4-甲基苯并-15-冠-5对某些镧系放射性核素的萃取

THE SOLVENT EXTRACTION OF SEVERAL LANTHANIDE RADIONUCLIDES WITH 4-METHYLBENZO-15-CROWN-5

本文研究了4-甲基苯并-15-冠-5三氯甲烷溶液从苦味酸水溶液中对某些镧系放射性核素(144Ce、147Nd、15^(2+)154Eu、170Tm和169Yb)的萃取。从斜率分析得出,被萃取状态为1:2:3(金属离子/冠醚/苦味酸根)络合物。在25℃,测定了三价镧系元素的苹取常数(Kex),得到下列次序:Nd^(3+)>Eu^(3+)>Ce^(3+)>Tm^(3+)>Yb^(3+)。结果表明,Nd^(3+)的离子大小(r=0.995)比其它镧系元素可能更接近4-甲基苯并-15-冠-5环孔的大小。为了将镧系元素与锕系元素作比较,还测定了4-甲基苯并-15-冠-5对Th4+、UO2^(2+)和Am^(3+)的萃取率,所得到的萃取率次序为Th4+>Am^(3+)》UO2^(2+)。实验证明,4-甲基苯并-15-冠-5将可能是溶剂萃取法分离铀和钍的有用试剂。溶剂和添加剂影响萃取实验表明,在有机相添加正丁醇或异戊醇,或者以高极性的溶剂(例如,硝基苯)替代三氯甲烷,都能显著地增加对镧系元素的萃取。

The solvent extraction of several lanthanide radionuclides(144Ce,147Nd,15^(2+)154Eu,170Tm and 169Yb)from aqueous picric acid solutions with 4-methyl-benzo-15-crown-5 in chloroform has been investigated.The extracted species are found to be 1:2:3(metal/crown/picrate)complex from slope analysis.The extraction equilibrium constants(Kex)have been determined at 25°C.The order of Kex values for trivalent lanthanide is Nd^(3+)>Eu^(3+)>Ce^(3+)>Tm^(3+)>Yb^(3+).This indicates that the ionic size of Nd^(3+)(r=0.995A)may better match the cavity size of 4-methylbenzo-15-crown-5 than the ionic sizes of other lanthanides.In order to compare lanthanides with actinides,the extractability of 4-methylbenzo-15-crown-5 for Th4+,UO2^(2+)and Am^(3+)has been determined.The sequence is Th4+(########Nd^(3+))Am^(3+)(#####Ce^(3+))######UO2^(2+).Therefore,4-methyl-benzo-15-crown-5 may be a useful reagent for separating uranium from thorium in the liquid-liquid extraction method.The effect of solvents and additives on the extraction has also been investigated.The extent of the extraction of lanthanides may be improved by addition of n-butanol or iso-pentanol to the organic phase,or by application of more polar solvent(e.g.,nitrobenzene)instead ofchloroform.