Vacuum Carbothermic Reduction Of Spodumene For Lithium Enrichment And Recovery Of Silicon And Aluminum

As a new type of energy metal,lithium has become a research hotspot in academia and industry with the rapid development of lithium-ion batteries,vehicle electrification,and grid energy storage.The current spodumene smelting process only focuses on the extraction of lithium from the ore,while the main components of silicon and aluminum in the ore are stored in the form of hazardous waste residue(the production of 1 ton of lithium carbonate produces about 8-10 tons of hazardous waste residue).This not only causes a great waste of resources,but also these hazardous waste residues can easily cause major environmental pollution.Considering the above problems,this article explores two new methods for extracting lithium and recovering silicon and aluminum from spodumene ore through theoretical calculations and experimental demonstrations.A clean process of adding Fe₂O₃ to vacuum carbothermal reduction of spodumene ore to enrich Li,preparing Si-Fe alloy,and recovering Al₂O₃ was proposed.This process realizes the comprehensive and efficient utilization of resources in spodumene ore,and provides a new idea for the development of lithium extraction technology from ore.The main research results of this article are as follows:(1)The thermodynamic calculations and experiments of the vacuum carbothermal reduction of spodumene ore to enrich Li while preparing Al-Si alloys show that SiO₂ in the spodumene ore is difficult to be reduced to Si,but a large amount of Si C and SiO are produced in a vacuum of 20 Pa.Li Al Si₂O₆ is difficult to obtain elemental Si and Al during the reduction process,but to obtain non-target products such as Si C,SiO,Al₂O,etc.The experimental results show that Li Al Si₂O₆ is difficult to be reduced,which may be hindered in kinetics.Therefore,the process of direct vacuum carbothermal reduction of spodumene ore to enrich Li while preparing Al-Si alloy is not feasible.(2)The thermodynamic calculations and experiments of the vacuum carbothermal reduction of spodumene ore to enrich Li,preparing Si-Fe alloy,and recovering Al₂O₃show that Fe₂O₃ and vacuum environment can greatly promote the carbothermal reduction reaction of SiO₂ and Li Al Si₂O₆ in the spodumene ore.The initial reaction temperature can be reduced by more than 400 K.After the experiment is completed,Li enters the gas phase in the form of metal vapor and is enriched in the soot.The reduction residue is mainly Si-Fe alloy and Al₂O₃.The best process conditions are:the reduction temperature is 1648 K,and the reduction time is 3 h.Under this process condition,the reduction rate of Li is 92.69%,the Li content in the condensate is 18.33%,the direct yield of Li is 29.56%,the direct yield of Si-Fe is 81.76%,and the direct yield of Al₂O₃is 69.23%.(3)The reaction mechanism of the vacuum carbothermal reduction of spodumene ore to enrich Li,prepare Si-Fe alloy,and recover Al₂O₃ is:Fe₂O₃ added at low temperature(less than 1100 K)is reduced to Fe,while Li Al Si₂O₆ decomposes into SiO₂and Li Al SiO₄.As the temperature increases,SiO₂ and Li Al SiO₄ are sequentially reduced with the participation of Fe to obtain Si-Fe alloys,Al₂O₃ and Li(g).When the reduction temperature is higher than 1600 K,SiO and Al₂O will be produced,resulting in the loss of Si and Al in the system.