Extraction of lanthanide and actinide elements by thermosensitive polymer gel copolymerized with acidic phosphorus compound

A new gel-liquid extraction technique using a thermosensitive gel was proposed. The thermosensitive gel shows the phase transition phenomena, the conformational change of polymer network with temperature. The effect of the conformational change of polymer network on the extraction behavior of metal ion was discussed. The extraction of lanthanide (La(III), Sm(Ill), Eu(III)) and actinide (Am(III)) ions in an aqueous solution containing nitrate ion was examined by using a thermosensitive gel, N-isopropylacrylamide (NIPA) copolymerized with an acidic phosphorus compound, 2-metacrolyl-oxyethyl-acid-phosphate (MR). The distribution ratios, K_d, for the extraction of these metal ions increased with increasing temperature. These metal ions can be extracted in the gel at the shrinking state (higher than 37 deg. C) and eluted by the conformational change of polymer network from shrinking to swelling with decreasing temperature. Temperature swing tests using Am(III) and Eu(III) were carried out to discuss the applicability to the practical process. These metal ions were extracted and eluted successfully by the temperature swing operation over the range of 3 to 40 deg. C. The equilibrium constant, K^Am_ex at the shrinking state corresponded to three times of that at swelling state. These results suggest that the phase transition phenomena of the thermosensitive gel is applicable to the extraction of lanthanide and actinide ions