Rare earth elements are usually divided into two groups:
1) light rare earths (also known as cerium group): lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium and gadolinium.
2) Heavy rare earths (also known as yttrium group): terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium.
The difference between cerium group and yttrium group is that the rare earth mixture obtained by mineral separation is often named because of the high proportion of cerium or yttrium.
Diffuse rare earth
First of all, a prominent family
Lanthanide elements (Ln) occupy a space in the periodic table, but there are 15 elements crowded together. Their atomic numbers range from 57 to 7 1. They are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd) and osmium. Adding scandium (Sc) and yttrium (Y) belonging to Ⅲ B group, the atomic numbers are 2 1 and 39 respectively. This 17 element is collectively called rare earth (re). Rare earths are usually divided into two groups. Seven elements from lanthanum to europium are light rare earths, and eight elements from gadolinium to lutetium are heavy rare earths. According to the needs of rare earth separation process, it can also be divided into three groups: light, medium and heavy.
They look like twin brothers and sisters. That is to say, the electronic arrangement of the outermost two layers of rare earth atoms is the same, so many chemical properties are very similar, and it is difficult to separate them by simple chemical methods, so that it took chemists and mineralogists 153 years to identify them one by one (yttrium was first discovered in 1794, and Cowell and Malinschi discovered1from lanthanide elements by ion exchange method. Because the internal electronic structure and atomic number of rare earth elements are different, they are different elements, so each member of rare earth has different temper and characteristics. They all have extraordinary skills and show their magical power in all fields of the national economy. Especially, by studying the unique and rich electronic energy levels of rare earth elements and developing functional new materials and devices with their excellent optical, magnetic, electrical and thermal properties, it is predicted that the contribution of rare earth family in the six new technical fields of information, biology, new materials, new energy, space and ocean in the 2 1 century will be outstanding.
Second, rare earths are not rare.
The origin of the name "rare earth" is a historical misunderstanding. /kloc-in the 0/8th century, it was found that there were not many minerals as raw materials for rare earth industry, and the independent minerals were few and scattered, which caused the illusion of scarcity. Their oxides are similar to soil oxides in nature and composition and insoluble in water, so they are named "rare earth". In fact, the content of rare earth in the earth's crust is not uncommon. Table 1 lists the abundance of rare earth elements in the crust, some of which are more than some common elements. For example, cerium is higher than tin, yttrium and lead are higher, and even rare thulium is more than silver and mercury.
China is a big country of rare earths, rich in rare earth resources and complete in light, medium and heavy rare earths. Both reserves and output rank first in the world. The dosage is only less than that of the United States. It produces nearly 1000 specifications and more than 400 products, and it is the main supplier of rare earth products in the world, accounting for 70-80% of the world market.
Third, the magical rare earth.
The magical function of rare earth is manifested in two aspects: first, rare earth members can be found in all fields of the national economy, creating huge economic and social benefits for the country every year. Second, with the progress of science and technology, it is playing an increasingly magical role.
1. industrial "vitamins"
Rare earth can purify inclusions and microalloying in molten steel and modified steel. Therefore, the strength, toughness, wear resistance and oxidation resistance of steel can be greatly improved by adding trace rare earth into steel. Known as industrial "vitamins". The service life of rare earth niobium heavy rail steel jointly developed by Baotou Steel, Steel Research Institute and Iron Research Institute has been increased by more than 50%, and the economic benefit is very obvious. Adding trace scandium and zirconium to aluminum alloy has high strength and toughness, good wear resistance and weldability. It is a new aluminum alloy material in aerospace, shipbuilding, nuclear energy and other fields. Rare earth is applied to aluminum wires and cables, which improves the conductivity and strength. It has become a standard product of the State Grid and has been successfully applied to 500 kV EHV transmission lines. The annual production capacity of aluminum wires and cables with rare earths in China exceeds 400,000 tons, and it can save 4 billion kWh of electricity every year after being put into use.
2. Rare earth catalyst
Using aluminosilicate molecules containing rare earth as cracking catalyst has reached 98% in China's oil refining industry. The catalytic cracking capacity is improved by 20-30%. The annual output of light oil is 3 million tons, and the direct economic benefit is more than 6 billion yuan. Automobile exhaust contains a lot of harmful substances, such as carbon monoxide and nitrogen oxides. It is converted into harmless carbon monoxide by using precious metal as catalyst.
3. Agricultural "vitamins" and new rare earth agricultural technologies
A great deal of research and demonstration by scientific and technological workers in China show that rational application of trace rare earths (mainly La and ce) can promote crops to take root and sprout, increase chlorophyll, promote crops to absorb nitrogen, phosphorus, potassium and calcium, and increase dry matter accumulation, thus increasing yield and improving quality. After 30 years, the application of rare earth has been extended to agriculture, animal husbandry and forestry.
Improving the utilization rate of sunlight is a good way to improve the quality and quantity of agricultural products. It is reported that the polynuclear organic complex of europium is added to agricultural plastic film as a sunlight conversion agent. The ultraviolet rays harmful to plants in the light are successfully converted into red light needed by plant photosynthesis, which promotes the growth of plants. The experiment was carried out with watermelons, tomatoes and strawberries that people like to eat. As a result, sugar increased, melons and fruits became sweeter, and the content of vitamin C also increased. The average yield increased by 10%, and the economic benefit increased by about 12%. In particular, it can promote the early maturity of crops and significantly improve the early yield of crops.
4. Application of rare earth in high-tech field
With the progress of science and technology and the development of high-tech testing instruments and methods, the development and application of new rare earth materials and devices are accelerating. The research and application of rare earth luminescent materials have become supporting materials in the fields of information display, lighting sources, photoelectric devices and so on, making our lives rich and colorful. For example, rare earth energy-saving lamps have high light efficiency, good light color and long service life. Compared with ordinary incandescent lamps, it can save electricity by 75-80%. Rare earth is an ideal luminescent material for color TV. Our products have reached the international level, and 40% are exported. In the future, it may enter the high-definition and wall-mounted large-screen color TVs of ordinary people's homes, and may also choose rare earth phosphors as display materials. The application of rare earth-containing fluorescent materials in solar energy also shows magic. The luminescent material (commonly known as noctilucent powder) developed in recent years can emit light in the dark for more than 12 hours without external power supply after absorbing and storing sunlight, and can be used as a symbol of dual-use for military and civilian purposes. Due to the development of information, communication, atomic energy, electronics industry and space technology in the past 30 years, rare earth oxides have become an important component of optical functional glasses such as optical glass, laser glass, optical fiber, infrared glass and radiation-resistant glass.
Nickel-metal hydride batteries containing rare earth have been used as nickel-cadmium batteries that pollute the environment, and are widely used in portable appliances such as mobile phones, audio equipment and notebook computers. The future goal is electric vehicles, which can completely solve the problem of automobile exhaust pollution.
The permanent magnet material containing rare earth is the best, and China has entered the third generation of rare earth permanent magnet-NdFeB magnet. Widely used in computer communication, automation, audio and video, electromechanical, instrumentation, aerospace, medical care and other fields. Magnetic refrigeration is a brand-new refrigeration technology, which uses solid magnetic materials without freon and compressor, and has two advantages: high efficiency, energy saving and no environmental pollution. Rare earth element gadolinium (Gd) is the main component of room temperature magnetic refrigeration materials. The key components such as permanent magnet and permanent magnet motor are all related to rare earth, so room temperature magnetic refrigeration technology is a typical application of rare earth high technology, and China is in the technical research stage. Others, such as magneto-optical storage materials, magnetostrictive materials, giant magnetoresistance materials, rare earth high-temperature superconducting materials, etc., are waiting for people to continue to explore the magical role of rare earths in order to change the current low proportion of rare earth applications in high-tech fields in China. Turning resource advantages into economic and technological advantages, China will be not only a rare earth power, but also a rare earth power!