Decomposition of Mixed Rare Earth Concentrates Using Solid KOH

Abstract

The Bayan Obo mixed rare earth concentrate, characterized by its complex composition and difficult-to-decompose bastnaesite, poses significant industrial processing challenges. Traditional methods using sulfuric acid and sodium hydroxide lead to environmental pollution and resource wastage. This article introduces a novel decomposition method using solid potassium hydroxide (KOH). Thermodynamic calculations indicate that reactions with KOH are spontaneous between 298 K and 573 K, making the decomposition of rare earth minerals and fluorite feasible. Studies using TG-DSC, XRD, SEM-EDS, and FT-IR reveal that, under the action of KOH, REFCO₃ is decomposed into RE(OH)₃. As the temperature increases, RE(OH)₃ decomposes into rare earth oxides, and REPO₄ reacts with KOH to form K₃PO₄. Under the conditions of roasting of 240°C, 60 min, and solid–alkali ratio of 1:1, a rare earth decomposition rate of over 96% has been achieved. Decomposition rates for phosphorus and fluorine reached 75.61% and 95.74%, respectively. The kinetic results of the roasting reaction were: E = 21.7 kJ mol⁻¹ and n = 2.12 between 180°C and 250°C. This method achieves high recovery rates for fluorine and phosphorus, and enables direct extraction of potassium, phosphorus, and other elements from waste solutions for fertilizer production. These aspects underscore its significance in environmental protection and comprehensive utilization.