Study On The Catalytic Oxidation Purification Of AsH₃ In Ore-smelting Furnace Tail Gas At Low-temperature And Trace-oxygen

In the phosphorus and coal chemical,non-ferrous metallurgy,ferrous metallurgy and other industrial production processes,the tail gas emitted from the ore-smelting furnace such as yellow phosphorus electric furnace,calcium carbide furnace,zinc-smelting electric furnace,and ferroalloy furnace is rich in CO.The disposal of these waste gases is currently performed using the flare combustion method for emptying,which results in the waste of large amounts of CO resources and air pollution,at the same time,the new combustion product CO₂ will indirectly affect the changes of the global natural environment.Reducing gas CO is a very valuable C1 chemical raw material gas.Its recycling has been a hot topic in recent years.However,in addition to the high concentration of CO,the ore-smelting furnace tail gas is accompanied by toxic and harmful impurities such as AsH₃,and the presence of these impurities directly affect the utilization of the ore-smelting furnace tail gas.At present,there is no article about the AsH₃ purification review at home and abroad.In China,due to the relatively low concentration of AsH₃ in the ore-smelting furnace tail gas,there are no specific technical guidelines for national regulations and standards,resulting in a low degree of attention for AsH₃ purification.The number of relevant studies on AsH₃ purification abroad is also very limited,and methods for modifying activated carbon and molecular sieves with transition metals or noble metals are mainly proposed and removed by a chemical adsorption process.the concentration of AsH₃,the mixing system in which it is located,and the operating conditions of the relevant catalysts are different in these references.The exhaust gas at the end of the cooling tower of the ore-smelting process is basically reduced to less than 150°C.At this time,the tail gas is exposed to low-temperature and trace-oxygen environment,and under this special process condition for AsH₃ purification is still in a blank stage.In the case of a serious lack of reference materials and theoretical guidance,given this project research has brought a series of technical problems and unprecedented challenges.After exploratory experiments,the direction of AsH₃ purification treatment technology was determined.AsH₃ is an inorganic and gaseous arsenic-contaminant,and arsenic is considered to be a special heavy metal element.If the arsenic compound is transformed from gaseous AsH₃ into liquid,it will cause secondary pollution to the water environment,and the migration and transformation capability will be greatly enhanced.The purpose and the key to technology of this project is to adsorb or catalyst gaseous AsH₃ in the ore-smelting furnace tail gas by some cheap solid materials,and convert it into relatively stable,high-aggregation arsenic oxidation state forms,such as As₂O₃ or As₂O₅,enriched in the prepared material,and the concentration of gaseous AsH₃ is lower than 1 mg·m^-3 to achieve the goal of purifying CO.The low temperature and trace-oxygen conditions in the ore-smelting furnace tail gas limit the oxidation of AsH₃.In view of the inertness of AsH₃ at the special conditions,a series of catalysts with good performance for the removal of AsH₃ have been prepared using inorganic materials such as activated carbon,molecular sieves,aluminum-containing hydrotalcite-like compounds as carriers,through single and double metal modification methods.To investigated the metal synergy and catalytic oxidation reaction mechanism with different types of adsorption catalytic materials on the process of AsH₃ removal.The main research results are as follows:?1?The activated carbon adsorbent impregnated with copper nitrate and sulfonated phthalocyanine cobalt solution has good adsorption performance for AsH₃ in the exhaust gas.When the preparation conditions were Cu?NO₃?₂ concentration=0.15mol·L^-1,calcination temperature=350°C;reaction conditions were that fixed bed reaction temperature=60°C,oxygen content=1.0 vol.%,the 100%removal efficiency of As H₃ could be maintained within 8 h.The material characterization results show that copper is mainly present on the surface of the catalyst in the form of CuO.The chemically adsorbed oxygen on the surface and the internal lattice oxygen are considered to be reactive oxygen species involved in the reaction.During the removal process of AsH₃,despite physical adsorption,chemical adsorption and catalytic oxidation are co-exist,catalytic oxidation is the main reaction.In addition,CO almost did not react with the CCA adsorbent,demonstrating that the adsorbent preferentially and selectively reacts with AsH₃ at low-temperature and trace-oxygen conditions.The exploration of the excellent properties of copper-based materials laid the foundation for the subsequent study of hydrotalcite-like frameworks of Cu-Al hydrotalcite-like compounds.?2?This study found that Mn-containing materials have a catalytic effect on the removal of AsH₃.The 5A molecular sieves impregnated with manganese nitrate solution were prepared at the following conditions:Mn?NO₃?₂ concentration=0.60mol·L^-1,calcination temperature=500°C;reaction conditions were that fixed bed reaction temperature was 150°C,oxygen content=1.0 vol.%,the Mn-5A modified molecular sieves catalyst has good catalytic oxidation performance for AsH₃ in simulated exhaust gas at 120°C-180°C.Through a series of characterization methods,the reaction mechanism for the removal of AsH₃ was studied as follows:AsH₃+MnO₂?As+Mn₂O₃+H₂O As+O₂?As₂O₅Mn₂O₃+O₂?MnO₂?3?Four kinds of Cu-Al framework hydrotalcite-like compounds catalysts were studied in this paper.By investigating the different metal active components and the influence factors of reaction temperature and oxygen content in the simulated exhaust gas,the issues such as AsH₃ removal efficiency,reaction activity and service life of each catalyst were explored.Using conventional material characterization methods,various changes in the catalytic oxidation reaction betwen the catalyst and AsH₃ were intensively discussed.The performance and reaction mechanism of catalytic oxidation and purification of AsH₃ by each catalyst were deduced.In general,the introduction of Zn acts as a co-catalyst and contributes to the formation of a more disperse CuO active component on the surface of the Cu-Al hydrotalcite-like catalyst.The introduction of Fe and Mn will make the hydrotalcite-like catalysts form a new structure of surface bimetals.The Cu-Fe binary system not only contains the CuO basic active component,but also contains a new active component Fe₂O₃,which synergistically enhances the material catalytic oxidation purification effect on AsH₃.The Cu-Mn binary hydrotalcite-like framework system also has MnO₂ active components,and Its performance has a certain increase on the basis of Cu-Fe.?4?Catalysts of Cu-Fe and Cu-Mn binary hydrotalcite-like framework system exhibit strong AsH₃ removal performance.At the same conditions,the AsH₃ removal efficiency is higher than that of CCA modified activated carbon adsorbent.From the analysis of the conclusion,the hydrotalcite-like structure is helpful to improve the selective catalytic oxidation of AsH₃,and the synergistic action of Cu-Fe and Cu-Mn binary bimetallic catalytic active components can promote the removal of AsH₃.In particular,the Cu-Mn binary hydrotalcite catalyst has excellent low-temperature and trace-oxygen catalytic oxidation performance for AsH₃,thereby avoiding CO oxidation.With the exception of the CuMgAl catalyst,the other three catalysts in the AsH₃ mixture containing high concentrations of CO not only efficiently catalytic oxidize AsH₃ at low-temperatures and trace-oxygen condition,but also do not react with CO at a reaction temperature of 60°C.The low-temperature stability of the CO allows the mixture gas to pass through the catalyst bed to obtain a purer CO reducing gas.