| Lithium-ion batteries(LIB)have brought great convenience to our life.At the same time,the treatment of a large number of waste lithium-ion batteries is increasingly apparent.If the waste lithium-ion batteries are not properly treated,the conductive agents,binders,heavy metals and other toxic and harmful substances contained in them will cause serious pollution to the environment.Based on the concept of environmental protection and sustainable development,the effective recycling of waste lithium-ion batteries not only has great social and environmental benefits,but also can alleviate the pressure of the shortage of cobalt,lithium and other mineral resources in China,which has significant economic benefits.In this paper,three kinds of organic acid and ascorbic acid leaching system were selected to study the leaching and recovery of cobalt and lithium in the cathode active materials.A rapid,efficient,economic and environmental protection leaching process of cobalt and lithium was proposed,which could be used for the industrial application of recycling valuable metals from waste lithium-ion batteries Provides a possibility.The main research contents are as follows:(1)Waste lithium-ion batteries were discharged in sodium chloride solution,and the best discharge conditions were obtained:solid-liquid ratio 20 g/L,discharge time 2h.After discharge,the voltage of spent lithium-ion battery can be reduced to less than 0.2V,which ensures the safety of dismantling the battery.The cathode active materials were separated from aluminum foil by ultrasonic assisted solvent dissolution method.The results showed that the best solid-liquid ratio was 10 g/L and the ultrasonic treatment was 30 min.After the separation test,the cathode active materials with high purity were obtained.(2)The results show that the optimal leaching conditions of citric acid+ascorbic acid system are as follows:citric acid dosage 3 g/g,ball milling speed 500 r/min,ball milling time 120 min,ball to material ratio 8 g/g,ascorbic acid concentration 0.2 mol/L,leaching temperature 80℃,leaching time 60 min.The optimal leaching efficiency of Co and Li were 84.26%and 92.19%respectively.The Avrami equation was used to describe the leaching reaction kinetics of citric acid+ascorbic acid system.The activation energies of cobalt and lithium were calculated to be 42.14 KJ/mol and 48.94 KJ/mol respectively.It was determined that the dominant control step of leaching reaction was the interfacial chemical reaction step.According to the fitting results,the prediction models of leaching efficiency under different leaching temperature and time were obtained.(3)The optimal leaching conditions of EDTA-2Na+ascorbic acid system were as follows:EDTA-2Na dosage 5 g/g,ball milling speed 500 r/min,ball milling time 60 min,ball to material ratio 8 g/g,ascorbic acid concentration 0.2 mol/L,leaching temperature 80℃ and leaching time 60 min.The optimal leaching efficiency of Co and Li were 93.13%and 94.37%,respectively.The shrinking core model(SCM)was used to describe the leaching reaction kinetics of EDTA-2Na+ascorbic acid system.The activation energies of cobalt and lithium were calculated to be 27.97 KJ/mol and 21.80 KJ/mol respectively.It was determined that the dominant control step of leaching reaction was the mixed control step of chemical reaction and mass transfer in porous layer.According to the fitting results,the prediction models of leaching efficiency under different leaching temperature and time were obtained.(4)The optimum leaching conditions of the system of triacetic acid+ascorbic acid were as follows:the amount of aminotriacetic acid added was 1 g/g,the ball milling speed was 500 r/min,the ball milling time was 60 min,the ball to material ratio was 3 g/g,the ascorbic acid concentration was 0.2 mol/L,the leaching temperature was 80℃,the leaching time was 15 min,and the optimal leaching efficiency of Co and Li were 98.27%and 98.19%respectively.The experimental results show that the system of ammonia triacetic acid+ascorbic acid leaching can greatly reduce the ratio of mechanically activated ball to material and acid leaching time,significantly improve the reaction efficiency,and has outstanding advantages in industrial promotion.The shrinking core model was used to describe the leaching reaction kinetics of the system.The activation energies of cobalt and lithium were calculated to be 18.85 KJ/mol and 20.35 KJ/mol,respectively.It was determined that the dominant control step of leaching reaction was the mass transfer control step of porous layer when the leaching temperature was higher than 40℃.According to the fitting results,the prediction models of leaching efficiency under different leaching temperature and time were obtained. |
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