Rare Earth Element (REE) Classification
The rare earth elements (also referred to as rare earth metals) are include seventeen metals in the periodic table. This group contains elements of yttrium, scandium and 15 lanthanides. (Lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium).
Rare metals are classified into 2 groups based on their atomic weight. These are light rare earth elements (LREEs) and heavy rare earth elements (HREEs).
LREEs are known as the ‘series’ which is including lanthanum, cerium, praseodymium, neodymium, samarium, and europium elements. In case of HREEs are known as ‘yttric’ which is including gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium elements. The structure of scandium is significantly different from the structure of the other rare-earth elements. In this context, scandium and yttrium classified into the heavy element category. In addition to this, Sm, Eu, and Gd classified into the classified as medium rare earth elements by scientists.
An estimated 200 minerals known to contain rare earths constitute almost 95% of the world’s REE reserves. It is that there are six different ores mineral from industry productions which include bastnasite, monazite, xenotime, loparite, apatite, and ion-adsorption clays. Bastnasite(70–75% REO), monazite (55–60% REO), xenotime (55–60% REO ) and laterite clays are currently mined for rare earths.
Bastnasite as a fluorocarbonate, is the source of rare earths has included cerium, lanthanum, and yttrium. Mountain Pass in U.S.A, Bayan Obo in Mongolia and Shandong Mining in China is constituting almost 95 percent of the rare earths used in the world.
Laterite clays (called ion absorption clays) are mainly composed of silica, alumina, and iron oxide; This clay is most commonly found in China’s Jiangxi province.
Monazite as a phosphate, is the third most important mining resource of rare earths. Monazite contains a considerable amount of radioactive thorium dioxide (ThO2) compared to bastnasite, so it must be stored with special environmental procedures. This situation causes the process to be costly.
Loparite contains titanium, niobium, tantalum, lanthanide and yttrium in its structure and rare earth elements extracted from mining as by-products. This ore is found on the Kola Peninsula in Russia and Paraguay.
Xenotime is a phosphate mineral, beneficiated in the heavy lanthanides and yttrium contains low quantity of the radioactive components Diuranium octoxide and thorium dioxide. The main producer of xenotime is Malaysia and deposits are found Norway and Brazil.