Determination of rare earth elements in CRT phosphors and NdFeB magnets residues using an ED-XRF portable spectrometer to assist field semi-quantitative screening

Rare earth elements (REE) are a series of chemical elements characterized by physicochemical properties that give them special niche applications. Neodymium-based permanent magnets and cathode-ray tube (CRT) phosphors are important components, widely used in critical electric and electronic devices that rely on those elements. Recycling rare earth elements from these residues is very beneficial from environmental and economic points of view. Energy-dispersive X-ray fluorescence (ED-XRF) is a conventional non-destructive technique that delivers fast and accurate results regarding chemical composition, particularly appropriate for field analyses when using a portable equipment. However, neither rare earth elements nor this kind of matrixes is included in portable XRF spectrometer manufacturer's calibrations, making this technique difficult to be used to evaluate the presence of REE. Therefore, in this work, calibrations for rare earth elements and other main elements present in cathode-ray tube phosphors and neodymium-based permanent magnets were developed, mimicking target matrixes with metal oxides and sulphides using different composition combinations according to literature reported contents. Calibrations were installed in a portable XRF equipment with the objective of providing an easy and fast method for operational industry measurements. Spectra obtained were treated using proprietary software taking in consideration the overlap of peaks and matrix effects. The final installed calibrations were tested with simulated and real waste specimens of waste materials. Implementing these calibrations on a portable XRF spectrometer can aid screening of target WEEE and estimation of REE content at e-waste recycling plants in a fast and accurate way. The results show quantification is possible in real samples for all key elements in CRT phosphors and NdFeB magnets, but also that magnets are far more challenging to work with.