Gadolinium Facts – Symbol Gd or Atomic Number 64

Gadolinium (atomic number 64, element symbol Gd) is a silvery-white, malleable, and ductile rare earth metal that belongs to the lanthanide series of the periodic table. It has remarkable magnetic and nuclear properties, making it valuable in medical imaging, materials science, and nuclear reactors. Gadolinium exhibits exceptional neutron absorption, high magnetic susceptibility, and useful electronic behavior in alloys.

History of Discovery, Naming, and Isolation

Gadolinium was first identified in 1880 by Swiss chemist Jean Charles Galissard de Marignac. He observed spectral lines indicating a new element while analyzing didymium (then thought to be an element, now known to be a mixture). In 1886, French chemist Paul-Émile Lecoq de Boisbaudran successfully isolated gadolinium oxide (Gd₂O₃) from the mineral gadolinite.

The element takes its name for Johan Gadolin (1760–1852), a Finnish chemist and mineralogist who made pioneering studies of rare earths. Though gadolinium metal itself wasn’t isolated until the 20th century, the oxide’s identification laid the groundwork for rare earth chemistry.

Location on the Periodic Table

Gadolinium is part of the lanthanide series, positioned between europium (Eu) and terbium (Tb).

• Symbol: Gd
• Atomic Number: 64
• Period: 6
• Block: f-block
• Group: Lanthanides

Appearance and Allotropes

At room temperature, gadolinium is as a shiny, silvery-white metal. It is relatively stable in dry air but oxidizes slowly in moist air, forming a dull oxide layer. Gadolinium crystallizes in a hexagonal close-packed (hcp) structure at room temperature (α-form), but transitions to a body-centered cubic (bcc) β-form at temperatures above above 1,235 °C (2,255 °F). These structural forms are physical allotropes.

Physical Properties

• Solid at room temperature
• Malleable and ductile
• Ferromagnetic below 20 °C (293 K), paramagnetic above
• Good conductor of heat and electricity

Chemical Properties

Gadolinium is a reactive metal that readily forms compounds, particularly oxides, halides, and sulfates. It oxidizes in air and reacts slowly with cold water and rapidly with hot water. It dissolves in acids to form Gd³⁺ salts.

Nuclear Properties

Gadolinium has one of the highest known thermal neutron capture cross sections, making it ideal for nuclear control rods and shielding. Isotopes like Gd-155 and Gd-157 are especially effective neutron absorbers.

Isotopes

Natural gadolinium consists of seven isotopes. Six of these isotopes are stable (Gd-154, Gd-155, Gd-156, Gd-157, Gd-158, Gd-160) and one is a radioisotope (Gd-152) with a very long half-life (1.3×10²¹ years). Gd-158 is the most abundant isotope and accounts for 248% of the element’s natural abundance.

Thirty-three radioisotopes are known. Isotopes with atomic masses lower than Gd-158 mainly decay via electron capture. Isotopes with higher atomic masses primarily decay via beta decay.

Gd-155 and Gd-157 are used in nuclear reactors and medical imaging. Several radioactive isotopes find use in research, including Gd-153, used in bone density scans.

Origin, Abundance, and Sources

Origin

Gadolinium is a primordial element, formed through stellar nucleosynthesis by both the slow (s-) and rapid (r-) neutron capture processes in stars.

Abundance

• Crustal abundance: ~6.2 mg/kg
• Oceanic abundance: ~0.0000007 mg/L

Sources

• Minerals: Found in monazite and bastnäsite, which contain several lanthanides.
• Occurrence: Primary mining locations are in China, United States, Brazil, India, Sri Lanka, and Australia.
• Extraction: Typically extracted by solvent extraction or ion exchange from these ores, then isolated by reduction of GdF₃ or GdCl₃ with calcium.

Uses of Gadolinium

Gadolinium’s applications span several fields due to its unique properties:

Medical

• MRI contrast agents: Gd³⁺ ions are used in chelated form to enhance image clarity.
• Bone density scanning: Gd-153 emits gamma radiation suitable for dual-energy x-ray absorptiometry.

Nuclear Industry

• Reactor control rods and shielding: Gd-155 and Gd-157 have high neutron absorption cross sections.

Materials Science

• Magnetic refrigeration: Based on the magnetocaloric effect near room temperature.
• Alloys: Used to improve workability, strength, and oxidation resistance of iron, chromium, and related alloys.

Electronics and Optics

• Phosphors: Used in cathode ray tubes, LEDs, and fluorescent lamps.
• Data storage: Used in magneto-optical recording media.

Oxidation States

Like the other rare earth’s, the principal oxidation state of gadolinium is +3. The +2 state occurs, but is uncommon. Oxidations states of 0 and +1 also rarely occur.

Chemistry and Compounds

Gadolinium forms a variety of compounds, most commonly in the +3 oxidation state. Notable compounds include:

• Gadolinium oxide (Gd₂O₃): A white powder used in ceramics and phosphors.
• Gadolinium chloride (GdCl₃): Used in research and as a precursor to other compounds.
• Gadolinium nitrate (Gd(NO₃)₃): Used in magnetic refrigeration studies.

Gd³⁺ compounds are typically colorless to pale yellow and highly paramagnetic.

Biological Role, Health Effects, and Toxicity

Biological Role

Gadolinium has no known biological function in humans or other organisms.

Health Effects and Toxicity

Free Gd³⁺ ions are toxic because they interfere with calcium-dependent processes. However, gadolinium is reasonably safe in medical imaging when tightly bound in chelates (e.g., gadopentetate dimeglumine). In patients with kidney disease, gadolinium-based agents sometimes lead to a rare condition called nephrogenic systemic fibrosis (NSF).

Gadolinium accumulates in the bones, liver, and skin. Its toxicity depends largely on its chemical form.

Gadolinium Safety in MRI Use

Magnetic Resonance Imaging (MRI) is a powerful diagnostic tool, and gadolinium-based contrast agents (GBCAs) improve image clarity. However, because gadolinium is a heavy metal, patients and healthcare providers alike often wonder: Why is gadolinium used in MRI? Is it safe? What are the risks and how long does it stay in the body? Here’s a closer look at these questions.

Why Is Gadolinium Used in MRI?

Gadolinium is used in MRI scans because of its strong paramagnetic properties. When placed in a magnetic field, gadolinium enhances the contrast between normal and abnormal tissues, making tumors, blood vessels, inflammation, or lesions much easier to detect.

However, free gadolinium ions (Gd³⁺) are highly toxic. To make it safe for medical use, gadolinium is chemically bound to ligands, forming a stable chelate. This prevents the toxic ion from interacting with tissues and allows it to be safely excreted by the body—usually via the kidneys.

Is Gadolinium Safe?

In most people with healthy kidney function, gadolinium-based contrast agents are considered very safe. Millions of MRIs with GBCAs are performed annually with few serious side effects. However, two major safety concerns have been identified:

Nephrogenic Systemic Fibrosis (NSF)

• A rare but serious condition associated with GBCAs in patients with severe kidney impairment.
• It causes thickening and tightening of the skin and connective tissues and can be disabling or fatal.
• To reduce this risk, screening for kidney function is standard before administering gadolinium, especially in high-risk patients.

Gadolinium Retention

• Studies indicate that trace amounts of gadolinium remain in the body—even in people with normal kidney function.
• It deposits in the brain (especially the dentate nucleus and globus pallidus), bone, and skin.
• There is no clear evidence yet that these deposits cause harm in people with normal kidney function, but research is ongoing.

Common Side Effects of Gadolinium-Based Contrast Agents

Most patients do not experience any side effects. When they do occur, they are typically mild and short-lived, such as:

• Nausea
• Headache
• Dizziness
• Cold sensation at the injection site
• A metallic taste in the mouth

Rarely, allergic reactions occur, including hives, itching, or anaphylaxis. These are more likely in people with a history of contrast agent allergies or asthma.

Where Does Gadolinium Deposit in the Body?

When retained, gadolinium tends to deposit in:

• Brain tissue (especially in regions with higher vascularity)
• Bone (acts as a long-term storage site)
• Skin (especially in NSF cases)

The amount deposited depends on the type of GBCA (linear agents tend to retain more than macrocyclic agents), the dosage, and the number of previous exposures.

How Long Does Gadolinium Stay in the Body?

• In healthy individuals, more than 90% of the gadolinium dose is eliminated in the urine within 24 hours, and nearly all is gone within a week.
• In people with reduced kidney function, elimination is much slower, which increases the risk of retention and adverse effects.
• Gadolinium that does deposit in tissues potentially remains for months or years, although the chemical form it takes once deposited is still under investigation.

Summary

Key Gadolinium Facts Table

Interesting Gadolinium Facts

1. Named After a Person (Gadolin)
   Gadolinium is one of the few elements named in honor of a person—Johan Gadolin, a Finnish chemist who helped pioneer rare earth chemistry.
2. Super Magnetic at Room Temperature
   It’s ferromagnetic below about 20 °C (room temperature), which is unusual for a lanthanide.
3. Used in MRI Scans
   Gadolinium-based contrast agents are crucial in MRI imaging, lighting up internal tissues and structures for better diagnosis.
4. Neutron Sponge
   Gadolinium-157 has the highest thermal neutron capture cross-section of any stable element—about 254,000 barns! It’s like a neutron magnet.
5. Magnetic Refrigeration Potential
   Thanks to the magnetocaloric effect, gadolinium shows potential for future eco-friendly refrigerators that don’t need gases like freon.
6. Glimpsed in the Sky
   NASA launched a satellite that uses gadolinium in its sensors due to its neutron detection ability.
7. Hidden in Everyday Alloys
   Metals in daily life often contain trace amounts of gadolinium, which improves the high-temperature performance of iron, chromium, and stainless steel alloys.
8. Toxic in Its Free Form
   Free gadolinium ions (Gd³⁺) are highly toxic, but they’re generally safe in chelated form—unless you have severe kidney disease.
9. Rare Earth but Not So Rare
   Despite being called a “rare earth element,” gadolinium is more abundant in the Earth’s crust than lead.
10. Changes Structure with Temperature
    It shifts from a hexagonal structure to body-centered cubic as it heats up—this change influences its magnetic properties.

References

• Coey, J.M.; Skumryev, V.; Gallagher, K. (1999). “Rare-earth metals: Is gadolinium really ferromagnetic?”. Nature. 401 (6748): 35–36. doi:10.1038/43363
• Gadolin, Johan (1794). “Undersokning af en svart tung Stenart ifrån Ytterby Stenbrott i Roslagen” [Examination of a black heavy type of stone from Ytterby Quarry in Roslagen]. Kongliga Vetenskaps Academiens Nya Handlingar [Royal Academy of Science’s New Proceedings] (in Swedish). 15: 137–155.
• Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
• Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton, Florida: CRC Press. ISBN 0-8493-0486-5.
• Murphy, K.J.; Brunberg, J.A.; Cohan, R.H. (1996). “Adverse reactions to gadolinium contrast media: a review of 36 cases”. American Journal of Roentgenology. 167 (4): 847–49. doi:10.2214/ajr.167.4.8819369