Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth Rare Earth In fact, this is just a misunderstanding left over from the 18th century. Several rare earth elements were discovered successively after 1787, but the corresponding mineral discoveries were few. Due to the limitations of science and technology at that time, people could only make some impure, earth-like oxides, so they left such a unique and interesting name for this group of elements.
According to the international union of pure and applied chemistry definition of rare earth elements, rare earth element is the third in the subgroup mendeleev periodic table of the atomic number from 57 to 71 15 lanthanides, namely, lanthanum, cerium (58), praseodymium (57) (59), nd (60), promethium (61), samarium (62), europium, gadolinium (64) (63), terbium, dysprosium (65), (66), holmium, erbium (68) (67), thulium (69), ytterbium (70), lutetium (71), coupled with its electronic structure and chemical properties of similar scandium (21) and yttrium (39), a total of 17 elements. In addition to scandium and promethium, the remaining 15 elements tend to co-exist.
According to some differences in physical and geochemical properties between rare earth elements and requirements of separation processes, scholars often divide rare earth elements into two groups: light group and heavy group, or light group, medium group and heavy group. The two groups were divided by gadolinium. Before gadolinium, 7 elements (lanthanum, dysprosium, cerium, praseodymium, neodymium, promethium, samarium and europium) were light rare earth elements, also known as cerium rare earth elements. Gadolinium and the following nine elements of terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and yttrium are known as heavy rare earth elements, also known as yttrium group rare earth elements. Although its atomic weight is only 89, yttrium is chemically closer to heavy rare earth elements because its ionic radius is within the ionic radius of other heavy rare earth elements. It also occurs in nature with other heavy rare earth elements. Therefore, it is classified as a group of heavy rare earths. There is no definite rule for the classification of three groups of rare earths: the insoluble cerium group, namely the light rare earth group, including lanthanum, cerium, neodymium and samarium; The microsoluble terbium group is the rare earth group, including europium, gadolinium, terbium and dysprosium. The more soluble yttrium group is the heavy rare earth group, including yttrium, holmium, erbium, thulium, ytterbium, lutetium. However, there is little difference in solubility between adjacent elements between groups. Currently, multiple extractive groups are used, such as two (2) ethyl-alkyl (phosphoric acid) (P204), which can be grouped between neodymium/samarium and then between gadolinium/terbium. We call lanthanum, cerium, praseodymium, neodymium light rare earth, samarium, europium, gadolinium medium rare earth, terbium, dysprosium, holmium, erbium, ytterbium, luteum and yttrium heavy rare earth.
The content of rare earth in the crust is not rare. The clark value of this group of elements is 0.0236%, among which the cerium group is 0.01592% and the yttrium group is 0.0077%. Than the common element copper (0.01%), zinc (0.005%), tin (0.004%), lead (0.0016%), nickel (0.008%), cobalt (0.003%), etc. This group of elements is not more soil, but a group of typical metallic elements, its activity is second only to alkali metals and alkali earth metals.
Table 1-1 abundance of rare earth elements in the crust
Rare earth elements in the periodic table of the position is very special, with 17 elements in the first Ⅲ B group, scandium, yttrium, lanthanum, respectively the fourth, five, six, and long cycle the first element of the transition elements in the series. Lanthanum is so similar to the next 14 that chemists have to put them in a lattice. No wonder they are treated as “isotopes”, though they are not really isotopes because of their different atomic Numbers. That is to say, they are very similar in nature, but not quite the same, which makes the separation of the elements difficult, but it also shows that it is possible to separate as long as the difference is made. On the other hand, their electron structure has an inner shell that is not fully filled, the 4f shell. Because of the different number of electrons in the 4f layer, each of these elements has a special personality, especially the optical and magnetic properties, like a piano with a full keyboard and a wide range of sounds.
Information, biology, new materials, new energy, space and oceans have been promoted by contemporary scientists as the six new science and technology groups. People attach great importance to rare earth, study rare earth, and develop rare earth elements, so as to give play to rare earth elements in these six science and technology groups. However, rare earth elements are still a group of elements not fully recognized by people, which requires great efforts to study and recognize them, so as to hold them and make them contribute more to human beings.