A multivariate approach at the thermodynamic properties of rare earth elements

Abstract

Rare earth elements (REE) are classified as light and heavy and present the lanthanide contraction effect, which keeps ionic radius and ΔfH° values between REE very close. Many information on thermodynamic parameters such as ΔfH°, ΔfS°, ΔfG° and S° 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 ΔfH°, ΔfS°, ΔfG° and S°, separated the compounds (REE)FeO3, (REE)PO4, (REE)2O3, (REE)O2, (REE)2O2CO3 II, (REE)2Zr2O7 and REE(OH)3, according to their molecular characteristics. Due to the greater influence of ΔfH° in relation to the other parameters, an HCA considered only ΔfH° 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.