Magnetic separation using nanoparticles: Prospects in nuclear waste management

Magnetic separation is a technique frequently employed in the minerals processing industry to target and capture contaminants (Figure 1). In recent years, the efficacy of this technique has improved significantly thanks to the development of iron-based magnetic nanoparticles.¹

Iron is one of the best known ferromagnets, meaning this metal can retain its magnetization even in the absence of an applied magnetic field. However, when iron oxides such as magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃) are shrunk to very small sizes, the material begins to exhibit superparamagnetic properties. In other words, the nanoparticles become strongly magnetized in the presence of an external magnetic field but become fully demagnetized once the field is removed. This behavior prevents the nanoparticles from agglomerating, which is highly beneficial for their effective use in dynamic and controlled separation processes, as well as cleaning of the particles for reuse.

In wastewater treatment, iron-based magnetic nanoparticles have successfully helped remove various contaminants.² In many cases, the surfaces of these nanoparticles are modified to exhibit specific functionalities.³ But some particles without surface modification perform well due to the inherent surface area available for sorption.⁴

Iron-based magnetic nanoparticles can also separate and extract radioactive contaminants, which makes them useful in nuclear waste management. For example, researchers previously developed magnetic nanoparticles functionalized with phosphate to selectively capture heavy metals and isotopes from liquid waste streams.⁵ After being bound, these complexes were separated from the nonradioactive waste using a magnetic field.

Additionally, compared to other magnetic separation approaches, magnetic nanoparticles perform well in nuclear waste management applications because of their high surface area-to-volume ratio, which enhances their binding capacity and efficiency. This attribute is particularly useful in dealing with the complex and diverse nature of nuclear waste, which often contains a mixture of elements in low concentrations.

Despite the potential of magnetic nanoparticles, several challenges hinder their widespread adoption. Researchers must address the nanoparticles’ long-term stability and recyclability to ensure this method is affordable and environmentally friendly. Comprehensive safety evaluations are also required to ensure the hazard-free usage of magnetic nanoparticles.

In the Nuclear, Optical, Magnetic, and Electronic (NOME) Materials Laboratory at Washington State University, the vitrification of nuclear waste into various glass waste forms is being studied. Finding alternative methods of pretreatment for other forms of nuclear waste, such as liquid waste streams, and implementing magnetic nanoparticles for magnetic separation are also important research areas. Currently, NOME researchers are investigating the redox chemistry of iron sulfide nanoparticles and their interaction with radionuclides in nuclear waste, such as is present at the U.S. Department of Energy Hanford cleanup site, as part of this alternative approach.

As a graduate student at Washington State University working in NOME, I have high hopes that these novel approaches will be crucial in solving the pressing problem of radioactive waste. Ultimately, magnetic nanoparticles may be our way to achieve effective and selective nuclear waste management.

About the author:
Nabil Ashraf Shuvo is a graduate student in chemistry at Washington State University. Since joining the Nuclear, Optical, Magnetic, and Electronic Materials Laboratory at Washington State led by John S. McCloy, his research has focused on magnetic nanoparticles and their interaction with radionuclides. In his free time, Nabil enjoys exploring nature and studying history and language.