Study On The Effect Of Pore-forming Agent And Adhesive On The Properties Of Red Mud Based Dry Desulfurizer

China is a large producer of alumina,and its production of 1t of alumina produces about 1.5t of by-products,which is red mud.Red mud is strongly alkaline,and its large amount of storage will cause serious harm to animals and plants,human beings and ecological environment.With the gradual increase of the accumulation of red mud,the application of red mud in environmental governance has gradually become the focus of people’s attention.The analysis of the composition of red mud shows that the content of Fe₂O₃ is 42.59wt%and the content of Ca O is 15.31wt%,and the active ingredient of desulfurization was high,which was suitable for the preparation of flue gas desulfurizer.Combined with the current situation of pollution and damage caused by SO₂ in the atmosphere,we make full use of the physicochemical properties of red mud to remove and adsorb SO₂,which provides an effective way for the disposal of red mud and makes some attempts to realize"waste to waste".Bayer red mud has many pores on the surface,adding appropriate amount of fly ash to it can improve the compressive strength and enhance the stability of red mud desulfurizer.Therefore,based on the pollution and hazards caused by the increasing accumulation of red mud in plants,we choose Bayer red mud and fly ash as raw materials and add porous agent and adhesive to prepare a kind of red mud strip desulfurizer with certain strength.The flue gas desulfurization test was carried out by using the desulfurization reaction device,and the optimal ratio of pore forming agent and adhesive and the optimal desulfurization temperature were further determined by examining the properties of red mud,the effects of the selection of pore forming agent and adhesive and their contents on red mud desulfurizer,and the effects of desulfurization temperature on red mud desulfurizer.In order to know the reaction mechanism in the red mud desulfurizer,the surface adsorption mechanism of the red mud desulfurizer and the reaction mechanism of the metal oxides contained in it with SO₂ were analyzed and discussed respectively.The best pore-forming agent was determined to be activated carbon,and the best ratio of the prepared red mud desulfurizer was activated carbon:red mud:fly ash=10:70:15,the penetration time at 20℃could reach 151min,and the penetration sulfur capacity was 9.152%.With the increase of desulfurization temperature,the penetration sulfur capacity generally shows a decreasing trend.Because the functional groups on the surface of activated carbon at 300°C are not sufficient for thermal decomposition and mainly physical adsorption occurs,the higher the temperature is,the more unfavorable the desulfurization is.In addition,the desulfurization test was carried out for the effect of adding calcium hydroxide on the red mud desulfurizer.It was concluded that the desulfurization properties of the red mud desulfurizer CH5 prepared by using the ratio of activated carbon:red mud:fly ash=10:70:15 with the addition of calcium hydroxide was better than that of the desulfurizer prepared by using red mud only.However,the addition of calcium hydroxide will form a film on the surface of the desulfurizer to inhibit the desulfurization process,and its desulfurization properties is not as good as that of the red mud desulfurizer CH5 without the addition of calcium hydroxide.After determining the ratio of activated carbon to red mud as 10:70,the adhesive was preferably selected and sodium silicate was determined as the adhesive,and the best ratio was red mud:sodium silicate:fly ash:activated carbon=70:20:15:10.The hardness of the prepared red mud desulfurizer was 126N/cm,and it was found that the penetration time of red mud desulfurizer showed a step increase with the increase of desulfurization temperature,and when the desulfurization temperature 300℃,the penetration time can reach 163min,and the penetration sulfur capacity is 9.152%.The sulfur capacity of the red mud desulfurizer was all lower than 11%,because the temperature of 300℃was not enough for the active ingredients in the red mud to fully react with SO₂ for desulfurization,and only a small reaction occurred on the surface of the pores of the desulfurizer.The desulfurization mechanism of red mud desulfurizer mainly depends on the surface adsorption mechanism and the reaction mechanism between metal oxides and SO₂.The surface adsorption of red mud desulfurizer mainly depends on its rich pore structure,specific surface area,pore size distribution and the active center of the surface.The adsorption and desorption curves of red mud desulfurizer belong to type II isotherm and H3 hysteresis loop.The surface adsorption process of red mud desulfurizer is complex because it contains more components,the main role is played by red mud and activated carbon,as red mud contains a large amount of Fe₂O₃,the activated carbon loaded on it has a strong desulfurization capacity,which improves the conversion efficiency of SO₂ to H₂SO₄ and Fe₂（SO₄）₃ to a certain extent.The desulfurization process of red mud desulfurizer belongs to gas-solid phase non-catalytic reaction,which mainly includes diffusion and adsorption of gas reactants,desorption and diffusion of reaction products.Metal oxides can play adsorption role and chemical reaction with SO₂.The determinants of the adsorption properties of desulfurizers are mainly lattice oxygen,adsorbed oxygen and acidic sites,and alkaline metal oxides contain many lattice oxygen and adsorbed oxygen,and the increase in surface adsorbed oxygen is found after desulfurization,and the increase in its mobility can generate more oxygen vacancies to facilitate the adsorption process.The presence ofα-Fe₂O₃（hematite）structure was found in the laser Raman mapping,and the presence of one A_1g(224 cm^-1)and two E_g(291 and 410 cm^-1)Raman active modes could be seen.Whether the Fe₂O₃ fraction in red mud promotes or inhibits the desulfurization process has not been precisely determined.However,it is known that the Fe₂O₃ fraction promotes the desulfurization of the calcium-based fraction,which will carry out the sulfidation reaction with Fe₂O₃ as the active center and make the generated CaSO₄ dispersed and stacked to facilitate the SO₂ diffusion.