Application of Eh-pH Diagrams on Acid Leaching Systems for the Recovery of REEs from Bastnaesite, Monazite and Xenotime

Abstract

Bastnaesite, monazite and xenotime are rare earth minerals (REMs) that are typical sources for rare earth elements (REEs). To advance the understanding of their leaching and precipitation behavior in different hydrometallurgical processes, Eh-pH diagrams were constructed and modified using the HSC 9.9 software. The aqueous stability of rare earth elements in H2O and acid leaching systems, i.e., the REE-Ligands-H2O systems, were depicted and studied based on the Eh-pH diagrams. This study considers the most relevant lixiviants, their resulting equilibrium states and the importance in the hydrometallurgical recovery of rare earth elements (REMs). A literature review was performed summarizing relevant Eh-pH diagrams and associated thermodynamic data. Shifting stability regions for REEs were discovered with additions of acid ligands and a narrow stability region for soluble REE-(SO4/Cl/NO3) complexes under highly acidic conditions. As such, the recovery of REEs can be enhanced by adjusting pH and Eh values. In addition, the Eh-pH diagrams of the major contaminants (i.e., Fe, Ca and Al) in leaching systems were studied. The resulting Eh-pH diagrams provide possible insights into potential passivation on the particle surfaces due to the formation of an insoluble product layer.

Selective Scandium (Sc) Extraction from Bauxite Residue (Red Mud) Obtained by Alkali Fusion-Leaching Method

“…(Table 4). The low extraction efficiency of Ce, Nd, and Th can be explained by the formation of insoluble compounds at high pH and Eh values, as was shown by Lin P. et al [48]. Sorption or extraction methods can be used to recover REEs from the resulting solution to increase the pregnant solution's concentration before REEs precipitation [28].…”

High-Selective Extraction of Scandium (Sc) from Bauxite Residue (Red Mud) by Acid Leaching with MgSO4

“…Lin et al [35] reported that the reduction in particle size and preliminary alkali and/or thermal activation greatly improved REE extraction from coal-related materials by mineral acids. As can be seen from the RM characterization, the RM-ESPD was already alkali and thermally activated; moreover, its particles were very fine.…”

“…As was shown in the literature [10,13,17] and in our previous research [14], Sc extraction by different acids was very low at pH values higher than 2.5 However, in this work, the extraction of almost all selected REEs was lower than 10% only at a pH of 6. Such low extractions of REEs, Fe, Al, and Ti using diluted acids are connected with the low accessibility of the REEs by H + ions in the solid matrix of iron minerals that remain unleached at this pH, The possible reason for this is connected with the pH of their hydroxides precipitation, i.e., Fe(OH) 3 begins to precipitate at a pH of 3 [35]. Sc(OH) 3 begins to precipitate at a pH higher than 6.…”

“…It should be noted that these elements make it difficult to recover REEs from the solution [21]. The low extraction of Nb and Y could be attributed to the formation of insoluble compounds at high pH values [35]. To further evaluate the effect of leaching parameters on the extraction of Sc, experiments were conducted at different pH values, MgSO 4 concentrations, temperatures, and times (Figure 5).…”

Knowledge mapping of research on strategic mineral resource security: A visual analysis using CiteSpace

“…(2) no se producen gases residuales durante el proceso, y los subproductos valiosos (el gas de cloro de alta pureza y el gas de hidrógeno) se generan simultáneamente por electrólisis, lo que puede compensar parte del costo de producción (Meng et al, 2020). El principal desafío en el mercado global de REE es aumentar la recuperación de los elementos durante el procesamiento metalúrgico (Lin, Yang, Werner, & Honaker, 2021).…”