The ion-exchange elution sequences have been established for some di- and trivalent ions in elations with those elands commonly used for the separation of macro quantities of rare earths. The sequences suggest some possible alternate retaining ions. For sepa¬rating all of the rare earths with EDTA, the possibilities include Bi+3, Ni+2, and Pb+2. For separating just the light rare earths, Zn+2, Co+2, or Cd+2 might be used.nThe elution sequence obtained with citric acid is quite different from the general character of the sequences obtained with the aminopolycarboxylic acid chelating agents. This difference makes citric acid valuable in removing non-rare-earth contaminants which result from the separation of the rare earths with the more efficient chelating agents. A method was described for the removal of thorium from the heavy rare earths. The same method could be used to remove aluminum or uranium.
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