Holmium oxide, also known as holmium trioxide, has the chemical formula Ho2O3. Holmium oxide is a compound composed of rare earth element holmium and oxygen. It is as famous as dysprosium oxide and is one of the most paramagnetic substances known. Holmium oxide is one of the components of erbium oxide minerals. In its natural state, holmium oxide often coexists with trivalent oxides of lanthanides, and a specific method is required to separate the two. Holmium oxide can be used to prepare special colored glass. The visible absorption spectrum of glass and solution containing holmium oxide has a series of sharp peaks, so it is traditionally used as a standard for spectrophotometer calibration.
Holmium oxide crystals belong to the cubic crystal system, but the structure is more complex, each unit cell has many atoms, and the lattice constant is relatively large, 1.06nm. This structure is a typical structure of oxides of heavy rare earth elements, such as Tb2O3, Dy2O3, Er2O3, Tm2O3, Yb2O3, and Lu2O3. The thermal expansion coefficient of holmium oxide is relatively large, reaching 7.4μm/℃.
Holmia (Holmia, the Latin name for Stockholm) was discovered in 1878 by Marc de la Fontaine and Jacques Luis Solé when they noticed an unusual absorption band of an unknown element. At the end of 1878, Pell Teodor Cliff also independently discovered this element in the study of erbium oxide.
According to the method developed by the chemist Carl Gustav Mossander, Cliff cleaned out the impurities in erbium oxide. Among the impurities, there are two kinds of impurities, brown and green. He named the brown substance after his hometown of Stockholm "Holmia", named the green substance "thulia". Later it was discovered that the substances he separated were actually holmium oxide and thulium oxide.
The typical extraction process of holmium oxide is briefly described as follows: mineral crushing and grinding. The electromagnetic beneficiation method is used repeatedly to separate the holmium oxide from the lanthanum phosphate ore. After beneficiation, it is treated with hot concentrated sulfuric acid to produce sulfates of several rare earth elements that are soluble in water. The acidic filtrate is partially neutralized with sodium hydroxide to a pH between 3-4. Thorium will precipitate out as hydroxide. Then, the solution is treated with ammonium oxalate to convert the rare earth salt into insoluble oxalate. Through annealing, oxalate is converted into oxide, and the oxide is dissolved in nitric acid, and the oxide of the main component cerium is insoluble in nitric acid, thus separating the cerium.
The most efficient method to separate holmium oxide from rare earth elements is ion exchange. The rare earth ions are adsorbed on a suitable ion exchange resin, and then a suitable complexing agent, such as ammonium citrate or nitrilotriacetic acid, is used to selectively wash out the rare earth ions.
Holmium oxide can be used as a yellow and red colorant for Soviet diamonds and glass. Glass containing holmium oxide and holmium oxide solution (usually perchloric acid solution) have sharp absorption peaks in the spectrum of 200~900nm, so they can be used as standards for spectrometer calibration and have been commercialized. Like other rare earth elements, holmium oxide is also used as a special catalyst, phosphor and laser material. The holmium laser has a wavelength of about 2.08μm and can be pulsed or continuous light. This laser is harmless to the eyes and can be used in medicine, optical radar, wind speed measurement, and atmospheric monitoring.
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