Abstract
The distributions of trivalent rare-earth elements such as lanthanum, cerium, praseodymium, neodymium. samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium between hydrochloric acid solutions and solutions of di-(2-ethylhexyl)-phosphoric acid (DEHPA) + pyridine (py) or its derivatives in kerosene have been examined under different conditions. Infrared and nuclear magnetic resonance spectra were made for the organic extracts. As a result, the addition of pyridine or its derivatives gave the synergistic effect on the extraction of rare-earth elements from hydrochloric acid solutions by DEHPA. In those extraction systems, however, the variation of the distribution coefficients for rare-earth elements plotted as a fuction of their elements in the atomic numbers revealed the curve in tetrad effect similar to the extraction by DEHPA alone. It was found that the seperation factors of adjacent elements resemble each other.
