| Red mud is a strong alkaline solid waste discharged in the alumina production process,and a large amount of storage will cause great harm to the environment.As countries pay more and more attention to environmental protection,the strong alkalinity of red mud limits the sustainable development of the alumina industry.Therefore,developing an efficient and clean red mud dealkalization treatment process is the key to solving the current problem.At the same time,red mud is a valuable resource,and scientific researchers have carried out a large number of researches on the comprehensive utilization of its resources,but the large-scale utilization of red mud has not yet been realized.Therefore,it is extremely necessary and urgent to study the red mud dealkalization and its resource utilization in this subject.Firstly,this paper studies the physical and chemical properties of Bayer red mud,which provides a foundation for efficient dealkalization and resource utilization of red mud.At the same time,taking the rate of dealkalization as the control index,the influence of the change law of alkali content of red mud with calcium oxide in the process of roasting and water leaching is studied,and the optimal conditions of microwave roasting and water leaching with calcium oxide are determined.Aiming at the characteristic of rich iron content in Bayer process red mud,a process of microwave thermal reduction of biomass rice husk and magnetic separation to recover iron was proposed.The influence factors of microwave reduction roasting process and magnetic separation process of biomass rice husk were deeply studied,and the optimal conditions for microwave reduction roasting and magnetic separation were determined.The research results of this paper are as follows:(1)The physical and chemical properties of red mud were studied,and it was found that the water content and p H value of red mud were high,the water content was 11.26%,and the p H value was 11.82.The particle size distribution of red mud is between 0.1 and 100?m,and it mainly aggregates around 3?m.The average specific surface area of red mud is 23.232m2/g,the average pore volume is 0.144 cm3/g,and the average pore diameter is 13.421 nm.It shows that red mud has the characteristics of small particle size,large specific surface area and good pore structure.(2)The main components of red mud are Fe2O3,Al2O3,Si O2,Ti O2,and Ca O,among which Fe2O3and Al2O3 account for more than 55%of the content of red mud,and their rich valuable metal components provide resources for the utilization of red mud.The contents of Na2O and K2O in red mud were 3.5%and 0.43%,respectively.The mineral composition of red mud is relatively complex,and the main phases are hematite,goethite,calcite,quartz,and sodalite.Among them,there is alkali metal sodium in sodalite,and the existence of this alkali is difficult to remove by simple water leaching.In addition,the heating of red mud in the microwave field is rapid,and it takes less than 17 min to heat to 700°C.(3)Under the same conditions,microwave roasting has better dealkalization efficiency and higher heating efficiency than traditional roasting.The process of microwave roasting and water leaching dealkalization of red mud was studied in depth.The results showed that the molar ratio of Ca O/Si O2 was 2.4,the activation time of the ball mill was 10 min,the microwave power was 2.5 k W,the microwave roasting temperature was 500?,the roasting time was 45 min,and the liquid Under the conditions of solid ratio of 8 m L/g,water immersion temperature of 90?and leaching time of 80 min,the dealkalization rate of red mud can reach 84.04%,and the Na2O content in red mud after dealkalization is 0.43%.Other valuable metal components in red mud remain unchanged during microwave roasting and water immersion,which is beneficial to the next step in the application of building materials.(4)Kinetic studies show that the reaction kinetics model of red mud added with calcium oxide in the leaching process of dealkalization water after microwave roasting belonged to the shrinkage Reactive nuclear membrane type internal diffusion control,The kinetic equation is 1+2(1-x)-3(1-x)2/3=kt,and the apparent activation energy of the reaction is36.409 k J/mol.(5)The biomass char,CO,and H2 produced by the rice husk pyrolysis process provide a reducing atmosphere for the reduction of hematite in red mud.Through thermodynamic analysis,the reduction of iron oxides by C,CO and H2 is mainly carried out in the order of Fe2O3?Fe3O4?Fe O?Fe obtain elemental iron.(6)The maximum iron grade and recovery of magnetic separation concentrate after reduction roasting in Muffle furnace are 42.23%and 66.34%,respectively,under the following conditions:mass ratio of red mud and rice husk with bulk feeding and admixture is 3,reduction roasting temperature is 1100?,roasting interval is 20 min,ball grinding time is 20 min,magnetic separation current is 4 A.Under these conditions,the maximum iron grade and iron recovery of the samples treated by magnetic separation after microwave roasting at 1200 W are 60.1%and 86.3%,respectively.The process of iron recovery by microwave reduction roasting of red mud and magnetic separation from rice husk was systematically studied.The results showed that under the conditions of mass ratio of red mud to rice husk of bulk feed and admixture 3,microwave power 1000 W,roasting temperature1000?,roasting time 20 min,ball milling time 20 min,magnetic separation current 4 A,the iron grade of iron concentrate was 59.93%and recovery was 85.56%.(7)The analysis of the magnetic separation concentrate obtained shows that the main phase is simple iron,containing a small amount of magnetite and ferrous oxide.Therefore,it is feasible to recover iron from Bayer process red mud by microwave biomass reduction.The recovered magnetic concentrate can be used in blast furnace ironmaking.The magnetic separation slag after iron separation mainly consists of alumina and silica,which creates favorable conditions for further research as geopolymer materials. |
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