The team outlined their magnetized chromatography method in a recent publication in ACS Sustainable Chemistry & Engineering.
Recycling rare earths from outdated or broken devices on a large scale can pose a challenge due to their integration into various components and their presence in small quantities. In discarded fluorescent lighting, mixtures of rare-earth-based phosphors, which contribute to the color of light, are typically found in a thin coating inside the bulb.
Laura Kuger, Matthias Franzreb, and their collaborators aimed to devise a low-tech method to gather these phosphors by leveraging the elements' weak magnetic properties.
The team of researchers employed a wire coil to externally administer a magnetic field to a glass chromatography column containing stacked stainless-steel mesh disks. Subsequently, they conducted a trial run using a prepared sample to assess its ability to capture phosphors.
Initially, the researchers acquired three distinct weakly magnetic rare-earth phosphors from a lamp manufacturer. Following this, they replicated aged fluorescent lamp components by blending the phosphor particles with a liquid solution comprising nonmagnetic silica oxide and highly magnetic iron oxide nanoparticles, representing the glass and metal constituents in the bulbs, respectively.
As the liquid was introduced and traversed through the chromatography column, the phosphors and iron oxide nanoparticles adhered to the magnetized stainless-steel mesh while the water and silica particles exited through the opposite end.
To remove phosphors from the column, the researchers gradually decreased the intensity of the external magnetic field while flushing the column with liquid. Ultimately, when the magnetic field was deactivated, the highly magnetic iron oxide nanoparticles were released from the column.
The researchers noted that their method successfully retrieved 93 % of the rare-earth phosphors from the initial mixture resembling lamp components. Although further efforts are required to isolate individual rare-earth elements from the phosphors and to adapt the method for industrial recycling purposes, Kuger, Franzreb, and their team assert that their approach represents an advancement toward a feasible means of transforming old light bulbs into new technologies, fostering a brighter and more sustainable future.
The study received funding from the German Research Foundation.
Journal Reference:
Kuger, L., & Franzreb, M. (2024) Design of a Magnetic Field-Controlled Chromatography Process for Efficient and Selective Fractionation of Rare Earth Phosphors from End-of-Life Fluorescent Lamps. ACS Sustainable Chemistry & Engineering. doi.org/10.1021/acssuschemeng.3c05707.