Solubilisation of Monazite in Organic Acids

Daniel E. Lazo PhD Candidate, Dr. Laurence G. Dyer, Dr. Richard Diaz Alorro

In the present study, the feasibility to employ organic acids in a hydrometallurgical process to extract rare earths elements (REEs) from monazite-bearing ore was studied. Conventional processing utilises aggressive reagents and high temperature and pressure to form minerals that are amenable to leaching. While the reagents are relatively cheap, large quantities are required and fully consumed in the reactions, leading to high energy, reagent and maintenance costs. The processes also have high associated health, safety and environmental concerns. Therefore there is a significant drive to identify alternatives to address these issues. The approach was based on previous studies performed in the geochemical area, showing that several acids, such as oxalic, citric and phthalic, aid in the release of REEs from monazite and apatite. To predict the REE leaching capacity of the organic acids, monazite was studied in varying conditions, pH, concentration, solid/liquid ratio, and residence time at room temperature. Oxalic acid has shown a strong ability to enhance the solubilization of phosphorus and transition of rare earths to an oxalate species. In an industrial context, the release of phosphorus in the solution, creation of rare earth oxalates and subsequent ability to form a rare earth hydroxide are highly important in viably processing REEs. The evidence may also suggest some selectivity in the process, leading to the possibility of decreasing the complexity of individual separation of the various REEs. The data presents the potential of this approach to provide an alternative conversion and leaching process that represents potential gains in cost, environmental impact, health and safety.