| Recycling used lithium-ion batteries,especially cathode materials,not only can recover the valuable metals in them and realize the secondary use of valuable metals,but also can avoid the pollution of the environment from the waste lithium-ion battery stockpiles.The traditional recycling process still has the disadvantages of environmental pollution and high energy consumption,and there is an urgent need for a green recycling method to recover lithium cobaltate cathode material.In this paper,a new ternary deep eutectic solvent composed of choline chloride,ethylene glycol and benzoic acid is designed to leach valuable metals from lithium cobaltate,a waste lithium-ion battery cathode material,effectively by taking advantage of the excellent metal solubility and green environmental protection of deep eutectic solvent.Details of the study are as follows.1.The viscosity of the ternary deep eutectic solvent decreases with the increase of temperature,and the conductivity increases with the increase of temperature,and the two values are inversely related,and the leaching rate of the ternary deep eutectic solvent for cobalt is high when the viscosity is small and the conductivity is large.The effect of each factor on the leaching rate of cobalt ions was investigated by single-factor experiments.2.Based on the single-factor experiments,the leaching process was optimized using the response surface method,and the results obtained were that temperature,time and the molar ratio of benzoic acid had significant effects on the leaching of cobalt by ternary deep eutectic solvent,while the stirring rate had no significant effect.The F-value of the regression equation model was 44.69 and the signal-to-noise ratio was 23.2283,which indicated that the designed experiment and the obtained regression equation were reasonable.The optimal solutions obtained after optimization were leaching temperature of 170°C,leaching time of 3h,and molar ratio of 0.4 accounted for by benzoic acid,and the leaching rate of cobalt ions obtained was 99.95% after three validation experiments.Finally,the leaching mechanism was analyzed by leaching kinetics,and it was determined that the cobalt ions were controlled by the diffusion of the solid product layer during the leaching process with an apparent activation energy of 77.219 k J/mol.The composition of the deep eutectic solvent and the feasibility of recycling were analyzed by infrared.3.The co-precipitation method was used to recover cobalt ions from the leachate,and oxalic acid was finally selected as the precipitant by comparing the recovery rates of carbonate and oxalate for cobalt ions in the leachate.Then the effect of precipitation process on the precipitation rate of cobalt ions was investigated,and the highest recovery of cobalt was 92.14% under the conditions of temperature of 25℃,mode of stirring and time of 10 minutes.Finally,the effect of calcination process on the precipitated cobalt oxalate dihydrate was analyzed,and the best morphology of the calcination product,cobalt tetraoxide,and the highest recovery of 98.79% were obtained at a calcination temperature of 400°C and a calcination time of 8h using SEM and XRD plots.Finally,the recovery of cobalt ions reached 91.03% using the co-precipitation method under the optimal conditions. |
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