Rare earth dissolution from polishing powder waste in H2O2-H2SO4 system: Condition optimization and leaching mechanism

Recycling high-grade rare earth polishing powder waste (REPPW) is crucial for protecting the environment and sustainable utilization of rare earth resources. Leaching REPPW in the eco-friendly H2O2-H2SO4 suffers from the lack of understanding of the leaching mechanism. Here, the leaching mechanism was investigated under the optimal leaching conditions, i.e., T = 353 K, L/S ratio = 40 mL/g, H2SO4 concentration = 4 mol/L and initial H2O2 concentration = 0.8 mol/L, by which leaching efficiency of Ce and La reached 99.3% and 99.1%, respectively. Furthermore, pseudo steady state kinetic analysis suggested a five-step leaching mechanism involving CeO2 hydroxylation, H2O2-CeO2 coordination, ≡CeIII−H2O2 deprotonation, ≡CeIV−HO2− reduction and ≡CeIII−HO2∗ protonation, which was verified by the agreement between experimental data and the proposed reaction model. This work proposes a leaching mechanism of REPPW and would help develop an effective and sustainable recycling process for rare earth secondary resources.