| The excellent performance of lithium iron phosphate battery meets the requirements of new energy electric vehicles,and its market capacity increases rapidly with the development of new energy vehicles.The life cycle of lithium ion batteries under normal working conditions is about 4-6 years.Therefore,in the near future,there will be a large number of waste ferrous lithium phosphate batteries need to be dealt with.Aiming at the deficiency of excessive consumption of acid,alkali and high temperature energy consumption in the current waste battery recovery technology,the technological route of selective leaching of valuable metal lithium by chemical equivalent sulfuric acid and hydrogen peroxide system was put forward for the first time in this paper.Iron and phosphate were combined to form iron phosphate precipitates and then separated by filtration.Finally,recovering lithium from leaching solution is achieved by chemical precipitation.In addition,the mechanism and influencing factors of leaching process and precipitation process have been studied in detail.At first,positive electrode and negative electrode were obtained after disassembly of the fully discharged iron phosphate lithium-ion battery.The separation of aluminum foil and positive active material in positive electrode was achieved by ultrasonic alkali leaching,and the aluminum foil was recovered in the form of sheets.The negative electrode sheet was separated from graphite by a series of process of crushing,sieving and air separation.The results show that when the particle size of the material is larger than 0.25mm,the grade of copper is 91.6%,which can be directly recovered as copper powder.And the grade of graphite powder is 96,6%when the particle size is smaller than 0.106mm.Then the copper is separated by air separation when the particle size is in the range of 0.106-0.25mm.The recovery of copper is 87.2%and the grade is 84.6%when the gas flow rate is 0.9 m/s.The graphite powder collected is characterized by XRD and SEM after acid washing(removal of residual lithium in graphite powder)and drying.The results show that the purity of graphite is high purity and can be reused.Then the positive electrode active material is selectively leached in a solution with proper amount of sulfuric acid and hydrogen peroxide.The effect of hydrogen peroxide is to oxidize Fe2+ in lithium ferrous phosphate to Fe3+and accelerate the reaction rate.By adjusting the pH of the reaction end point,PO43-in lithium iron phosphate can be combined with Fe3+ to form FePO4 precipitate.The optimum conditions are as follows:the molar ratio of H2SO4/Li is 0.55、60℃,the molar ratio of H2O2/Li is 2.36,the concentration of sulfuric acid is 0.3mol/1,the reaction time is 100 min.The leaching rates of llithium,iron,phosphorus under the optimum conditions are 96.84%,0.00302%and 1.975%,respectively.The iron phosphate after drying was analyzed by XRD,SEM and particle size.It showed that its purity was very high and its crystal shape was complete.Finally,the lithium containing solution was purified and concentrated,and the lithium was recovered by adding trisodium phosphate into the solution.The optimum process conditions are as follows:reaction time of 150 min,reaction temperature of 80℃,the stirring speed of 200rpm,the concentration of Li20O8g/L,and the molar ratio of Li/PO43-3:1.The precipitation rate of lithium reached 95.8%.The analysis of XRD,SEM and particle size about the product showed that the purity of lithium phosphate was high and the crystal shape was relatively complete.The product after secondary treatment could meet the standard of industrial grade products.In this paper,an efficient and new green technical route for the comprehensive recovery and utilization of waste phosphor lithium batteries is initiated,which provides a reliable theoretical guidance for the optimization of the existing technology by using chemical equivalent sulfuric acid and hydrogen peroxide to extract lithium from waste lithium phosphate and convert it to high value lithium phosphate. |
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