The role of REE3+ in the crystallization of lanthanites

Abstract

The formation of crystalline rare earth element (REE) (e.g. La, Ce, Pr, Nd) carbonates from aqueous solutions was examined at ambient temperature using UV-Vis spectrophotometry, combined with X-ray diffraction, high-resolution microscopy and infrared spectroscopy. In all experiments REE-lanthanites (REE 2(CO3)3·8H2O) formed via a highly hydrated, nanoparticulate and poorlyordered REE-carbonate precursor. The lifetime of this precursor as well as the kinetics of crystallization of the various REE-lanthanites were dependent on the specific REE 3+ ion involved in the reaction. The induction time and the time needed to fully form the crystalline REE-lanthanite end products increase linearly with the ionic potential. The authors show here that the differences in ion size and ionic potential as well as differences in dehydration energy of the REE 3+ ions control the lifetime of the poorly ordered precursor and thus also the crystallization kinetics of the REE-lanthanites; furthermore, they also affect the structural characteristics (e.g. unit-cell dimensions and idiomorphism) of the final crystalline lanthanites.