Rare earth is the general term for the lanthanide elements, scandium and yttrium in the periodic table of 17 metal elements. There are 250 kinds of rare earth mines in nature.
The first discovery of rare earths was the Finnish chemist John Gadolin (John Gadolin). In 1794, he separated the first rare earth “element” (yttrium soil, or Y2O3) from a heavy ore that looked like asphalt.
Because few rare earth minerals were discovered in the 18th century, only a small amount of water-insoluble oxides could be produced by chemical methods at that time. Historically, these oxides were customarily called “soil”, hence the name rare earth.
According to the structure and physicochemical properties of the atomic electron layer of rare earth elements, as well as their symbiosis in minerals and the characteristics that different ionic radii can produce different properties, the 17 rare earth elements are usually divided into two groups:
Light rare earths include: lanthanum, cerium, praseodymium, neodymium, promethium, samarium, and europium.
Heavy rare earths include: gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, and yttrium.
Classified by extraction separation:
Light rare earth (P204 weak acidity extraction)-lanthanum, cerium, praseodymium, neodymium;
Middle rare earth (P204 low acidity extraction)-samarium, europium, gadolinium, terbium and dysprosium;
Heavy rare earth (P204 acidity extraction)-holmium, erbium, thulium, ytterbium, lutetium, yttrium.
Physical and chemical properties
One is the lack of sulfides and sulfates (only a few), which shows that rare earth elements have oxygen affinity;
The second is that rare earth silicates are mainly island-like, without layered, frame-like and chain-like structures;
Third, some rare earth minerals (especially complex oxides and silicates) present an amorphous state;
The fourth is the distribution of rare earth minerals. Magmatic rocks and pegmatites are mainly silicates and oxides, and hydrothermal deposits and weathered crust deposits are mainly fluorocarbonates and phosphates. Most of the yttrium-rich minerals are found in granite rocks and related pegmatite and gas-water hydrothermal deposits;
Fifth, rare earth elements often coexist in the same mineral due to their similar atomic structure, chemical and crystal chemical properties. That is, rare earth elements of the cerium group and yttrium group often coexist in the same mineral, but these elements do not coexist in equal amounts. The minerals are mainly rare earths containing cerium, and some minerals are mainly yttrium.
Among the more than 250 kinds of rare earth minerals and minerals containing rare earth elements that have been discovered, there are only more than 10 industrial minerals that are suitable for current processing conditions.