Gadolinium, REE HandBook

Gadolinium

Look, it’s a bird, it’s a plane, it’s gadolinium. Disguised as a mild-mannered rare earth, gadolinium is the superman of the elements with superhero properties resulting from its half-full electron shell. It is the final member of the light-group rare-earth elements (LREE), which started at lanthanum, and is filled halfway with 7 electrons that are all spinning in the same direction. With this electron configuration it is able to stop neutrons traveling faster than a speeding bullet, is able to bend water molecules with a single molecule, and able to jump plane domain walls in a single bound.

Applications

Gadolinium contrast agents are injected into the patient to enhance the clarity of MRI scans.
Gadolinium-157 is used in nuclear reactor control rods to control the fission process.
Yttrium gadolinium garnet or yttrium gallium garnets (YGG) are used in various electronic components for communications and radar.

Interesting Facts

Using gadolinium alloy Gd₅(Si₂Ge₂) in magnetic refrigeration has the potential to cut electrical heating and cooling costs by as much as 80%.
Gadolinium metal demonstrates the magnetocaloric effect in which its temperature increases when it is put in a magnetic field and decreases when it is removed from a magnetic field.
On a molecular level, Gadolinium molybdate exhibits a rarely seen jump-like motion in an electric field, the significance of which is not yet known.
Gadolinium is unusual in that the Curie temperature is very close to room temperature, unlike the other ferromagnetic elements, iron, nickel, and cobalt.

Discovery

As early as 1853, Swiss chemist and mineralogist Jean-Charles Gallisard de Marignac realized that Carl Gustav Mosander’s didymium was an impure mixture of several elements. From 1848 to 1878 he taught mineralogy and chemistry at the University of Geneva and continued his researches on discovering a new element. In 1880, Marignac finally separated a new earth from the mineral samarskite which he provisionally named Ya (Spencer, J. F., 1919). In 1886, Lecoq de Boisbaudran obtained another earth from the mineral gadolinite, which proved identical to the element Marignac discovered in 1880. Lecoq de Boisbaudran proposed the name gadolinium with Marignac’s approval (Weeks and Leicester, 1968, p. 684). The element is named in honor of Finnish chemist Johan Gadolin, who discovered the first rare earth in 1794 (Gadolin, 1794).

Definition

Gadolinium is a silvery-white metallic metal that is malleable and ductile. It is relatively stable in dry air but in a moist environment will form an oxide coating. The metal has a hexagonal close packed structure at ambient temperatures but transforms at 1262 °C to a body centered cubic structure. Gadolinium has a density of 7.895 gm/cm³, a melting point of 1312 °C, and a boiling point of 3000 °C. Gadolinium oxide, or gadolinia, occurs as a sesquioxide with the formula Gd₂O₃. The trivalent oxide is a white powder with a specific gravity of 7.60 gm/cm³ and a formula weight of 362.50. Gadolinium has 17 isotopes of which 7 are naturally occurring. Gadolinium is ferromagnetic at temperatures below 20 °C (68 °F) and is strongly paramagnetic above this temperature.

Preparation of Metal

Gadolinium metal is typically prepared by calciothermic reduction of the trihalide, typically GdF₃, in a tantalum crucible. A tungsten crucible can be used if an impurity level of 0.012 atomic weight percent tungsten could be tolerated. Gadolinium metal has a high melting point with a vacuum melting temperature of 1800 °C, similar to Y, Tb, and Lu. The high vacuum melting temperature necessitates a distillation step to remove tantalum impurities introduced during the reduction and vacuum melting steps. The distillation process is done in a tungsten crucible and occurs at a slow rate to keep impurities at a low level. A vacuum of better than 1.3 x 10^-6 Pa is needed (Beaudry and Gschneidner, Jr., 1978). Gadolinium metal is formed when the fluoride preferentially separates from gadolinium fluoride at high-temperature and combines with calcium metal forming calcium fluoride and a high-purity gadolinium metal.

Source

Large resources of gadolinium are contained in LREE-enriched minerals. Gadolinium occurs in the Earth’s crust at an average concentration of 5 parts per million. The primary source of gadolinium 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. Gadolinium is also a 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 (Hedrick, 2010). Gadolinium sourced from the LREE-mineral loparite is recovered from a large alkali igneous intrusion in Russia (Hedrick, Sinha, and Kosynkin, 1997).

Mining

Gadolinium, a light-group rare-earth element (LREE) 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
Samarakite-(Y)	(Y,Fe⁺³,Fe⁺³,U,Th,Ca)₂(Nb,Ta)₂O₈
Samarakite-(Y)	(Y,Fe⁺³,Fe⁺³,U,Th,Ca)₂(Nb,Ta)₂O₈
Gadolinite-(Y)	Y₂Fe²⁺Be₂(Si₂O₁₀)

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.

Gadolin, Johan, 1794, Undersökning av en svart tung stenart ifrån Ytterby stenbrott I Roslagen [Understanding of a new heavy mineral from Ytterby mine at Roslagen]: Kungl. Svenska Vetenskapsakademien Handlingar, p,137-155.

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., Rare earth history: unpublished manuscript, 11 p.

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., 1991, Rare earths—The lanthanides, yttrium, and scandium: chapter in Minerals Yearbook 1991, U.S. Geological Survey, v. 1, p. 1211-1237.

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.

Lecoq de Boisbaudran, Pierre E., 1879, Nouvelles raies spectrales observées dans des substances extradites de la samarskite [New spectral lines observed in substances extracted of samarskite]: Comptes Rendus, February 17, v. 88, p. 322-324.

Shur, V.YA., E.V. Nikolaeva, E.L., Rumyantsev, E.I. Shishkin, A.L. Subbotin, and V.L. Kozhevnikov, 1999, Smooth and jump-like dynamics of the plane domain wall in gadolinium m0olybdate: Ferroelectrics, v. 222, p. 323-331.

Spencer, J. F., 1919, The metals of the rare earths: Longnans, Green, and Co., London, p. 2-10.

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