Rare Earth Resources and Related Industries in Japan

The periodic table of the elements, shown in Table 1, highlights 17 elements comprising Scanndium, Yttrium and 15 elements known as “lanthanoids”1. The elements are lined up according to the atomic number displayed horizontally and the same type of electrons in the outermost shell vertically. The electron number and type of each element gives the physical and chemical properties2. It can be said that these elements called “rare earth elements” are similar to each other in some physical and chemical characters because the outermost electrons are the same1. Although there is no defined classification in rare earth, Table 2 shows common classifications of two methods. One is to classify into two categories and the other is into three categories. Solubility of potassium sulfate double salt into water is used in the case of three categories, e.g. not to solve; light rare earth, difficult to solve; middle rare earth, easy to solve; heavy rare earth3.