Reduction Ammonia Leaching And Recycling Valuable Metals From Spent Lithium-ion Batteries

Lithium-ion batteries are widely used in consumer electronics,electric vehicles,and energy storage equipment due to their advantages,such as high capacity,long life cycle and no memory effect.As many countries around the world have promulgated regulations prohibiting the sale of fuel vehicles,large-scale application of lithium-ion batteries will become inevitable.Taking into account many factors such as resources,environment and economy,more and more people pay attention to the recycling of spent lithium-ion batteries.The method of ammonia leaching is considered to be an economical and environment-friendly method that can be applied for the efficient leaching of spent lithium-ion batteries.However,the current research about reducing agents and buffer solutions in the ammonia leaching process lacks systematicity and it is difficult to carry out the resource utilization of valuable metal elements under the ammonia leaching system.Therefore,this study explored the differences between the leaching behaviors of valuable metal elements in the spent cathode material under different reducing agents and buffer solutions systems,then analyzed different mechanisms in the ammonia leaching process in detail,and found these results.Without the addition of buffer solution,the reducing agent could promote the leaching of metal elements and their promotion effect has the following order: ammonium sulfite>sodium sulfite?sodium thiosulfate?sodium phosphite.If some buffer solution was added,the leaching process of main metal elements(nickel,cobalt and lithium)would be promoted by reducing agents in the following order: sodium sulfite ? ammonium sulfite>sodium thiosulfate>sodium phosphite.The dissolution of aluminum was more easily affected by the buffer solution,and when there was no buffer solution,most of the aluminum element would be dissolved.When ammonium sulfite or some buffer solution was added,the dissolution process of the aluminum element would be inhibited.The buffer solution can significantly increase the dissolution efficiency of other metal elements except the aluminum element.Binary buffer solution has advantages over unary one,which might be because binary buffer solution can provide more suitable p H.Through the study of NH3-(NH4)2CO3-Na2SO3 selective ammonia leaching system,it was found that 79.1% of lithium,86.4% of cobalt and85.3% of nickel were leached out during the single-stage leaching process,and only1.45% of manganese was dissolved into the solution.Almost all the metals(98.4%for lithium,99.4% for cobalt and 97.3% for nickel)were dissolved during the multistage leaching process,and the manganese carbonate product with high purity(>99%)was simultaneously synthesized.The introduction of carbonate ions not onlyprovided the basis for the synthesis of manganese carbonate,but also greatly reduced the consumption of reducing agent.Through the reaction kinetic analysis,the leaching behaviors of lithium,cobalt and nickel under this system were mainly controlled by the surface chemistry reaction model,and the apparent activation energies of those elements were 48.58,49.84 and 48.96 k J/mol,respectively.