1. State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China
2. School of Applied Chemistry and Engineering, University of Science and Technology of China, Hefei 230026, P. R. China
3. Department of Industrial Chemistry, Addis Ababa Science and Technology University, P. O. Box, 16417, Addis Ababa, Ethiopia