) is characterized by endothermicity and spontaneity. This signifies that the process is energetically favorable and has potential for efficient Hg(II) removal. Therefore, the Q-ZIF-67-SH sorbent emerges as a promising and advantageous option for the removal of Hg(II) from water.

Enhanced Hg(II) removal using thiourea-functionalized graphene oxide: Lab to pilot scale evaluation

Here, a thiourea-formaldehyde functionalized graphene oxide (G3DTF) is shown to effectively remove mercury (Hg) from various water sources, including ultrapure, bottled, and seawater. Over 99 % of the Hg in each water source is removed with only 10 mg/L of G3DTF resulting in a residual Hg concentration < 1 μg L−1. This concentration falls within the permissible limits established by the European drinking water guidelines. Notably, the presence of chlorocomplexes in seawater does not reduce the sorption efficiency of G3DTF. The sorption process across all water matrices can be accurately described by pseudo-second-order kinetics, with an R2 > 0.99 suggesting chemical interactions between Hg ions and G3DTF functional groups. The equilibrium isotherms demonstrate a remarkably high maximum adsorption capacity (qm) of 1039 mg g−1, exceeding the values reported in literature for the sorption of Hg on carbon-based materials. Remarkably, G3DTF retains its performance in the presence of other metal ions such as Cu, Cd, and Pb. Incorporating G3DTF into commercially activated carbon (AC) at a concentration as low as 2 wt % significantly enhances the efficiency of Hg(II) removal in fixed bed adsorption. The breakthrough curve exhibits enhanced absorption, attaining a 99.7 % removal of Hg(II) within a span of 2 h, surpassing the efficiency of AC. This relevant result represents a substantial advancement towards the adoption of graphene-based nanocomposites as effective commercial remediation materials.

Bacterial and microalgal co-fixation for remediation of industrial wastewater contaminated with arsenic, mercury, and other pollutants

Microbial remediation is an efficient approach for improving heavy metal-contaminated water environments. Herein, this article developed a composite bacterial agent (CBA) with a high heavy metal tolerance. Within 12 h, the CBA demonstrated removal efficiencies of 65.18 ± 1.53% for As and 60.73 ± 0.94% for Hg in wastewater. This study prepared bacterial–algal fixed spheres (BAFS) to further enhance the removal efficiencies of As and Hg. Moreover, during desorption using 0.1 mol/L HNO3 for 60 min, the BAFS maintained high removal efficiencies for As and Hg after five adsorption–desorption cycles. Applying BAFS to industrial wastewater collected from factory outfall caused substantial reductions in chemical pollutants and other heavy metals. Scanning electron microscopy analysis further revealed that the internal cavities formed through the crosslinking of immobilized materials provided excellent survival carriers for bacteria and microalgae. Infrared spectroscopy analysis demonstrated the involvement of three functional groups, namely -OH, -CH2-, and C-O-C, in pollutant adsorption. Additionally, microbial community diversity analysis indicated that immobilization effectively preserved the pollutant adsorption ability of the microorganisms, increasing the abundance of functional microbial populations. These characteristics improved the efficiency of industrial wastewater treatment while promoting recycling.

Investigation of elemental mercury removal performance and mechanism of rice straw biochars from a fluidized bed pyrolysis system impregnated by NH4Br

To remove Hg0 from flue gas efficiently and economically, the rice straw biochars prepared in a fluidized bed pyrolysis system and then modified with NH4Br are employed as the sorbents. The mercury adsorption capacity of Br-modified biochar (1786.85 μg/g) is superior to that of activated carbon (207 μg/g), which indicates Br-modified rice straw biochar sorbent displays higher Hg0 adsorption efficiency and can replace high-cost activated carbon. The sorbents are characterized by Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The effects of pyrolysis temperature, pyrolysis atmosphere, reaction temperature, the components of flue gas (O2, NO and SO2) on mercury removal efficiency, kinetics, thermodynamics and mercury removal mechanism are investigated. The results indicate elevating pyrolysis temperature and oxygen content significantly enhance the Hg0 removal efficiency. The Hg0 adsorption process is better fitted by pseudo-second-order kinetic model and proves a spontaneous endothermic process. The presence of O2 and NO in flue gas enhances Hg0 adsorption, while the presence of SO2 restrains it. After Hg0 adsorption, the peak area ratio of C=O (288.5 eV) and C-Br (69.1 eV) by Br-modified rice straw biochars produced under 8 %O2 and 500 °C atmosphere decreases from 17.03 % and 70.14 % to 6.55 % and 50.50 %, respectively, while that of Br− (68.1 eV) increases from 29.86 % to 48.50 %, indicating the surface O* and Br* species are responsible for Hg0 removal, and the products are mainly HgO and HgBr2. This work provides a kind of cost-effective Hg0 removal sorbent and explores the mechanism of Hg0 removal by Br-modified biochars.

Microcosmic insights into Hg0-SO2 interaction on CuFe2O4 catalyst

CuFe2O4 is considered as a very promising kind of catalysts for Hg0 oxidation in the industrial flue gas. The flue gas produced by solid-fuel combustion usually contains acid gas component SO2, which can exhibit the versatile effects on Hg0 oxidation. However, the effects of SO2 on Hg0 oxidation catalyzed by CuFe2O4 catalyst and its reaction mechanism remain elusive. Herein, the reaction mechanism governing the effects of SO2 on Hg0 oxidation was investigated via the Hg0 oxidation experiments and density functional theory (DFT) calculations. The experimental results show that the temperature change and SO2 presence can affect the Hg0 removal efficiency of CuFe2O4 catalyst. SO2 has a certain degree of inhibition effect on the Hg0 oxidation of CuFe2O4 catalyst. The inhibition effect of SO2 is relatively weak in the low temperature range of 50–150 °C, which is closely associated with the competitive adsorption between SO2 and Hg0. SO2 exhibits a relatively strong inhibition effect on Hg0 oxidation in the high temperature range of 200–350 °C, which is related to the high-temperature sulfation of CuFe2O4 catalyst surface. Mercury species on the CuFe2O4 catalyst surface mainly exists in the forms of HgSO4 and HgO in the presence of SO2. The DFT-calculation results indicate that the conversion process of SO2 to SO3 includes two steps: SO2 adsorption and SO2 oxidation. The activation energy barrier of SO2 oxidation reaction is 216.42 kJ/mol. The oxidation of Hg0 on the surface of CuFe2O4 catalyst includes four steps: Hg0 adsorption, Hg* oxidation into HgO*, HgO*-to-HgSO4* conversion and HgSO4 desorption. HgSO4 is formed by the bimolecular reaction of HgO* and SO3* on CuFe2O4 catalyst. Hg* oxidation into HgO* is found to be the rate-determining step of HgSO4 formation.

In situ self-activation strategy for the synthesis of double-layered S/Cl co-doped sorbents for elemental mercury removal from oxy-fuel combustion flue gas

Mercury capture from oxy-fuel combustion flue gas remains an enormous challenge for carbon capture and storage because of the lack of cost-effective, sulfur-resistant and water-resistant sorbent. In this work, double-layered S/Cl co-doped sorbents (CDSs) were synthesized through an in situ self-activation method i.e. co-pyrolysis of waste tire and PVC plastic, which were adopted for elemental mercury (Hg0) immobilization from oxy-fuel combustion flue gas. A synergistic effect between waste tire and PVC plastic was observed during co-pyrolysis. For this reason, chlorine was successfully doped into the CDSs in the form of covalent chlorine and ionic chlorine. The CDSs showed high Hg0 removal efficiency (>80 %) over a wide temperature range (20–140 °C) and excellent sulfur and water resistance. Both the initial Hg0 adsorption rate and adsorption capacity of CDSs were far higher compared with raw tire char. The Hg0 removal mechanisms were further proposed, where Hg0 preferentially reacted with covalent chlorine instead of active sulfur species. Density functional theory calculations revealed that the Hg0 adsorption over CDSs was chemisorption with an adsorption energy of −249.85 kJ/mol. The synergistic effect between sulfur and chlorine was beneficial for the formation of HgCl2 whereas it had negligible effect on the formation of HgCl.