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PreprintCC BYChemRxiv

Cooling-induced liquid–liquid separation promotes monazite precipitation through segregation of rare earth elements

  • Hassan Gezzaz1,2,3,4
  • Cristiana L. Ciobanu1,2
  • Nigel J. Cook1,2
  • Kathy Ehrig1,2,5
  • Yuxiang Wu3,4
5 affiliations
  1. 1School of Chemical Engineering
  2. 2Adelaide University
  3. 3Department of Materials Science and Engineering
  4. 4Monash University
  5. 5BHP Copper SA, 10 Franklin Street, Adelaide, Australia, SA5000
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Abstract

Monazite, (Ce,La,Nd)PO4, is a major source of rare earth elements (REEs), which play a vital role in green technology and electronics industries. Investigation into mechanisms of monazite formation from silicic melts provide valuable insights into its stability and behavior at varying temperature. This knowledge is crucial for improving the efficiency of REE extraction from mine slags, which could potentially contribute to expanding demand for critical materials. The present study leverages high-resolution scanning transmission electron microscopy to characterize the behavior of monazite during slag cooling and the PARROT module available in Thermo-Calc software to predict thermodynamic conditions that control monazite crystallization within the system SiO2‒P2O5‒Ce2O3. Using an objective optimization technique that incorporates experimental data from various sources, the study provides a representation of phase equilibria. The mechanisms of monazite formation are examined, with CePO4 identified as a stable phase at specific compositions and temperature ranges. A relative enrichment in REE and P is, however, insufficient to ensure monazite crystallization. Local composition, degree of supersaturation, nucleation barriers, and cooling rate also impact on whether a chemically segregated domain crystallizes or becomes kinetically arrested as glass. Although seamless extrapolation of the three component binary systems to the SiO2‒Ce2O3‒P2O5 ternary is currently precluded by a lack of reliable experimental data or ab-initio computational constraints, this optimization work enhances understanding of phase behavior, with relevance for potential REE recovery from copper slags, a largely untapped source of critical materials.

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Cite

BibTeXRIS
BibTeX
@misc{gezzaz2026coolinginduced,
  title = {{Cooling-induced liquid–liquid separation promotes monazite precipitation through segregation of rare earth elements}},
  author = {Hassan Gezzaz and Cristiana L. Ciobanu and Nigel J. Cook and Kathy Ehrig and Yuxiang Wu},
  howpublished = {ChemRxiv},
  year = {2026},
  month = oct,
  doi = {10.26434/chemrxiv.15010066/v1},
  url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010066/v1},
  note = {CC BY},
}
RIS
TY  - UNPB
TI  - Cooling-induced liquid–liquid separation promotes monazite precipitation through segregation of rare earth elements
AU  - Hassan Gezzaz
AU  - Cristiana L. Ciobanu
AU  - Nigel J. Cook
AU  - Kathy Ehrig
AU  - Yuxiang Wu
PY  - 2026
DA  - 2026/10/07
PB  - ChemRxiv
DO  - 10.26434/chemrxiv.15010066/v1
UR  - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010066/v1
AB  - Monazite, (Ce,La,Nd)PO4, is a major source of rare earth elements (REEs), which play a vital role in green technology and electronics industries. Investigation into mechanisms of monazite formation from silicic melts provide valuable insights into its stability and behavior at varying temperature. This knowledge is crucial for improving the efficiency of REE extraction from mine slags, which could potentially contribute to expanding demand for critical materials. The present study leverages high-resolution scanning transmission electron microscopy to characterize the behavior of monazite during slag cooling and the PARROT module available in Thermo-Calc software to predict thermodynamic conditions that control monazite crystallization within the system SiO2‒P2O5‒Ce2O3. Using an objective optimization technique that incorporates experimental data from various sources, the study provides a representation of phase equilibria. The mechanisms of monazite formation are examined, with CePO4 identified as a stable phase at specific compositions and temperature ranges. A relative enrichment in REE and P is, however, insufficient to ensure monazite crystallization. Local composition, degree of supersaturation, nucleation barriers, and cooling rate also impact on whether a chemically segregated domain crystallizes or becomes kinetically arrested as glass. Although seamless extrapolation of the three component binary systems to the SiO2‒Ce2O3‒P2O5 ternary is currently precluded by a lack of reliable experimental data or ab-initio computational constraints, this optimization work enhances understanding of phase behavior, with relevance for potential REE recovery from copper slags, a largely untapped source of critical materials.
ER  -