Applications

Interesting Facts

Discovery

Axel Fredrik Cronstedt first described a new mineral in 1751. It had a high-specific gravity and was found in the copper and bismuth ores at the Bastnäs Mine, Riddarhyttan, Sweden. It was described as a being difficult to analyze and was named "tungsten (heavy stone) of Bastnäs". Although several scientists analyzed the mineral and determined it contained no tungsten (wolfram), its rare-earth content remained elusive. The mineral remained unnoticed for years until it was examined independently in 1803 in Germany by Martin Heinrich Klaproth and in Sweden by Jöns Jakob Berzelius and Wilhelm Hisinger. M. H. Klaproth discovered a new earth in the mineral which he called terre ochroite (Klaproth, 1803). Wilhelm Hisinger and Jöns Jakob Berzelius announced they had found a new earth in it and named it cerous oxide because a second earth of a different color was also present (Hisinger and Berzelius, 1804) (Berzelius, 1816). The element was initially named cererium by Klaproth, but that name was soon abandoned. In tribute to the discovery of the dwarf planet Ceres in 1801, circling in the asteroid belt between Mars and Jupiter, the new element was named cerium and the mineral from which it was extracted, cerite. The dwarf planet itself was named after the Roman Goddess of agriculture, grain crops, fertility, and motherly relationships, Ceres (Weeks and Leicester, 1968, p. 529).

Definition

Cerium is a lustrous silvery-dark grey metal that oxidizes readily in air. Finely divided cerium metal is very unstable in air. The metal is malleable and will likely ignite if cut with a knife. The element has three valence states, +2, +3, and +4, with the +2 state being rare. Cerium metal has five allotropes and four metal crystal forms: α´ cerium occurs in C-centered orthorhombic at a pressure of 5.8 GPa and 25 °C; α cerium occurs in face centered cubic at atmospheric pressure and -196 °C; β cerium occurs in double hexagonal close packed at atmospheric pressure and 25 °C; γ cerium occurs in face centered cubic at atmospheric pressure and 25 °C; and δ cerium is body centered cubic at atmospheric pressure and 768 °C. Cerium has a specific gravity of 6.771 g/cm³, a melting point of 798 °C, and a boiling point of 3433 °C. Cerium oxide, or ceria, occurs as the dioxide, its most stable form, with the formula CeO₂. It also occurs as the sesquioxide with the formula, Ce₂O₃. The oxide is a white powder with a specific gravity of 7.3 gm/cm³, a melting point of 2210 °C, and a formula weight of 172.12 (Daane, 1961).

Preparation of Metal

Cerium metal was prepared by William Francis Hillebrand and Thomas H. Norton in 1875 by electrolyzing fused cerous chloride (Hillebrand and Norton, 1875). Cerium metal is typically prepared by calciothermic reduction of the trihalide, typically CeF3, in a Ta crucible. Cerium metal has a low melting point and high boiling point, similar to La, Pr, and Nd. To prepare the CeF₃, a mixture of anhydrous hydrofluoric acid and 60% argon is streamed over Ce2O3 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 CeF₃ 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). The Ca metal combines with the F to form CaF₂ and the remaining product is a high-purity cerium metal.

Source

Large resources of cerium are contained in LREE-enriched minerals. Cerium is the most abundant rare-earth element in the Earth's crust and occurs at an average concentration of 60 parts per million. The primary source of cerium 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. Cerium 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, carbonatites, and alkaline complexes. Cerium sourced from the LREE-mineral loparite is recovered from a large alkali igneous intrusion in Russia (Hedrick, Sinha, and Kosynkin, 1997).

Mining

Cerium 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 bastnäsite 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 cerium minerals

Bastnäsite-(Ce)	(Ce,La,Nd,Pr)(CO3)F
Monazite-(Ce)	(Ce,La,Nd,Th)(PO4)
Loparite-(Ce)	(Ce,Na,Ca,Sr,Th)(Ti,Nb,Ta,Fe+3)O3
Allanite-(Ce)	(Ca,Ce)(Al2,Fe+2)(Si2O7)(SiO4)O(OH)
Parisite-(Ce)	Ca(Ce,La)2(CO3)3F2
Ancylite-(Ce)	SrCe(CO3)2(OH) · H2O
Britholite-(Ce)	Ca2(Ca,Ce)3(SiO4,PO4)3(OH,F)
Cerite-(Ce)	(Ca,Ce)9(Fe,Mg)(SiO4)3(HSiO4)(OH)3

References

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.

Berzelius, Jöns J., 1816, Analyse de la gadolinite, Annales des Chimie et des Physique, September, v. 2, no. 3, p.26-34.

Daane, Adrian H., 1961, Physical properties of the rare earth metals: chapter 13 in The rare earths, Spedding and Daane, (eds.), John Wiley & Sons, New York, p. 177-189.

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., 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.

Hisinger, Wilhelm, and Jöns J. Berzelius, 1804, Account of cerium, a new metal found in a mineral substance from Bastnäs, in Sweden: Nicholson’s Journal, December, v. 9, p. 290-300.

Hillebrand, W.F., and T.H. Norton, 1875, Elecktrolytisch Abscheidung des Cers, Lanthans, und Didyms [Electrolytic deposition of cerium, lanthanum, and didymium]: Leipzig, Germany, Annalen der Physik und Chemie (Poggendorff, v. 155, no. 8, p. 633-639.

Klaproth, Martin H., 1803, Neues Metall [New Metal]: Neues Allgemeines Journal der Chemie, p. 462-463.

Weeks, Mary E., and Henry M. Leicester, 1968, Discovery of the Elements (7th ed.): Easton, Pennsylvania, Journal of Chemical Education, 896 p.