1. R. Chi and D. Wang: Benefication and Extraction of Rare Earth Ore, Science Press, Beijing, 1996, pp. 305–21 (in Chinese).
2. X. Huang, Z. Long, and H. Li: J. Rare Earth, 2005, vol. 23 (1), pp. 1–4.
3. R. Chi and Z. Xu: Metall. Mater. Trans. B, 1999, vol. 30B, pp. 189–95.
4. Wei Zhen and Shumao Wang: Rare Earth, 1996, vol 17 (6), pp. 59–62 (in Chinese).
5. Tetsuya and Hoshino: J. Non-Crystalline Solids, 2001, vol. 283, pp. 129–36.