The recovery of rare earth elements (REE) including La, Nd and Ce from spent batteries is important issues to reuse scarce resources. Herein, we present a simple recovery process to obtain lanthanum oxide (La2O3) from spent Ni-MH batteries, and demonstrate the conversion mechanism from NaLa(SO4)2 · H2O to La2O3. This strategy requires the initial preparation of NaLa(SO4)2 · H2O and subsequent metathesis reaction with Na2CO3 at 70 o C. This metathesis reaction resulted in the crystalline lanthanum carbonate hydrate (La2(CO3)3 · xH2O) powder with plate-like morphology. On the basis of TGA result, the La2(CO3)3 · xH2O powder was calcined in air at three different temperatures, that is, 300 o C, 500 o C, and 1000 o C.
As the calcination temperature increased, the morphology of powder was changed; prism-like (NaLa(SO4)2 · H2O)→platelike (La2(CO3)3 · xH2O)→aggregated irregular shape (La2O3). Futhermore, XRD results indicated that the crystalline La2O3 could be synthesized after the metathesis reaction with Na2CO3, followed by heat-treatment at 1000 o C, along with a change of crystallographic structures; NaLa(SO4)2 · H2O→La2(CO3)3 · xH2O→La2O3.