Fundamental Research On Synergistic Removal Of Impurities In The Hydrometallurgy Process Of Spent Lithium-ion Battery Cathodes

The rapid development of new energy automobile industry has led to the production of a large number of spent lithium-ion batteries,which has seriously affected the sustainable development of the industry.Great importance has been attached to the recycling and disposal of lithium-ion batteries.The recycling of spent lithium-ion batteries can not only improve the utilization of resource and reduce environmental pollution,but also has important significance for the sustainable development of new energy automobile industry.Hydrometallurgical technology is currently the main technology for the recycling of lithium-ion batteries.However,this technology is restricted by impurity elements,resulting in a lengthy removal process,large losses of valuable metals,and serious discharge of heavy metal pollutants.In order to solve these problems,this research puts forward the idea of synergistic removal of impurity elements based on induced crystallization.By controlling the crystallization process,the synergistic removal of impurities in the hydrometallurgy process is realized.The focus is on the process optimization,thermodynamic analysis and mechanism of the synergistic leaching process of NCM and LiFePO4 cathode materials and the process of Al3+and Fe3+impurity removal.The main research contents are as follows:(1)In order to reduce the cost of chemical reagent and the introduction of impurity elements in the leaching process,a new method of synergistic leaching of ternary lithium-ion batteries(NCM)and LiFePO4 cathode materials is proposed.By controlling the process of crystal nucleation and growth,Fealand PO3-is transformed into FePO4-2H2O,the leaching rate of valuable metal elements in the synergistic leaching process is over 96%,and the impurities Fe and P is recovered as FePO4·2H2O.The study of the mechanism shows that the addition of seed crystals can induce the precipitation of FePO4-2H2O,thereby promoting the complete progress of the synergistic leaching reaction.(2)The simulated acidic solution containing valuable metals(Li,Ni,Co,Mn)and impurities Al and Fe was set as the research object,and the phosphate method is used to deeply remove Al and Fe.The efficiencies of impurity removal and the loss of valuable metal were set as evaluation criteria,under the conditions of phosphoric acid addition amount 0.8M(M is the theoretical addition amount),pH=4.0,reaction temperature 80?,reaction time 60min,high efficiencies(>96%)of impurity removal is achieved and the loss of valuable metals is less than 1%.(3)A method for inducing and strengthening the synergistic removal of aluminum and iron impurities in a closed loop of seed crystals was developed.The effect of seed crystal induced impurity removal was compared with the effect of no seed crystal,and the influence of phosphoric acid addition,pH,impurity removal temperature,and seed crystal addition amount on the impurity removal effect was investigated.Through a series of XRD,SEM,EDS,particle size distribution and other characterization of the experimental results,the mechanism of seed-induced enhanced impurity removal was explored,and the subsequent treatment process for impurity removal was proposed.