Simultaneous Catalysis Of Sulfite Oxidation And Removal Of Selenium In Wet Desulfurization Slurry

Flue gas from coal-fired furnaces is a crucial cause of acid rain,haze,and other pollution-related phenomena.The composition of this gas is complex because it contains various pollutants such as dust,SO₂,NOx,and heavy metals;pollutants have caused serious harm to the atmospheric environment in China.The wet desulfurization is the most widely used to purify flue gas at present,among which ammonia desulfurization has attracted more and more attention owing to its high desulfurization efficiency,its small footprint,small investment and byproduct（NH₄）₂SO₄ resource.However,due to the relatively low oxidation rate of ammonium sulfite,it is difficult to integrate such oxidation into a desulfurization process.This problem has become the paramount bottleneck of the oxidation concentration technology.Therefore,the key to ensure the recovery of desulfurization by-product is to convert sulfite into sulfate.In addition,when the volatile toxic pollutant Se contained in flue gas are in reverse contact with desulfurizing liquid,existing forms of Se may migrate and transform with the absorption process.Finally,a large number of particles are collected in the form of SeO₃^2-or SeO₄^2-in the desulfurization slurry.Although the content of Se in the desulfurizing slurry is not very high,the problems such as high toxicity,difficult degradation,easy enrichment and so on will also lead to greater environmental risks.Therefore,the catalytic oxidation of ammonium sulfite and the removal of selenium have become an important problem to be solved in desulfurization slurry.In this paper,SBA-15-SH bifunctional catalyst adsorbent was prepared through Co impregnation and sulfhydryl（-SH）decoration with SBA-15 as catalyst carrier.The catalyst–adsorbent can simultaneously remove Se and catalyze sulfite oxidation.The toxic effect of Se adsorption on the catalysis activity of Co species was studied.The adsorption thermodynamics,kinetics and isothermal adsorption model of Co-SBA-15-SH on Se were obtained by fitting,and the inhibitory effect of Co-SBA-15-SH on Se⁰re-emission was revealed.The results demonstrated that the high concentration of selenium has a certain toxicity to Co-based catalysis.The adsorption process occurs at a multimolecular layer in Co-SBA-15-SH with a maximum adsorption capacity of223.24 mg/g.The experimental results followed the pseudo-second-order kinetics model to confirm that the removal of Se is controlled by the chemical adsorption process of thiol groups.Through a series of characterization methods and DFT calculation,the mechanism of selenium migration and the toxic effect of Se on the catalysis of sulfite oxidation were further confirmed.The results can be used as a reference for scholars investigating the simultaneous removal of toxic pollutants and catalysis of sulfite oxidation within the wet-desulfurization process.In this study,a cobalt-based 4A molecular sieves（Co-MS-4A）catalytic adsorbent was synthesized by impregnation method based on ammonia flue gas desulfurization process.It was used in ammonia flue gas desulfurization for the simultaneous catalytic oxidation of ammonium sulfite and removal of toxic pollutants Se from slurry.The morphology and surface chemistry of 4A molecular sieves（MS-4A）before and after cobalt loading were investigated using SEM,TEM,BET,XRD and XPS characterization methods;The properties of Co-MS-4A for the simultaneous catalytic oxidation of ammonium sulfite and adsorption of selenium were studied.The effects of different experimental conditions on the adsorption properties of Se were discussed.The adsorption kinetics and isothermal adsorption models of Co-MS-4A on Se were obtained by data fitting.Compared with unmodified 4A molecular sieves material,the Co-MS-4A material increased the oxidation rate of ammonium sulfite by more than8 times.The Freundlich model can better describe the adsorption behavior of Co-MS-4A on Se,which showed that the removal of selenium oxide anion is a multi-layer adsorption process,and the maximum adsorption capacity for Se is 50.24mg/g;A pseudo-second-order model confirmed that the removal of Se by Co-MS-4A is controlled by the chemisorption process.