  Rare Earth Elements (REE) are critical minerals (metals) for the transition
from fossil fuels to renewable and clean energy. Accurate thermodynamic
properties of REE minerals and other crystalline solids are crucial for
geochemical modeling of the solubility, speciation, and transport of REE in ore
formation, extraction, chemical processing, and recycling processes. However,
the Gibbs free energies of formation (DGof, REEX) for these solids from
different sources vary by 10s kJ/mol. We applied the Sverjensky linear free
energy relationship (LFER) to evaluate their internal consistency and predict
the unavailable DGof of the REE solids. By considering both the effects of
ionic radius size and corresponding aqueous ion properties, the Sverjensky LFER
allows estimates with much accuracy and precision. Here, rREEZ+ represents the
Shannon-Prewitt ionic radii of REEZ+, and DGon, REEZ+ denotes the non-solvation
contribution to the DGof of the aqueous REEZ+ ion. X represents the remainder
of the compounds. In this study, the parameters aREEX, bREEX, and beta REEX
were regressed from DGof compilations in the literature for 13 isostructural
families. Based on these linear relationships, we recommend a set of internally
consistent DGof, REEX for 119 end-members of REE oxides, hydroxides, chlorides,
fluorides, carbonates, hydrous carbonates, and ferrites. These DGof, REEX are
combined with experimental or predicted values of So, Vo, and Cpo from the
literature and incorporated into a new SUPCRT database, which allows the
calculations of thermodynamic properties to high P-T conditions (e.g., up to
1000 oC and 5 kb).
