1. U.S. Department of Energy. Critical materials strategy, DOE/PI-0009; December 2011.
2. Humphries M. Rare earth elements: The global supply chain; December 16, 2013.
3. European Commission. Report on critical raw materials for The EU; May 2014.
4. Mineral commodity summaries 2016;U.S. Geological Survey,2016
5. Recycling of rare earths: a critical review;Binnemans;J Clean Prod,2013