T.G. Levitskaia, E.M. Garcia, W. Hasley-Velez, N.P. Bessen, V. Drozd, Y. Katsenovich, A. Medley, P. Zhang
Pacific Northwest National Laboratory,
United States
Keywords: Rare earth, phosphogypsum, DGA, solvent extraction
Summary:
The US phosphate mining industry produces over 30 million tons of phosphogypsum (PG) waste annually, with over 2 billion tons accumulated in the PG stacks in Florida alone. All PG is currently stacked. This practice causes numerous environmental and economic challenges. Considering that PG is a significant resource for rare earth elements (REEs), fertilizer components (such as P, S, and Mg), and ingredients for construction materials, these challenges can be addressed by total utilization of PG and greatly reducing its stacking. With an average rare earth elements (REE) content of over 300 ppm, PG is a significant unconventional resource potentially meeting over 50% of the U.S. annual demand for REE. Our research focuses on the bulk recovery of REE from PG by leaching and solvent extraction, resulting in purified mixed REE concentrate. We previously demonstrated that moderately concentrated (>3 M) HNO3 successfully leached REE from PG. The separation and purification of REE from the PG leachate is accomplished by solvent extraction (SX) using N,N,N′,N′‐tetraoctyldiglycolamide (TODGA), a tridentate ligand with high affinity and selectivity towards lanthanides. Although TODGA preferentially extracts REE, it partially extracts calcium due to its high concentrations in PG leachate (1000-fold over REE) creating a challenge. Our prior studies investigated REE batch SX using TODGA-based organic solvent generated thermodynamic equilibrium distribution information used to design a dynamic flowsheet with three major steps, 1) REE extraction from PG leachate, 2) scrubbing for removing impurities (i.e. calcium), and 3) stripping of REE generating the purified mixed REE concentrate. We are currently testing the developed flowsheet for processing of the actual PG leachate using banks of counter-current centrifugal contactors. Our to-date results will be discussed. Acknowledgements This work is supported by the Critical Materials Innovation Hub, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Critical Minerals and Energy Innovation (CMEI), Advanced Manufacturing and Materials Technologies Office (AMMTO). Pacific Northwest National Laboratory (PNNL) is operated by Battelle Memorial Institute for the U.S. Department of Energy under contract DE-AC05-76RL01830. Post Doctorate appointment of Elizabeth Garcia at PNNL is gratefully acknowledged. Post Masters appointment of Willow Hasley-Velez at PNNL is gratefully acknowledged.