关于冠醚对稀土元素萃取性能的研究
A STUDY ON THE EXTRACTION OF RARE EARTH ELEMENTS WITH CROWN ETHERS
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摘要: 本文研究了十一种冠醚对稀土苦味酸盐的萃取。观察了冠醚的空腔大小、空间结构以及溶剂、对阴离子、水相酸度等对冠醚萃取性能的影响。不同冠醚萃取苦味酸镧能力的次序为:12-冠-4>单环己基-12-冠-4>苯并-12-冠-4;15-冠-5>苯并-15-冠-5>4-甲基苯并-15-冠-5;18-冠-6>苯并-18-冠-6>二苯并-18-冠-6;苯并-15-冠-5>苯并-18-冠-6>苯并-12-冠-4;二环己基-18-冠-6(DCC)的异构体A(I_A)>异构体A和B的混合物>异构体D(I_D)。 研究了三种冠醚对十五个单一稀土元素的萃取,测定了各元素的分配比(D)。logD对logC_L(C_L为冠醚总浓度)作图,其直线斜率对于苯并-15-冠-5和苯并-18-冠-6为2,对于DCC(I_A)为1(从La-Pr)和4/3(从Nd-Lu)。分配比随原子序数呈现有规律的变化,对于苯并-15-冠-5和苯并-18-冠-6,由La至Lu先增加,Sm处呈现最大,然后逐渐下降;而对于DCC(I_A),则由 La 至Lu依次降低。 得到了相邻稀土元素间的分离因数(β)。β_(Nd)~(Pr)随着DCC(I_A、I_D)浓度的降低而增大,最大分离因数可达3.66。Abstract: Solvent extraction studies of rare earth picrate are carried out with eleven crown ethers, having various ring sizes and various substituents on it. The effect of structure of crown ethers, counter anion, solvent, acidity of aqueous phase etc., on extraction properties of rare earth elements with crown ether in dichloromethane are studied. Abilities on the extraction of lanthaniurn picrate from lithium picrate aqueous solution decrease in the order of 12-crown-4>cyclohexyl-12-crown-4>benzo-12-crown-4;15-crown-5>benzo-15-crown-5>4-methylbenzo-l 5-crown-5;18-crowri-6> benzo-1 8-crown-6>dibenzo-18-crown-6; benzo-15-crown-5>benzo-18-crown-6>benzo-12-crown-4; isomer A (IA) of dicyclohexyl -18-crown-6 (DCC)>mixture of isomer A and B>/isomer D (ID).The distribution-ratio (D) of fifteen individual rare earth elements are determined with three different crown ethers.(L).The plots of log D against log CL give straight lines with a slope of 2 for benzo-15-crown-5 and benzo-18-crdwn-6 and 1 (from La to Pr) and 4/3 (from Nd to Lu) for DCC (IA). The distribution ratio of rare earths exhibits a maximum at Sm for benzo-15-crown-5 ar.d benzo-18-crown-6, while for DCC (IA) de-creases monotonously from La to Lu.The separation factor (β) of neighbouring rare earth elements are obtained.βPr Nd increases apparently with the decrease of concentration of DCC (IA, ID). The largest βPr Nd reaches 3.66.