1. Umland JB, Bellama JM (1999) General chemistry, 3rd edn. Brooks Cole Publishing Company, Pacific Grove
2. Whitten KW, Gailey KD, Davis RE (1988) General chemistry, 3rd edn. Saunders College Publishing Company, New York
3. Silberberg HS (2000) Chemistry: the molecular nature of matter and change, 2nd edn. McGraw Hill, New York
4. Barbalace K (2015) Periodic table of elements.
http://environmentalchemistry.com/
. Accessed 3 Dec 2015
5. European Parliament (2015) Recovery of rare earths from electronic wastes: an opportunity