Description
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Thulium is a lanthanide that has a bright silver grey appearance in its natural solid state. It is soft enough to be cut with a knife, and it has some anti-corrosive properties. Thulium has an atomic weight of 168.9342, a melting point of 2813 °F, and a boiling point of 3542 °F. As one of the rarest rare earth elements, thulium is extremely expensive and is not used much for commercial purposes. In the past, it was used as a laser light, but it was too expensive to keep producing.
Isolation
Thulium is found in nature in very small amounts in some minerals and clays. Isolation procedures are needed to isolate thulium from these sources.
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The clays and minerals that thulium occur in also contain high amounts of other lanthanides. The mineral monazite is in the ore which is used the most for thulium extraction and isolation. Due to the fact that all the lanthanides have similar chemical characteristics, separating them from the minerals in which they occur in together is very difficult. The complexity of the isolation process, and the rarity of the metal, makes small scale laboratory isolation of thulium nearly impossible.
The isolation process of thulium begins with treating the ore monazite to sulfuric acid, hydrochloric acid, and sodium hydroxide. This mixture extracts the lanthanides, including thulium, out in their salt form. Additional treatments using solvent extractions and ion exchange chromatography further isolate thulium from the other lanthanides. The reduced fluoride from of thulium is then reacted with pure calcium under heated conditions to yield a purer form of thulium metal. Any calcium contaminants that remain are removed through vacuum processes.