Recovery of Rare Earth Oxide from Waste NiMH Batteries by Simple Wet Chemical Valorization Process

Abstract

Nickel metal hydride (NiMH) batteries contain a significant amount of rare earth metals (REMs) such as Ce, La, and Nd, which are critical to the supply chain. Recovery of these metals from waste NiMH batteries can be a potential secondary resource for REMs. In our current REM recovery process, REM oxide from waste NiMH batteries was recovered by a simple wet chemical valorization process. The process followed the chemical metallurgy process to recover REM oxides and included the following stages: (1) H2SO4 leaching; (2) selective separation of REM as sulfate salt from Ni/Co sulfate solution; (3) metathesis purification reaction process for the conversion REM sulfate to REM carbonate; and (4) recovery of REM oxide from REM carbonate by heat treatment. Through H2SO4 leaching optimization, almost all the metal from the electrode active material of waste NiMH batteries was leached out. From the filtered leach liquor managing pH (at pH 1.8) with 10 M NaOH, REM was precipitated as hydrated NaREE(SO4)2·H2O, which was then further valorized through the metathesis reaction process. From NaREE(SO4)2·H2O through carbocation, REM was purified as hydrated (REM)2CO3·H2O precipitate. From (REM)2CO3·H2O through calcination at 800 °C, (REM)2O3 could be recovered.

Keywords

• spent nimh batteries
• circular economy
• rare earths
• valorization