| The emission of mercury from the coal-fired flue gas could cause a series of ecological and environmental problems,threatened human health.Thus,researching the new technologies of low-cost,high-performance and centralized control of Hg~0 pollution,with significant environmental and economic benefits.Magnetic Mn-Fe spinel is an inexpensive material with excellent low-temperature oxidation performance and can be used to adsorb Hg~0 in flue gas.In this study,Mn-Fe spinel was synthesized by coprecipitation method.The adsorption and removal of Hg~0 and SO2 were investigated under the low temperature simulated flue gas condition.The mechanism of-adsorption reaction was analyzed by XPS.The regeneration process of Mn-Fe spinel after Hg~0 capture was explored,and the mechanism of regeneration was discussed in detail.Finally,the activity and stability of Mn-Fe spinel adsorption were studied.The main conclusions are as follows:(1)Mn-Fe spinel showed an excellent ability for the simultaneous capture of Hg~0 and SO2 in the temperature range of 50?100?.The gaseous Hg~0 adsorbed on the cation vacancy of Mn-Fe spinel and then oxidized by Mn4+ cations to form HgO.The chemical adsorption of SO2 on Mn-Fe spinel caused to a decrease of the cation vacancies,resulting in an inhibition of Hg~0 capture on Mn-Fe spinel.The sulfation of Mn-Fe spinel was promoted in the presence of H2O,meanwhile,water vapor may compete with gaseous Hg~0 for the adsorption site on Mn-Fe spinel.(2)Mn-Fe spinel after Hg~0 capture can regenerated by the washing of an acidic NaCIO solution,and washed away the water-soluble sulfates and most of the HgO on the surface to recovery of adsorption performance.Besides,the toxicity of regenerated Mn-Fe spinel can be approximately neglected due to the toxic Hg2+ on the surface was removed by washing.(3)The efficiencies of Mn-Fe spinel for Hg~0 and SO2 removal were both always higher than 95%during the 5 cycles test.Magnetic Mn-Fe spinel can be injected into the flue gas before the WESP to simultaneously capture gaseous Hg~0 and SO2,then be collected by an electromagnet embedded in the WESP,resulting in the separation from the mixture with ultrafine fly ash.Then,the spent Mn-Fe spinel will be washed by the NaCIO solution to reclaim Hg and regenerate the spent Mn-Fe spinel.At last,the regenerated Mn-Fe spinel can be injected into the flue gas for the next cycle.During the procedure,the emission of Hg~0 from the flue gas can be reclaimed as a high concentration of Hg2+ solution for safe disposition.and the low concentration of SO2 in the flue gas can be deeply removed as a co-benefit of the centralized control of Hg~0 emission. |
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