Mixed Acid Leaching And Recycling Of Valuable Metal Elements From The Spent Ternary Lithium-ion Batteries

Due to advantages of high energy density,large capacity and no memory,lithium-ion battery has been recognized as the most promising power battery and has been widely used in new energy vehicles.With the rapid development of new energy vehicle industry,the production and sales of lithium-ion power battery are increasing rapidly.With the end of battery life,waste lithium-ion batteries will be produced on a large scale in the future.Waste lithium-ion batteries have the dual properties of resource utilization value and environmental harm.It has important resource and environmental benefits to recycle valuable resources and realize harmless disposal of harmful components.Centered on the resource utilization of valuable metals in the waste lithium-ion battery,this paper took the waste positive active materials of ternary lithium-ion battery as the research object,used microwave roasting technology to pretreat ternary positive active materials and further analyzed the effect of microwave roasting on the leaching efficiency of valuable metals.Using mixed acid（sulfuric acid+citric acid）as leaching system,the valuable metals from active materials of positive electrode were recycled.The effects of reaction conditions and parameters on the leaching efficiency of valuable metals were analyzed by single factor and response surface optimization.Based on the principle of solvent-out crystallization,ethanol was used as precipitator to separate and recover valuable metals from the leach solution,which was used to prepare ternary precursor materials.The results of microwave roasting pretreatment of ternary positive active materials show that compared with the traditional high temperature pretreatment method,microwave roasting treatment has higher efficiency and can significantly improve the leaching efficiency of valuable metals Mn,Ni and Co,and the leaching rate increases with the increase of microwave roasting power.However,the optimal roasting time existed under different microwave roasting power,and too long or too short roasting time was not conducive to metal leaching reaction.Combined with process,energy consumption,cost and other factors,microwave roasting power of 600 W and roasting time of 6 min were determined to be the optimal pretreatment conditions.The effect of microwave roasting on metal leaching efficiency is mainly due to the instantaneous high temperature generated by the induced discharge of metal particles in the active material.The instantaneous high temperature can（1）destroy the original layered structure of the active material,and make the reduction reaction of some metals with acetylene black to form Li₂CO₃,Ni O and other substances that are easier to be leached.（2）Removes the organic matter coated on the surface of the metal particles to improve the metal exposure and the mass transfer efficiency in the leaching reaction process.The positive active material of valuable metals in the mixed acid（sulfuric acid+citric acid）leaching results show that under the condition of single factor analysis of total acid concentration is 0.6 mol/L（0.2 mol/L+citric acid sulfate 0.4 mol/L）,reaction temperature 80℃,reaction time 60 min,under the condition of solid-liquid ratio of 20g/L,Li valuable metals,Mn,Ni,Co leaching rate were 98%,100%,93%and 98%respectively.Through response surface test,the optimal operating conditions were obtained as follows:total acid concentration 0.8 mol/L（sulfuric acid 0.6 mol/L+citric acid 0.2 mol/L）,reaction temperature 84℃,reaction time 40 min and solid-liquid ratio20 g/L.Under these conditions,the leaching rates of Li,Mn,Ni and Co were 96%,95%,95%and 96%,respectively.Citric acid plays the role of reducing agent and chelating agent in the whole leaching reaction process.In the mixed acid leaching system,citric acid plays the role of reducing agent when the reaction time is 0～10 min,which can reduce Co³⁺,Ni³⁺and Mn⁴⁺into Co²⁺,Ni²⁺and Mn²⁺,and plays a certain chelating role.After the reaction time of 10～15 min,reduction was weakened and chelation increased gradually.After the reaction time of 15～20 min,the reduction stopped and chelation was the main application.The effective separation and recovery of Mn,Ni and Co in the leach solution can be achieved by using ethanol as the solvent,while the separation and recovery of Li cannot be achieved.Under the conditions of total acid concentration of 0.9 mol/L（sulfuric acid 0.6 mol/L+citric acid 0.3 mol/L）,leaching time of 60 min,and the ratio of ethanol to leach solution 3.5:1,The recoveries of Li,Mn,Ni and Co were 0.2%,43.5%,85.4%and 84.1%,respectively.After precipitation and drying,the valuable metals were regenerated to prepare precursor materials.The XRD and SEM analysis showed that the prepared materials had sharp diffraction peak,high crystallinity and good spheroidal particle morphology.