Separating critical elements from a NdFeB magnet with aminophosphonic acid functionalised 3D printed filters and their detailed structural characterisation with X-ray tomography

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. Before 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 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. The results indicate that the PA-TP260 filters are robust and fully reusable. Overall, the results demonstrated that the highly porous 3D printed filters efficiently separate critical elements from the NdFeB magnet leachate only by using ecofriendly MSA, ammonium chloride, and potassium oxalate solutions paving the way towards greener separation processess for the critical elements.