Researchers swap acid baths for atomic channels to separate rare earths

Splitting neodymium from lanthanum usually means acid baths and organic solvents in many-stage extraction plants, because the 17 rare earths are chemically so similar that pulling one out of the rest is unusually hard. A Nature Chemical Engineering paper this week from the University of Chicago's Pritzker School of Molecular Engineering, with Northwestern and Argonne collaborators, points at a different lever.

The team uses a layered manganese-oxide mineral whose interlayer gap is just a few water molecules wide. Without help, the channel is too floppy to discriminate the trickiest near-neighbor pairs. Magnesium ions added as a scaffold pin the gap to a fixed width, so rare-earth ions slip through at different rates based on the size of their hydration shell rather than the radius of the bare ion. That single change pushes neodymium-over-lanthanum enrichment from 1.6x to 5.4x, and two cycles yield 97% pure neodymium, per the UChicago press release.

The cell runs in water with an electric current, no organic solvents. Co-author George Schatz calls that a chemistry that "could actually change how and where that processing gets done," tying it to the US and EU push to onshore rare-earth separation from China. The honest scale is a lab proof of concept, not a replacement for the solvent-extraction trains that purify these metals today. Liu's group is now testing the remaining lanthanides; Schatz is refining the density-functional-theory models that predict the channel behavior.