Rare Earth Elements (REE) phosphates (monazite, xenotime, and rhabdophane) are critical REE-bearing minerals typically formed in hydrothermal and magmatic ore deposits. The ther-modynamic properties of those REE minerals are crucial to understanding the solubility, speciation, and transport of REE complexes. However, the reported standard state Gibbs free energy of for-mation (∆Gof) for these minerals in the literature vary up to 25 kJ mol−1. Here, we present linear free energy relationships that allow the evaluation and estimation of the ∆Gof values at 25 °C and 1 bar for the three minerals from the ionic radius (rREE3+) and the non-solvation Gibbs energy contribution to the REE3+ aqua ion (∆Gon, REE3+): ∆Gof, monazite – 399.71 rREE3+ = 1.0059 ∆Gon, REE3+ – 2522.51; ∆Gof, xenotime – 344.08 rREE3+ = 0.9909 ∆Gon, REE3+ – 2451.53; ∆Gof, rhabdophane – 416.17 rREE3+ = 1.0067 ∆Gon, REE3+ – 2688.86. Moreover, based on the new dataset derived for REE end-members, we re-fitted the binary Margules parameter (W) from previous theoretical calculations into linear correlations: W + 0.00204 ∆Go'n, monazite = 39.3549 ∆V + 0.0641; W + 0.00255 ∆Go'n, xenotime = 25.4885 ∆V – 0.0062. The internally con-sistent thermodynamic properties of these REE phosphates are incorporated into the computer program SUPCRTBL, which is freely available at the site https://models.earth.indiana.edu.
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Title:
Recommended standard thermodynamic dataset of monazite, xenotime, and rhabdophane