Gadolinium: the essentials
Gadolinium is silvery white, has a metallic lustre, and is is malleable and ductile. 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.
Gadolinium: historical information
Spectroscopic lines due to gadolinium were observed by Jean Charles Galissard de Marignac in 1880 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.
Gadolinium: physical properties
Gadolinium: orbital properties
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.
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