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Seventeen kinds of rare earth element is a general term of elements of scandium, yttrium, lanthanides, etc. in the Periodic Table Group â…¢B (RE represents common). The atomic number ranges from 21 (Sc), 39 (Y), 57 (La) to 71 (Lu). The characteristics of extranuclear electronic structures determine their chemical properties are similar. Rare earth element in gadolinium boundary, called light rare earth (cerium group rare earths), from gadolinium, terbium, dysprosium, holmium, erbium from lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, thulium, ytterbium, lutetium It is called heavy rare earth (or rare earth rare earth).
The discovery of rare earth elements was late. In 1787, Arrhenius of Sweden discovered the first ore near Stockholm. In 1947, the United States, JARIS (Marisky) and other uranium fission products were obtained. So far, I have experienced nearly 160 years. From the history of development and application of rare earths, it can be roughly divided into four stages: (1) 1787~1891 is the initial stage of development. During this period, people have conducted scientific investigations and understanding of rare earths, and they have not been used in industry. (2) 1891~1930 is the initial application stage. During this period, rare gas lamp is mainly used for coal incandescent mantles pyrophoric alloy, a carbon arc electrode. (3) 1930~1960 is a wide application stage. In the meantime, atomic energy research has driven the development of rare earth scientific research, mastered various properties and separation methods of rare earth elements, and established a special rare earth research center. (4) Since 1960, it has been the stage of rapid development of rare earth applications to breadth and depth. Due to the widespread use of rare earths in various sectors of the national economy, the production and consumption of rare earths has soared.
China has the most abundant rare earth resources in the world, but the rare earth industry is still a new industry developed after liberation. At the end of the 1950s, China produced all rare earth metals except strontium (made in 1972) and began industrial production in the early 1960s. Since 1978, due to carry out a wide range of rare earth ore beneficiation, smelting, separating, alloys, materials research work, and vigorously promote the use of rare earth work, China's rare earth production and consumption in rapidly increasing rise. China's rare earth concentrates and rare earth products have entered the international market.
First, the nature and use of rare earth
Rare earths are typical metal elements, and their metal reactivity is only a secondary alkali metal and an alkaline earth metal. The electronic layer structure and core structure of rare earth elements determine the properties of rare earth elements and their compounds, and many unique properties of rare earths determine their application. The relationship between the structure and properties of rare earths is shown in Table 1. The application of rare earth began in the late 19th century and has undergone more than 60 years of development. Due to the complicated extraction process, the product is expensive, the development speed is slow, and the consumption is not large. After the 1950s, the rare earth separation technology has developed rapidly. The modern ion exchange method and solvent extraction method have replaced the classical fractional crystallization and step precipitation methods, and obtained various pure single rare earth products in industrial production. This laid the foundation for the application of rare earths. In recent years, rare earth is widely used in metallurgy, petrochemical, glass, ceramics, new materials.
Table 1 Relationship between structure and properties of rare earth
In the metallurgical industry: the rare earth metal or fluorides, silicides added steel, refining can play, desulfurization, and low-melting impurities deleterious effects, and may improve the processing properties of steel; rare-earth iron-silicon alloy, a rare earth ferrosilicon magnesium alloy As a spheroidizing agent for the production of rare earth ductile iron, this kind of ductile iron is especially suitable for the production of complex ductile iron parts with special requirements. It is widely used in machinery manufacturing such as automobiles, tractors and diesel engines; rare earth metals are added to magnesium, aluminum and copper. In the non-ferrous alloys such as zinc and nickel , the physical and chemical properties of the alloy can be improved, and the mechanical properties of the alloy at room temperature and high temperature can be improved.
In the petrochemical industry: the molecular sieve catalyst made of rare earth has the advantages of high activity, good selectivity and strong resistance to heavy metal poisoning, thus replacing the aluminum silicate catalyst for the petroleum catalytic cracking process; in the process of ammonia production, A small amount of rare earth nitrate is used as a cocatalyst, and its treatment gas volume is 1.5 times larger than that of nickel-aluminum catalyst. In the process of synthesizing butadiene rubber and isoprene rubber, the product properties obtained by using naphthenic acid rare earth-triisobutyl aluminum catalyst are obtained. It is excellent, has the advantages of less equipment hanging glue, stable operation and short post-treatment process; composite rare earth oxide can also be used as catalyst for exhaust gas purification of internal combustion engine, and barium naphthenate can also be used as paint drier.
In terms of glass ceramics: rare earth oxides or processed rare earth concentrates can be used as polishing powders for the polishing of optical glass, spectacle lenses, picture tubes, oscilloscope tubes, flat glass, plastic and metal tableware; In the glass making process, the cerium oxide can be used to have a strong oxidation effect on iron, and the iron content in the glass can be reduced to achieve the purpose of removing green in the glass; the addition of rare earth oxide can produce optical glass and special for different purposes. Glass, including glass that can pass infrared rays, absorb ultraviolet rays, glass that is resistant to acid and heat, glass that prevents X-rays, etc.; adding rare earth in ceramic glaze and enamel can reduce the fragmentation of glaze and make products appear Different colors and gloss are widely used in the ceramic industry.
In terms of new materials: rare earth cobalt and lanthanum, iron, boron permanent magnet materials, with high remanence, high coercivity and high magnetic energy product, are widely used in the electronics and aerospace industries; pure rare earth oxides and ferric oxide The garnet-type ferrite single crystal and polycrystal can be used in the microwave and electronics industries; the yttrium aluminum garnet and bismuth glass made of high-purity cerium oxide can be used as a solid laser material; the rare earth hexaboride can be used for making electrons. The cathode material emitted; yttrium-nickel metal is a newly-developed hydrogen storage material in the 1970s; strontium chromate is a high-temperature thermoelectric material; in recent years, superconducting materials made of yttrium-based oxides modified by bismuth-copper oxide have been used in various countries around the world. Superconductors can be obtained in the liquid nitrogen temperature zone, which has made a breakthrough in the development of superconducting materials.
In addition, rare earth is also widely used in lighting sources, projection TV phosphors, inductive screen phosphors, trichromatic phosphors, and copy lamp powders. In agriculture, the application of trace amounts of rare earth nitrate to field crops can increase the yield by 5~ 10%; in the textile industry, rare earth chloride is also widely used in tanned fur, fur dyeing, yarn dyeing and carpet dyeing.
Second, rare earth deposits
1. Industrial requirements for deposits
Clark rare earth elements in the crust is 0.0153%, and common elements zinc, tin, cobalt content similar; Clark even smaller values thulium, lutetium, terbium, europium, holmium and the like, than bismuth, silver, mercury High content.
Although rare earth elements are widely distributed in the earth's crust, not all rare earth-bearing deposits meet the requirements of industrial development and utilization. According to the current technical level of mineral processing and extraction, the industrial index requirements for rare earth deposits are listed in Table 2.
Table 2 Industrial indicators of rare earth deposits
Deposit type
Boundary grade
Industrial grade
Available thickness
m
Stone removal
Thickness, m
Fluorite-bearing ore-bearing, primary deposit of monazite
Ce 2 O 3 or R 2 O 3
0.5%
Ce 2 O 3 or R 2 O 3
1%
1~2
2
Xenotime should be placed pegmatite and carbonate rocks and other deposits gadolinite
Y 2 O 3 or R 2 O 3
Y 2 O 3 or R 2 O 3
0.05~0.1%
1~2
2
Monazite sand mine and weathering crust deposit
Monazite
100~200g/m 3
Monazite
300~500g/m 3
1
1~2
Phosphonium ore deposit and weathering crust deposit
Phosphonium ore 30g/m 3
Phosphate ore 50~70
g/m 3
0.5~1
2
If the rare earth element is recovered as a companion component in the deposit, the industrial index requirements may depend on the main useful elements in the deposit. For China's unique ion and adsorption type rare earth deposits, the industrial index requirements are still to be studied and formulated.
2. Deposit type
China's rare earth deposits have many types, large reserves and wide distribution. Among them, the Inner Mongolia Bayan Obo rare earth symbiotic deposit is the world's largest proven rare earth deposit; the Jiangxi ion adsorption rare earth deposit is a unique rare earth deposit in China. Foreign rare earth deposits are mainly distributed in the United States, the Soviet Union, Australia, Brazil, India and other countries. At present, the types of deposits that have been developed and have industrial value at home and abroad are listed in Table 3. [next]
Table 3 Types of rare earth deposits
Deposit type
Main mineral
Place of origin
Bayan Obo rare earth symbiotic deposit
Bastnasite, monazite, magnetite, hematite, coltan , lanthanum rutile, fluorite , neolithic, and a small amount of minerals such as calcite , barite , quartz, etc.
Inner Mongolia, China
Carbonate type rare earth deposit
Bastnasite, calcite, barite, and silicate minerals, etc.
California, USA
Shandong China
Solitary, fluocinolate, bastnasite, fluorite, calcite, and silicate
Minerals, etc.
Hubei, China
Bastnasite, monazite, xenotime, siderite, barite,
Calcite, etc.
Soviet Union
Yanbin Sand Mine and Alluvial Sand Deposit
Monazite, iron titanium, zircon, rutile, and the like silicate minerals
Australia, India, Brazil, the United States, China
Phosphonium, cassiterite, zircon, monazite, ilmenite, and silicate
Matter
Malaysia, Nigeria, Brazil
Ion-adsorbed rare earth deposit
Heavy rare earth or light rare earth is adsorbed on kaolin and clay minerals in ionic form. Other minerals include monazite, quartz and other minerals.
Jiangxi, Fujian, China
Granite -type rare earth deposit
Monazite, xenotime and containing galena, sphalerite, or comprising quartz and wolframite
Soviet Union
Jiangxi, China
Rare earth-bearing uranium deposit
Euxenite, fergusonite mineral, zircon, rutile, magnetite, silicate minerals, titanium minerals, or associated with a uranium, uraninite, pitchblende thorium, etc.
Canada, United States, Brazil, South Africa
铈铌Perovskite deposit
铈铌Perovskite, apatite, nepheline,
Feldspar and other minerals
Soviet Union
3. Rare earth industrial minerals and their physical and chemical properties
1. Occurrence of rare earth elements and classification of minerals
There are three kinds of rare earth elements in the earth's crust: (1) participating in the mineral lattice, forming an indispensable component of the mineral, forming an independent mineral (such as monazite, bastnasite), which is the rare earth element in the earth's crust. The main form of occurrence in (2) is dispersed in rock-forming minerals and other rare minerals in the form of isomorphic substitutions (calcium, strontium , barium, manganese, etc.), which is a secondary form of occurrence; 3) Adsorption in the form of ions on other mineral surfaces or between particles, which is a rare form of occurrence.
According to the chemical composition of rare earth minerals, the rare earth minerals that have been discovered can be classified into nine categories, and various typical rare earth minerals are listed.
Table 4 Classification of rare earth minerals
category
Main mineral
Fluoride
Fluorite, fluorocalcium sodium vermiculite, fluoroanthrite, etc.
Carbonate, fluorocarbonate
Bastnasite, yellow river mine, barium carbonate mine, etc.
Phosphate
Monazite, xenotime
Silicate
Silicon germanium ore
Oxide
Brown earth mine, easy stone, black gold mine
Arsenate
Arsenic ore
Borate
Mink calcium borax
Sulfate
Fluorine hydrate
Citrate
Antimony ore
2. Major industrial minerals and their physical and chemical properties At present, there are more than 250 kinds of rare earth-containing minerals found in the world, and there are about 50-60 kinds of rare earth minerals with research and utilization value, which have industrial exploitation and practical value. There are only a few rare earth minerals, and the physical and chemical properties of the important rare earth minerals are listed in Table 5. [next]
Table 5 Physical and chemical properties of rare earth minerals
Mineral name
Chemical properties
Physical properties
English name
Molecular formula
REO
%
Soluble
density
g/cm 3
hardness
Specific magnetic susceptibility × 10 -6 cm 3 /g
Dielectric constant
Crystal form
Bastnasite
CeCO 3 F
74.77
Soluble in HCl
4.72~5.12
4~5.2
12.59~10.19
5.65~6.90
Trigonal system
Bastnaesite
Monazite
CePO 4
67.76
Soluble in H 2 SO 4 , HCl, H 3 PO 4 slightly soluble in NaOH
4.83~5.42
5~5.5
12.75~10.58
4.45~6.69
Monoclinic system
Monazite
Phosphonium ore
YPO 4
63.23
Soluble in H 2 SO 4 , H 3 PO 4 slightly soluble in NaOH
4.4~4.8
4~5
31.28~26.07
8.1
Orthogonal system
Xenotime
Fluorite
Ce 2 Ca(CO 3 ) 3 F 3
60.30
Soluble in HCl, H 2 SO 4 , HNO 3
4.2~4.5
4.2~4.6
14.37~11.56
Trigonal system
Parisite
Silicon germanium ore
Y 2 FeBe(SiO 4 ) 2 O 2
51.51
Soluble in HCl, slightly soluble in NaOH
4.0~4.65
6.5~7
62.5~49.38
Monoclinic system
Cadolinite
Easy stone
(CeThY)(TiNb) 2 O 6
29.36
Soluble in H 2 SO 4 , H 3 PO 4 soluble in HF, H 2 SO 4 +(NH 4 ) 2 SO 4
5~5.4
4.5~6.5
18.04~12.92
4.4~4.8
Orthorhombic system
Eschynite
Barium perovskite
(NaCeCa)(TiNb)O 3
28.71
Insoluble in HCl, H 2 SO 4 , HNO 3 soluble in HF
4.58~4.89
5.8~6.3
6.54~5.23
5.56~7.84
Isometric crystal system
Loparite
Complex gold mine
Y(TiNb) 2 (O·OH) 6
29.28~33.43
Soluble in H 2 SO 4 , H 3 PO 4 , HF
4.28~5.05
4.5~5.5
21.05~18.00
Orthorhombic system
Polycrase
Black gold mine
Y(NbTi) 2 (O·OH) 6
20.82~29.93
Soluble in HF, H 2 SO 4 , H 3 FO 4
4.2~5.87
5.5~6.5
27.38~18.41
3.7~5.29
Orthorhombic system
Euxenite
Brown sugar mine
YNbO 4
39.94
Soluble in H 2 SO 4 , HNO 3
4.89~5.82
5.5~6.5
29.2~21.16
4.5~16
Tetragonal system
Fergusonite
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