Study On Simultaneous Removal Of SO₂ And NO_x By Water-quenched-manganese-slag After Thermal Activation Modification

The metal smelting industry has been characterized by high pollution,high energy consumption,and resource-based,from which the environmental deterioration resulted from the exhaust gas emission has been prominent,thus restricting the sustainable development of the metal smelting industry.At present,most smelting plants have utilized high-concentration SO₂ flue gas for sulfur recovery to produce acid,which process improves the economic benefits of smelters.However,the sulphuric acid tail gas still contains the SO₂concentration of 500?3000 mg/m³ and a part of NO_x which is not effectively removed.The direct emission of acid-making tail gas would cause serious environmental pollution.Therefore,it is urgent for the metal smelting industry to develop a novel,low-cost,high-efficiency technology to simultaneously remove SO₂and NO_x from flue gas.In this paper,water-quenched-manganese-slag(WQMS)after thermal activation was used to prepare novel desulfurization and denitrification slurry to remove SO₂ and NO_x from metal smelting flue gas,which the aim was to fundamentally improve the desulphurization and denitrification performance of smelting slag slurry by simple pretreatment method.The mechanism of activity regulation of WQMS was illustrated by characterization analysis.In addition,combined with in-situ product analysis,the reaction mechanism of desulphurization and denitrification was put forward.Meanwhile,the process conditions were optimized to provide the theoretical basis for industrial application.The main findings are as follows:(1)Through the characterization and analysis of the raw WQMS,it was found that the main chemical compositions of the raw WQMS were Ca O,SiO₂,Mn,Al₂O₃,Mg O,S,K,and Na.The content of alkali metal oxides was high,which was beneficial to the desulfurization and denitration reaction.However,the structure and nature of main mineral phases in raw WQMS,including Ca₃Mg(SiO₄)₂,Ca₃Al₂(SiO₄)₃,Mn₇O₈(SiO₄),etc.,were stable,thus limiting the activity in chemical reactions.In addition,the Mn-containing phases mainly existed in the form of MnS and MnO.Among them,MnS would consume part of the oxidant and compete with NO_x and SO₂to lower removal efficiency during the desulfurization and denitrification reaction process.The effect of different oxidants(including KMnO₄?H₂O₂?NaCl O and K₂Cr₂O₇)on SO₂ and NO_x removal in WQMS composite slurry was investigated.The results indicated that the KMnO₄/WQMS composite slurry obtained the highest oxidation ability compared to other oxidants in slurry,which was attributed to the higher oxidation-reduction potential,and the oxidant ability was not affected by the p H of the solution.(2)The effects of different thermal activation temperature and time,the type and amount of phase regulator on SO₂ and NO_x removal were investigated.The results show that the addition of WQMS after thermal activation can improve the denitrification of pure KMnO₄,and there is a synergistic effect between the two.The WQMS prepared by adding 20%Ca O as a phase regulator and roasting at 900°C for 120 minutes has the best desulfurization and denitrification performance,the NO_x and SO₂ removal efficiency are 84.9%and 100 respectively;Through characterization and analysis,the reasons for the improved desulfurization and denitrification performance under the optimal pretreatment conditions are as follows:A more thorough phase change occurred in the WQMS,so that the phase that inhibits denitrification is transformed into a phase structure that promotes denitrification;Compared with other pretreatment conditions,there are some new phases(MnSO₄,Ca MnO₃)that can promote denitrification;Adding Ca O as a phase regulator to roasting the WQMS can increase the content of high-valence manganese in the WQMS,and the high-valence manganese is easier to oxidize NO_x;The strong alkaline buffer solution formed by WQMS slurry after pretreatment is more conducive to denitrification due to the increase in p H.(3)The solid and liquid phase of the WQMS slurry during the reaction were characterized,and the reaction mechanism was derived by combining thermodynamic calculations.Finally,it is believed that the denitrification path of the WQMS composite slurry is mainly through the oxidation of NO by KMnO₄,the hydration reaction of NO₂,and the oxidation of the active phases Ca MnO₃,MnO₂,etc of the WQMS.The three have a synergistic effect to promote denitration;The desulfurization path is mainly through the hydration reaction of SO₂,the oxidation of KMnO₄ and the catalytic oxidation of metal ions.In addition,the alkaline buffer environment of the pulp is also conducive to the absorption of SO₂ and NO_x by the slurry.(4)The process conditions in the SO₂ and NO_x removal reaction process on are explored.The results show that when the flue gas flow increases,part of the NO_x due to the rapid flow of the gas causes its residence time in the reactor to be too short and does not fully contact the slurry to react,thereby reducing the NO_x removal;The stirring speed of the slurry needs to be controlled within a certain range,so that the slurry can be fully mixed,and sufficient contact reaction time can be ensured,so as to obtain a high denitration rate without consuming excess mechanical energy;The concentration of slag in the slurry not only affects the amount of active components and the p H value of the slurry,but also increases the stirring resistance;The dissolution of SO₂ can generate SO₃^2-and HSO₃^-,which can react with NO₂,promote the absorption of NO₂,and increase the denitrification.