A STUDY ON THE EXTRACTION OF RARE EARTH ELEMENTS WITH CROWN ETHERS

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.