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Fe3O4-based materials are widely used for magnetic separation from wastewater. However, they often suffer from Fe-leaching behavior under acidic conditions, decreasing their activity and limiting sustainable practical applications. In this study, covalent organic frameworks (COFs) were used as the shell to protect the Fe3O4 core, and the Fe3O4@COF core-shell composites were synthesized for As(III) removal from acid wastewater. The imine-linked COFs can in situ grow on the surface of the Fe3O4 core layer by layer with [COFs/Fe3O4]mol ratio of up to 2:1. The Fe-leaching behavior was weakened over a wide pH range of 1-13. Moreover, such composites keep their magnetic characteristic, making them favorable for nanomaterial separation. As(III) batch adsorption experiments results indicated that, when COFs are used as the shell for the Fe3O4 core, a balance between As(III) removal efficiencies and the thickness of the COF shell exists. Higher As(III) removal efficiencies are obtained when the [COFs/Fe3O4]mol ratios were

Oxidation of sulfite and competitive absorption existed in Na2SO3 solution for simultaneous removal of NOx and SO2, inhibited the long-term high-efficiency when used for practical applications. A matching strategy was developed to solve these problems. Antioxidants combination was used to retard the oxidation of antioxidant and enhance inhibition of S(IV) (tetravalent sulfur) oxidation. Hydroquinone (HQ) and sodium thiosulfate (ST) showed a positive synergistic effect on inhibition of S(IV) oxidation. When SO2 concentration was 500 and 2000 ppmV, the addition of 0.1 wt.% HQ and 1 wt.% ST decreased the percentage of S(IV) oxidized by oxygen by over 30% and 40%, respectively. Alkali (Na2CO3) alleviated the competitive absorption between NOx and SO2. Moreover, Na2CO3 exhibited an enhancement effect on the absorption of NOx and SO2 when coupled with anti-oxidants. While the increase of oxygen pressure accelerated the oxidation of S(IV), the anti-oxidants can retard the oxidation. The measurement of pH suggested the removal efficiency of NOx highly depended on SO32⁻ concentration rather than pH. The further investigation of the mechanism suggested the match effect was related to the interaction between ST and the intermediate product of HQ. The match strategy holds a potential for application of SO32⁻ to denitration.

Arsenic is extremely toxic to humans with water as its carrier. One challenge for arsenic control is the complete elimination of As(III) due to its high toxicity, mobility, and solubility. Herein, an active FeS

Sulfur trioxide (SO

Fine particles with the size below 1 μm are difficult to be captured with the traditional dust removal devices because of their poor charge capacity and filterability. Using the agglomeration pretreatment can realize the fine particles growth, then facilitating the capture process. In this study, a novel system with the combination of corona discharge and embedded turbulence was put forward. The results showed that the device can agglomerate the smaller particles into bigger ones, and the maximum decrease of number concentration for small particles can reach 40% in the bipolar corona discharge condition. The median diameters of fine particles can be improved by 47% maximumly in the condition of arrangement of turbulence bars and loopholes with a lower flow velocity. The simulated calculation and pilot scale test were conducted and the results were consistent with experimental conclusions.

Herein, a novel Na2SO3 process enhanced with an oxidation inhibitor was proposed for the synergic removal of SO2 and NO2 from nonferrous smelting flue gas. The co-absorption and reduction character...

Adsorption is one of the most promising methods for gaseous mercury (Hg0) uptake from industrial flue gas, and the designing and synthesis of a sorbent are of significance for utilization. However,...

Purposively designing environmental advanced materials and elucidating the underlying reactivity mechanism at the atomic level allows for the further optimization of the removal performance for contaminants. Herein, using well facet-controlled I-Cu2WS4 single crystals as a model transition metal chalcogenide sorbent, we investigated the adsorption performance of the exposed facets toward gaseous elemental mercury (Hg0). We discovered that the decahedron exhibited not only facet-dependent adsorption properties for Hg0 but also recrystallization along the preferential [001] growth direction from a metastable state to the steady state. Besides, the metastable crystals with a predominant exposure of {101} facets dominated the promising adsorption efficiency (about 99% at 75 °C) while the saturated adsorption capacity was evaluated to be 2.35 mg·g-1. Subsequently, comprehensive characterizations and X-ray adsorption fine structure (XAFS), accompanied by density functional theory (DFT) calculations, revealed that it might be owing to the coordinatively unsaturated local environment of W atoms with S defects and the surface relative stability of different facets, which could be affected by the change in surface atom configuration. Hence, the new insight into the facet-dependent adsorption property of transition metal chalcogenide for Hg0 may have important implications, and the atomic-level study directly provides instructions for development and design of highly efficient functional materials.

Ozone oxidation and absorption is an effective technique for air pollutant removal from industrial flue gas. However, it is hard to remove Hg0 because of the competition reaction between O3 and NOx...

Chalcogen-based materials have been confirmed to possess large adsorption capacities for gaseous elemental mercury (Hg0) from SO2-containing flue gas. However, the interface reaction mechanisms and the interfacial stability are still ambiguous. Here, we selected some commonly used chalcogen-based sorbents (e.g., X, ZnX, CuX. X = S, Se) to investigate the in-depth reaction mechanisms. The adsorption capacities, structure effect on thermal and surface mercury stability, and interfacial reaction mechanism in the absence/presence of SO2 were evaluated. The experimental results indicated that Cu-chalcogenide had higher Hg0 adsorption capacity and surface Hg-X bonding stability compared with zinc one, while they exhibited an opposite degree of thermal stability. Moreover, all the chalcogenides showed well SO2 tolerance but with a slight difference. Chalcogenides with the same crystal structures, like ZnX or CuX, exhibited similar properties in stability and interfacial Hg0 and SO2 reaction mechanism. X− in chalcogenides have a better affinity to mercury, while in the Hg0 capture process, the existence of multivalent metal elements (like Cu2+ and Cu+) can faster the Hg0 oxidation for the further chemical-adsorption. This work provides a basic understanding of the application for efficiently enriching and recycling gaseous Hg0 from industrial SO2-containing flue gas.

Excessive oxidation of sulfite can lead to low utilization efficiency and inhibit its application in the wet flue gas denitration process. Using organic absorbent can retard the sulfite oxidation r...

The rate of gaseous Hg0 adsorption onto natural sphalerite increased by approximately 1.9-7.7 times after Cu2+ activation during flotation of the natural sphalerite to remove impurities. Via a new pathway involving CuS, physically adsorbed Hg0 was oxidized by CuS to HgS on natural sphalerite after Cu2+ activation. In a similar intrinsic ZnS pathway, physically adsorbed Hg0 was oxidized by ZnS to HgS. The rate of the CuS pathway for Hg0 capture was generally significantly larger than that of the intrinsic ZnS pathway. Thus, Hg0 adsorption onto natural sphalerite was notably accelerated after Cu2+ activation. However, the kinetic analysis indicated that the capacity of natural sphalerite for Hg0 capture did not vary. Because the properties of the activated sphalerite for Zn smelting were barely degraded after Hg0 capture, the spent activated sphalerite for Hg0 capture can be reused for Zn smelting. Moreover, most of the gaseous Hg0 captured by activated sphalerite can be recovered eventually as liquid Hg0 in the condenser unit of Zn smelters. Thus, Hg0 recovery by activated sphalerite is a cost-effective and environmentally friendly technology to recover Hg0 from Zn smelting flue gas, thus replacing the complex and dangerous Boliden-Norzink process.

Sulfidation has been an efficient method for arsenic (As) removal from acid wastewater, yet it is inefficient under neutral and weak acid conditions. The higher pH values resulted in the formation of the unstable As-S precipitates, especially employing Na

Oxidation-reduction-absorption based on sulfite is a promising process for simultaneous removal of NO

The method of enhancing mass transfer and improving reaction efficiency by confinement has attracted much attention in the electrochemical research field. In this research, to make low diffusion-limited electrochemical reactors fieldable, a new electrochemical reactor in flow-through mode was established with the mass-produced Ti/RuO

Hierarchical Ag-SiO2@Fe3O4 magnetic composites were selected for elemental mercury (Hg0) removal from non-ferrous metal smelting flue gas in this study. Results showed that the hierarchical Ag-SiO2@Fe3O4 magnetic composites had favorable Hg0 removal ability at low temperature. Moreover, the adsorption capacity of hierarchical magnetic composite is much larger than that of pure Fe3O4 and SiO2@Fe3O4. The Hg0 removal efficiency reached the highest value as approximately 92% under the reaction temperature of 150°C, while the removal efficiency sharply reduced in the absence of O2. The characterization results indicated that Ag nanoparticles grew on the surface of SiO2@Fe3O4 support. The large surface area of SiO2 supplied efficient reaction room for Hg and Ag atoms. Ag-Hg amalgam is generated on the surface of the composites. In addition, this magnetic material could be easily separated from fly ashes when adopted for treating real flue gas, and the spent materials could be regenerated using a simple thermal-desorption method.

Developing the catalysts that can efficiently degrade brominated volatile organic compounds (Br-VOCs) is a priority due to the low activity, the low product selectivity, and the low resistance to Br-poisoning. In this work, Co3O4/CeO2–Co3O4 hierarchical binary oxides were designed as a high-performance catalyst for the catalytic oxidation of dibromomethane (CH2Br2) as a model pollutant for Br-VOCs. The surface of carbon spheres was coated with a layer of CeO2 nanoparticles, and core-shell CSs@CeO2 were the precursors of Co3O4/CeO2–Co3O4 hierarchical binary oxides. Co3O4/CeO2–Co3O4(HS) had a hierarchical porous structure, there was a strong interaction between Co3O4 and CeO2·Co3O4/CeO2–Co3O4(HS) showed an excellent catalytic activity, and its T90 value was only 321 °C. Meanwhile, Co3O4/CeO2–Co3O4(HS) showed good stability for at least 30 h. Co3O4 provided the active sites for CH2Br2 oxidation, and the hierarchical porous structure and high specific surface area were conducive to the adsorption of CH2Br2 molecules. Meanwhile, CeO2 promoted the oxygen mobility of the composite and the oxidation performance of Co3O4. CH2Br2 molecular firstly adsorbed on Co3O4/CeO2–Co3O4(HS) surface, and dissociated to form the intermediates (i.e., formate species, and methoxy species), which were finally oxidized to CO and CO2, and Br species were removed in the form of HBr and Br2.

In order to remove and recycle elemental mercury from nonferrous smelting flue gas, cobalt sulfide sorbents were synthesized and tested. The mercury adsorption capacity of sorbent at 100 °C was 43.03 mg/g with 50% breakthrough threshold. The influences of the flue gas components and reaction temperature on the mercury adsorption capacity were investigated, respectively. The results shown that SO2, H2O, NO and O2 had negligible impact on mercury adsorption of sorbents. Transmission electron microscopy (TEM), X-ray diffractometer (XRD), mercury programmed desorption (Hg-TPD) and X-ray photoelectron spectroscopy (XPS) were employed to characterize the sorbents. The mercury desorption activation energy from the sorbent was calculated based on a model built by the mercury temperature-programmed desorption data. Additionally, the used cobalt sulfide sorbent was regenerated. The results showed that the cobalt sulfide sorbent could maintain good adsorption performance after regeneration during several cycling tests. Therefore, cobalt sulfide is a suitable sorbent for the mercury removal and recycling from nonferrous metal smelting flue gas.

The high acidity of mercury ions (Hg2+) contained wastewater can complicate its safe disposal. MgAl-LDHs supported [SnS4]4- clusters were synthesized for Hg2+ removal from acid wastewater. The active sites of [SnS4]4- clusters were inserted into the interlayers of MgAl-LDHs using an ion-exchange method. The experimental results indicated that [SnS4]4−/MgAl-LDHs composite can obtain higher than 99% Hg2+ removal efficiency under low pH values. The maximum mercury adsorption capacity is 360.6 mg g−1. It indicated that [SnS4]4- clusters were the primary active sites for mercury uptake, existing as stable Hg2(SnS4) on the surface of the composite. Under low pH values, such a composite seems like a “net” for HgSO4 molecules, exhibiting great potential for mercury removal from acid solutions. Moreover, the co-exist metal ions such as Zn2+, Na+, Cd2+, Cr3+, Pb2+, Co2+, and Ni2+ have no significant influences on Hg2+ removal. The adsorption isotherms and kinetics were also studied, indicating that the adsorption mechanism follows a monolayer chemical adsorption model. The [SnS4]4−/MgAl-LDHs composite exhibits a great potential for Hg2+ removal from acid wastewater.

Ag nano-particles (NPs) with high dispersion possess the capacity for elemental mercury (Hg0) removal in low temperature. To further enhance its thermo-stability and electron transfer ability, Ag-Fe3O4@rGO ternary magnetic composite was synthesized for gaseous Hg0 capture. Results indicated that such composite has a Hg0 removal performance with higher than 92% removal efficiency at 100 °C. The ternary composite has a higher Hg0 removal performance than that of pure rGO and Fe3O4@rGO. The physical-chemical characterization results indicated that Ag nano-particles in-situ grow on the surface of Fe3O4@rGO support. The large surface area of rGO supply efficient reaction room for Hg and Ag atoms. Ag-Hg amalgam is ascribed to the mercury uptake mechanism. The spent materials can be regenerated by a simple thermal-desorption method. In addition, this magnetic material provide an opportunity that can be separated from fly ashes when used in real flue gas.