Gadolinium (64)

Gadolinium is silvery white, has a metallic luster, and is is malleable (capable of being extended or shaped by beating with a hammer or by the pressure of rollers) and ductile (capable of being drawn out into wire or threads). It is ferromagnetic (strongly attracted by a magnet).

The metal is relatively stable in dry air, but in moist air it tarnishes with the formation of a loosely adhering oxide film which "spalls" off and exposes more surface to oxidation. The metal reacts slowly with water and is soluble in dilute acid. Gadolinium has the highest thermal neutron capture cross-section of any known element. 

•Name: Gadolinium
•Symbol: Gd
•Atomic number: 64
•Atomic weight: 157.25 (3) [see note g]
•Standard state: solid at 298 K
•CAS Registry ID: 7440-54-2
•Group in periodic table: 
•Group name: Lanthanoid
•Period in periodic table: 6 (lanthanoid)
•Block in periodic table: f-block
•Color: silvery white
•Classification: Metallic

Historical information
Gadolinium was discovered by Jean de Marignac at 1880 in Switzerland, and named for J. "Gadolin", a Finnish chemist and minerologist. Spectroscopic lines due to gadolinium were observed in samples of didymia and gadolinite. Gadolinia, the oxide of gadolinium, was separated by Paul-Emile Loq de Biosbaudran in 1886. The element was named for the mineral gadolinite from which this rare earth was originally obtained. The element itself was isolated only recently. 

Physical properties 
•Melting point: 1585 [or 1312 °C (2394 °F)] K
•Boiling point: 3523 [or 3250 °C (5882 °F)] K
•Density of solid: 7901 kg m-3

Orbital properties
•Ground state electron configuration: [Xe].4f7.5d1.6s2
•Shell structure: 2.8.18.25.9.2
•Term symbol: 9D2

Isolation
Gadolinium metal is available commercially so it is not normally necessary to make it in the laboratory, which is just as well as it is difficult to isolate as the pure metal. This is largely because of the way it is found in nature. The lanthanoids are found in nature in a number of minerals. The most important are xenotime, monazite, and bastnaesite. The first two are orthophosphate minerals LnPO4 (Ln deonotes a mixture of all the lanthanoids except promethium which is vanishingly rare) and the third is a fluoride carbonate LnCO3F. Lanthanoids with even atomic numbers are more common. The most comon lanthanoids in these minerals are, in order, cerium, lanthanum, neodymium, and praseodymium. Monazite also contains thorium and ytrrium which makes handling difficult since thorium and its decomposition products are radioactive.

For many purposes it is not particularly necessary to separate the metals, but if separation into individual metals is required, the process is complex. Initially, the metals are extracted as salts from the ores by extraction with sulphuric acid (H2SO4), hydrochloric acid (HCl), and sodium hydroxide (NaOH). Modern purification techniques for these lanthanoid salt mixtures are ingenious and involve selective complexation techniques, solvent extractions, and ion exchange chromatography. 

Pure gadolinium is available through the reduction of GdF3 with calcium metal.

2GdF3 + 3Ca → 2Gd + 3CaF2

This would work for the other calcium halides as well but the product CaF2 is easier to handle under the reaction conditions (heat to 50°C above the melting point of the element in an argon atmosphere). Excess calcium is removed from the reaction mixture under vacuum.