The rare earth elements (REEs) are a group of 17 chemical (metallic) elements which ap-pear in the periodic table. The group consists of 15 lanthanide elements along with yttrium and scandium (Table 1). They share many similar properties, which is why they occur together in geological deposits. Although commonly referred to as “rare,” they are really quite common; the reason they are perceived as rare is because it is not common to find them in commercially viable concentrations.
These metals are critical to advanced technology, ranging from smart phones to global positions system (GPS) receivers, medical devices and jet engines. They are critical in green, high-tech and defense industries (Fig.1 and 2). Although there have been increasing efforts to find alternative supplies, these efforts have been complicated by the pollution that rare earth mining and processing creates.