Enhancing green recovery of Nd and Fe using TGA–ChCl DES and vermiculite: sustainable leaching of NdFeB magnets with deep eutectic solvents (DES)

The critical role of NdFeB permanent magnets in the digital electronics and renewable energy sectors underscores the necessity for sustainable recovery methods for Neodymium (Nd). Traditional recovery techniques, predominantly reliant on solvent extraction, face drawbacks including high energy demands, extensive chemical use, and significant secondary organic waste generation. This study presents an innovative methodology employing Thioglycolic Acid and Choline chloride (TGA-ChCl) to synthesize deep eutectic solvents (DESs) for the leaching of Nd from spent NdFeB magnets. Vermiculite is introduced as an adsorbent in the subsequent recovery process. Key analyses, such as FTIR, confirm the formation of DES and its effectiveness in leaching, while NMR spectroscopy highlights the aliphatic hydrocarbon presence within DES. XRD and SEM analyses detail the crystallinity and surface morphology of the vermiculite adsorbent, respectively. The study examines variables influencing leaching efficiency, including solid-to-liquid mass ratio, time, and temperature, achieving a maximum leaching efficiency of 93.7% and enabling DES reuse upto 4 times with 91 -92% and then down to 84–87% for further reuse. The minor decline in leaching performance with repeated use is attributed to partial saturation of DES components and trace accumulation of impurities during stripping. However, the DES retained over 84% of its initial efficiency even after 10 cycles, highlighting its stability and reusability compared to conventional acidic systems. Vermiculite adsorption was optimized at 1.2 g/L dosage, 300 rpm stirring rate, and 60 °C, with calcium chloride providing the highest desorption efficiency, facilitating adsorbent recycling. Additionally, an Artificial Neural Network (ANN) model, comprising one hidden layer with 15 neurons, accurately predicted optimal Nd recovery conditions. Comparative analysis using Power BI demonstrated the enhanced efficiency of this approach over previous methods, establishing the DES-vermiculite system as a promising solution for sustainable Nd recovery from waste magnets.