Study On Extracting Li And Fe From Scrap LiFePo₄ By Alkaline Roasting Process

With the rapid development of the electric vehicle industry and electronic products,lithium-ion batteries play a crucial role as energy carriers.In the future trend of the"dual carbon"goal,lithium-ion power batteries will gradually replace traditional petroleum fuels in daily life and production applications.With the continuous growth of the lithium-ion battery market,its inherent lifespan will lead to the generation of more scrapped ion batteries,which will reach a wave of scrapping in the coming years.Scrapped lithium batteries contain a large amount of valuable metals and toxic and harmful substances.If only treated by simple landfill,it will not only pollute the natural environment and endanger human health,but also be a waste from a resource perspective.The positive electrode materials of lithium-ion power batteries are rich in valuable metal elements,therefore,it is imperative to study the high-value green recycling of discarded lithium-ion power battery positive electrode materials.This paper aims to study the high-value recycling and utilization of LiFePO₄cathode materials with good market prospects.The main research focuses on the distribution characteristics of valuable metal elements in LiFePO₄after calcination at different temperatures and systems,as well as the key influencing factors on the extraction rate of Li andFevaluable metal elements in the alkaline calcination acidic leaching system.From the perspective of reaction mechanism,the migration forms and transformation mechanisms of chemical elements are revealed,The main research findings are as follows:（1）Under closed conditions,LiFePO₄ positive electrode material exhibits significant weight gain above 300℃,exhibiting thermodynamic instability accompanied by physical and chemical changes;During the mixed roasting process of LiFePO₄and Na₂CO₃,significant mass and heat changes occur,exhibiting thermodynamic instability and showing certain differences compared to a single positive electrode material.LiFePO₄and Na₂CO₃were mixed and roasted in a mass ratio of 1:0.67 at different temperatures,and acidic leaching experiments were conducted on the roasted products at different final p H values.As the calcination temperature increases,the olivine structure of LiFePO₄is gradually oxidized and destroyed,and the occurrence forms of Li andFeelements change;When the calcination temperature is 550℃,the structure of the positive electrode material LiFePO₄is completely destroyed;When the calcination temperature range is between650℃～1000℃,the phase composition remains relatively stable,and the final forms of Li andFeelements are Fe₂O₃,Fe₃O₄,Li Fe₅O₈,Na Li₂PO₄,and Li Na₅（PO₄）₂.The evolution law of the occurrence forms of Li andFeelements is Li:LiFePO₄→Li₃Fe₂（PO₄）₃→Na Li₂PO₄,Li Na₅（PO₄）₂;Fe:LiFePO₄→Li₃Fe₂（PO₄）₃、Fe₂O₃→Fe₂O₃、Fe₃O₄、Li Fe₅O₈.The mixed roasting product is accompanied by obvious sintering phenomenon,with a color change of gray black→brown→reddish brown,but stratification occurs above 450℃.The lower part of the roasting product changes in color from brown→orange yellow→orange.Based on ICP-OES data analysis,the calcined product at 400℃contains a large amount of unreacted LiFePO₄raw material.Li andFeelements are simultaneously released through leaching,and the extraction rates of Li andFeelements are both around 70%.As the temperature increases,the changes in the occurrence forms of Li andFeelements gradually lead to differences in the extraction rate of valuable metals.At 800℃,the extraction rate of Li element reaches 88.58%,and the extraction rate ofFeelement is 8.26%.Some Li elements combine withFeelements in the form of Li Fe₅O₈,and the oxide ofFehas a certain tolerance in phosphoric acid solution.Finally,the leaching residue phase composition becomes Li Fe₅O₈and the oxide of Fe.The different roasting temperatures under closed conditions are the key factors affecting the extraction of Li andFeelements during the acid leaching process.（2）Based on the research conclusions under closed conditions,conduct roasting experiments under open conditions at different temperatures.Under open conditions,LiFePO₄and Na₂CO₃were mixed and roasted in a mass ratio of 1:0.67（800℃～950℃）,and acid leaching experiments were conducted on the calcined products obtained at different temperatures.Thermodynamic instability occurs during the mixed roasting process of LiFePO₄and Na₂CO₃,accompanied by physical and chemical changes,resulting in changes in the occurrence forms of Li andFeelements,ultimately evolving into Fe₂O₃,Fe₃O₄,Na Li₂PO₄,and Li Na₅（PO₄）₂.Compared to sealed conditions,the Li Fe₅O₈phase in the calcined product obtained under this open condition disappeared.From the macroscopic analysis,there was no layering or sintering phenomenon,which was due to the abundance of O₂under open conditions and the lack of CO₂interference,allowing the reaction to proceed fully.The evolution law of the occurrence forms of valuable metal elements is Li:LiFePO₄→Li₃Fe₂（PO₄）₃→Na Li₂PO₄,Li Na₅（PO₄）₂;Fe:LiFePO₄→Li₃Fe₂（PO₄）₃、Fe₂O₃→Fe₂O₃、Fe₃O₄.After roasting under open conditions within the range of 800℃～950℃and acidic leaching,the extraction rate of Li element is above 98%,and a small amount ofFeelement is extracted into the solution,achieving partial extraction ofFeelement and basic complete extraction of Li element.（3）The economic evaluation shows that based on the recycling process conditions of open conditions,alkaline roasting acidic leaching,it is planned to recover 1 ton of scrapped LiFePO₄cathode material,which requires a material cost of approximately 77500 yuan.It can obtain approximately 0.24 tons of Li₃PO₄,0.08 tons ofFePO₄,and 1.6 tons of Na₃PO₄,with a cumulative economic profit of approximately 28700 yuan.Effectively reducing the cost of traditional heavy metal recovery processes,improving labor productivity,and significantly increasing enterprise benefits,promoting sustainable ecological development.