1. 1) K. A. Gschneidner and L. Eyring: Handbook on the physics and chemistry of rare earths, (Elsevier, 2001).
2. 2) G. B. Haxel, J. B. Hedrick and G. J. Orris: Rare earth elements critical resources for high technology, (Reston (VA): United States Geological Survey, 2006).
3. 3) R. Chi and J. Tian: Weathered Crust Elution-Deposited Rare Earth Ores, (Nova Science Publishers, Inc., New York, 2008).
4. 4) J. Tian, Y. Jingqun, C. Ruan, R. Guohua, J. Mintao and O. Kexian: Hydrometallurgy 101 (2010) 166–170.
5. 5) E. Romera, F. Gonzalerz, A. Ballester, M. L. Blazquez and J. A. Munoz: Bioresource Technol. 98 (2007) 3344–3353.