PNNL

The Science

Magnetic fields influence groups of ions and particles in solutions, but the exact details of these effects remain unclear. Researchers developed a new theoretical framework to better understand and predict how external magnetic fields affect the interaction between nanoscale domains consisting of paramagnetic ions in solution. Their work uses surface magnetic regions to represent groups of ions that comprise nanodomains. The team used experimental data to validate the simplifying approximations within the theoretical framework, assessing the accuracy of the approach. Simulations showed that external magnetic fields significantly affect how nanoscale domains of magnetically susceptible ions interact in solutions, which is in contrast to the behavior of free ions distributed in bulk solution. These magnetically driven interactions can compete with other intermolecular forces, opening an avenue for new approaches to magnetic separation of critical minerals like rare earth elements.

The Impact

Rare earth elements are a class of critical minerals that have proven particularly challenging to separate, as collocated ions have similar chemical and physical properties. However, these ions differ in their responses to magnetic fields, offering a potential avenue for effective separations. Making these separations practical requires knowing how ions in solution respond to magnetic fields. This theoretical framework will enable researchers to have a deeper understanding to predict how magnetic fields influence the structure, domain formation, and transport of paramagnetic ions in solution—a crucial step to developing tailored separation processes. Future work will extend the framework to enable investigations of the dynamic evolution of micro- and nanoscale correlated liquid domains under external fields relevant to magnetophoresis in solution.

Summary

Although external magnetic fields may influence the interactions between paramagnetic ions in liquids, their effects remain insufficiently understood. Researchers developed a simplified model of solvated nanodomains that consist of localized magnetic surface regions, which represent groups of paramagnetic ions. These groups can form nanodomains with an effective magnetic dipole moment at least one order of magnitude greater than that of individual ions. They used classical density functional theory to estimate the effective interactions between localized magnetic nanodomains solvated in a diamagnetic solvent. Results indicate that, unlike individual ions, magnetic dipole interactions of nanodomains in the localized magnetic regions model indeed compete with other intermolecular interactions. The effective interactions between two nanodomains change at relatively short separations—on the order of 1 nm or less. This indicates that the interactions driven by an external magnetic field play a critical role in aggregation for nanodomains. Importantly, these effects are observed for relatively weak magnetic fields achievable with inexpensive permanent magnets, opening up new opportunities for critical mineral separations.  

Contact

Hadi Dinpajooh, Pacific Northwest National Laboratory, hadi.dinpajooh@pnnl.gov 

Funding

This study was supported by a collaborative effort funded by the Laboratory Directed Research and Development program at Pacific Northwest National Laboratory, under the Non-Equilibrium Transport Driven Separations Initiative. PNNL is operated by Battelle for the Department of Energy under Contract No. DE-AC05-76RL01830. Computing resources were generously allocated by PNNL’s Institutional Computing program. T.E.L. acknowledges the start-up funds from the University of Delaware Department of Physics and Astronomy.