Review of Recovery and Purification Processes of Rare Earth Elements from Nickel-Metal Hydride Spent Batteries

The concept of a circular economy for rare earth elements (REEs) is being developed. The circular economy involves optimising the lifecycle of products to achieve sustainable and efficient consumption. REEs are considered critical elements of high economic value. Considering limited rare earth reserves, secondary source REEs are very important to sustainable use. Spent nickel-metal hydride (Ni-MH) batteries are electronic waste containing valuable REEs. Ni-MH batteries that have reached their age limit, if thrown away, will become hazardous waste. Recycling Ni-MH battery waste efficiently enables REEs to be recovered and reused. The REE recovery process has challenges that must be considered such as efficiency, low REE concentration, environmental concerns and scalability, thus requiring the development of new, efficient recovery methods and processes for REE. Currently the hydrometallurgical method is preferred for REE recovery from Ni-MH batteries because it has high yields, low energy requirements, ease of separation from base metals and low greenhouse gas emissions. One such REE recovery using hydrochloric acid on a pilot scale yielded 91.6% lanthanum.