The Study Of Transformation Law By The Additive Of NaFeO₂ In Red Mud

Red mud is a strong alkaline waste produced in alumina production.With the rapid development of China's industrialization process,alumina industry has achieved rapid development,followed by the red mud emissions also showed an increasing trend year by year.The massive accumulation of red mud not only takes up a lot of land resources,but also brings great pressure to the sustainable development of economy and ecology,and brings serious security risks.Red mud itself is rich in a large number of aluminum,sodium,iron and other metal elements and a wide range of rare elements,which is a high-value secondary resource.At present,most of the researches focus on the"calcification carbonization"method to extract alumina and alkali from red mud.However,the utilization of sodium ferrite as an additive for high-temperature dissolution of red mud needs further research.In this paper,a new method of extracting alumina and alkali from red mud with sodium ferrite as additive was studied,and the optimum sintering conditions of sodium ferrite were studied.Sodium ferrite was used as additive to treat Bayer red mud in high concentration alkali solution and high temperature.The main contents and conclusions are as follows:(1)The K value method was used to quantify the relative content of sodium ferrite,and the response surface method was used to optimize the sintering process.Finally,the sintering kinetics of sodium ferrite was studied The results show that when the sintering temperature is1000?,the sintering time is 90 min,and the ratio of sodium carbonate to ferric oxide is 1.2,the relative percentage of sodium ferrite is up to 100%.At 800-850?,the apparent activation energy is 21.82 k J/mol and the kinetic equation is 1-2?/3-(1-?)^2/3=0.021exp(-21825.3/RT)t;At 850-1000?,the sintering process is controlled by internal diffusion,the apparent activation energy is 19.133 k J/mol,and the kinetic equation is 1-2?/3-(1-?)^2/3=0.017exp(-19133.59/RT)t?(2)In the experiment of recovering alumina and alkali from red mud by adding sodium ferrite,the technological conditions affecting the extraction rate of alumina and alkali were studied through single factor experiment,and the sintering process was optimized by response surface methodology.The optimum technological conditions were obtained as follows:temperature 280?,holding time 3 h,?=12,sodium oxide concentration 220 g/L,C/S=2,sodium ferrite dosage 20%of total mass.Under these conditions,the A/Sand N/S of the leached residue decreased from 0.82 and 0.32 to 0.21 and 0.03 respectively,and the recovery rates of alumina and alkali in red mud were 74%and 91%respectively.(3)The product was characterized by XRD,SEM,XRF and FTIR.The results show that the hydrographite phase Ca₃(Fe_0.87Al_0.13)₂(Si O₄)_1.65(OH)_5.4 and Ca₃Al Fe(Si O₄)(OH)₈ were formed by hydrothermal reaction of red mud.The reason is that in the high molecular ratio alkaline solution,calcium enters into Sodalite,replaces sodium to form almandine,aluminum is replaced by iron,and finally forms iron hydrated garnet,which reduces A/S and N/S in red mud.The leaching residue is spherical in size of 300-500 nm,and its surface is compact and smooth with uniform distribution.