Solvent extraction of lanthanum (III), samarium (III), and dysprosium (III) by kerosene solutions of phosphoric acid esters has been investigated to elucidate the structure effect of the phosphates on the extraction behaviors of these elements. As a result, it is found that the position of alkyl side chain in the organic groups of the phosphoric acid esters plays an important role in the extraction phenomena of the rare earths, and that the shorter the distance between the substituent and PO (OH) group, the greater the dependence of the extractability of rare earth on the pH of the aqueous phase is. It is also indicated that the separation factors between the elements are affected by the steric hindrance of the organic group of the phosphates. The factors of the substituent effect on the extraction phenomena are examined by using CNDO (Complete Neglect of Differential Overlap method) molecular orbital calculations.
