Lanthanides refer to the collective designation of 15 elements from No. 57 to No. 71 elements with similar chemical properties in the periodic table of elements. They are lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium ( Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu).
Most of the lanthanides are silver active metals with very strong reducing ability. Among them, lanthanum is the most active, followed by cerium, praseodymium, neodymium and europium. Lanthanide elements are easy to react chemically with halogen, oxygen, acid, sulfur, nitrogen, hydrogen, etc. Therefore, to prevent the lanthanide metals from tarnishing due to the reaction, they are usually waxed or preserved in mineral oil.
The answer to this question depends on how you understand the word rare. Lanthanides are all rare earth elements. However, the "rare" in the name does not refer to the low element content, but mainly refers to the fact that they are difficult to extract from ores or compounds containing other substances. In terms of abundance alone, cerium, one of the most abundant elements in the lanthanides, has an abundance of 46 ppm, which is higher than that of the common metal tin.
But lanthanides are undeniably difficult to extract, leading them to be considered rare. Because the properties of lanthanides are very similar, and they often gather in the same substance, it is very difficult to discover and separate them.
The physicochemical properties of the various lanthanides are nearly identical, so separating them is an extremely difficult task. Attempts to separate them can only be made by slight differences in their basic properties, stability or solubility. Two commonly used methods for separating lanthanides are ion exchange and valency change.
Ion exchange is the most important, fast and reliable separation technique for lanthanides. The process of separating lanthanide elements by this method is mainly represented by the following equation:
Ln3+(aq) + 3H(resin)(s) —— Ln(resin)3(s) + 3H+(aq)
Ln(resin)3 + 3H+ + (citrate)3- —— 3H(resin) + Ln(citrate)
Ln(citrate) + C2O4(2−) —— (citrate)3- + Ln2( C2O4)3
2Ln2( C2O4)3 + 2O2 —— 2Ln2O3 + 12CO2
1) Use synthetic ion-exchange resin solution to immobilize Ln3+ ions on the resin.
2) React the product in 1) with a citric acid/ammonium citrate buffer solution (eluent) to separate Ln from the resin and form a stable complex with citrate ions. The solution leaving the column is collected by a separate automatic fraction collector. Lanthanides with smaller ions are removed from the column earlier and collected separately in a metal-rich solution fraction.
3) Add ammonium oxalate into these collected solution components, and the rare earth element is precipitated in the form of oxalate.
4) Heat oxalate precipitates to get rare earth oxides.
This method is mainly used to separate elements with different valences in lanthanides. The oxidation states of a few lanthanides are (+IV) or (+II), which are quite different from (+III), so it is easier to separate them. The following is an example of the separation of Cerium using valency change method.
The separation of cerium is simple compared to other lanthanides because it is the only lanthanide with stable Ln 4+ ions in aqueous solution. The separation process is mainly represented by the following equation:
Ce3+ + NaOCl ＋ OH- → Ce(OH)4 + NaCl
Ce(OH)4 → CeO2 + H2O
1） Under alkaline conditions, add sodium hypochlorite (NaOCl) into a solution containing a mixture of Ce 3+ ions. The reaction produces stable Ce 4+ ions, which are precipitated in the form of Ce(OH)4.
2) Heat the Precipitate Ce(OH)4 to obtain CeO2.
Adding lanthanum to glass can improve the optical properties of the glass, such as the refractive index, so lanthanum is used to make some special lenses.
Additionally, lanthanum is used to make electrodes for high-intensity carbon-arc lamps used in film studios and searchlights.
Cerium is used as a catalyst to make ammonia, which is used in jet engine components.
Cerium is also used in the synthesis of antiknock agents in gasoline, reducing the "knock" sound in engines sometimes produced by poor-quality fuel.
Cerium(IV) oxide is used to extract color from previously colored glass and is also used in enamel and ceramic coatings.
Cerium alloy is often used as a "flint" in cigarette lighters because it creates a spark when the friction of a metal wheel is applied.
Praseodymium is used as an alloying agent with magnesium to make high-strength metals used in aircraft engines.
Praseodymium compounds are used in the manufacture of yellow glass, enamel and ceramics.
The main application of neodymium is to make high-strength permanent magnets of Nd2Fe14B, which are used in high-performance electric motors and generators, and spindle magnets for computer hard drives and wind turbines.
Neodymium is used in the electronics industry to make steel in a variety of ferrous and non-ferrous alloys and as components.
Neodymium is used to make neodymium-stabilized yttrium aluminum garnet (Nd:YAG), an important component of many modern lasers.
Promethium is used to generate electricity in atomic batteries. When a small promethium source is sandwiched between two semiconductor plates, the beta particles produced by promethium 147 are converted into electrical current.
Promethium is also used as a source of X-rays and radioactivity in measuring instruments.
Samarium is used in nuclear power plant control rods, carbon arc lamps, and optical masers and lasers.
Samarium is also used in the manufacture of optical glass.
Samarium can be used as a catalyst in the production of ethanol.
Samarium-cobalt alloys are used to make one of the most magnetic permanent magnets, samarium-cobalt magnets.
Europium is one of the most effective elements for capturing neutrons and is therefore used in the control systems of nuclear reactors.
Some compounds of europium have fluorescent properties, so they are used in the manufacture of phosphors for televisions.
Gadolinium captures neutrons so efficiently that it can be used in nuclear power reactors.
Gadolinium is used to make phosphors used in color televisions.
Gadolinium is also used as a superconductor due to its strong magnetic properties at very low temperatures.
Compounds of terbium glow green when hit by electron beams, so it's used as a phosphor in color televisions.
Terbium is used as a dopant in calcium fluoride, calcium tungstate, strontium molybdate and solid state device materials.
Dysprosium has a high affinity for neutrons and is therefore used in the control rods of nuclear reactors.
Due to its magnetic properties, dysprosium alloys can be used in ships' sound navigation and ranging systems for applications in the marine industry.
Alloyed with vanadium, dysprosium are used to make laser devices for laser cutting, law enforcement, medicine, printers, and even communications.
Holmium has a high neutron capture cross section and is therefore used to produce control rods used in nuclear reactors.
Adding holmium oxide to glass can make it appear yellow or red, so holmium oxide is widely used in the production of colored glass and colored zirconia.
Holmium is used as a dopant in certain semiconductors for doping compounds such as yttrium iron garnet and yttrium lithium fluoride.
Erbium salts are pink and used as colorants to add color to glass, porcelain, and other materials. Erbium chloride can be used as a catalyst for the reaction of alkanols and phenols.
Erbium bromide is a water-soluble compound that can be used to treat wastewater.
Thulium is used in portable X-ray equipment and is widely used as a radiation source in nuclear reactions.
Thulium has also been used in high-temperature superconductors just like yttrium.
Thulium, which fluoresces blue when exposed to ultraviolet light, was added to euro banknotes as an anti-counterfeiting measure.
Ytterbium is used as a dopant to improve grain refinement, strength and other mechanical properties of stainless steel.
Ytterbium clocks are known for their stability in ticking.
Yb3+ ions are also used as dopant materials in active laser media.
Lutetium is beneficial for the processes of alkylation, hydrogenation, and polymerization, and it is used as a catalyst for cracking hydrocarbons in the oil refining industry.
Lutetium can be used as a detector in positron emission tomography to detect cellular activity in the human body.
The lanthanides refer to lanthanum and 14 other elements that are chemically similar to lanthanum. Lanthanides find the most applications in catalysts and glass production. But from a value standpoint, their use in phosphors and magnets is more important.
Stanford Materials Corporation (SMC) is a worldwide supplier of lanthanides, including their pure metals, oxides, compounds, sputtering targets, and evaporation materials. You can send us an inquiry if you are interested in high quality lanthanide materials.
Eric Loewen
Eric Loewen graduated from the University of Illinois studying applied chemistry. His educational background gives him a broad base from which to approach many topics. He has been working with topics about advanced materials for over 5 years at Stanford Materials Corporation (SMC). His main purpose in writing these articles is to provide a free, yet quality resource for readers. He welcomes feedback on typos, errors, or differences in opinion that readers come across.
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