Synthesis of Ni and rare earth metal (La, Pr, and Nd) oxides from spent Ni–MH batteries by selective precipitation with formic acid an investigation of photoluminescence properties

A new chemical method was developed for the separation of Ni and rare earths (RE = La, Pr, and Nd) from spent Ni–MH batteries using formic acid as leaching and chelating agent. Ni and RE formates were characterized by FTIR, XRD, TG/DTG, SEM, EDS, and ICP-OES. The photoluminescence properties of RE formate were also investigated. When excited at 420, 421, 422, and 435 nm, RE formate exhibited narrow emission bands at 834, 837, 842, and 867 nm, respectively, attributed to 3H4 → 3P2 transitions of Pr3+ and dominated by the abnormally high intensity of the intraconfigurational transition 1D2 → 1G4. Thermal decomposition of Ni formate resulted in the formation of NiO and PrNiO3. The oxides obtained from RE formate consisted mainly of a crystalline phase of Pr2O3.