Synergistic Recovery of Valuable Metals from Spent Nickel–Metal Hydride Batteries and Lithium-Ion Batteries

Abstract

This research presents a sustainable approach for the simultaneous recycling of spent lithium-ion batteries (LIBs) and nickel–metal hydride batteries (NiMHs). First, dissolution of LIBs and NiMHs were found to be mutually co-promoted, resulting in above 98% extraction of Li, Co, Ni, and rare-earth elements (REEs) without the need for any oxidant or reductant additions. After leaching, >97% of REEs were recovered as a REEs-alkali double sulfate precipitate with the addition of NaOH and Na2SO4 precipitants. This REEs-free solution was then further processed to separate and recover the battery metals present: Mn, Co, Ni, and Li. The resultant residual solution (rich in NaOH and Na2SO4) was redirected to the REEs precipitation step, decreasing both the need of precipitants (e.g., Na2SO4) as well as the costs related to the treatment of the high-Na waste solution. Moreover, the Li remaining in the waste solution can be circulated back into the main process, resulting in an exceptionally high Li recovery of >93% in the form of high-purity Li3PO4 (99.95%). This is a marked improvement over the previously reported Li recovery levels of 60–80%. Overall, this newly developed process has considerable environmental and economic advantages for the recovery of valuable metals from mixed LIBs and NiMHs wastes.