| Various types and sizes of batteries emerge in endlessly and are widely used in all walks of life since the actual commercialization of lithium-ion batteries,which promotes the rapid development of society.But generally speaking,the service life of lithium-ion batteries is about 3 to 5 years,and a large number of spent lithium-ion batteries will be eliminated every year.Effective recycling of spent lithium-ion batteries can not only reduce the environmental pollution,but also alleviate the precious metal resource crisis.China has been vigorously developing ternary lithium-ion batteries since 2017 to meet market demand.It is expected that there will be a large number of spent ternary lithium-ion batteries in the Chinese market that need to be recycled after 2022.In this thesis,the most common 18650 type spent ternary lithium-ion battery was selected as the research object,and two different hydrometal lurgical recovery process routes were developed.The separation and recovery performances of metal ions were systematically investigated,which will provide certain technical support for the ultimate realization of effective recovery of spent ternary lithium-ion batteries in China.The lithium-ion batteries were firstly pretreated by discharging,disassembling,separating the cathode,cutting,dissolving the aluminum sheet and decomposing the adhesive to obtain the ternary cathode active material.The acidic dissolution conditions of the cathode active material with the system of propionic acid and hydrogen peroxide were investigated.Under the optimal leaching conditions,the dissolution efficiency of Ni2+,Co2,,Mn2+ and Li+reached up to 97.4%,97.1%,97.5%and 99.2%,respectively.The study results of leaching kinetics demonstrated that the leaching process of the cathode active material was controlled by chemical reactions.Then Ni2+,Co2+and Mn2+ were recovered by fractional precipitation with diacetyloxime(DMG),KMnO4 and C2H2O4,and various recovery conditions were investigated.It was relatively difficult to recover Li+ in the filtrate,so after concentration of the filtrate,thermal decomposition of organic matter and re-dissolution,recovery of Li2CO3 was achieved by adding Na2CO3 at pH 12.The purity of Li2CO3 reached up to 99.9%by XRD analysis and purity test.The final recovery efficiencies of Li+,Ni2+,Co2+and Mn2+ reached up to 71.2%,96.5%,96.3%and 94.7%.In order to shorten the recovery process and increase the recovery efficiency of ions,the thermally-reduced method was used to treat the pre-treated cathode active material,which realized the reduction of metal ions from high valence state to low valence state,resulting in the transformation of cathode active material to Li2CO3,Ni,Co and MnO demonstrated by XRD analysis.According to the solubility difference of the above substances in water,Li+was firstly dissolved and recovered.The effects of factors such as reduction calcination temperature,CO2 and NH4HCO3 on the dissolution efficiency of Li+in water were investigated.Under the optimal conditions,the dissolution efficiency of Li+reached up to about 90%and Li+could be recovered in the form of Li2CO3.After that,other metals are acid-dissolved by sulfuric acid.The effects of reaction time,reaction temperature and sulfuric acid concentration on the dissolution efficiencies of each metal ion were also investigated.Under the optimal dissolution conditions,the dissolution efficiency of each metal ion could reach up to about 99.0%.DMG,KMnO4 and C2H2O4 were used to recover Ni2+,Co2+ and Mn2+ by fractional precipitation under the optimal recovery conditions.Finnaly,the recovery efficiencies of Li+,Ni2+,Co2+ and Mn2+ have all been improved,reaching 84.7%,97.6%,97.9%and 95.8%,respectively. |
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