| Lithium ion batteries(LIBs)are widely used in energy storage,green transportation and portable devices,etc.In recent years,with the rapid increase in the production of LIBs,the disposal of waste LIBs has become an urgent problem.The waste LIBs contain a large number of valuable metal resources such as Li,Co,Ni and Mn,which have great recycling value.In the research field of LIBs recycling,traditional hydrometallurgical processes depend on acid,alkali in high concentration or organic acid with high price.Studies on the mechanism of the enhanced leaching process based on mechanochemical technology are still scarce,and comprehensive understanding is lacked in aspects such as the orderly crystal dissociation by enhanced techniques,the chemical bonds rupture and restruction,chemical reaction paths of raw materials,multi-phase transfer in mild leaching process,etc.These situations become the bottleneck problems synchronously efficient recovery of valuable metals in ternary cathode materials,industrial cathode materials mixtures.The ternary cathode material(LNCM)were taken as the research object in this thesis,and the advanced oxidation process(AOP)was applied in this research field.The cathode material-ammonium persulfate-sucrose wet milling system was built on the basement of zero-valent iron.The strong eletrophilicity of free radicals generated from the persulfate activation was utilized to result in the crystal dissociation and efficient delamination of metal atoms.Finally,valuable metals in the leachate were efficiently recovered by stepwise recycling,and the corresponding analysis of the economic and environmental benefits was discussed.In general,the contents of this thesis include the following three aspects.(1)Optimization of ball grinding and leaching conditionsBy single factor experiment and Eh-p H predominance area diagram analysis,the effects of leaching conditions(including the leaching time,leaching,p H and temperature)on the valuable metal leaching rate was explored.The leaching kinetics conform to the surface chemical reaction-controlled shrinking core model.Then on the basis of the optimal leaching conditions,the effects of ball-milling conditions(including rotating speed of ball mill,ball milling time,mass ratio)on valuable metal leaching rate was explored.Finally,the response surface methodology was used to analyze two-factor interaction,and an overall optimization was carried out.It was found that the influences of rotating speed,milling time and NHS/LNCM mass ratio on leaching rates of Li,Co,Ni,Mn were significant,and the influence of Suc/LNCM mass ratio on leaching rates of Li,Co,Ni,Mn was less significant.The optimized leaching conditions were as follows:the leaching temperature was 25°C,the leaching time was 15 min,the leaching p H was 2.0,and the solid-liquid ratio was 25 g/L.The optimized ball grinding conditions were as follows:the rotate speed was 800 rpm,the milling time was 3 h,NHS/LNCM=2.22,Suc/LNCM=1.67,and the ball material ratio was 20.Under the above milling and leaching conditions,the actual leaching rates of Li,Co,Ni and Mn were98.13%,95.85%,98.46%and 99.09%,respectively.(2)Study on mechanism of mechanochemically enhanced mild leaching processBy analyzing the XRD,FT-IR and XPS patterns of raw materials,ball-milling products and leaching residue,the transformation paths of elements were judged preliminary.It was combined with the experiments of PDS activation,free radicals quenching experiment,Eh-p H predominance area diagram analysis and AIMD simulation calculation,and the reaction mechanism of ball-milling in this study was discussed as follows:ammonium persulfate was activated by zero-valent iron and generating the sulfate free radicals(SO4-·),it was combined with the ball-milling with high strength mechanical force and the cathode material crystal structure was dissociated.The reduction of sucrose can effectively reduce the redox potential of the system and made Co,Ni and Mn transform to the soluble phase in the low-valence state.During the ball-milling reaction,the persulfate ion was converted to sulfate ion,the valuable metal was converted from metal oxide to corresponding soluble sulfate,and the sucrose was converted to carboxylate.The above reaction mechanisms of ball-milling jointly promoted the efficient leaching of valuable metal Li,Co,Ni and Mn phases under mild conditions(25°C,p H=2.0).(3)Economic and environmental benefit analysis of valuable metal separation and recoveryThrough the combination of precipitation,complexation,concentration,crystallization and other processes,the stepwise removal of impurity elements Fe and Al in the leaching solution and the efficient separation of valuable metals Li,Co,Ni and Mn were realized.More than 99%removal rate of the impurities Fe,Al can be achieved by adjusting p H to 5.3.The recovery rate of Mn was 99.17%by potassium permanganate oxidation method.The recovery rate of Ni was 98.69%by the method of dimethylglyoxime precipitation.By cobalt hydroxide precipitation method,the p H of the solution was adjusted to 9.0,and the recovery rate of Co was 99.52%.The recovery rate of Li was 98.5%at 90°C by lithium phosphate precipitation.The total recovery rates of Li,Co,Ni and Mn were 96.65%,91.25%,94.63%and 97.46%,respectively.Through the calculation of process cost and product income,it is found that the net economic income of recovery of each ton of LNCM anode material is 24,625 RMB/t LNCM,which shows the huge economic and environmental benefits of this process. |
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