gadolínium

Gadolinium is a chemical element with the symbol Gd and atomic number 64. It is a silvery-white lanthanide metal that tarnishes slowly in air and is relatively stable under normal conditions. In nature, gadolinium occurs primarily in minerals such as gadolinite, monazite, and bastnasite, and it is typically extracted as part of rare-earth concentrates.

Occurrence and production

Gadolinium is not found free in nature. It is obtained from mixed rare-earth ores and refined through processes such as solvent extraction and ion-exchange to separate it from other lanthanides. Major producers include countries with large rare-earth industries, and refining work often occurs in regions with substantial mineral resources and established processing facilities.

Properties

Gadolinium has a melting point of about 1313°C and a density around 7.9 g/cm³. Its magnetic behavior changes with temperature: it is ferromagnetic below the Curie point of about 20°C and becomes paramagnetic above. It has a relatively high neutron capture cross section for certain isotopes, making it useful in nuclear applications. Gd compounds are typically colorless or white solids and can form a variety of coordination complexes.

Isotopes and occurrence

Natural gadolinium comprises seven stable isotopes and several radioactive isotopes with half-lives far shorter than geological timescales. The stable isotopes include Gd-152, -154, -155, -156, -157, -158, and -160, with varying natural abundances.

History

Gadolinium was identified in 1880 by the Swiss chemist Jean Charles Galissard de Marignac while studying gadolinite. The element was named after the Finnish scientist Johan Gadolin, in recognition of his work on rare-earth minerals.

Applications and safety

Gadolinium compounds are widely used as contrast agents in magnetic resonance imaging (MRI), especially when combined with chelating ligands to form gadolinium-based contrast agents. They are also used in nuclear reactors and shielding due to their high neutron capture cross sections. In medicine, gadolinium-based contrast agents are generally safe for people with normal kidney function, but exposure carries risks for those with severe kidney impairment, including nephrogenic systemic fibrosis in the past and concerns about gadolinium deposition with repeated use. Safer choices favor macrocyclic over linear chelates.