OMNIA: Rare Earth Separations Made Simple

By Rebecca Guenard

The Claw! Descending into a congregate of plush toys, the claw pulls out a single prize and isolates it from the pack. We are all familiar with the popular arcade game; now imagine such a mechanism put to use at the atomic level. Eric Schelter, associate professor of chemistry, has discovered a molecular claw can be handy for separating rare earth metals. 

Though employed in a number of industrial applications—cell phone batteries, wind turbines, and electric car engines—rare earths are difficult to collect and concentrate. The metals are chemically quite similar.

Schelter has spent his career considering the problem of how to improve the current, laborious process of separating rare earth metals from mined ores while at the same time investigating how to recycle the metals already unearthed.  “At this point there are more rare earths in landfills than there are in global reserves in the ground in rocks,” says Schelter.

For the past five years the Schelter lab has focused on selectively changing the charge on one type of ion in a mixture of metal ions, hoping to use that unique charge as a separation method. While testing a molecule they had synthesized for this purpose, Schelter’s students noticed that
one metal ion complex had different solubility properties.

“It started as a simple inorganic coordination chemistry project with the end goal of potentially improving rare earth separations,” says Justin Bogart, a graduate student assigned to the project. “I don’t think either of us had any idea of where the project would end up.”

The compound Schelter’s students made is known as a ligand, which attaches to metal ions dissolved in a solution. But this ligand does something unique. When it encounters a neodymium ion the three prongs of the ligand open just enough to accommodate the dissolved metal cations.

“The nature of the ‘tripod’ ligand is such that it grabs onto the ion like a little claw, and depending on the size of the ion it fits into the claw in a slightly different way,” says Schelter.

The spacing of the tripodal ligand with neodymium nestled in the center results in a structural arrangement that allows a second ligand to join the ligand–metal ion complex. Two ligands linked to the metal ion exhibit completely different properties than just one. When the tripodal ligand is attached to a different metal ion its size will not allow a second ligand to connect. This difference in chemistry is harnessed to separate neodymium from other metal ions in solution.

What is remarkable about this accomplishment is that neodymium is being isolated from other rare earth metals based on a minuscule size difference, a couple hundredths of an Angstrom (10 to the -10 meters).

“It’s a really hard problem,” says Schelter. “That’s part of the reason we don’t have an efficient process for doing this.”

So far Schelter’s group has been able to separate neodymium from dysprosium—key elements used in very strong permanent magnets—in laboratory experiments. The group plans to look for other size-selective ligands and to use the tripodal ligand to separate other rare earth pairs. They will also explore methods to separate yttrium from europium—a mixture disposed of after mercury is removed from compact fluorescent bulbs.

Schelter notes that the group was lucky to discover the size-specific claw while looking for a charge separation method. “This is how research works much of the time. Maybe it wasn’t exactly how we planned to do the separation, but it works.”

Arts & Sciences News

The Power of Penn Arts & Sciences

On April 12, 2018, the Power of Penn Arts & Sciences fundraising campaign was announced by the Board of Overseers. Launched in conjunction with the University’s Power of Penn campaign, it aims to raise $550 million for the School of Arts and Sciences.

View Article >
2018 Penn Arts and Sciences Dean’s Scholars

Penn Arts and Sciences has named 20 students from the College of Arts and Sciences, the College of Liberal and Professional Studies, and the Graduate Division as Dean’s Scholars. This honor is presented annually to students who exhibit exceptional academic performance and intellectual promise.

View Article >
Joseph Subotnik Named Edmund J. and Louise W. Kahn Term Professor

Joseph Subotnik, Professor of Chemistry, has been named Edmund J. and Louise W. Kahn Term Professor of Chemistry. A theoretical chemist who focuses on electronic processes in the condensed phase, Dr. Subotnik has made key contributions in electronic structure theory, chemical dynamics, and statistical mechanics.

View Article >
Two Penn Arts and Sciences Professors Named Guggenheim Fellows

Charles L. Bosk, Professor of Sociology, and Charles Yang, Professor of Linguistics and Computer Science, have been awarded 2018 John Simon Guggenheim Memorial Foundation fellowships.

View Article >
Ahmad Family Endowment Supports Penn Global Seminars

Hyder Ahmad, W’90, and his family have made a generous gift to establish the Ahmad Family Endowment for Penn Global Seminars in Arts and Sciences.

View Article >
Abraham Nitzan Named Donner Professor of Physical Sciences

Abraham Nitzan, Professor of Chemistry, has been named Donner Professor of Physical Sciences. Nitzan’s research focuses on the interaction of light with molecular systems, chemical reactions in condensed phases and interfaces and charge transfer processes in such environments.

View Article >
2018 Teaching Award Recipients Announced

Steven J. Fluharty, Dean of Penn Arts and Sciences, and Paul Sniegowski, Stephen A. Levin Family Dean of the College of Arts and Sciences, have announced the recipients of the 2018 awards for distinguished teaching in the School.

View Article >
College Graduation Speakers for 2018 Revealed

Angela Duckworth, G’03, GR’06, Christopher H. Browne Distinguished Professor of Psychology, will address the Class of 2018 at the graduation ceremony for the College of Arts and Sciences on Sunday, May 13, 2018. She will be joined by student speaker Helena von Nagy, C’18.

View Article >
Individualized Care Will Become the Standard for Depression Patients

In a new paper for the Annual Review of Clinical Psychology, researchers Robert DeRubeis, Samuel H. Preston Term Professor in the Social Sciences, and Zachary Cohen of Psychology, address precision medicine, also known as customized-care, in the context of treatment for depression.

View Article >
Restoring Vacant Lots Reduces Gun Violence and Crime

In cities across the U.S., about 15 percent of land is considered vacant or abandoned. These areas can foster criminal activity, and urban residents, especially those in low-income neighborhoods, often view vacant land as a threat to their health and safety.

View Article >
Robert DeRubeis: Samuel H. Preston Term Professor in the Social Sciences

Professor of Psychology Robert DeRubeis has been named the Samuel H.

View Article >