Extraction of Trivalent Rare Earth Ions with an Acidic Tridentate Extractant, 6-<i>N,N</i>-Di-<i>n</i>-Octylcarbamoyl-Pyridine-2-Carboxylic Acid

Extraction properties of trivalent rare earth ions (RE(III)) from acidic chloride solutions with 6-N,N-di-n-octylcarbamoyl-pyridine-2-carboxylic acid (CPCA), which has three functional groups: an amide, a carboxylic acid and a pyridine, were investigated by slope analyses of the distribution ratio (D) of RE(III) and FT-IR measurements. The dependence of D on pH and CPCA concentration indicated that the 1:3 RE(III)−CPCA complex was predominantly formed in the organic phase. FT-IR analysis of the Dy(III) complex extracted with CPCA suggested that the coordination mode of CPCA to Dy(III) was tridentate. Plots of extraction percentage (E%) of RE(III) versus atomic number revealed that E% increased from La(III) to Er(III) and then remained almost constant until Lu(III). The E% of Y(III) was similar to that of Sm(III).