Peptide-assisted High-Gradient Magnetic Separation for Recovery of Rare Earth Elements

The recovery of critical raw materials from a complex waste of electrical and electronic equipment is becoming an increasingly important issue in the transfer towards a more sustainable economy. The main challenges are to separate fine particles, with sizes below 10 microns, in a highly selective and feasible process. In this context, short peptide chains with a high selectivity for inorganic surfaces have the potential to play a key role in innovative particle separation processes.

Using phage surface display, our team has identified peptide sequences that selectively bind to the surface of valuable Rare Earth Element containing phosphors present in compact fluorescent lamps. Subsequently, the biomolecules were chemically immobilized on the surface of superparamagnetic carriers, including magnetic nanoparticles and micron-sized composite beads, to render these particles selectivity for the targeted phosphors. Separation experiments of virgin and end-of-life phosphors were performed in a high-gradient magnetic-separator that allows for a high-throughput process, which can be scaled up readily.

The next goal is to be able to tune the interaction of reusable peptide-functionalized superparamagnetic carriers with the target phosphors, to allow for an integrated magnetic separation process with rapid cycles of: 1) target-carrier sorption 2) separation of target from nontarget particles 3) target-carrier desorption and 4) carrier recovery. Currently, we are further investigating the nature of the peptides’ selective interactions with the phosphors’ surfaces, by means of isothermal titration calorimetry, binding experiments in different media and zetapotential measurements.

Hence, we are working towards a proof-of-concept for the recovery of currently not recyclable fine particles, by applying bio-inspired surfaces to allow for a higher selectivity and lower process cost than conventional separation methods.