Study On Separation And Recovery Of Lithium From Spent Lithium-ion Battery Cathode Materials

As the demand for lithium-ion batteries increases,a large number of lithium-ion batteries will be bound to enter a large-scale end-of-life period The recovery of valuable elements(such as Li,Co,Ni)from spent lithium-ion batteries is essential for environmental protection,energy conservation and emission reduction.However,traditional methods have insufficient recovery efficiency of metal ions,which hinders the development of this industry.As a new type of green solvent,ionic liquid has the characteristics of high thermal stability,good solubility,and almost no volatilization,making it easy to dissolve metal oxides and separate metal ions steading of inorganic acid and volatile organic solvent.In this thesis,a functional ionic liquid(FIL)based on carboxyl group is used as an extractant to replace the traditional volatile extractant to extract and recover lithium ions in a complex system.A carboxyl-based eutectic solvent leaching agent was designed to replace inorganic acid to solve the problems of equipment corrosion and environmental pollution.The precipitation method separated the metal ions.The main research conclusions are as follows:(1)A novel process for selective extraction towards lithium ion from spent lithium-ion batteries by carboxyl functionalized ionic liquids was successfully demonstrated.It was revealed that the lithium ion in the leach liquor(sulfuric acid as the leachate)was feasible to recovery using organic phase composed of 80.0%TBP extractant and 20.0%carboxyl-based ILs at the initial pH of 3.0,A/O ratio of 1:2,and the secondary extraction efficiency was 63.2%,the extraction efficiency of lithium was up to 96.80%after the five-stage extraction.The infrared spectroscopy and slope method are used to infer that the extraction mechanism of the extraction reaction is the displacement reaction of hydrogen ions in ionic liquid cations and lithium ions in the water phase.The organic phase loaded with lithium ions was washed and extracted.Other metal ions could be removed by the solution containing 0.50 mol/L H2SO4 and 0.50 mol/L Li2SO4.Lithium ions in the organic phase can be completely eluted by 1.00 mol/L H2SO4.Through the study of the thermodynamic function of the extraction system,it is obtained that the system is a spontaneous exothermic reaction with increased disorder(△H<0,△S>0 and △G<0).The ionic liquid extractant can be reused,which provides an effective solution for improving the recovery rate of lithium in waste lithium-ion batteries.(2)Based on carboxyl-based eutectic solvent(Betaine·HCl-6EG)leaching and separation of spent lithium-ion battery ternary materials,using single factor variable method to determine the best leaching conditions:hydrogen bond donor and hydrogen bond acceptor ratio 6:1;solid-to-liquid ratio was 50.0 g/L;reducing agent was 0.4 wt%H2O2;leaching temperature was 80℃;leaching time was 15.0 h.Under these conditions,the waste material could be completely leached.The leaching mechanism is the oxidation-reduction reaction combined with the infrared spectrum analysis.Lithium-nickel and cobalt-manganese could be separated at low temperatures because of the changes in the leaching system.The separation coefficient of lithium/cobalt was up to 253.3,and lithium/manganese,nickel/cobalt,nickel/manganese also had a good separation effect with separation coefficients of 193.7,72.2 and 54.2.The separation of lithium and nickel could be realized by the hydroxide precipitation method and the separation of cobalt and manganese could be achieved well by the hydroxide precipitation and the reflux of ammonia water.Lastly,the eutectic solvent was recovered by distillation under reduced pressure.The eutectic solvent replaces the traditional leaching agent and solves the problems of corrosion to equipment and environmental pollution.