Ion exchange materials of environmentally friendly having high selectivity for metal ions have been investigated, as such (1) preparation of coated solvent impregnated resin, to prevent from leakage of extractant, and its application to selective separation of metal ions and (2) novel ion exchange material based on photo-swing adsorption and its application to adsorptive separation of rare earth metals. The leakage of the extractant from the solvent impregnated resin, during operation, can be successfully suppressed by coating the solvent impregnated resin by cross-linked water-soluble polymer, although adsorption capacity is slightly decreased. Selective separation of rare earth metals can be achieved with column mode operation using the coated solvent impregnated resin. Novel photo-swing ion exchange material is also developed to decrease in the amount of eluent solution. Extractant and carbon nanotube, as molecular heater, are immobilized on thermosensitive polymer. The adsorption amount can be controlled by photo-irradiation, since phase transition of the thermosensitive polymer is occurred by the photo-irradiation. The difference in the adsorption amount, with and without photo-irradiation, can be increased by decrease in the cross-linking, although the immobilization of the carbon nanotube becomes difficult. The immobilization of the carbon nanotube can be improved by introducing pyrene group on the ion exchange material. Separation ability of several combinations of rare earth metals is increased by photo-irradiation.

A hybrid donor compound 2,2’-[(2-ethylhexyl)imino]bis[N,N-bis(2-ethylhexyl)acetamide] (DAMIA-EH) impregnated silica-based adsorbent [(DAMIA-EH+1-dodecanol)/SiO₂-P] was prepared. Its adsorption performance toward Pd(II) in nitric acid solution was investigated by examining the effect of contact time, temperature etc. It was found that the adsorption rate of Pd(II) was fairly fast and can reach a constant state within only 10 min. (DAMIA-EH+1-dodecanol)/SiO₂-P exhibited an excellent recognition ability toward Pd(II) than other 14 types of co-existing metal ions and could maintain this selectivity when the concentration of HNO₃ varied from 0.5 to 5 M. On the other hand, the maximum adsorption amount of Pd(II) was calculated to be as high as 0.440 mmol/g when [HNO₃] = 2 M. Moreover, with increasing the temperature in solution, the uptake ratio of Pd(II) slightly decreased, it still exhibited a dominant selectivity toward Pd(II) in a wide temperature range from 288 to 323 K. The fitted thermodynamic parameters revealed that the adsorption process of Pd(II) was exothermic in nature and happened spontaneously.

Sr adsorption behavior of potassium dititanate which is a layered ion exchanger was examined under high Na concentration. Potassium dititanate adsorbed Sr²⁺ even if the coexisting Na concentration was high. Moreover, when Na⁺ coexisted above a certain amount, the distribution coefficient of Sr increased with increasing pH, and the adsorbed amounts of Sr²⁺ and Na⁺ both increased. From the Sr and Na concentration of the liquid phase before and after Sr adsorption, X-ray diffraction pattern of the solid phase, IR spectrum, Raman spectrum, etc., crystallinity of potassium dititanate reduced because some Ti-O-Ti bonds were broken due to contact with water. However, it was suggested that Sr²⁺ was adsorbed between the layers and Na⁺ was adsorbed at the surface hydroxyl groups, although the crystallinity was reduced. The distribution coefficient of potassium dititanate for Sr was 1.7×10⁷ mL/g or higher in the region of equilibrium pH 12 and equilibrium Na concentration of 40 mmol/L or higher, showing higher Sr adsorption ability than the previously reported Sr adsorbent.