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

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.