Study on the technology for decomposition of Binh Thuan monazite concentrate by NaOH under high pressure

Abstract

This study addresses the challenges of inefficient and environmentally harmful recovery of rare earth elements (REEs) from monazite ore by proposing a high-pressure sodium hydroxide (NaOH) decomposition method for Binh Thuan monazite concentrate. The research investigates key process parameters, including NaOH-to-ore ratios (1:1–3:1), reaction temperatures (120–240°C), durations (1–4 hours), and particle sizes (<55 µm to 75–106 µm). Results show that a 3:1 NaOH-to-ore ratio achieves the highest recovery efficiencies for La (99.30%), Pr (99.68%), and Ce (95.43%), while uranium (U) and thorium (Th) recoveries are less influenced by this factor. Optimal decomposition temperatures were determined as 180°C for La, Pr, and Y (with recoveries of 99.15%, 97.55%, and 94.79%, respectively) and 210°C for Ce and Nd (94.18%). Extending the reaction time to 4 hours improves REE recovery, though Th recovery peaks at 91.03% after 2 hours. Finer particle sizes (<55 µm) enhance REE recovery, while coarser particles (75–106 µm) significantly reduce U recovery (from 49.63% to 27.95%). The formation of insoluble CeO₂ is identified as a factor limiting Ce recovery. This NaOH decomposition method not only improves extraction efficiency but also reduces energy consumption by 50–70% and minimizes environmental emissions, presenting a sustainable solution for REE recovery with potential application in Vietnam’s mineral processing industry.