Influence of the Alkali-promoted phase transformation in monazite for selective recovery of rare-oxides using deep eutectic solvents

Sergio Sanchez-Segado, Shannon Stodd, Vitalis Chipakwe, Edward Loye, Martin Smith, Frances Wall, Andrew Abbott, Animesh Jha

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The physico-chemical changes occurring during the high-temperature phase transformation of monazite in the presence of Na2CO3 at 1000 °C for 2 h duration at monazite: Na2CO3 ratios between 1.0 and 5.0, were investigated. The formation of sodium lanthanide phosphates was prevalent above a monazite:alkali ratio of 2, however, below this ratio, the dephosphorization of monazite as Na3PO4 and Ce1-xLnxO2-x/2 solid solutions occur offering unique selectivity for rare-earth oxide separation from the mineral matrix. Cyclic voltammetry of pure CeO2, La2O3, Nd2O3, and PrO2/Pr2O3 was carried out in the deep eutectic solvent Ethaline (1:2 mixture of choline chloride and ethylene glycol) proving the electrochemical activity of these oxides. Electrodissolution of pure oxides and water-leached monazite after high-temperature reaction with a ratio of 1:1 was carried out in a 0.1 mol/L glucose solution in Ethaline showing a preferential solubility of 23.85% for pure Nd2O3. In contrast, pure oxides of CeO2, La2O3 and PrO2/Pr2O3 were found to be insoluble. We also observed that electrodissolution of the water leached monazite was not possible because of the inert behaviour of Ce1-xLnxO2-x/2 solid solutions. Avoiding cerium oxidation during the high-temperature process will lead to a method for further selectivity for rare-earth oxide processing using staged electro-chemical winning of oxides.
Original languageEnglish
Article number107564
Number of pages11
JournalMinerals Engineering
Publication statusPublished - 26 Apr 2022

Bibliographical note

Funding Information:
The authors acknowledge the financial support from the NERC Minerals Security of Supply, SoS RARE grants (NE/M011429/1), (NE/M011267/1), (NE/M01147X/1), Tellurium and Selenium Cycling and Supply (TeaSe) grant NE/M010848/1 and from the NERC's Catalyst Grant reference NE/L002280/1. Dr Sanchez-Segado acknowledges the support from The Ministry of Science, Innovation and University of Spain (“Beatriz Galindo” Fellowship BEAGAL18/00079).

Publisher Copyright:
© 2022 The Authors


  • mineral processing
  • rare earth element
  • alkali roasting
  • deep eutectic solvent
  • monazite
  • electrodissolution


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