Comment on “Synthesis of ceria (CeO2 and CeO2−x) nanoparticles via decarbonation and Ce(III) oxidation of synthetic bastnaesite (CeCO3F)” by Montes-Hernandez et al.

Here, we provide further evidence that the natural bastnäsite-(Ce) employed in the study by Gysi and Williams-Jones [3] decomposed to form REE oxyfluorides (i.e., CeOF, LaOF, PrOF and NdOF) and not CeO2, and supply explanations for why Montes-Hernandez et al. [5] erroneously concluded that CeO2 is produced during decomposition of this mineral under N2 and Ar atmospheres. In so doing, we hope to provide new insights into the decomposition of bastnäsite-(Ce) that will help guide future studies of this fascinating mineral. We also show how the thermodynamic data of Gysi and Williams-Jones [3] can be used to evaluate the conditions at which bastnäsite-(Ce) is stable in hydrothermal fluids.