Separating critical elements from NdFeB magnets with aminophosphonic acid functionalised 3D printed filters and their detailed structural characterisation

Abstract

3D printed filters containing 70 wt% of polyamide (PA) nylon-12 as a polymer matrix and either 30 wt% of a commercial aminophosphonic acid functionalised resin (Lewatit TP260) or a synthetized aminobisphosphonic acid (1) as an additive were investigated for the separation of elements from a NdFeB magnet waste. Prior separation studies, the magnet was leached with 10 v/v% methanesulfonic acid using S/L ratio of 5 g/l for 20 h at 60 °C. The PA-TP260 filters adsorbed rare earth elements (REE) more efficiently than transition and main group elements and showed greater uptake than the PA-1 filters at the studied pH range of 0.15–4.00. Thus, the PA-TP260 filters were selected for the separation process, wherein Fe was first selectively precipitated from the leachate, while solid-phase extraction was used to separate the remaining elements from the leachate to four distinct fractions: REEs; B, Co; Cu; and Al. Neither significant decrease in the adsorption and desorption percentages of the PA-TP260 filters over 50 adsorption-desorption cycles, nor structural changes, as confirmed by the detailed X-ray tomography studies, were observed. Overall, the results demonstrate that the highly porous and reusable 3D-printed filters efficiently separate critical elements from NdFeB magnet leachate using only eco-friendly solutions of MSA, ammonium chloride, and potassium oxalate, paving the way for greener separation processes for these critical elements.