TY - JOUR
T1 - Influence of the Alkali-promoted phase transformation in monazite for selective recovery of rare-oxides using deep eutectic solvents
AU - Sanchez-Segado, Sergio
AU - Stodd, Shannon
AU - Chipakwe, Vitalis
AU - Loye, Edward
AU - Smith, Martin
AU - Wall, Frances
AU - Abbott, Andrew
AU - Jha, Animesh
PY - 2022/4/26
Y1 - 2022/4/26
N2 - 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.
AB - 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.
KW - mineral processing
KW - rare earth element
KW - alkali roasting
KW - deep eutectic solvent
KW - monazite
KW - electrodissolution
U2 - 10.1016/j.mineng.2022.107564
DO - 10.1016/j.mineng.2022.107564
M3 - Article
VL - 182
M1 - 107564
ER -