Basic Research On Active Pulsing Airflow Separation Of Current Collectors From Spent LIBs

The annual domestic output of lithium-ion batteries?LIBs?reached 1,178,947,000in 2017,representing an increase of 31.25%over the previous year.The recycling of the spent lithium ion batteries can not only greatly alleviate the shortage of the important metals in our country,but also avoids serious environmental pollution.In turn,it brings considerable economic and social benefits.Recently researchers mainly focus on the recovery of cobalt from the spent lithium ion batteries,and recycling of copper foil and aluminum foil from spent lithium ion batteries is seldom studied.In this paper,the shear and vertical impact crushers were used to crush batteries and untreated current collectors.The-2+0.25 mm materials which enrich the current collector is applied to separate with the active pulsing air classification.Experiments were conducted to determine the influencing factors and separation efficiency.Based on the simulation of two-phase flow,the sorting mechanism of flaky particles in the active pulsing air was studied,which lays a theoretical foundation for separating current collectors in batteries.In order to study the physical and chemical properties of the current collector after waste lithium-ion batteries were crushed,the particle size and surface property of the actual and simulated materials were analyzed.The size distribution of the particles meets approximately a normal distribution.The particles have regular shape,but there are fewer spherical particles and most of them are thick sheets by observing the circularity and length-diameter ratio distribution of the particles.The actual material composition is more complicated by analysis of scanning electron microscope?SEM?.The actual material contains the current collectors and a small part of the housing materials.The graphite and LiCoO₂ particles contained on the surface of the actual materials are important factor that causes different sorting effect between actual material and simulated one.Based on the difference in the density of the copper foil and the aluminum foil,the active pulsing air sorting experiments of the simulated materials were carried out.Optimum sorting conditions are obtained by adjusting the rate of gas flow,the pulsation frequency and the feed rate.The airflow velocity affects the drag force of the particles and has the greatest effect on the separation efficiency.The response surface tests result in a maximum separation efficiency were 71.22%for-1+0.5 mm simulated material,and 73.15%for-0.5+0.25 mm simulation material.Comparing the separation efficiency of the simulated materials with different particle sizes,the particle size and the narrowness of the particle size fraction also affected the separation effect.The CFD-DEM coupled calculation of the entire sorting process was performed with reference to the optimum sorting conditions of the simulated materials.There were no significant pressure changes at the feed end and the heavy product discharge end.This provides good conditions for the relative stability in the feed and sorting areas.The movement of the particles is periodic.Most of the aluminum particles become the light products and the copper particles become the heavy products.The particle's displacement,velocity,and drag force also show periodic changes.Quantitatively analyzing movement speed,the total force and torque change of the two sets of particles can obtain following results:The Saffman shear lifting force and the virtual mass force which are much smaller than the gravity during the sorting process can be neglected.The magnitude of the Basset force,which is significantly affected by the acceleration of the particles,is one thousand of gravity and has little effect on the particles'movement.In addition to collision resistance,gravity and drag force play a leading role in sorting in the process of pulsating active pulsing air separation.Drag force is a key factor for effective separating different density particles.The simulation is consistent with the actual sorting results.In the sorting process,the shape properties of particle do not eliminate the effect of density on the sorting effect.After the actual material was broken again,the shape of the materials is changed.However,the factors which influencing the separation efficiency are not changed.The optimal sorting conditions of-1+0.5 mm materials by response surface tests is:The airflow rate was 7.62 m/s,the pulsation frequency was 3.91 Hz,and the feed rate was0.62 g/s.The maximum separation efficiency was 63.68%,the copper recovery rate was 67.64%,and the recovery rate of aluminum is 96.21%.The optimal sorting condition of-0.5+0.25 mm materials is:The airflow rate was 6.10 m/s,the pulsation frequency was 7.15 Hz,and the feed rate was 0.5 g/s.The maximum separation efficiency was 68.19%,the copper recovery rate was 83.82%,and the recovery rate of aluminum is 84.37%.