Cumulative study on solvent extraction of elements by N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TODGA) from nitric acid into n-dodecane Original Research Article

The extraction of 75 elements by N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TODGA) from nitric acid to n-dodecane was investigated and discussed concerning distribution ratios (D) of metal ions and their ionic radii. The extractability for elements depends strongly on their oxidation state. Monovalent and pentavalent ions were not extractable. In divalent metal extraction, Ca(II) (ionic radius: 100 pm) showed the highest D-value and the D decreased with increase or decrease of the ionic radius. Trivalent and tetravalent ions with ionic radii of 87–113 and 83–94 pm, respectively, showed the D over 1000, and the extracted chemical forms were determined to be M(TODGA)3(NO3)n or M(TODGA)4(NO3)n (n = 3 or 4). The oxonium ions with higher oxidation states than tetravalent one forms the complicated metal-complex with TODGA, and the number of TODGA associated in those extraction reactions was confirmed to be two at most.