Study On Recovery And Reuse Of Valuable Metals From Waste Ferrous Lithium Phosphate Cathode Materials By Roasting-Leaching Method

In 2021,the state proposed a carbon neutral development strategy,aiming to reduce carbon dioxide emissions,encourage enterprises to invest in low-carbon clean technologies,actively develop renewable energy,and increase China’s support for the green new energy industry.Green energy storage equipment represented by lithium batteries stands out.In recent years,the output of lithium iron phosphate batteries has been increasing year by year,and the amount of scrapped lithium iron phosphate batteries is also increasing.If these waste batteries are not handled scientifically,it will not only waste a lot of resources,but also cause great harm to the natural ecology.Therefore,this paper scientifically recovers lithium carbonate and iron phosphate by roasting-leaching of waste lithium iron phosphate cathode materials,and synthesizes lithium iron phosphate materials with recovered lithium carbonate and iron phosphate,and makes them into batteries for electrochemical performance research.Lithium was extracted from waste lithium iron phosphate by iron sulfate roasting-water leaching method,and lithium carbonate was recovered from the leaching solution.The effects of roasting conditions such as Fe₂（SO₄）₃/Li Fe PO₄molar ratio,roasting temperature and roasting time on lithium leaching rate were studied.The results show that the optimum roasting conditions are as follows:the molar ratio of Fe₂（SO₄）₃/Li Fe PO₄is 1:2,the roasting temperature is 450°C,and the roasting time is 5 h.The leaching rate of Li can reach 98.53%.The recovery rate of Li is 82%and the purity of Li₂CO₃is about 95%.The lithium extraction waste residue was leached under the conditions of hydrochloric acid concentration of 3 mol/L,liquid-solid ratio of 15 m L/g,leaching temperature of 65°C and leaching time of 4 h to obtain the leaching solution,and then the iron phosphate was recovered from the leaching solution by precipitation method.The precipitation thermodynamics of Fe³⁺-Al³⁺-PO₄^3--H₂O system in the leaching solution was studied,and the conversion mechanism and theoretical optimum conditions for the preparation of iron phosphate from the filtrate were determined.The effects of reaction temperature,feeding rate and solution p H value on the ratio of phosphorus to iron in iron phosphate precipitation were studied.The results show that the reaction temperature is95°C,the feeding rate is 1.5 m L/min,and the p H value of the solution is 1.5,which is most conducive to the precipitation and crystallization of iron phosphate.At this time,the ratio of phosphorus to iron is closest to 1.The recovered lithium carbonate and iron phosphate were used as raw materials to synthesize lithium iron phosphate materials by carbothermal reduction method,and the synthesized materials were regenerated into batteries for electrochemical performance test.The first charge-discharge specific capacities of the battery were 153 m Ah·g^-1and 147 m Ah·g^-1at 0.1 C,respectively,and the first charge-discharge efficiency reached 96.1%.The initial discharge specific capacity was 136.0m Ah·g^-1at 0.5 C.After 100 cycles,the discharge specific capacity decreased to 130.3 m Ah·g^-1,and the capacity retention rate was 95.8%.The initial discharge capacities at 0.1 C,0.2 C,0.5 C,1C and 2 C were 147.9,144.9,136.6,124.6 and 111.4 m Ah·g^-1,respectively.The percentages of initial discharge capacities at different rates relative to 0.1 C were 97.97%,92.36%,84.25%and75.32%,respectively.