Study On New Process And Mechanism Of Enhancing Separation And Extraction Of Iron And Scandium By Segregation Roasting From Low Iron Sc-bearing Red Mud

Red mud is the main solid waste generated when the aluminum industry extract alumina.It is estimated that the global aluminum industry generates approximately 120 million tonnes of red mud annually,and the cumulative amount of red mud discharged to the environment will reach 1.5 billion tonnes by 2021 in China.Owing to the huge accumulation of red mud,and the red mud has highly alkaline and corrosive harmful substances,so the vast accumulation of red mud in the open pit environment has brought heavy pressure on the surrounding environment.Simultaneously,red mud is considered an important secondary resource,which contains a certain amount of iron,titanium,rare metals,rare earth elements,etc.Therefore,recycling the useful components in the red mud can not only realize the comprehensive utilization of solid waste resources,but also reduce the negative impact of red mud on the environment.In this thesis,taking the red mud provided by Yunnan Wenshan aluminum plant as the research object,the process mineralogy analysis was carried out to clarify the occurrence state and symbiotic relationship of iron and scandium in the red mud,and finally provide a basis for the separation and extraction of iron and scandium.The red mud segregation roasting-magnetic separation-wet leaching process is studied to realize the comprehensive recovery of scandium and iron in the red mud.Then,use relevant detection methods and scientific analysis,the phase transition law and reaction mechanism of scandium and iron in red mud during roasting and leaching were revealed from the micro level.The main conclusions are as follows:(1)Research on the process mineralogy characteristics of red mud shows that the phase occurrence state in red mud is complex,mainly phases of hematite,hydrocalumite,quartz,etc.The red mud has fine particles,and iron mainly exists in the form of hematite.Scanning electron microscopy,energy spectrum analysis and electron probe microanalysis have shown that there are no independent scandium minerals in the red mud,and the scandium-containing minerals are mainly silicate minerals(feldspar,hydrogrossular,etc.).(2)Based on the red mud segregation roasting-magnetic separation,it showed that the final magnetic concentrate sorting index with TFe of 78.54%,Sc₂O₃ content of 0.0015%and overall iron recovery rate of 91.35%was obtained under the roasting temperature of1100?for 60 min,mass ratio of red mud/sodium chloride/coke/sodium sulfate of100:15:15:10,and magnetic separation of the roasted ore by grinding up to 90%passing0.045 mm at magnetic field intensity of 0.22 T.The content of Sc₂O₃ in the magnetic separation tailings reached 124.21 g/t,which was increased of 159.94%compared with 78g/t of the red mud.Thereby,the separation of scandium and iron in the red mud is realized,and the magnetic separation tailings serves the raw material for the subsequent scandium acid leaching test.(3)Based on the red mud magnetic separation tailings leaching scandium,it showed that a maximum Sc leaching efficiency of 90.12%was obtained at optimum leaching conditions of20 wt.%hydrochloric acid solution,10 wt.%aid leaching agent sodium fluoride,solid/liquid ratio of 1:10(g/m L),-48?m sample particle size and 80°C for 3 h leaching duration.(4)Based on the red mud sodium salt segregation roasting mechanism,it showed that proper amount of sodium sulfate has enhanced the effect on iron recovery from segregation roasting-magnetic separation of red mud,and it also reduces the content of iron silicate and promotes the release of iron.On the one hand,SO₃ produced by the reaction of sodium sulfate with aluminum and silicon minerals,it can react with chlorination agents to promote the generation of hydrogen chloride,thus strengthening the chlorination reaction of iron oxide.On the other hand,Na₂O produced by sodium sulfate in a reducing atmosphere can react with silicate minerals to form low-melting nepheline,it destroys the original ore structure,and the formation of low melting point nepheline accelerates the formation of the molten phase.The formation of the molten phase accelerates the migration rate of metallic iron particles,promotes the growth of metallic iron particles,and strengthens the distinction between metallic iron and gangue minerals.(5)Based on thermodynamics and kinetics of hydrochloric acid leaching process of red mud magnetic separation tailings,it showed that the reaction of each oxide with hydrochloric acid has a larger reaction tendency and can proceed spontaneously at room temperature.However,the higher the acid leaching temperature,the better the selective leaching of scandium.The apparent reaction activation energy of the acid leaching process was 26.77 k J/mol and the frequency factor A=6.83 s^-1.The process of leaching scandium with magnetic separation tailings conforms to the kinetic characteristics of multiphase liquid-solid region reaction,controlled by the chemical reaction step.