Processing of Li-ion battery active material through hydrometallurgy - Study of ferrous iron reductive leaching catalysed by metallic copper (Université de Liège)

Abstract

Ever-growing electrification rates and secondary battery-powered appliances development together with increased environmental concerns and sustainable exhaustible resources management are leading to improved battery waste handling. This is specifically the case of Li-ion Batteries (LIBs) which great energy density embodied in relatively light packages, charge and lasting perfor-mances have turned them into partners of choice. Though conventional recycling routes may involve pyrometallurgical treatments or classical sulfuric acid-based hydrometallurgical processing enhanced with hydrogen peroxide to recover the major contained metals (Al, Co, Cu, Fe, Li, Mn and Ni), alternative routes are increasingly suggested. This work contributes to the diversification of the reducing agent nature required for dissolving the metals from sorted, discharged, crushed and sieved LIBs of mixed cathode chemistries (~ 60%wt LiCoO2, 20%wt. LiMnO2 and 20%wt. Li(NixMnyCoz)O2) identified by microscopical studies. A reduction mechanism of the transition metals involving ferrous ions oxidation followed by Fe(II) regeneration by metallic copper through electron release is considered. It is found that not only does Cu play a role in the reduction of the black mass but also Al. Moreover, the reduction mechanisms of copper (ferric to ferrous ions transformation) seem to be more straightforward than aluminium’s (hydrogen intermediary and potential Cu cementation). The kinetics points in favour of Fe(II)-loaded systems enhancing the metals dissolution rate and Cu reductive action. All systems are made comparable through the introduction of a Co-Mole Equivalent (CME) concept that suggests an ideal stoichiometric ratio metal-to-reduce:reductant:acid of 1:1:2 ([CME:CME:molacid]). Experiments reveal a practical efficiency of the reductants lower than 100%, with only 38 to 58% of the theoretical reducing power used for reducing purposes. The missing fraction is attributed to reducer consumption by side reactions and/or transition metals (TMs) oxidation states underestimation. With up to 97% of TMs recovery without additional re-grinding nor binder vaporisation treatment, liberation and binder concerns are deemed negligible in the present investigation.