Date of Award

Fall 12-12-2025

Degree Type

Thesis

Degree Name

Master of Science in Metallurgical/Mineral Processing Engineering

Department

Metallurgy

Committee Chair

Courtney A Young

First Advisor

Hsin-Hsiung Huang

Second Advisor

Richard LaDouceur

Abstract

Neodymium-iron-boron (NdFeB) magnets account for over 60% of global magnet sales and are widely used in high-tech, military, and clean-energy applications (Ormerod, 2022). However, they contain critical rare earth elements such as Nd, Pr, and Dy which poses supply chain and geopolitical risks for country like the United States, which rely extensively on foreign sources. Recycling end-of-life NdFeB magnets provides a sustainable solution that diminishes environmental impact, strengthens supply security, and supports stable domestic production of important rare earth elements. A three-stage process has been developed for recycling the REE-content of NdFeB magnets. While the focus is on neodymium (Nd), praseodymium (Pr) and dysprosium (Dy) were not ignored. Leaching and Precipitation are accomplished in Stage 1 (L) with sulfuric acid at moderate temperatures. In stage 2, the REEs are precipitated (P) with MOH to produce a double salt [MNd(SO4)2(H2O)x] where, M can be NH4, Na, or K and x ranges from 0 to 4. The leaching and precipitation reactions are thermodynamically modeled using StabCal and free energies of the double salts are determined. Finally, in Stage 3 (C), the resulting precipitates are fluorinated with either NH4F or NH4F•HF to convert them to NdF3. Each stage was examined using Design-of-Experiment (DOE) studies. Results are discussed in detail with the understanding that the final NdF3 product becomes feedstock to metal production using molten-salt electrolysis. Based on the results discussed with NaOH in this regard, double-salt precipitation was the fastest and most effective as compared to KOH and NH4OH precipitation times were 2, 3 and 12 hours and Nd % recoveries were 96.58, 90.00, and 77.25%, respectively. In H2SO4 environment, the order of increasing solubilities for precipitating reagents is NaOH < KOH < NH₄OH. Optimal pH and temperature ranges were identified as 1.5 – 1.9 and 25 – 80°C respectively. From the fluorination analysis, it was determined that both NH4F and NH4F.HF can be utilized to convert the double salts to a high purity REF with NH4F recording the highest recovery.

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