There are 17 rare earth elements, namely lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, ymium, erbium, thulium, ytterbium, lutetium, scandium and yttrium. Rare earth elements have optical, electromagnetic and other physical characteristics. When rare earth elements are added into other materials, the quality and performance of products can be greatly improved, and the effect of "the Midas touch turns to gold" is known as the "vitamin" of modern industry. A common metaphor is that if oil is the blood of industry, rare earths are its vitamins. Rare earth minerals can be widely used in atomic energy, glass, petroleum, textile, boot leather, dyeing, petrochemical, optics, laser, hydrogen storage, display panel, magnetic materials and other industries. Nowadays the global demand for rare earth resources is huge for military, science, technology and people's livelihood.
Gravity separation of rare earth minerals is carried out by using the density difference between rare earth minerals and gangue minerals. For example, coastal placer mineral containing rare earth often adopt gravity separation and rare earth vein ore always use gravity separation for pre-concentration.