Recovery of Rare Earth (i.e., La, Ce, Nd, and Pr) Oxides from End-of-Life Ni-MH Battery via Thermal Isolation

Abstract

In this study, rare earth elements (REEs, i.e., La, Ce, Nd, and Pr) were thermally isolated in oxide form, from Ni-metal hydride (Ni-MH) batteries via an oxidation–reduction process. The anode part of the batteries (metal hydride anode, MHA) (with chemical composition of 54 wt % Ni, 23.7 wt % La, 6.7 wt % Ce, 5.4 wt % Co, 3.6 wt % Nd, and 3.4 wt % Mn) sourced from e-waste was subjected to an oxidation process in air at 1000 °C for 60 min followed by reduction at 1550 °C for 90 min using waste developer kit (>99 wt % Fe) as a reducing agent. Oxides of nickel and cobalt were reduced and diffused into metallic iron, resulting in the formation of ferronickel alloy. In a separate process, pure hematite was mixed with the MHA as oxidizing agent, and the resulting mixture underwent a 90 min heat treatment at 1550 °C. Both processes resulted in a successful separation of Fe-based metal (ferronickel) and rare earth oxide (REO) phases. The mechanism of thermal isolation of REEs in both processes is explained in this paper. The distribution of elements between Fe-based metal and oxide phases was observed using energy-dispersive X-ray spectroscopy (EDS)/electron probe microanalysis (EPMA) elemental mapping. Oxide phase was rich in La, Ce, Nd, and Pr, and these elements did not remain in the metal phase. Iron and nickel were the main components of the metal phase.