| Mercury is a highly toxic heavy metal pollutant that is persistent and bioaccumulative.It is considered to be one of the most harmful environmental pollutants to humans and other living organisms.Currently,the main cause of global mercury pollution is the emission of mercury from human production activities that greatly exceeds natural geological sources.Among the mercury pollution caused by anthropogenic activities,coal-fired power plants are by now the largest perceived source of emissions.While the control of mercury emissions depends mainly on the removal of Hg0 from coal combustion flue gas.And activated carbon injection mercury remuval technology is currently the most effective technology for the removal of Hg0 from coal-fired power plants.The technical bottleneck of the activated carbon injection mercury removal technology is that the activated carbon after adsorption cannot be recycled and the residence time of the adsorbent is short,which makes the utilization rate of the adsorbent low.Therefore,the development of low-cost,high-efficiency removal and product recovery and recycling of adsorbents is the key to the current jet mercury removal technology.Magnetic adsorbents are considered as among the most prospective adsorbents for mercury emission control due to their good adsorption performance,easy separation and recovery,low toxicity,and good chemical stability.The magnetic adsorbent has better magnetization performance compared to other adsorbents and is easy to separate from fly ash.Therefore,the development and design of magnetic adsorbents with low cost,high efficiency removal,green sustainability,and high regeneration capacity are the key to current mercury emission control.First of all,in this paper,the magnetic porous composite Fe3O4/MOF-199 was synthesized and used for simulating flue gas mercury removal by successfully loading Fe3O4 on the surface of MOF-199.In order to further enhance the performance of the magnetic adsorbent for mercury removal,we also synthesized HS-Fe3O4/MOF-199,a magnetic adsorbent with stronger mercury removal capacity,by loading Fe3O4 on MOF-199 after thiol functionalization.And modeling flue gas mercury removal experiments indicated that the adsorption capability of the thiol-functionalized magnetic adsorbent was much larger than that of the unmodified material and material adsorption capacity up to 66.5 ?g/g.However,in the cycling experiments,the material structure was partially destroyed due to high temperature desorption resulting in poor cycling performance.In order to improve the thermal stability of the material,the magnetic metalorganic skeleton Fe3O4/UiO-66 was synthesised with the additional magnetic properties of the more stable zirconium-based metal-organic framework material UiO-66.Due to its large number of pores it has a weak dispersion force and does not effectively capture the mercury in the flue gas,resulting in a low adsorption capacity.Therefore,we enhanced the dispersion force and thermal stability of the magnetic metal-organic framework material Fe3O4/UiO-66 by introducing activated carbon material into the synthesis process to improve its adsorption capacity for Hg0 in simulated flue gases.We have synthesized a series of magnetic adsorbents AC/Fe3O4/UiO-66-X(X=C:Zr)by adding different amounts of activated carbon during the synthesis of the materials.The adsorbent was analyzed by XRD,SEM,HRTEM,TGA,ect and proved that the activated carbon was successfully introduced into the magnetic metal-organic framework material,and the material has excellent stability and magnetic properties.The experiments of modelling flue gas mercury removal showed that the addition of activated carbon greatly improved the performance of the magnetic metal organic skeleton material for mercury removal,and the adsorption of mercury by the material was in the order of:AC/Fe3O4/UiO-66-1.0>AC>AC/Fe3O4/UiO-66-2.0>AC/Fe3O4/UiO-66-0.5>Fe3O4/UiO-66.Among them,the magnetic composite AC/Fe3O4/UiO-66-1.0 has the best adsorption effect on monomeric mercury when the doping amount of activated carbon is C:Zr=1:1,and the adsorption capacity can reach 85.9 ?g/g.The cyclic regeneration experiments of the magnetic adsorbent AC/Fe3O4/UiO-66-1.0 showed that the material had good regeneration performance and maintained good mercury removal performance after four regenerations,with a decrease of only 8.4%compared to the fresh adsorbent after four experiments.Despite the partial improvement in adsorption properties,however,the magnetic properties have decreased,causing the magnetic recovery of the material to become more difficult.In order to further enhance the magnetic properties of magnetic activated carbon to improve its recovery performance in the flue,Ni0.5Zn0.5Fe2O4-AC material with stronger magnetic properties of Ni0.5Zn0.5Fe2O4 was synthesized as the magnetic medium in this paper.This material,with Ni0.5Zn0.5Fe2O4 as the magnetic medium,can be synthesized rapidly and in large quantities,without adding co-solvents,without washing,with short pre-processing time and preparation cycle,low cost,easy to industrialize,with strong adsorption capacity for Hg0 and good magnetic properties,and easy magnetic separation.The experimental results of the material simulated flue gas mercury removal showed that the adsorbent adsorbed mercury in the simulated flue gas in the following order:Ni0.5Zn0.5Fe2O4-AC-7>Ni0.5Zn0.5Fe2O4-AC-8>Ni0.5Zn0.5Fe2O4-AC-6>Ni0.5Zn0.5Fe2O4-AC-5>AC.And the maximum adsorption amount of Ni0.5Zn0.5Fe2O4-AC-7 can reach 172.3?g/g.From the results of the cycle regeneration experiments of the adsorbent,it can be seen that the adsorption capacity of the magnetic activated carbon Ni0.5Zn0.5Fe2O4-AC-7 can still maintain 86.5%of that of the fresh adsorbent after five cycles of regeneration.The material meets both the magnetic recovery requirements and the efficiency of mercury removal. |
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