Abstract
A new gel-liqnid extraction technique using a thermosensitive gel was proposed. The thermosensitive gel shows the conformational change of polymer network with temperature, which is known as the phase transition phenomena of gel. The extraction rate and equilibrium of Am(III) in an aqueous solution containing nitrate ion were measured batchwise by using a thermosensitive gel, N-isopropylacrylamide (NIPA) copolymerized with 2-methacryloyloxy- ethylacidphosphate (MR). The effects of the conformational change of polymer network on the extraction rate and equilibrium were discussed.
The distribution ratio of Am(III) showed a large value at higher than LCST (low critical solution temperature; 34°C) and was decreased by the phase transition of gel from shrinking to swelling with decreasing temperature. The extraction of Am(III) in the aqueous solution and the release of Am(III) extracted in the gel were repeated stably by the temperature swing operation between 40 and 3°C. The extraction mechanism of Am(III) was described simply as
Am3+ ＋3R－OH＝ (R－O)3Am＋3H+ (R-OH: MR).
The equilibrium constant at the shrinking state (40°C) was more than 3 times of that at swelling state (3°C). The gel-phase diffusivity of Eu(III) used as a substitute of Am(III) was evaluated as the order of 10-12 m2/s at either of 3 or 40°C, which was similar to those for practical extraction chromatographic resins. The temperature-response of gel for the extraction of Eu(III) was very excellent without delay even for the rapid temperature change at 10°C/min. These results suggest that the extraction and release of Am(III) in an aqueous solution can be controlled by the conformational change of polymer network of thermosensitive gel.
