The Potential Application of UV-Vis Spectroscopy in Rare Earths Concentration Monitoring: A case study of NdFeB recycling

NdFeB magnet recycling relies on both short and long loop processes. One of the key challenges in hydrometallurgy is achieving real-time, on-line or in-line analysis of metal concentrations. Other process parameters such as temperature, pressure, pH, oxidation-reduction potential, density and viscosity have dedicated probes and routinely measure such parameters on-line or in-line. In the case of metal concentration, the current process still relied on periodic sampling in combination with lengthy and destructive off-line analysis such as Inductively Coupled Plasma - Optical Emission Spectroscopy (ICP-OES). REEs in aqueous solution exhibit distinctive absorption bands in the visible region due to their electronic transition within the 4f configuration. This is a notable phenomenon as visible spectroscopy has advantages over ICP-OES, including being non-destructive, more affordable, and faster. Thus, we explore the applicability of using UV-Vis spectroscopy to monitor REEs composition in long-loop NdFeB recycling. It involves dissolving the nitrate or chloride salts of the desired elements in deionised water, HCl and HNO3. The impact of different matrices on molar absorptivity was studied for each element commonly found in NdFeB magnets. Finally, data processing via univariate and multivariate approach for REEs concentration monitoring were compared.