Separation of lanthanide elements by ion recognition of polymer gel copolymerized with acidic phosphorus compound

研究了热敏聚合物凝胶- - - 2-甲基氧乙基乙酸酯(MR) - - - n-异丙基丙烯酰胺（NIPA）凝胶对镧系离子的萃取作用。该聚合物凝胶表现出一种相变现象，即随着温度的升高，凝胶的结构由膨胀变为收缩。测定了镧系离子La（III）和Sm（III）在水溶液中的萃取平衡。分布比Kd随温度升高而增大。这些金属离子可以在凝胶收缩状态下被提取出来，并随着温度的降低，聚合物网络的构象由收缩变为膨胀。根据ph对Kd的依赖性估计，在收缩和膨胀条件下，镧系离子的萃取机理可以简单地描述为ln ^<3+> + 3rh <双箭头> LnR_3 + 3h ^+。由收缩和膨胀条件下的萃取常数得出的萃取镧系离子的有效磷分子数，在收缩条件下约占共聚磷分子的80%，在膨胀条件下约占30%。进行了热摆试验，以检验实际应用的可能性。在长期使用中保持凝胶的萃取能力具有重要的现实意义。通过热振荡操作，保持Kd的温度依赖性，以重复提取和洗脱。这些结果表明，热敏凝胶的相变现象适用于金属离子的萃取和洗脱操作。

The extraction of lanthanide ion between an aqueous solution and a thermosensitive polymer gel, n-isopropylacrylamide (NIPA) gels copolymerized with 2-metacrloxyethylacidphospate (MR) was examined. This polymer gel shows a phase transition phenomena, that is, the structure of gel changes from swelling to shrinking with increasing temperature. The extraction equilibrium of lanthanide ions, La(III) and Sm(III), in an aqueous solution was measured batchwise. The distribution ratio, Kd, increased with increasing temperature. These metal ions can be extracted in the gel at the shrinking condition and cluted by the conformation change of polymer network from shrinking to swelling of gel with decreasing temperature.The extraction mechanism of lanthanide ion, which was estimated from the pH-dependency on Kd, was described simply asLn^<3+> + 3 RH <double arrow> LnR_3 + 3 H^+at both the shrinking and swelling conditions. The number of effective phosphorus molecules for the extraction of lanthanide ion, which was derived from the extraction constants at the shrinking and swelling conditions corresponded to about 80% of copolymerized phosphorus molecules at the shrinking condition and was reduced to about 30% at the swelling condition.The thermal swing tests were carried out to examine the possibility of practical use. It is important practically to maintain the extraction capability of gel in a long-term use. The temperature-dependency of Kd was maintained for repcating the extraction and elution by the thermal swing operation. These results suggest that the phase transition phenomena of thermosensitive gel is applicable to the extraction and elution operations of metal ion.