Separation of rare earth elements from waste NdFeB magnets: The influence of hematite seeds and agents on the hematite precipitation in nitric acid medium

Nowadays with the evolution of technology and rare earth elements (REE) are raw materials for a multitude of products, especially in technological applications. Large amounts of electronic waste rich in REE are produced, and this can be utilized as a valuable resource. For these reasons, efforts and research are focusing on secondary production, which is recycling and recovery of REE and specifically neodymium (Nd) from end-of-life components. In this study, the recovery of REE from NdFeB was investigated based on Box-Behnken experimental design technique. The effect of the experimental parameters in the hydrolysis of Fe3+ to hematite in a nitric acid medium in the hydrothermal reactor was examined in detail. Afterwards, the influence of the temperature, time, and hematite precipitation agents including starch (C6H10O5) n, sucrose (C12H22O11), and hematite seeds (Fe2O3) on the recovery of REE, and hematite precipitation were analyzed by statistical analyses. The optimal parameters for maximum REE recovery and iron removal under pressure and temperature were determined to be a process temperature of approximately 145°C, a process time of approximately 6 hours with the starch addition. The optimum parameters are in harmony with the validation experiments.