Simultaneous Catalysis Of Sulfite Oxidation And Removal Oval Of Heavy Metals In Magnesia Desulfurization Slurry

Magnesia-based desulfurization is a typical Sulfur-utilization process.Its by-product can be transformed into MgSO4·7H2O after oxidation,evaporation,and crystallization,which can be used as fertilizer and industrial material.Due to the low oxidation rate of the magnesium sulfite in the conventional desulfurization process,the concentration of product magnesium sulfate is quite low,resulting in the high energy consumption during the water evaporation.Therefore,the efficient magnesium sulfite oxidation and the magnesium sulfate recovery have become the key issue in the sulfur utilization.However,the heavy metals can be finally collected in desulfurization slurry after series steps,such as selective catalytic reduction denitration,dust removal and flue gas desulfurization,which can bot be removed by adjusting pH,causing high environmental risks.Herein,the synchronous removal of heavy metals in magnesia-based desulfurization slurry has been regarded as another issue in sulfur utilization.This article proposed a project with decoupling flue gas desulfurization from by-product oxidation process,that the magnesium sulfite can be oxidized and the heavy metals be absorbed at the same time outside the absorber tower by using the bifunctional catalysis/adsorbent.By this method,much economic benefit can be achieved by MgSO4·7H2O,and the environmental hazard of the heavy metals can be greatly reduced.Various heterogeneous recycled catalysts have been prepared in order to accelerate the magnesium sulfite oxidation process,including Co-SBA-15,Co3O4-NPs@KIT-6,and Co-C3N4.The effect of oxygen partial pressure,magnesium sulfite concentration,catalyst concentration,reaction temperature,and pH on magnesium sulfite oxidation have been investigated.Many parameters regarding to the reaction have been obtained such as oxygen reaction order,magnesium sulfite reaction order,catalyst reaction order,apparent activation energy(Ea),reaction rate constant(k),enhancement factor(E),and Hatta value.The mechanism of the heterogeneous catalytic oxidation of magnesium sulfite has been inferred by analyzing physical-chemical properties,surface morphology,and composition of catalysts by N2 adsorption-desorption,X-ray diffraction,X-ray photoelectron spectroscopy,hydrogen temperature-programmed reduction,inductively coupled plasma-optical emission spectrometry,scanning electron microscopy,transmission electron microscopy and electron spin resonance techniques.The bifunctional catalysis/adsorbent(BISC)were further developed,which features both catalytic performance of magnesium sulfite oxidation and heavy metals adsorption.The macrokinetics and the mechanism of heterogeneous catalysis of magnesium sulfite oxidation catalyzed by BISC was investigated.The adsorption properties of BISC towards mercury,lead,and chromium were investigated,whose adsorption capacity were 120.8 mg·g-1,120.3 mg·g-1,21.8 mg-g-1,respectively.The adsorption behavior of heavy metal ions by bifunctional catalytic/absorbent were clarified by fitting with adsorption isotherms and adsorption kinetics models.The results showed that the adsorption isotherm and kinetic data of heavy metal ions were in accordance with Langmuir isotherm model and pseudo-second-order kinetic model,indicating that the adsorption of mercury,lead,and chromium were monolayer chemical adsorption.Moreover,the synergistic control of catalytic oxidation of magnesium sulfite and heavy metal ions adsorption,and the relationship between the sulfite catalytic oxidation and the heavy metal ions adsorption were investigated.Combined with DFT theoretical calculation,the mechanism of magnesium sulfite catalytic oxidation and synchronous removal of heavy metals by bifunctional catalysis/adsorbents are analyzed in detail.In addition,the removal mechanism,migration and transformation process,and environmental fate of various heavy metal ions in the magnesia-based desulfurization were clarified.The results can provide a significant theoretical reference for the sulfur utilization in magnesium desulfurization process.