Lanthanum, the first light-group rare-earth element (LREE) was discovered hidden inside a cerium compound by a relentless chemical sleuth who spent over a year on the trail. As the first element of the lanthanide group it has no f-electrons, but as f-electrons are added to each subsequent lanthanide the ionic radii of the elements decrease in a progression called lanthanide contraction.
The radii decrease from 103 picometers for La3+ to 86.1 picometers for Lu3+.
High-end camera lenses, microscopes, telescopes, riflescopes, and binoculars use lanthanum oxide to improve visual clarity.
Lanthanum fluoride is used to in fiber optics to increase data transmission rates.
Hybrid and electric vehicles use lanthanum nickel-metal hydride (NiMH) rechargeable batteries. These batteries are used for power tools, toys, laptop computers, telephones, and cameras.
Lanthanum is essential in the production of fuel for planes, trains, and automobiles.
Lanthanum oxide is used in the manufacture of infrared-absorbing glass used in night vision goggles.
Hot tubs and swimming pools can use lanthanum carbonate to reduce algae growth and balance pH.
Lanthanum carbonate is used to reduce blood levels of phosphate in patients with kidney disease.
Using lanthanum in the refining process of crude oil keeps the cost down by increasing the yield.
In 1839, Carl Gustav Mosander, a Swedish pharmacist, physician, army surgeon, and curator of the mineral collection at the Stockholm Academy of Sciences, extracted a new rare earth from an impure cerium nitrate.
He was also in charge of the medical school's chemical laboratory at the Caroline Institute where he was a professor of chemistry and mineralogy (Weeks and Leicester, 1968, p. 673).
Mosander prepared the new earth by heating an impure cerium nitrate and partly decomposing the compound with dilute nitric acid.
Based on ceria's insolubility in dilute nitric acid, dissolved extract from this reaction was a new earth, lanthana (lanthanum oxide), which he separated from the ceria (cerium oxide) residue (Mosander, 1839).
The term lanthanum is derived from the Greek word lanthano, meaning hidden or concealed.
Lanthanum is a silvery-gray metal that oxidizes readily in air.
Finely divided lanthanum metal powder can ignite spontaneously in air.
The metal is ductile and malleable and soft enough to be cut with a knife.
Dependant on temperature, the metal occurs in three crystal systems.
At ambient temperatures, lanthanum occurs in hexagonal form with a specific gravity of 6.174 g/cm3, above 310 °C it occurs in face-centered cubic form with a specific gravity of 6.186 g/cm3, and above 868 °C it occurs in body-centered cubic form with a specific gravity of 5.98 g/cm3.
It has a melting point of 918 °C, and a boiling point of 3464 °C.
Lanthanum oxide, or lanthana, occurs as a sesquioxide with the formula La2O3.
The oxide is a white powder with a specific gravity of 3.86 gm/cm3, a melting point of 2410 °C, and a formula weight of 325.82.
Preparation of Metal
Lanthanum metal is typically prepared by calciothermic reduction of the trihalide, typically LaF3, in a Ta crucible.
Lanthanum metal has a low melting point and high boiling point, similar to Ce, Pr, and Nd.
To prepare the LaF3, a mixture of anhydrous hydrofluoric acid and 60% argon is streamed over La2O3 at 700 °C for 16 hours in a platinum-lined Inconel furnace tube.
This produces a lanthanum fluoride with approximately 300 ppm oxygen as an impurity.
In a second purification step the oxygen content is lowered to less than 20 ppm by heating the fluoride to about 50 °C above its melting point in a platinum crucible within a graphite cell.
The LaF3 is placed in a Ta crucible, reduced with a 15% excess of the theoretical amount of calcium metal required, and heated in an induction vacuum furnace under an inert Ar atmosphere to a temperature above the highest melting reductant or product (Beaudry and Gschneidner, Jr., 1978).
Large resources of lanthanum are contained in LREE-enriched minerals.
Lanthanum occurs in the Earth's crust at an average concentration of 30 parts per million.
The primary source of lanthanum is from carbonatites and the LREE-mineral bastnäsite.
Bastnäsite deposits in China and the United States constitute the largest percentage of the world's rare-earth economic resources.
Lanthanum is also a major constituent in the LREE-mineral monazite which constitutes the second largest segment of rare-earth resources.
Monazite deposits are located in Australia, Brazil, China, India, Malaysia, South Africa, Sri Lanka, Thailand, and the United States in paleoplacer and recent placer deposits, sedimentary deposits, veins, pegmatites, carbonaties, and alkaline complexes.
Lanthanum sourced from the LREE-mineral loparite is recovered from a large alkali igneous intrusion in Russia (Hedrick, Sinha, and Kosynkin, 1997).
Lanthanum is mined from a variety of ore minerals and deposits using various methods.
Bastnäsite is mined in the United States as a primary product from a hard-rock carbonatite.
The deposit is mined via bench-cut open pit methods.
Ore is drilled and blasted, loaded into trucks by loaders, and hauled to the mill. At the mill the blasted ore is crushed, screened, and processed by flotation to produce a bastnńsite concentrate.
In China, bastnäsite and lesser amounts of associated monazite are also mined from a carbonatite.
The ore is recovered as a byproduct of iron ore mining by hard-rock open pit methods.
After crushing the ore is separated from the iron ore by flotation to produce a bastnäsite concentrate and a bastnäsite-monazite concentrate (Hedrick, 1990).
Monazite is recovered from heavy-mineral sands (specific gravity >2.9) deposits in various parts of the world as a byproduct of mining zircon and titanium-minerals or tin minerals.
Heavy mineral sands are recovered by surface placer methods from unconsolidated sands.
Many of these deposits are mined using floating dredges which separate the heavy-mineral sands from the lighter weight fraction with an on-board wet mill through a series of wet-gravity equipment that includes screens, hydrocyclones, spirals, and cone concentrators.
Consolidated or partially consolidated sand deposits that are too difficult to mine by dredging are mined by dry methods.
Ore is stripped by typical earth-moving equipment with bulldozers, scrapers, and loaders or by water jet methods.
Ore recovered by these methods is crushed and screened and then processed by the wet mill described above.
Wet mill heavy-mineral concentrate is sent to a dry mill for processing to separate the individual heavy-minerals using a combination of scrubbing, drying, screening, electrostatic, electromagnetic, magnetic, and gravity processes.
Vein monazite has been mined by hard-rock methods in South Africa and the United States (Hedrick, 2010). Loparite is mined by underground methods using room and pillar methods. Ore is drilled and blasted and removed from the mine.
The ore is then processed by the same hard-rock methods as applied to bastnäsite to make a loparite concentrate.
Selected lanthanum minerals
Beaudry and Bernard J. and Karl A. Gschneidner, Jr., 1978, Preparation and Basic Properties of the Rare Earth Metals: chapter 2 in Handbook of the Physics and Chemistry of Rare Earths-Volume 1:Metals, (Gschneidner, Jr. and Eyring, editors), North-Holland, New York, p. 173-232.
Gschneidner, Karl A. Jr., 2011, The Rare Earth Crisis - The Supply/Demand Situation for 2010-2015: article in Material Matters, Aldrich Chemical Co., Milwaukee, Wisconsin, v. 6, no. 2, p. 34-35.
Hedrick, James B., 2010, Rare earths: chapter in Mineral commodity summaries 2010, U.S. Geological Survey, p. 128-129.
Hedrick, James B., 1990, Rare earths - The lanthanides, yttrium, and scandium: chapter in Minerals Yearbook 1990, U.S. Geological Survey, v. 1, p. 903-922.
Hedrick, James B., Shyama P. Sinha, and Valery D. Kosynkin, 1997, Loparite - a rare-earth ore (Ce,Na,Sr,Ca)(Ti,Nb,Ta,Fe+3)O3: Journal of Alloys and Compounds, v. 250, p. 467-470.
Mosander, Carl G., 1839, Lantan, ein neues Metall: Poggendorf Annalen der Physik und Chemie, v. 46, p. 648-649.
Weeks, Mary E., and Henry M. Leicester, 1968, Discovery of the Elements (7th ed.): Easton, Pennsylvania, Journal of Chemical Education, 896 p.