Holmium Facts – Ho or Atomic Number 67

Holmium is a rare earth element with exceptional magnetic properties, striking orange-yellow color in compounds, and relatively high abundance among the lanthanides. It plays important roles in nuclear reactors, lasers, and even modern medicine. This article explores key holmium facts, covering its discovery, physical and chemical properties, sources, uses, and biological impact.

Key Holmium Facts

• Symbol: Ho
• Atomic Number: 67
• Element Category: Lanthanide (rare earth metal)
• Named After: Stockholm (Latin: Holmia)
• Appearance: Silvery-white, soft metal
• Magnetic Properties: Among the most magnetic elements at low temperatures
• Oxidation State: +3 is most stable and common
• Common Uses: Lasers, nuclear control rods, MRI contrast agents, glass coloring
• Abundance: Moderately abundant in Earth’s crust; found in monazite and bastnäsite
• Biological Role: No known essential role; low toxicity

History of Discovery, Isolation, and Naming

Holmium was discovered in 1878 by Swiss chemists Marc Delafontaine and Jacques-Louis Soret, who observed unusual spectral lines in rare earth samples. They initially called it “Element X.” Independently, Swedish chemist Per Teodor Cleve isolated holmium oxide (Ho₂O₃) in the same year from the mineral erbia, which itself was contaminated with multiple rare earths.

Cleve named the new element holmium after his native city of Stockholm, Sweden (Latin: Holmia). Its isolation as a pure metal was not accomplished until much later (1939 by Heinrich Bommer), with early methods relying on ion-exchange chromatography and later electrolysis of its fused halide salts.

Periodic Table Location and Group

Holmium is part of the lanthanide series, characterized by filling of the 4f subshell and similar chemical behavior. It lies between dysprosium (Dy) and erbium (Er).

• Atomic Number: 67
• Period: 6
• Block: f-block
• Group: Lanthanides (no numbered group in IUPAC system)
• Series: Rare earth elements

Appearance and Physical Description

• Color: Silvery-white metallic
• Texture: Soft, malleable, and ductile
• Luster: Bright metallic
• Oxidation in Air: Slowly oxidizes in moist air, forming a yellowish oxide layer
• Storage: Typically stored under oil or inert atmosphere to prevent surface oxidation

Physical and Chemical Characteristics

Holmium displays the general trends of lanthanides but stands out for its magnetism:

• Melting Point: 1461 °C (2662 °F)
• Boiling Point: 2600 °C (4712 °F)
• Crystal Structure: Hexagonal close-packed (hcp)
• Hardness: Relatively soft (Mohs ~3.0)
• Malleability: Malleable and ductile
• Corrosion Resistance: Poor in moist air; oxidizes readily
• Magnetic Properties: Extremely high magnetic moment; ferromagnetic at room temp; strongest paramagnet at low temps (below 20 K)

Isotopes of Holmium

Holmium has one stable isotope:

• ¹⁶⁵Ho (100% natural abundance; stable)

Several radioactive isotopes have been synthesized, including:

• ¹⁶³Ho (t₁/₂ ~4570 years)
• ¹⁶⁴Ho, ¹⁶⁶Ho, and others with half-lives ranging from milliseconds to hours

These isotopes are useful in nuclear medicine and scientific research.

Origin, Abundance, and Sources

Holmium, like all rare earth elements, forms in supernovae through neutron capture and stellar nucleosynthesis.

Abundance

• Crustal Abundance: ~1.3 ppm
• More abundant than: Silver, mercury, thallium

Sources

Found in rare earth minerals, including:

• Monazite ([Ce,La,Nd,Th]PO₄)
• Bastnäsite ((Ce,La)(CO₃)F)
• Xenotime (YPO₄, with trace holmium)

Extracted via:

• Solvent extraction
• Ion-exchange separation
• Electrolysis of HoCl₃ or HoF₃ with lithium or calcium

China is currently the largest producer of holmium and other rare earths.

Uses of Holmium

Holmium finds use in several high-tech and medical applications:

Industrial and Scientific

• Nuclear Control Rods: Ho has a high neutron absorption cross-section, making it ideal for regulating nuclear reactions.
• Alloys: Combined with other rare earths to form high-strength magnets and alloys.
• Lasers: Holmium-doped yttrium aluminum garnet (Ho:YAG) lasers are used in surgery (especially lithotripsy and eye surgery).

Optical and Magnetic

• Permanent Magnets: Holmium addition to neodymium-iron-boron (NdFeB) magnets improves their performance at high temperatures by increasing coercivity and reducing demagnetization. These high-strength magnets are used in motors, turbines, sensors, and electronic devices.
• Magnetic Field Calibration: Due to its large magnetic moment, holmium serves as a standard reference material for calibrating magnetometers and magnetic field sensors.
• Glass and Ceramics: Holmium oxide colors glass and synthetic gemstones such as cubic zircona a yellow or amber hue.
• Spectrophotometry Calibration: Holmium oxide has distinct absorption bands in the UV and visible range, making it ideal for calibrating UV/Vis spectrophotometers.

Medical

• MRI Contrast Agents: Holmium’s paramagnetism is useful in enhancing MRI imaging (experimental).
• Radiotherapy: Radioisotopes of holmium are used in cancer treatment and bone marrow ablation.

Oxidation States

• Common Oxidation State: +3
• Others: +1 and 0 states exist but are rare and unstable

The +3 state forms:

• Holmium oxide (Ho₂O₃)
• Holmium fluoride (HoF₃)
• Holmium nitrate (Ho(NO₃)₃)

Chemistry and Compounds

Holmium is chemically reactive:

• Reacts slowly with cold water and rapidly with hot water
• Forms basic oxides and salts
• Combines with halogens, acids, and other nonmetals
• Forms trivalent compounds (e.g., HoCl₃, Ho₂O₃)

Notable Compounds:

• Ho₂O₃ (Holmium(III) oxide): Pale yellow, insoluble in water, basic oxide
• HoCl₃ (Holmium(III) chloride): Yellow hygroscopic salt
• HoF₃ (Holmium(III) fluoride): White, insoluble in water

Biological Role, Health Effects, and Toxicity

Biological Role

• No known biological role in humans or other organisms
• Not considered an essential element

Health Effects

• Low toxicity in small amounts
• Dust or compounds may cause skin or eye irritation
• Inhalation of powder may affect the lungs

Environmental Impact

• Not considered highly bioaccumulative
• May pose risks if improperly disposed of in large quantities

Holmium Facts Table for Scientists

Comparison With Other Lanthanides

Holmium shares many characteristics with other lanthanides, but it also stands out in key ways that make it unique among rare earth elements. Here’s how it compares to some of its nearest neighbors:

Key Differences:

• Holmium has the highest magnetic moment of any naturally occurring element, surpassing even dysprosium in some conditions.
• Holmium oxide appears distinctly yellow, useful for color filtering, while erbium and dysprosium oxides are more muted.
• Holmium is less abundant than either neighbor, making its applications more specialized.

Interesting Holmium Facts

• Named after a city: Holmium gets its name from Holmia, the Latin name for Stockholm, Sweden.
• Magnetic marvel: At low temperatures, holmium exhibits the strongest known paramagnetism of any element.
• Colorful chemistry: Holmium oxide has a pale yellow color that tints glass and cubic zirconia.
• Nuclear use: Holmium’s high neutron absorption cross-section makes it suitable for nuclear control rods.
• Rare but not the rarest: Holmium is more abundant than silver and even iodine in Earth’s crust.
• Spectral standard: Solutions of holmium oxide calibrate UV/Vis spectrophotometers due to their sharp absorption lines.
• First isolated from erbia: Holmium was originally separated from a sample thought to be pure erbium oxide.

Frequently Asked Questions (FAQs)

Q: Is holmium magnetic?
A: Yes, holmium is extremely magnetic. It has the highest magnetic moment of any naturally occurring element, especially when cooled to cryogenic temperatures.

Q: What does holmium look like?
A: Holmium is a silvery-white, soft, and lustrous metal. It slowly tarnishes in moist air, forming a yellowish oxide layer.

Q: What is holmium used for?
A: Holmium has uses in lasers, nuclear control rods, calibration standards for spectrophotometers, and in making yellow-colored glass and ceramics.

Q: Is holmium toxic or radioactive?
A: Natural holmium (¹⁶⁵Ho) is not radioactive and displays low toxicity. Like many lanthanides, it still requires careful handling to avoid inhalation or ingestion of dust.

Q: Where is holmium found?
A: Holmium is found in monazite, bastnäsite, and xenotime minerals, often alongside other rare earth elements. It is extracted via ion exchange and solvent extraction methods.

Q: Is holmium useful in medicine?
A: Yes, holmium has uses in radiotherapy, MRI contrast agents, and holmium laser lithotripsy for breaking up kidney stones.

Q: How was holmium discovered?
A: Holmium was discovered in 1878 by Per Teodor Cleve, who isolated it from contaminated erbium samples. Its name honors his hometown of Stockholm.

Q: Can holmium be recycled?
A: Yes. Like other rare earth elements, holmium is recoverable from magnet and alloy scrap, though its small market means recycling is not widespread.

References

• Emsley, John (2011). Nature’s Building Blocks: An A-Z Guide to the Elements. Oxford University Press. ISBN 978-0-19-960563-7.
• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. doi:10.1016/C2009-0-30414-6. ISBN 978-0-08-037941-8.
• Haley, T. J. (1965). “Pharmacology and toxicology of the rare earth elements”. Journal of Pharmaceutical Sciences. 54 (5): 663–70. doi:10.1002/jps.2600540502
• Naumann, R. A.; Michel, M. C.; Power, J. L. (1960). “Preparation of long-lived holmium-163”. Journal of Inorganic and Nuclear Chemistry. 15 (1–2): 195–196. doi:10.1016/0022-1902(60)80035-8
• Strandburg, D. L.; Legvold, S.; Spedding, F. H. (1962). “Electrical and Magnetic Properties of Holmium Single Crystals”. Physical Review. 127 (6): 2046–2051. doi:10.1103/PhysRev.127.2046