High-Value Development And Utilization Of Red Mud Waste As DeNO_x Catalyst

Red mud?RM?is a byproduct of the digestion of bauxite ores for alumina production,and is a major industrial solid waste.The disposal of red mud leads to a serious environmental threart and the multi-metal waste of resources because of its high alkaline value.Therefore,the utilization of red mud has become a curcial issue in the aluminum industry.In recent years,many studies have proposed different approaches for the reuse of red mud,such as building materials,fillers,and metal extraction elements.However,due to high pretreatment cost and the low value of red mud-based products,the market-oriented prospects of these technologies are not promising.Based on the acid-base precipitation activation method,a series of modified red mud materials with different pore structure and surface properties were prepared by changing the acid hydrolysis extent of red mud.XRF,XRD,BET and SEM to examine their textural and chemical characteristics.The multiple characterization further revealed that the strong alkalinity of the original solid waste was removed together with the increase of surface acidity as well as large specific surface area and rich surface microstructure for the obtained red mud catalyst with the increase of acid amount.The particles precipitated on the surface of acid slag are nano-sclae and uniform in size,finally aggregated with each other.By the solid-liquid separation treatment of acidified slurry and combined with the changes of composition and structure of acid slag and filtrate reprecipitation,it is possible to quantifity the extent of the acidolysis process,and the dissolvability of metal elements such as Al,Fe and Ti was obtained.The activity and stability of those acid-modified red mud material for the selective catalytic reaction of NO with NH₃?NH₃-SCR?was studied.It showed that RM catalyst demonstrate excellent activity and stability with above 80%NO conversion during 325⁴50^oC in the presence of SO₂ and H₂O.The greater of the acid hydrolysis extent,the greater DeNO_x activity.The activity approaches the peak level when the dissolution rate of Al and Fe reached 80%.Combined with the activity of acid slag and filtrate reprecipitation,it is known that the precipitated species are beneficial for the reduction of NO by NH₃,while the acid slag tends to oxidize NH₃ to NO.According to the DRIFTs,NH₃ oxidation and SCR performance results,the NH₃-SCR route over modified RM material mainly follows the Br?nsted-acid inspired E-R mechanism at high temperature,which involves a competitive relationship between NH₃ reduction and NH₃ oxidation.The red mud catalyst was doped and modified with multi-active species,and the pilot production and molding exploration experiments were carried out.In consideration of trace ammonia removal from tail gas and red mud solid waste utilization in SNCR denitration process,a RM-based powder catalyst was used to eliminate the trace ammonia thought the proposed process of directly spraying the catalyst into SNCR tail gas.The effects of temperature,space velocity,NH₃concentration and water vapor on ammonia removal capacity of the catalyst were investigated in details,and excellent removal efficiency could be achieved with 100%NH₃ conversion above 450°C as well as above 80%selectivity of N₂ between400-500°C.With significant convenient and efficient advantages,catalyst can be reused after subsequent dust collection and not have to large-scale modification of existing boiler equipment.It is expected to provide a new technical solution for the treatment of trace ammonia escaping in SNCR exhaust gas.