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 synthesized aminobisphosphonic acid (1) as an additive were manufactured via selective laser sintering and investigated for the separation of elements from a NdFeB magnet waste. Prior to separation studies, the magnet was leached with 10 v/v% methanesulfonic acid using an S/L ratio of 5 g l⁻¹ for 20 h at 60 °C. The PA-TP260 filters adsorbed rare earth elements (REEs) 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; Al; and Cu. 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 X-ray tomography and Fourier transform infrared spectroscopy studies, were observed. Overall, the results demonstrate that highly porous and reusable 3D printed filters efficiently separate critical elements from the 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.