A hyphenated optical-electrochemical set-up was used to investigate the early-stage dissolution mechanism of NdFeB permanent magnets immersed in acetic, citric, and formic acids at concentrations of 0.01 and 0.1 M. This approach enabled a direct correlation between quantifiable surface changes and dissolution behaviour under open-circuit potential (OCP) conditions. Despite minimal OCP variation (180 mV) across all conditions and rapid stabilisation within approximately 300 s, significant optically-detectable surface changes continued throughout the measurement period (1 h). This emphasises that surface dissolution kinetics, rather than thermodynamics, predominantly control the early-stage dissolution of NdFeB. Kinetic parameters obtained by fitting mean activity-level curves with a sigmoidal model revealed that higher acid concentrations result in shorter induction periods and faster surface activation. In-situ optical analysis indicated a consistent dissolution mechanism characterised initially by localised activation, followed by the progressive expansion of active sites across the surface. Post-immersion analysis confirmed preferential dissolution of rare-earth-rich phases at grain boundaries and triple points, alongside intragranular dissolution observed in 0.01 M citric acid. Among the tested conditions, dilute citric acid (0.01 M) emerges as particularly suitable medium for practical control, as its relatively long induction period (∼1378 s) allows monitoring and controlling local dissolution before rapid surface activation begins. The combined optical-electrochemical approach also revealed that, while rare-earth-rich sites are preferentially activated, early signs of matrix activation are detectable, underscoring the value of in-situ optical analysis for advancing process control in NdFeB recycling.

An evaluation of neodymium‑iron‑boron permanent magnets (NdFeB PMs) from different end-of-life products, as a secondary resource of rare-earth elements (REEs), is presented. De-coating of PM was investigate as pre-treatment to facilitate efficient direct magnet recycling. Thus, critical aspects from disassembling to the de-coating of the magnets were addressed. A challenge for the de-coating process is that the magnets have different sizes, weights, and their coating compositions are not known beforehand. It was shown that ammonia-based solutions was thermodynamically suitable to dissolve nickel and zinc coatings selectively, while keeping the bulk magnet stable. Nevertheless, the dissolution of Zn was much faster than the Ni one, and more efficient.