The enhancement of benzene total oxidation over RuxCeO2 catalysts at low temperature: The significance of Ru incorporation.

Catalytic oxidation is considered to be the most efficient technology for eliminating benzene from waste gas. The challenge is the reduction of the catalytic reaction temperature for the deep oxidation of benzene. Here, highly efficient RuxCeO2 catalysts were utilized to turn the number of surface oxygen vacancies and Ce-O-Ru bonds via a one-step hydrothermal method, resulting in a preferable low-temperature reducibility for the total oxidation of benzene. The T50 of the Ru0.2CeO2 catalyst for benzene oxidation was 135 °C, which was better than that of pristine CeO2 (239 °C) and 0.2Ru/CeO2 (190 °C). The superior performance of Ru0.2CeO2 was attributed to its large surface area (approximately 114.23 m2·g-1), abundant surface oxygen vacancies, and Ce-O-Ru bonds. The incorporation of Ru into the CeO2 lattice could effectively facilitate the destruction of the CeO bond and the facile release of lattice oxygen, inducing the generation of surface oxygen vacancies. Meanwhile, the bridging action of Ce-O-Ru bonds accelerated electron transfer and lattice oxygen transportation, which had a synergistic effect with surface oxygen vacancies to reduce the reaction temperature. The Ru0.2CeO2 catalyst also exhibited high catalytic stability, water tolerance, and impact resistance in terms of benzene abatement. Using in situ infrared spectroscopy, it was demonstrated that the Ru0.2CeO2 catalyst can effectively enhance the accumulation of maleate species, which are key intermediates for benzene ring opening, thereby enhancing the deep oxidation of benzene.

Removing and recycling mercury from scrubbing solution produced in wet nonferrous metal smelting flue gas purification process.

Wet purification technology for nonferrous metal smelting flue gas is important for mercury removal; however, this technology produces a large amounts of spent scrubbing solution that contain mercury. The mercury in these scrubbing solutions pose a great threat to the environment. Therefore, this research provides a novel strategy for removing and recycling mercury from the scrubbing solution, which is significant for decreasing mercury pollution while also allowing for the safe disposal of wastewater and a stable supply of mercury resources. Some critical parameters for the electrochemical reduction of mercury were studied in detail. Additionally, the electrodeposition dynamics and electroreduction mechanism for mercury were evaluated. Results suggested that over 92.4% of mercury could be removed from the scrubbing solution in the form of a Hg-Cu alloy under optimal conditions within 150 min and with a current efficiency of approximately 75%. Additionally, mercury electrodeposition was a quasi-reversible process, and the controlled step was the mass transport of the reactant. A pre-conversion step from Hg(Tu)42+ to Hg(Tu)32+ before mercury electroreduction was necessary. Then, the formed Hg(Tu)32+ on the cathode surface gained electrons step by step. After electrodeposition, the mercury in the spent cathode could be recycled by thermal desorption. The results of the electrochemical reduction of mercury and subsequent recycling provides a practical and easy-to-adopt alternative for recycling mercury resources and decreasing mercury contamination.

Development of Recyclable Iron Sulfide/Selenide Microparticles with High Performance for Elemental Mercury Capture from Smelting Flue Gas over a Wide Temperature Range.

Fast and effective removal of elemental mercury in a wide temperature range is critical for the smelting industry. In this work, a recyclable magnetic iron sulfide/selenide sorbent is developed to capture and recover Hg0 from smelting flue gas. Benefiting from Se doping, the Hg0 capture performance of prepared FeSxSey is significantly enhanced compared with traditional iron sulfide, especially at high temperatures. Considering the recyclability and working temperature, FeS1.32Se0.11 exhibits the best Hg0 capture performance. The average capture rate of FeS1.32Se0.11 is 3.661 µg/g/min at 80 °C and its saturation adsorption capacity is 20.216 mg/g. The flue gas compositions have almost no effect on Hg0 capture. X-ray photoelectron spectroscopy and mercury thermal programmed desorption suggest that the stable active Se-Sn2- adsorption site can combine with Hg0 to form HgSe, consequently improving Hg0 capture performance at high temperatures. After Hg0 capture, the spent FeSxSey can be collected by magnetic separation and regenerated through selective extraction, which facilitates harmless treatment and resource reuse of mercury. With the advantages of excellent Hg0 capture performance, wide operating temperature range, and remarkable recycling property, FeSxSey microparticles may be a promising sorbent for Hg0 capture in industrial applications, while opening a new avenue to realize the resource utilization toward toxic elements.

Selective recovery of mercury from high mercury-containing smelting wastes using an iodide solution system.

The mercury resources recovery and safe disposal of mercury-containing waste is an urgent problem. In this study, a new method using an iodide solution system was proposed to selectively recover mercury from high mercury-containing smelting wastes. The mercury leaching efficiency, yields, leaching kinetics and thermodynamics were researched. The major factors which affect mercury leaching efficiency including iodide concentration, oxidant, pH and temperature were evaluated. Over 97% and 93% of mercury can be efficiently leached from wastewater treatment sludge (W-S) and acid sludge (A-S). After leaching, the mercury concentration during leaching toxicity test is under the limits set for hazardous waste. Additionally, the electrolytic technology can efficiently recover mercury from leachate in the form of elemental mercury, and the leachate after electrolytic can be reused for mercury leaching. The mercury leaching kinetics follows the shrinking core diffusion model and is controlled by solid product diffusion. The mechanism research shows the leaching efficiency was strongly dependent on the distribution of mercury species in smelting waste. The consequence on mercury leaching and recovery could provide nonferrous smelters with a practical and yet easy-to-adopt perspective to reduce the risk of mercury contamination and selectively recover mercury resources from mercury-containing smelting wastes.

Transport and transformation of mercury during wet flue gas cleaning process of nonferrous metal smelting.

Reducing mercury emission is hot topic for international society. The first step for controlling mercury in fuel gas is to investigate mercury distribution and during the flue gas treatment process. The mercury transport and transformation in wet flue gas cleaning process of nonferrous smelting industry was studied in the paper with critical important parameters, such as the solution temperature, Hg0 concentration, SO2 concentration, and Hg2+ concentration at the laboratory scale. The mass ratio of the mercury distribution in the solution, flue gas, sludge, and acid fog from the simulated flue gas containing Hg2+ and Hg0 was 49.12~65.54, 18.34~35.42, 11.89~14.47, and 1.74~3.54%, respectively. The primary mercury species in the flue gas and acid fog were gaseous Hg0 and dissolved Hg2+. The mercury species in the cleaning solution were dissolved Hg2+ and colloidal mercury, which accounted for 56.56 and 7.34% of the total mercury, respectively. Various mercury compounds, including Hg2Cl2, HgS, HgCl2, HgSO4, and HgO, existed in the sludge. These results for mercury distribution and speciation are highly useful in understanding mercury transport and transformation during the wet flue gas cleaning process. This research is conducive for controlling mercury emissions from nonferrous smelting flue gas and by-products.

The electrochemical selective reduction of NO using CoSe2@CNTs hybrid.

Converting the NO from gaseous pollutant into NH4+ through electrocatalytical reduction using cost-effective materials holds great promise for pollutant purifying and resources recycling. In this work, we developed a highly selective and stable catalyst CoSe2 nanoparticle hybridized with carbon nanotubes (CoSe2@CNTs). The CoSe2@CNTs hybrid catalysts performed an extraordinary high selectivity for NH4+ formation in NO electroreduction with minimal N2O production and H2 evolution. The specific spatial structure of CoSe2 is conductive to the predominant formation of N-H bond between the N from adsorbed NO and H and inhibition of N-N formation from adjacent adsorbed NO. It was also the first time to convert the coordinated NO into NH4+ using non-noble metal catalysis. Moreover, the original concept of employing CoSe2 as eletrocatalyst for NO hydrogenation presented in this work can broaden horizons and provide new dimensions in the design of new highly efficient catalysts for NH4+ synthesis in aqueous solution.

Selenium catalyzed Fe(III)-EDTA reduction by Na2SO3: a reaction-controlled phase transfer catalysis.

Fe(II)-EDTA, a typical chelated iron, is able to coordinate with nitric oxide (NO) which accelerates the rates and kinetics of the absorption of flue gas. However, Fe(II)-EDTA can be easily oxidized to Fe(III)-EDTA which is unable to absorb NO. Therefore, the regeneration of fresh Fe(II)-EDTA, which actually is the reduction of Fe(III)-EDTA to Fe(II)-EDTA, becomes a crucial step in the denitrification process. To enhance the reduction rate of Fe(III)-EDTA, selenium was introduced into the SO3 (2-)/Fe(III)-EDTA system as catalyst for the first time. By comparison, the reduction rate was enhanced by four times after adding selenium even at room temperature (25 °C). Encouragingly, elemental Se could precipitate out when SO3 (2-) was consumed up by oxidation to achieve self-separation. A catalysis mechanism was proposed with the aid of ultraviolet-visible (UV-Vis) spectroscopy, Tyndall scattering, horizontal attenuated total reflection Fourier transform infrared (HATR-FTIR) spectroscopy, and X-ray diffraction (XRD). In the catalysis process, the interconversion between SeSO3 (2-) and nascent Se formed a catalysis circle for Fe(III)-EDTA reduction in SO3 (2-) circumstance.