Samarium

Samarium: the essentials

 Brief description: samarium has a bright silver lustre and is reasonably stable in air. It ignites in air at 150°C. It is a rare earth metal. It is found with other rare earth elements in minerals including monazite and bastnaesite and is used in electronics industries.

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Isolation

Isolation: samarium 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 samarium is available through the electrolysis of a mixture of molten SmCl₃ and NaCl (or CaCl₂) in a graphite cell which acts as cathode using graphite as anode. The other product is chlorine gas.

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