The Elements of Innovation Discovered
The Elements of Innovation Discovered
Metal Tech News - April 9, 2025
Scientists estimate that only around 1.3 pounds of naturally occurring promethium exists on Earth at any given time.
Oak Ridge National Laboratory scientists have discovered hidden features of promethium that are providing a better understanding of all the lanthanide elements.
From left: Alex Ivanov, Santa Jansone-Popova, and Ilja Popov are among the scientists leading groundbreaking promethium research at Oak Ridge National Laboratory.
Though rare earth elements are not as rare as their name implies, promethium is an exception – a truly elusive element with no stable isotopes and an extremely short half-life. Scientists estimate that only around 600 grams (1.3 pounds) of promethium exist on Earth at any given time.
While promethium is virtually non-existent in nature, the U.S. Department of Energy Isotope Program at Oak Ridge National Laboratory (ORNL) is able to "mine" promethium-147 from other radioactive elements.
Considering that promethium was discovered at ORNL in 1945, then Clinton Laboratories, it is fitting that this national lab in Tennessee be the only place on earth where the exceptional rare earth is produced.
The promethium recovered at ORNL is used for luminous paints for glow-in-the-dark watch dials, gauges, and signs; in nuclear batteries that power devices like pacemakers, guided missiles, and communications equipment; and in cutting-edge technologies such as radioactive imaging and cancer treatment research.
Although ORNL has long been able to synthesize promethium-147, the constant decay of this isotope has made its study difficult. Now, scientists at the lab have succeeded in stabilizing promethium-147 in solution by binding it to an organic molecule, creating a compound that enables unprecedented study of this fleeting element that seems to be the keystone in the rare earth family of elements.
Oak Ridge National Laboratory scientists have discovered hidden features of promethium that are providing a better understanding of all the lanthanide elements.
Setting aside its rarity and difficulty to study, promethium is a scientific curiosity that could provide a better understanding of all rare earths.
For starters, promethium is one of only two radioactive elements on the periodic table with non-radioactive elements before and after it – technetium being the other. More importantly to the ORNL research, promethium is at a waypoint of a rare earth phenomenon known as lanthanide contraction.
Lanthanide contraction refers to the gradual decrease in ionic radius across the rare earth series, a phenomenon that makes these elements smaller than expected compared to others on the periodic table. As the atomic numbers of the lanthanides increase from 57 to 71, their ions become smaller, and the bonds between atoms grow shorter.
Holding a charge within a shrinking space is a feature that provides rare earth elements with many of their distinctive properties.
Lanthanide contraction accelerates over the first five rare earth elements, up to and including promethium, and then suddenly, the rate of elemental shrinkage slows, and the bond lengths decrease at a decreased pace.
"The contraction of this chemical bond accelerates along this atomic series, but after promethium, it considerably slows down," Alex Ivanov, an ORNL scientist, said during a promethium breakthrough in 2024. "This is an important landmark in understanding the chemical bonding properties of these elements and their structural changes along the periodic table."
From left: Alex Ivanov, Santa Jansone-Popova, and Ilja Popov are among the scientists leading groundbreaking promethium research at Oak Ridge National Laboratory.
With promethium-147 stabilized in a compound with an organic molecule in water, ORNL researchers used X-ray absorption spectroscopy to measure the length of the bonds between promethium and the oxygen atoms it was bound to. These precise measurements offer new insights into promethium's chemical behavior and help unravel the mechanics of lanthanide contraction.
By uncovering promethium's role in this phenomenon, the ORNL scientists are gaining a more detailed understanding that could lead to improved separation methods for producing larger quantities and purer forms of the elusive element.
This deeper understanding lays the groundwork for innovations in rare earth separation that could help secure future supplies of this suite of tech elements.
"You cannot utilize all these lanthanides as a mixture in modern advanced technologies, because first you need to separate them," said Santa Jansone-Popova, a scientist at ORNL. "This is where the contraction becomes very important; it basically allows us to separate them, which is still quite a difficult task."
With more than 17 years of covering mining, Shane is renowned for his insights and in-depth analysis of mining, mineral exploration, and technology metals.
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