Competitive extraction of lanthanides by solvent extraction using Cyanex 272: Analysis, classification and mechanism

The competitive simultaneous extraction and separation of 14 lanthanide elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) from perchloric acid aqueous solution by solvent extraction using bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) as an extractant was studied. The effect of different parameters such as aqueous phase equilibrium pH and Cyanex 272 concentration in the organic phase on the extraction/separation behavior was investigated. From the experimental data a suitable cation exchange mechanism has been proposed. Dependencies of log D versus pH and log D versus log [Cyanex 2721 and the cation exchange mechanism were analyzed and the proposed mechanism validated. Mathematical models (2D and 3D) were developed to correlate metal extractability. Hierarchical cluster analysis reveals the existence of (dis)similarity among elements in the series. Statistical cluster analysis divides the series into four different groups within the broad grouping of light and heavy lanthanides. An interesting diagonal relationship with consecutive elements was observed. (C) 2011 Elsevier B.V. All rights reserved.