Red Mud Sodium Removal, Iron Extraction And Oxygen Storage Performance Regulatio

Red mud is the residual waste residue after alumina production from bauxite ore.China’s alumina production has reached more than half of the global production,producing a large amount of red mud piled up and not utilized.Red mud generally has30-60%Fe₂O₃,which is highly similar to the composition of conventional iron-based oxygen carriers,and therefore red mud is considered an ideal material for oxygen carriers in chemical chain combustion.Chemical chain combustion technology is often used for efficient separation and capture of CO₂.About 6%of the anthropogenic CO₂ emissions come from steel mills,and steel,as an important raw material,has been produced close to 1 billion tons per year in recent years.Blast furnace gas is the most emitted tail gas from steel mills,and the CO₂ produced has a great impact on the environment.In this paper,we used red mud from five different origins,namely,Vietnam,Guangxi,Henan,Shandong and Wenshan,as oxygen carriers to capture CO₂ from blast furnace gas by chemical chain combustion technology,and studied the activity and cyclic stability of red mud during the reaction process,and systematically characterized the physicochemical properties of red mud oxygen carriers by XRF,XRD,H₂-TPR and XPS to explore the differences in chemical composition,physical phase composition and reaction process behavior of red mud in each place.The differences in chemical composition,physical phase composition and reaction process behavior were investigated.For the red mud after cyclic reaction and the red mud which is not suitable as oxygen carrier,this paper proposes to use nitric acid to leach the Na,Al,Si and Ca components in the red mud and keep Fe in the solid phase,the valuable metals in the liquid phase are extracted by grading,and the iron-rich solid phase is then used to react with nitric acid and phosphoric acid in the high-pressure reactor to finally synthesize iron phosphate.The results of reaction activity evaluation and characterization analysis of red mud and blast furnace gas show that red mud as oxygen carrier for chemical chain combustion is feasible,and all red mud can completely convert CO in blast furnace gas.The content of active components（Fe₂O₃）in red mud has a great influence on the reaction performance,and the synergistic effect of inert components（Al₂O₃,Ca O,Na₂O,Mg O）directly affects the cyclic stability of red mud oxygen carriers at high temperature,and Guangxi red mud shows better reactivity and cyclic stability than other red mud,which is attributed to the formation of magnesium-iron-aluminum spinel phase after roasting（Mg Fe Al O₄）.Wenshan red mud with typical composition was selected to improve the oxygen storage capacity of red mud by loading Cu O,and the best loading amount of Cu O was selected as 15%,which reduced the reaction temperature and energy consumption while maintaining the cyclic stability of red mud.The best leaching process conditions were determined for the nitric acid concentration of 1.5 mol/L,reaction temperature of 80℃and reaction time of 3 h.The leaching rate of red mud was 90.6%at this time.The complex salts in the red mud were decomposed by adjusting the p H,and the amount of Fe₂O₃ incorporated into the nitric acid solution in the red mud was controlled to obtain the material of iron-rich components,and the components of Ca,Al,Si and Na incorporated into the liquid phase were extracted by grading to finally achieve the separation and extraction of the main components in the red mud.The iron-rich fraction and leachate can be further reacted with phosphoric acid to obtain iron phosphate（Fe PO₄）,silicon phosphate（Si₅O（PO₄）₆）,calcium hydrogen phosphate dihydrate（Ca PO₃（OH）·2H₂O）with good crystallinity,respectively,and the physical phase is in basic agreement with the standard card.