Oak Ridge, Tennessee — Researchers have long revered a violet glow in their laboratories, a signal that something rare and valuable lurks just out of reach: promethium, element 61 on the periodic table. This elusive element has remained largely unstudied, but recent advancements at the Oak Ridge National Laboratory (ORNL) have finally shed light on its properties, filling a critical gap in the understanding of rare earth elements (REEs).
Rare earth elements, though prevalent in various technologies, are not as rare as their name suggests. They are essential for devices ranging from smartphones to electric vehicles. Known for their unique magnetic and phosphorescent characteristics, REEs play a crucial role in modern technology. However, the extraction and processing of these elements remain challenging, particularly as most of the world’s supply is sourced from China, prompting researchers to seek more sustainable methods of extraction and recycling.
Promethium was first identified in 1945 within the wartime reactors at Clinton Laboratories, now part of ORNL. A natural scarcity, along with the radioactivity of its isotopes, has complicated efforts to study this element. Currently, only about a pound of promethium exists naturally in the Earth’s crust, and all of its isotopes are unstable, making it difficult to obtain. ORNL is the only U.S. facility capable of producing small batches of promethium-147 for experimental purposes.
A team of ORNL scientists, led by Alex Ivanov, has developed a new approach to studying promethium in solution. By creating a unique diglycolamide ligand that binds to promethium atoms, the researchers successfully dissolved the isotope in water, allowing them to direct intense X-ray beams at it. This groundbreaking technique marked the first instance of measuring promethium’s hydrated radius, which has implications for understanding its chemical behavior.
The researchers compared this new bond length to data from other lanthanide elements and illustrated how the size of ionic radii changes across the series. Their findings revealed that the contraction pattern accelerates until reaching promethium before slowing down for subsequent elements. These insights were corroborated by computer simulations utilizing ORNL’s Summit supercomputer, validating long-held theories about lanthanide behavior.
Promethium presents unique qualities distinct from the more commonly utilized rare earth metals. Its stable beta radiation has powered long-lasting nuclear batteries in medical devices and spacecraft instruments. With a half-life of just 2.62 years, engineers can design devices that gradually fade over time, a beneficial trait for many applications.
The new findings have significant implications for the development of advanced technologies. For instance, a better understanding of how promethium interacts with various solvents can enhance purification processes, potentially leading to innovative uses like compact power sources for deep-sea sensors.
The separation of REEs remains a complex and expensive process, often requiring extensive solvent-extraction techniques. Understanding the ionic size of promethium and other lanthanides facilitates more efficient separation, crucial for their application in advanced technologies. “You cannot utilize all these lanthanides as a mixture in modern advanced technologies,” said Ilja Popovs, another co-leader of the study.
The collaboration between ORNL and Brookhaven National Laboratory exemplifies how cutting-edge research can unravel atomic mysteries. The high-precision measurements and simulations conducted may set the stage for future inquiries related to promethium and its bonding characteristics, paving the way for advances in battery materials and medical applications.
As the study progresses, the violet glow that once mystified scientists now illuminates a clearer understanding of lanthanide chemistry. With promethium finally characterized, the periodic table appears more complete, promising to enhance the performance of technologies that rely on these vital elements. The meticulous research at ORNL ushers in new hope for achieving a deeper understanding of rare earth elements and their critical roles in the modern world.