Fundamental Research On Properties Of Nanobubbles And Their Application In Flotation Separation Of Electrode Materials From Spent Lithium Ions Batteries

The main components in electrode materials of spent lithium ions batteries(LIB)are graphite and lithium cobalt oxide(LCO).The efficient separation of them with flotation is a key part of flowsheet of LIB recycling process,which is difficult to be realized in practice with conventional flotation technique due to their smaller particle size than normal flotation particles.The possibility of enhanced separation of electrode materials assisted by nanobubbles was explored in this work.The present work was started in terms of nanobubbles generation methods,where the possibility of nanobubbles generation with the following four methods including ultrasonic irradiation,temperature change,pressured water and ethanol-water exchange were explored.The results show that nanobubbles weren't found on HOPG after ultrasonic irradiation.Besides,ultrasonic irradiation didn't show any significant influence on settling behavior and flotation performance of graphite.Nanobubbles can be generated with temperature change,depositing pressured water and ethanol-water exchange respectively.The sparse nanobubbles were generated with the first two methods while abundant nanobubbles or a layer of nanobubbles covering the entire surface were observed on HOPG with the last method.The formation,properties and factors were investigated.Surface nanobubbles can be removed with AFM tip under contact mode and they disappeared after evaporation.The height of nanobubbles decreases with the increase of A_set/A_freeeven a hollow was formed in the center of a nanobubble.The smaller nanobubbles have the higher stiffness compared with the bigger nanobubbles.The height of nanobubbles increases firstly and then decreases but increases again with the increase of amplitude.No nanobubbles were found on hydrophilic and hydrophobized silicon wafer and alumina surface in room temperature water but found on hydrophobized substrate with temperature change.The formation of nanobubbles on HOPG with temperature change depends to some degree on surface roughness of substrate,that is,nanobubbles were generated preferentially at rough region.The bigger nanobubbles can be generated on substrate with the higher terminal temperature.The salt concentration,solution p H and surfactant concentration all show a neglectable effect on the number of nanobubbles.Besides,p H and surfactant don't show a significant influence on lateral size and height distributions either while the introduction of lithium chloride causes a decrease in the height of nanobubbles.Overall,the contact angles are still lower than the real wetting angle of substrate.The effect of nanobubbles on particle-particle,particle-bubble was investigated.In natural water,a weak electrostatic force was detected during approach of graphite probe to HOPG substrate and no obvious?snap in?phenomenon was observed during approach.The adhesion behavior between graphite and HOPG substrate was observed during retract process.The adhesion force between graphite and HOPG substrate distributes evenly and the largest is about 5 n N.With the method of temperature change,the adhesion force between particle and HOPG substrate can be divided into low adhesion force region and high adhesion force region.In the former,the weak repulsive force was detected during approach process and adhesion behavior with a adhesion force of 5 n N was observed during retract process.In the latter region,?snap in?behavior was observed at all measurement points during approach,and high adhesion force up to about 50 n N was detected during retractation.In natural water with an acidic p H,?snap in?phenomenon occurs during approach and adhesion behavior with the smaller adhesion force was observed during retraction.In cold water with p H=4,?snap in?behavior was found and the large adhesion force up to about 100 n N was detected at almost all measurement points.Besides,a slight repulsive force was detected during approach before?snap in?.In natural water with p H=10,the strong electrostatic repulsive force was detected during the entire approach process.During retraction,no adhesion force was detected at all measurement points except for several points where the weak adhesion forces were detected and the graphite probe experienced a long range electrostatic repulsive force.In cold water with p H=10,the graphite probe shows?snap in?behavior during approach in such a region where large adhesion force was detected and the graphite probe experienced a long range electrostatic repulsive force before?snap in?.During retraction,adhesion behavior occurred.The apparent size distribution of graphite agglomerations in room temperature water decreases with the increase of p H and increases with the concentration of ions.In cold water with the same physical and chemical conditions,graphite agglomerations show a larger apparent size distribution.The attachment performance between graphite and a bubble was gradually improved with the decrease of p H and with the increase of the concentration of ions.Under the same p H and ions concentration,attachment performance was improved in the presence of nanobubbles.In the last part of this dissertation,efficient flotation experiment for electrode materials based on nanobubbles was designed and verified.At the same flotation time,the combustible recovery with the method of temperature change is always higher than that with room temperature water and meanwhile the better flotation selectivity can be obtained in the former.In room temperature water,the combustible recovery increases from about 34%to 66%while it increases from about 44%to 74%as flotation time increases from 2 min to 8 min.In flotation with the pressured water,the combustible recovery increases with flotation time and is higher than that in flotation with room temperature water.The combustible recovery in pressured water with 3 Bar from 41%to 79%,increased by 7-13%compared with the case of natural water.The combustible recovery increases with the decrease of p H of slurry.In acidic environment the combustible recovery and flotation selectivity are improved in the presence of nanobubbles and in alkaline environment flotation selectivity are improved in the presence of nanobubbles.The combustible recovery increases in the presence of ions.Compared with the flotation performed in room temperature water,combustible recovery increases in the flotation with temperature change and the improvement effect of nanobubbles on flotation performance is more obvious with a low concentration of ions.Flotation selectivity is improved in a slurry with a low concentration of ions while is deteriorated with a high concentration of ions.There have 110 pictures,3 tables and 170 references in this dissertation.