| The grade of valuable metals contained in waste lithium-ion batteries is much higher than that of metal ore.Therefore,in recent years,it has been a research feature in the field of solid waste recycling.However,since a part of organic matter is added as a conductive agent and binder during the manufacturing process of lithium-ion batteries,the presence of these organic matter not only hinders the separation of the electrode active material and the current collector,but also forms an organic film that prevents the metal elements from being in the form of ions.Dissolve into the solution.In this paper,spent ternary lithium battery(model 18650,cathode material NCM523)is used as the main research object to conduct in-situ thermal reduction mechanism research and optimal parameter exploration of the material.On this basis,after the cathode and anode sheets are mixed and pyrolyzed,the efficient separation and recovery of all components is realized according to the difference of the physical and chemical properties of the materials.The feasibility of the reduction reaction between the organic matter in the electrode material and the electrode active material shows that the surface organic matter will burn and decompose directly during thermal reduction under air conditions.After the heat treatment in a nitrogen atmosphere,the cathode material and the organic matter undergo a reduction reaction.After removing the binder,the cathode material is mixed with the anode material and pyrolysis analysis shows that the anode active material and the anode binder will not react with the cathode material at this temperature.Using TG and TG-G-MS analysis results,it can be seen that the cathode material is mainly divided into three pyrolysis stages during the pyrolysis process.The temperature range of the first weight loss stage is 30-150? and the weight loss rate is 0.63%.The temperature range of the second weight loss stage is 150-360? and the weight loss rate is 1.37%.The pyrolysis products produced in the first two stages are mainly some esters.Class compound.The temperature range of the third weight loss stage is 360-600?,and the weight loss rate is 1.60%.The substances produced by pyrolysis in this stage are mainly fluorine-containing compounds.Based on the above analysis,it can be seen that during the pyrolysis process of the cathode material,the surface electrolyte is heated and volatilized.As the temperature rises,the electrolyte inside the electrode material is further decomposed by heat.When the temperature reaches 460?,the organic binder PVDF begins to decompose.The Frideman differential method was used to analyze the pyrolysis kinetics of the cathode material during thermal reduction.The activation energy change of the cathode material in the pyrolysis process is divided into three stages.With the increase of the conversion rate,the average activation energy of each stage is 117.53 KJ/mol,169.68 KJ/mol,and 196.95 KJ/mol,respectively.The law of activation energy change is consistent with the law of pyrolysis weight loss.Under anaerobic conditions,the effects of pyrolysis temperature,temperature retention time,and heating rate on the thermal reduction effect of cathode materials were explored.The thermally reduced cathode material was leached at H2SO4 concentration of 4 mol/1,leaching temperature of 85?,stirring speed of 300 rpm,and liquid-to-solid ratio of 10 ml-g-1.XRD,XPS,ICP-MS were used to analyze the changes in phase,valence size and content,and metal ion leaching efficiency of the thermally reduced cathode material under various parameters.When the temperature is maintained for the same time,increasing the temperature level can accelerate the process of the thermal reduction reaction.When the pyrolysis temperature reaches a certain level,the temperature holding time has a decisive effect on the thermal reduction effect.As the temperature retention time increases,the reduction reaction becomes more intense,and the element tends to be in a stable state of low valence.Under the optimal pyrolysis temperature and temperature retention time,the change of the heating rate has a greater impact on the weight loss behavior of the organic matter during the thermal reduction process.The effect on the improvement of leaching efficiency is limited.The best thermal reduction parameters of the cathode material are the pyrolysis temperature of 600?,the temperature retention time of 120min,and the heating rate of 25?/min.Under these conditions,the average leaching efficiencies of Li,Ni,Co,and Mn are 99.03%?99.23%?99.30%?98.64%,respectively.Under the best pyrolysis parameters of the cathode material,the positive and negative plates are mixed and pyrolyzed and then crushed and sieved.The combined process of sieving-magnetic separation-leaching-chemical precipitation is proposed to realize the full-component recovery process of the valuable components in the anode and cathode sheets.The magnetic rod with a magnetic flux of 6000GS is used for magnetic separation of particles above 0.1mm,and the recovery rate of copper foil is above 99%.After the magnetic substance is mixed with the-0.1mm material,it is subjected to water immersion(25?,liquid-solid ratio 30ml/g,stirring speed 300rpm,leaching time 60min)to obtain Li2CO3 product,and the recovery rate of lithium element reaches 99.67%.After drying the filtrate after water immersion,use alkaline leaching(NaOH concentration 2mol/L,temperature 50?,liquid-solid ratio l0ml/g,stirring speed 300rpm,leaching time 60min)and then use hydrochloric acid solution to remove the partial aluminum in the filtrate The acid radical is converted into Al(OH)3 and precipitated to obtain Al(OH)3 product.The recovery rate of A1 element reaches 98.99%.After the alkali leaching filter is cleaned and dried,it is washed and dried with acid leaching(H2SO4 concentration 4mol/L,temperature 85?,liquid-solid ratio 10ml/g,stirring speed 300rpm,leaching time 60min)and then the filter is washed and dried to obtain graphite product.Almost all graphite recovery has been achieved.The leaching solution after acid leaching is in order with CoC2O4 solution(concentration of 1.25mol/L,temperature of 55?,stirring speed of 100rpm,time of 60min),Na2CO3 solution(PH=7.5,concentration of 2mol/L,temperature of 30?,Stirring speed 100rpm,time 60min),C4H8N2O2 solution(PH=9.0,concentration 0.5mol/L,temperature 30?,stirring speed 100rpm,precipitation time 60mi)as precipitating agents to form CoC2O4·2H2O,Co2+?Mn2+and Ni2+respectively MnCO3,Ni(C4H6N2O2)2.The final precipitation recovery rates of Ni,Co,and Mn reached 98.37%,97.56%,and 99.87%,respectively.This paper has 30 pictures,12 tables,and 82 references. |
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