- Gadolinium (Gd) is a silvery-white, malleable, and ductile rare earth metal with atomic number 64, belonging to the lanthanide series of the periodic table.
- Its electron configuration is [Xe] 4f⁷ 5d¹ 6s², featuring a half-filled 4f subshell that imparts notable magnetic properties. Gadolinium most commonly exists in the +3 oxidation state, forming Gd³⁺ ions, although the +2 state can be observed in some compounds under controlled conditions. The atomic structure contains sixty-four protons, generally ninety-three neutrons in its most abundant isotope, and sixty-four electrons arranged in six shells.
- Naturally occurring gadolinium is composed of seven stable isotopes, with gadolinium-158 (¹⁵⁸Gd) being the most abundant at around 24.8%. Several isotopes, particularly gadolinium-155 (¹⁵⁵Gd) and gadolinium-157 (¹⁵⁷Gd), have extraordinarily high thermal neutron capture cross-sections, making them valuable in nuclear applications.
- Gadolinium is not found in free metallic form in nature but occurs in minerals such as monazite and bastnäsite, alongside other rare earth elements. Significant deposits are found in China, the United States, Brazil, India, and Australia. Extraction typically involves separating gadolinium from other lanthanides through solvent extraction and ion-exchange processes.
- The element was discovered in 1880 by Swiss chemist Jean Charles Galissard de Marignac, who detected its unique spectral lines while analyzing the mineral samarskite. It was later isolated in a purer form by French chemist Paul-Émile Lecoq de Boisbaudran in 1886. Gadolinium was named after the Finnish chemist Johan Gadolin, a pioneer in rare earth chemistry.
- Gadolinium’s most notable property is its strong paramagnetism at room temperature, which becomes ferromagnetic below its Curie point (about 20 °C). This, combined with its high neutron capture capability, has led to a wide range of applications. In nuclear reactors, gadolinium is used as a neutron absorber in control rods and as a burnable poison to manage reactivity. In medicine, gadolinium compounds—particularly gadolinium chelates—are widely used as contrast agents in magnetic resonance imaging (MRI) due to their strong effect on local magnetic fields, which enhances image clarity. Gadolinium is also used in manufacturing gadolinium garnets for optical and microwave applications, as well as in alloys to improve workability and resistance to oxidation.
- Chemically, gadolinium is moderately reactive. It oxidizes slowly in dry air but more rapidly in moist conditions, forming a protective oxide layer. It reacts slowly with cold water and more quickly with hot water, producing gadolinium hydroxide and hydrogen gas. Gadolinium readily reacts with acids, forming Gd³⁺ salts that are typically colorless to pale pink.
- Biologically, gadolinium has no known essential function in living organisms. While metallic gadolinium and its insoluble salts are considered to have low toxicity, soluble gadolinium compounds can be toxic, especially if not bound in stable chelates. This is particularly relevant in medical applications, where improper clearance of gadolinium-based contrast agents has been linked to nephrogenic systemic fibrosis in patients with kidney impairment.
- From an environmental standpoint, gadolinium in its mineral form is stable and not inherently hazardous. However, increased anthropogenic release of gadolinium from medical imaging waste into aquatic systems has raised concerns about its accumulation in the environment and potential long-term ecological effects.
