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.
Highlights
Owing to the strategic, economic, and industrial importance of rare earth metals (REMs), the EU has classified them as critical raw materials (CRMs)
A criticality assessment of metals based on economic importance and supply risk done in 2017 resulted in the EU considering heavy rare earth metals (HREMs), light rare earth metals (LREM), and Sc as CRMs [1,2]
The nickel metal hydride (NiMH) battery could be a secondary resource for REMs like Ce, La, and Nd, as it contains a significant amount of these elements
Summary
Economic, and industrial importance of rare earth metals (REMs), the EU has classified them as critical raw materials (CRMs). By efficiently recycling NiMH waste batteries, the REMs can be recovered and circulated in the industrial ecosystem This could simultaneously address issues like urban mining, environmental directive, and CRM supply chain challenges, and could secure the supply of these metals for industrial development. Yang et al reported a HCl leaching and oxalic acid precipitation route for the recovery of REM oxide by calcination [11]. Korkmaz et al reported a HCl acid leaching and oxalic acid precipitation route for the recovery of REM from waste NiMH batteries [18]. Oxide recovery by heat treatment.ofThe chemical metallurgy process, which has the following stages: (1) H2SO4 leaching; (2) separation the novelty this process is described. Mostly follow pyrometallurgical or pyrometallurgical-dominated processes, in contrast to our ii It is a simple acid leaching and precipitation process for the recovery of REMs. developed process which is hydrometallurical.
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