Intensification Of Leachability Of Lithium Fixed In Simulated Slag After Pyro-treatment Of End-of-life Lithium-ion Battery

Energy is the foundation of supporting the development of modern society.The global warming which is brought by the burning of fossil energy has prompted people to develop new kinds of energy.However,most of these new energy sources are unstable as well as cannot be stored,thereby requiring transition through energy storage medium.Lithium-ion batteries(LiBs)are the most widely energy storage medium currently.Large amounts of lithium resources are consumed and end-oflife LiBs are produced due to large usage of LiBs.The Umicore's pyrometallurgical method of disposing end-of-life LiBs do not require complicated pretreatment of batteries as well as consume many chemical reagents,which attracts much attention.An alloy phase and a lithium-bearing slag phase are formed after ultra-high temperature treatment of LiBs.At present,the alloy phase is recycled.However,the lithium-bearing slag phase is abandoned,causing a waste of lithium resources.It has the economic benefits for extracting lithium from slag whose lithium content is close to the lithium ores after analyzing the composition of actual slag phase.However,there are also some Si,Al,and O are contained in the slag phase,which can form a stable and insoluble silicate structure with Li.How to convert lithium in silicates into leachable lithium salts is the important technology of extracting of lithium from slag phase.This article will conduct research on this topic.According to the fact that cation with a large radius can exchange cation with a small radius which is presented in the ion diffusion of chemical strengthening of silicate glass,this article proposed that Ca2+with a large radius could replace Li+in the simulated slag effectively and leachable lithium salts were generated.Na+was used to replace Ca2+ to construct a composite eutectic sodium salt system in the following study because the roasting temperature had a huge influence on the separation equipment and cost,which could reduce the roasting temperature of the process and optimize the conditions for extracting lithium.This paper further proposed to use K+instead of Na+to construct a roasting system based on ion substitution of potassium/sodium salt to increase the ion exchange reaction rate and shorten the roasting time to avoid increase of energy consumption in the separation process.Finally,sulfuric acid without secondary pollution was employed as roasting agent to extract lithium.The corresponding results are as follows.(1)The system of pure LiAlSi2O6 and CaCl2 was studied firstly.The thermodynamic calculation results showed that the reaction of LiAlSi2O6 and CaCl2 could occur spontaneously when the temperature was above 500?.Li+in the LiAlSi2O6 could be exchanged by Ca2+according to the XRD results of roasted samples.The system of simulated slag and CaCl2 was then researched.It was found that the mixture of slag and CaCl2 showed an obvious endothermic peak between 600? and 800? through TG-SDTA experiments.The diffusion rate of Ca2+to the phase interface increased as the temperature increasing.X-ray diffraction results of roasted sample contained LiCl and CaAl2Si2O8,which further proved that Li+in the slag was replaced by Ca2+.The roasted sample was leached with water,and the filtrate was analyzed by ICP-OES.The result showed that lithium extraction efficiency of simulated slag could reach to 90.58%.(2)The system of pure LiAlSi2O6 and Na2SO4/NaCl was researched firstly.The thermodynamic calculation results showed that the reaction between LiAlSi2O6 and Na2SO4/NaCl could only occur spontaneously above 500?.Na+can exchange Li+in LiAlSi2O6 on the basis of XRD results of roasted samples.The system of simulated slag and Na2SO4/NaCl was then studied.It was also found that Na2SO4/NaCl could form eutectic salts according to the TG-SDTA results.XRD results showed that NaAlSi2O6 and NaLiSO4 were formed after Na+exchanging with Li+effectively.The roasted sample was leached with water,and the filtrate was analyzed by ICP-OES.The result showed that lithium extraction efficiency of simulated slag could reach to 97.23%.A higher lithium extraction efficiency was obtained under a lower roasting temperature compared to the above system.(3)The system of pure LiAlSi2O6 and K2CO3/Na2CO3 was studied firstly.It was found that Li+could be released due to easily broken of Li-O bonds after adsorption of K+/Na+on the LiAlSi2O6 crystal through quantum chemistry calculations.K+and Na+could exchange with Li+in LiAlSi2O6 according to the XRD results of roasted samples.The system of simulated slag and K2CO3/Na2CO3 was then researched.Thermal analysis results showed that K2CO3 and Na2CO3 could form eutectic salts.It can also be found that K+and Na+could exchange with Li+in the simulated slag quickly to form KAlSiO4 through XRD analysis of roasted samples.The roasted sample was leached with water,and the filtrate was analyzed by ICP-OES.The result showed that lithium extraction efficiency of simulated slag could reach to 93.87%.A lower roasting time was adopted compared to the above system,which proved higher ion exchange rate of this process.(4)The system of pure LiAlSi2O6 and H2SO4 was researched firstly.It was found that the reaction of LiAlSi2O6 and H2SO4 cannot proceed spontaneously and the toxic gases such as SOx might be released under high temperatures according to the thermodynamic calculation results.The results of quantum chemistry calculations showed that the Li-O bonds in the LiAlSi2O6 crystal were more likely to be broken and the steric hindrance of isolation of Li+ from the crystal lattice was reduced.H+could exchange with Li+in LiAlSi2O6 according to the XRD results of roasted samples.The system of simulated slag and H2SO4 was then studied.It could also be found that toxic gases such as SOx would not be released during the roasting process from 30 to 300? according to the thermal analysis combined with mass spectrometry.XRD results showed that HAlSi2O6 was presented in the roasted samples,which proved that Li+in the simulated slag was successfully exchanged by H+.The roasted sample was leached with water,and the filtrate was analyzed by ICP-OES.The result showed that lithium extraction efficiency of simulated slag could reach to 93.25%.Finally,the filtrate was separated and purified to prepare crystalline Li2CO3 whose purity was 99.24%.Finally,this method was used in the real slag system and the extraction rate of lithium was 90.82%,which proved that this process was also suitable for the extraction of lithium in the real slag.