Metrology of rare earths and other elements in waste fluorescent lamp powder - A methodological comparison

The recycling of rare earth elements (REEs) from electronic waste is critical for supporting clean energy technologies, yet accurate quantification remains challenging due to the lack of standardized analytical methods and certified reference materials. Waste fluorescent lamp powder (FLP) is a promising secondary source of REEs, but its heterogeneous composition and complex matrices hinder reliable analysis. This study addresses the problem of method selection for FLP characterization by comparing multiple sample preparation and analytical techniques to identify workflows that ensure accurate and reproducible quantification.

Four sample preparation methods: 1) alkaline fusion for solutions (AFS), 2) alkaline fusion for glass disks (AFG), 3) microwave digestion (MWD), and 4) focused infrared digestion (FIRD) were evaluated using ICP-MS/MS, ICP-OES, MP-AES, and ED-XRF. A synthetic FLP material and seven real FLP samples were analyzed to assess accuracy and feed variability. AFS achieved complete dissolution and provided the most consistent results across plasma-based techniques, while AFG enabled stable fused disks for XRF analysis. Acid digestion with phosphoric-sulfuric mixtures improved recoveries compared to aqua regia but remained less effective than fusion. ICP-MS/MS and ICP-OES delivered comparable accuracy for REEs, whereas MP-AES underestimated REEs and ED-XRF slightly overestimated Eu. Temporal analysis of real FLP samples revealed significant compositional variability, underscoring the need for robust protocols.

Alkaline fusion combined with ICP-MS/MS or ICP-OES offers the most reliable approach for FLP characterization, while ED-XRF on fused disks provides a practical option for routine monitoring. These findings establish a validated analytical framework for e-waste streams lacking certified reference materials, supporting accurate resource recovery and advancing circular economy initiatives.