Study On The Influence Of Impurities On Recovery Of Lithium From Spent NCM Cathode Powder By Reduction Roasting-leaching Process

Lithium,as an important strategic metal,is an essential key component of lithium-ion batteries;The demand for lithium has also grown rapidly as the production of new-energy vehicles and consumer electronics continues to grow;As a secondary resource of lithium-rich,the spent lithium-ion batteries have become a potential resource for lithium extraction and attracted wide attention from all sectors of society.At present,the usual spent NCM cathode lithium-ion batteries mainly focus on the recovery of high-value metals such as cobalt and nickel,relatively speaking,the recovery of lithium is ignored,and the recovery rate of lithium is then low.In recent years,a series of processes have been developed for the recovery of lithium from spent NCM cathode,among which the reduction roasting-water leaching process has the advantages of simple process,environment friendly and easy industrial implementation,which has a small-scale industrial application and shows good application prospects.However,the current treated raw materials are mainly the waste from the production process,with the low content of impurities,which has little impact on the process.The actual spent battery materials will inevitably contain fluorine,aluminum,phosphorus impurities,which has an negative influence on the recovery rate of lithium.In this paper,pure spent NCM cathode powder and spent NCM cathode powder containing fluorine/phosphorus/aluminium impurities were processed by carbothermal reduction roasting-water leaching process and hydrogen reduction roasting-water leaching process,focusing on the influence of typical impurities such as fluorine/phosphorus/aluminum to lithium extraction,and clarifying the reaction behavior and the mechanism affecting the effect of lithium leaching.The specific research conclusions are as follows:(1)The optimal conditions of carbothermal reduction roasting-carbonation water leaching process to pure spent NCM cathode powder are:roasting temperature of800?,coke dosage of 15%,roasting time of 60min,liquid solid ratio of 10:1ml/g,leaching time of 30min,carbon dioxide flow of 30ml/min,leaching temperature of20?,and the leaching rate of lithium is 89.12%.The optimal conditions of carbothermal reduction roasting-carbonation water leaching process to spent NCM cathode powder containing fluorine/phosphorus/aluminium impurities are:roasting temperature of 800?,coke dosage of 15%,roasting time of 120min,liquid solid ratio of 10:1 ml/g,leaching time of 15min,carbon dioxide flow of 30ml/min,leaching temperature of 20?,and the leaching rate of lithium is 71.86%.Within the test range,the leaching rate of lithium of pure spent NCM cathode powder is obviously higher than spent NCM cathode powder containing fluorine/phosphorus/aluminium impurities.(2)The optimal conditions of hydrogen reduction roasting-water leaching process to pure spent NCM cathode powder are:roasting temperature of 500?,hydrogen flow of 100ml/min,roasting time of 30min.Under this conditions,the roasted samples were leached at liquid solid ratio of 10:1ml/g,leaching time of120min,leaching temperature of 900?,and lithium leaching rate is 98.71%.The optimal conditions of hydrogen reduction roasting-water leaching process to spent NCM cathode powder containing fluorine/phosphorus/aluminium impurities are:roasting temperature of 500?,hydrogen flow of 100ml/min,roasting time of 90min,and the maximum lithium leaching rate is 84.74%,obviously lower than pure spent NCM cathode powder.(3)Using reduction roasting-water leaching proces,the difference between lithium leaching effect of the two raw materials is closely related to fluorine/phosphorus/aluminum impurities.Lithium in the pure spent NCM cathode powder exists as a Li₂CO₃after carbothermal reduction roasting,and lithium in the spent NCM cathode powder containing fluorine/phosphorus/aluminium impurities is not only generating Li₂CO₃,but also generating three poor water-soluble lithium products,such as Li F,Li₃PO₄and Li Al O₂.Thus,the leaching rate of lithium of spent NCM cathode powder containing fluorine/phosphorus/aluminium impurities by carbonate water leaching process is significantly lower than the pure spent NCM cathode powder;Lithium in the pure spent NCM cathode powder mainly was transformed to Li OH after hydrogen reduction roasting,and because of the existence of C in the raw material,there are also small part of Li₂CO₃.However,part of lithium in the spent NCM cathode powder containing fluorine/phosphorus/aluminium impurities were converted into poor water-soluble Li F,Li₃PO₄,and Li Al O₂during hydrogen reduction roasting,therefore,the leaching rate of lithium is also significantly lower than that of pure spent NCM cathode powder.