Utilization Of Spent Lithium-ion Batteries Cathodes As Adsorbents For Heavy Metals Removal From Aqueous Solutions

With the rapid development of power battery market,the number of spent lithium-ion batteries has increased dramatically all over the world.The recycling and disposal of spent lithium-ion batteries have attracted wide attention.Based on the extensive sources of spent lithium-ion batteries and the characteristics of their cathode materials such as large specific surface area and functional groups containing metal oxides,which are suitable for adsorbing heavy metal ions in water,a series of experiments were carried out to recover and pretreat spent lithium-ion batteries.The adsorption mechanism of spent lithium-ion batteries cathode materials for adsorbing Cu2+,Pb2+,Cd2+and Zn2+in water was discussed.Spent lithium phosphate(SLFP)and spent lithium manganate(SLMO)batteries were used as adsorbents for heavy metals,and commercial lithium iron phosphate(LFP)and lithium manganate(LMO)cathode materials were selected.With reference to the material,the adsorption effects of the positive adsorbent materials for spent lithium batteries on Cu2+,Pb2+,Cd2+and Zn2+were analyzed.The effects of initial concentration,reaction time,temperature and coexisting ions on the adsorption of heavy metal ions were investigated.The characteristics of LFP,SLFP,LMO and SLMO before and after adsorption were characterized by means of SEM,BET,XRD and Raman.The adsorption mechanism was discussed by isotherm,adsorption thermodynamics and kinetics.The adsorption experiments show that LFP,LMO,SLFP and SLMO have good adsorption capacity for heavy metals.The maximum adsorption capacity of SLFP for Cu2+,Pb2+,Cd2+and Zn2+reached 44.28 mg/g,39.54 mg/g,25.63 mg/g and 27.34 mg/g,respectively.The maximum adsorption capacity of SLMO for Cu2+,Pb2+,Cd2+and Zn2+reached 32.51 mg/g,31.83 mg/g,26.24 mg/g and 25.25 mg/g,respectively.With the increase of reaction time,the adsorption capacity increased gradually,and the time to reach adsorption equilibrium was 12 hours.The effect of coexisting ions on the adsorption efficiency of four adsorbents was not significant when the concentration of NaCl was below 5 mg/L,With the increase of NaCl concentration,the adsorption capacity of heavy metals showed a decreasing trendThe analysis of adsorption isotherm shows that Langmuir isotherm model can well describe the adsorption process of Cu2+by SLFP and SLMO(R2>0.96).With the increase of temperature,the adsorption capacity of Langmuir monolayer of SLFP increased from 41.75 mg/g to 56.72 mg/g.Temkin isothermal model showed that both SLFP and SLMO adsorbed Cu2" were endothermic reactions.The results of D-R model show that the main adsorption types of Cu2+by SLFP and SLMO are chemical adsorption.Thermodynamic analysis showed that the adsorption of Cu2+,Pb2+3 Cd2+,Zn2+by SLFP and SLMO was spontaneous and belonged to endothermic reaction.The adsorption kinetics analysis showed that the adsorption process of Cu2+,Pb2+,Cd2+,and Zn2+by SLFP and SLMO could be accurately reflected by the quasi-second-order kinetic model(R2>0.99),indicating that the adsorption process was mainly chemical adsorption,and the average adsorption capacity fitted by the model was similar to that obtained by experiments.The simulation results of intraparticle diffusion equation show that the adsorption of heavy metals by SLFP and SLMO mainly includes two complex processes:external surface adsorption and internal diffusion.Elovich equation simulation results show that the initial adsorption rates of SLFP and SLMO for Pb2+ are 108.03 mg/(g h)and 72.59 mg/(g h),respectively,which are higher than those for other heavy metals.BET,SEM,XRD and Raman spectroscopy were used to characterize the adsorption mechanism of four adsorbents for heavy metal ions.SEM and BET results show that the adsorbent surface is irregular and not smooth,and has a large specific surface area,which can provide a certain adsorption site.XRD and Raman results show that the adsorbent obtained by dismantling the cathode of waste lithium ion batteries does not destroy the crystal structure and is a good adsorbent.The results of desorption and regeneration experiments show that SLFP and SLMO are reusable heavy metal adsorbents.After four desorption and regeneration cycles,the removal rates of Cu2+,Pb2+ by SLFP can still reach 80.5%and 82.3%,and the removal rates of Cu2+,Pb2+by SLMO can still reach 73.1%and 75.6%.It is proved that SLFP and SLMO have good recyclability and can be continuously and effectively applied to the treatment of heavy metal polluted water.