Decomposição térmica de monazita e separação do tório dos elementos terras raras leves em meio clorídríco, pela técnica de extração por solvente

Abstract

Monazite is one of the primary light rare earth minerals and it is always associated with the presence of thorium. This poses challenges in processing due to the strong radiation present in this mineral. This study addresses the separation of thorium from light rare earth elements in hydrochloric acid medium from desphosphorized monazite. The steps used to obtain an aqueous solution involved: addition of NaOH to the concentrate, heating at a temperature of 400°C for 3 hours, washing with water, and subsequent leaching of the residue with HCl. Samples from the aqueous phase were analyzed by ICP-OES. To assess the feasibility of alkaline fusion, thermodynamic modeling with different reagents was performed, and thermodynamic calculations of probable reactions were conducted using the HSC Chemistry 6.0 software database. NaOH appears as the most effective reagent from a thermodynamic and energetic standpoint. The separation of thorium from light rare earth elements was carried out through solvent extraction using compounds such as Cyanex 572, 272, 923, 921, and mixtures. Theoretical modeling was conducted using the Spana software to compare conditions in nitric and hydrochloric media. It was observed that Cyanex 572 and its mixtures extract 98% of the thorium in ane single stage, while Cyanex 272 extracts 70% of the thorium and 40% of the LREEs. The results show that thorium can be separated from light rare earth elements in hydrochloric medium, both by Cyanex 272 and Cyanex 572, requiring an additional extraction stage when using Cyanex 272. The other extractants did not yield satisfactory results in the separation. The results indicate that extraction capacity can be improved by using long-chain diluents, an acidic pH below 2, and a concentration of 5% for Cyanex 572 and 10% for Cyanex 272.