Study on the Preparation of Magnetic Mn–Co–Fe Spinel and Its Mercury Removal Performance

Abstract

In this study, the manganese-doped manganese–cobalt–iron spinel was prepared by the sol–gel self-combustion method, and its physical and chemical properties were analyzed by XRD (X-ray diffraction analysis), SEM (scanning electron microscope), and VSM (vibrating sample magnetometer). The mercury removal performance of simulated flue gas was tested on a fixed bed experimental device, and the effects of Mn doping amount, fuel addition amount, reaction temperature, and flue gas composition on its mercury removal capacity were studied. The results showed that the best synthesized product was when the doping amount of Mn was the molar ratio of 0.5, and the average mercury removal efficiency was 87.5% within 120 min. Among the fuel rich, stoichiometric ratio, and fuel lean systems, the stoichiometric ratio system is most conductive to product synthesis, and the mercury removal performance of the obtained product was the best. Moreover, the removal ability of Hg0 was enhanced with the increase in temperature in the test temperature range, and both physical and chemical adsorption play key roles in the spinel adsorption of Hg0 in the medium temperature range. The addition of O2 can promote the removal of Hg0 by adsorbent, but the continuous increase after the volume fraction reached 10% had little effect on the removal efficiency of Hg0. While SO2 inhibited the removal of mercury by adsorbent, the higher the volume fraction, the more obvious the inhibition. In addition, in an oxygen-free environment, the addition of a small amount of HCl can promote the removal of mercury by adsorbent, but the addition of more HCl does not have a better promotion effect. Compared with other reported adsorbents, the adsorbent has better mercury removal performance and magnetic properties, and has a strong recycling performance. The removal efficiency of mercury can always be maintained above 85% in five cycles.

Review and Perspectives of Mercury Removal by Spinel Compounds

“…The combustion characteristics, oxidation state, and crystal phase can all be affected by the fuel/oxidant ratio. − For example, the combustion of the fuel agent releases a large amount of gas, and therefore, the synthesized products have a porous structure and large specific surface area. Spinel compounds perform best for mercury removal in a stoichiometric solution, which is superior for grain growth. , When it comes to low-temperature needs and affordability, the sol–gel approach performs better than the other methods. Good homogeneity, precise composition adjustment, and an adjustable distribution of particle sizes are benefits of the sol–gel technique.…”

“…To examine the impact of Mn doping on the removal of mercury, researchers employed the sol–gel self-combustion method to produce Mn-doped Mn–Co–Fe spinel compound. The optimal Hg 0 removal performance was achieved when the Mn doping amount was 0.5 …”

“…Figure illustrates the experimental findings on the influence of the reaction temperature on Hg 0 removal (see Supporting Information Table S2). Most researchers ,− , found that the removal efficiency of Hg 0 using spinel catalysts first increased and then decreased with increasing temperature. Other researchers found that the removal of Hg 0 by spinel catalysts gradually decreased with increasing temperature. ,,, The early improvement in Hg 0 removal efficiency may result from the promotional impact of temperature on the chemisorption of Hg 0 over the catalyst.…”

“…The global mercury emissions from industrial flue gas are depicted in Figure . Forty-eight to fifty percent of mercury comes from smelting of nonferrous metals, whereas 23–28% comes from coal combustion. − Coal-fired power plants (CFPPs) in China as the major source of mercury emission accounted for 47% of the total mercury emission in 2010 …”

“…With its magnetic response and high catalytic activity, MF 2 O 4 spinel oxides (M = Mg, Mn, Ni, Zn, Cu, Fe, Co) have been extensively exploited in different disciplines . However, relatively little research has been conducted on the removal of mercury from flue gas.…”