A multivariate approach at the thermodynamic properties of rare earth elements

Rare earth elements (REE) are classified as light and heavy and present the lanthanide contraction effect, which keeps ionic radius and Delta fH degrees values between REE very close. Many information on thermodynamic parameters such as Delta fH degrees, Delta fS degrees, Delta fG degrees and S degrees of REE compounds have been reported in recent decades. To obtain a consistent mathematical interpretation of these data, a multivariate statistical study was performed using Hierarchical Cluster Analysis (HCA) and Principal Component Analysis (PCA) to compile and compare relevant information about the thermodynamic properties of REE. The PCA identified four distinct groups of linkers: halides, oxyanions, REE3+ hydrate group and REE2+ halides group. Analysis of HCA performed with the values of Delta fH degrees, Delta fS degrees, Delta fG degrees and S degrees separated the compounds (REE)FeO3, (REE)PO4, (REE)(3)O-3, (REE)O-2, (REE)(2)O2CO3 II, (REE)(2)Zr2O7 and REE(OH)(3), according to their molecular characteristics. Due to the greater influence of Delta fH degrees in relation to the other parameters, an HCA considered only Delta fH degrees was performed, classifying REE into three groups, Eu, LREE and HREE. Therefore, this work shows how multivariate statistical tools can help us to better understand the thermodynamics of REE.