T h e iminocliacetic acids ha\^ been examined a s possible complesing agents in the chromatographic separation of the rare earths \\-it11 cation exchange rcsitis. The a n i r n o~i i~~m salts of these acids form cotiiples ions in\~olving both one ant1 two iniinodiacetate ions of increasing staRility with the rare carth elements of greater atomic number. A~Ietliods greatly reducing the time and material req~~iremelits arc presented for the separation of thc cerium group elements \vith nitrilotriacetic a c~d . IntroductionConsiderable success ill the separation of the rare earth eleinents has been achieved recently in tlle application of chromatogi-aphic techniques to cation exchange resins (6, 18, 21.). Elution wit11 a con~plesi~lg agent, generally citric acid, was found to move the adsorl~ecl rare earth ions thl-ough an excha~lger bed a t different rates. The elenlents of higher atomic number, which formed the inore stable coinplex ions u~it11 citric acid, were collected in correspondingly earlier portions of the eluate. Careful control ol p1-I ancl ion co~~centrations was necessary to achieve the desired ion-exchange and exploit to a m a x i~~~u n~ the slight differences in behavior of the elements (19,20). However, with the large volun~es of eluate and fi~~-t-her separations requirecl, the purification of appreciable quantities of these elements still remained laborious.T h e iminocliacetic acids, RN(CH?COOH)t, are excellent conlplexing agents for most cli-ancl trivalent cations, and interest in the present work has centered on their clevelop111ent as eluting agents for the rare earth elements. These compounds are weak acids \vith "znritterion" or dual type ion formation causing considerable difference in the dissociation of the acid groups.\?Then partially neutl-alized, these acids readily for111 complex ions with most cations, chelate fol-mation occurring through the nitrogen and acid groups. In many cases, basic ions are indicated a t high pH values and often the metal hydroxide may be precipitated on adclitioll of strong base. For personal use only.

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