Rare Earths 101
Rare Earths include the unique elemental suite known as the Rare Earth Elements (REE‘s) and a select group of specialty metals produced primarily for technology applications. Rare Earth Elements(‘REE‘) are non-toxic elements essential to obtaining a cleaner environment with reduced reliance on fossil fuels.
Rare Earth Elements are most simply defined as those chemical elements ranging in atomic numbers 57-71. These elements include Lanthanum, from which rare earth metals get their collective name ofLanthanides to Lutetium. For reasons of chemical similarity, an additional metal, Yttrium, is commonly found in rare earth metals deposits. Therefore, they are frequently referred to as Rare Earth Metals. Other collateral metals often found amongst REE deposits include Uranium,Beryllium, Niobium and Zirconium.
The Rare Earth Elements posses varying ionic radii, which produce different properties, therefore, have been broadly classified into two groups: Heavy Rare Earth Elements (HREE) and Light Rare Earth Elements (LREE).
Light REE‘s or the ceric sub-group made up of the first seven elements of the lanthanide series. They are as follows: Lanthanum (La, atomic number 57), Cerium (Ce, atomic number 58),Praseodymium (Pr, atomic number 59), Neodymium (Nd, atomic number 60) Promethium (Pm, atomic number 61) and Samarium (Sm, atomic number 62).
Heavy REE‘s, which typically have high value relative to other REE‘s, are the following higher atomic numbered elements from the lanthanide series: Europium (EU, atomic number 63), Gadolinium(Gd, atomic number 64), Terbium (TB, atomic number 65), Dysprosium (Dy, atomic number 66),Holmium (Ho, atomic number 67), Erbium (Er, atomic number 68), Thulium (Tm, atomic number 69), Ytterbium (Yb, atomic number 70) and Lutetium (Lu, atomic number 71).
Historically the term ‘rare earths’ has been applied to the lanthanide group of elements, which range from lanthanum (atomic number 57) to lutetium (atomic number 71), plus yttrium (atomic number 70), which has similar properties.
The rare earth elements do not fit well into the periodic table. Therefore they are usually separated from the main groupings. As mentioned above, the element yttrium is also considered to be a rare earth as it is chemically similar.
Here is a great article from National Geographic on Rare Earths http://ngm.nationalgeographic.com/2011/06/rare-earth-elements/folger-text