1. School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei 230026, P. R. China
2. State Key Laboratory of Rare Earth Resources Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China
3. Baotou Research Institute of Rare Earths, No. 36 Huanghe Street, Rare-Earth
Development Zone, Baotou 014030, P. R. China