Water-based method separates rare earths without toxic solvents

University of Chicago researchers report separating rare earth elements in water using layered manganese oxide, no organic solvents.

Researchers led by Associate Professor Chong Liu at the University of Chicago's Pritzker School of Molecular Engineering, working with Northwestern University and Argonne National Laboratory, report a way to separate rare earth elements from one another without toxic chemicals. The work was published in Nature Chemical Engineering.

The method uses a layered form of manganese oxide with gaps engineered to be only a few water molecules wide, and relies on electrochemical intercalation — ions moving in and out of those layers — in water rather than organic solvents. It exploits the fact that each dissolved rare earth ion carries a shell of water of a slightly different size; lighter elements like lanthanum have larger shells, heavier ones like dysprosium have smaller. Adding magnesium ions and an electric current pinned the channel spacing, sharpening the separation: enrichment of neodymium over lanthanum rose from 1.6-fold to 5.4-fold, and two purification cycles yielded a neodymium sample 97% pure. Density functional theory simulations matched synchrotron X-ray measurements from Argonne.

Rare earth separation today leans on harsh chemistry, which is a major environmental and supply bottleneck for magnets, motors, and clean-tech generally. A solvent-free, water-based route would cut that cost and ease the chokepoint. The caveats are real: some of the most useful elements were too similar to separate before the magnesium refinement, and the team calls the method competitive but has not demonstrated it at manufacturing scale. The source text was truncated.

Source: Phys.org