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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.
Highlights
Rare earth elements (REEs) are indispensable constituents in many industrial applications including fuel cells, mobile phones, permanent magnets, lamp phosphors, rechargeable batteries and catalysts [1,2]
A literature review was performed relating to the Eh-pH diagrams of three
Eh-pH diagrams of RE minerals in hydrometallurgical systems that were not previously reported in the literature were developed in this study
Summary
Rare earth elements (REEs) are indispensable constituents in many industrial applications including fuel cells, mobile phones, permanent magnets, lamp phosphors, rechargeable batteries and catalysts [1,2]. In addition to the primary mineral sources, it has become increasingly crucial to recycle REEs from end-of-life products, such as permanent magnets, fluorescent lamps, batteries and catalysts, which contain a fair amount of REEs [4,5,6,7]. REE primary and secondary sources are often treated with physical separation processes followed by hydrometallurgical methods. Froth flotation is used to produce a REE mineral concentrate followed by leaching, solvent extraction and/or selective precipitation to extract the REEs from their mineral matrix [3,8]
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