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 thi...