Extraction Theory and Form of the Extraction Complex for the Metals Dysprosium, Holmium, Thulium, and Curium in the Synergistic System Kerosene/HTTA/TBP/Dilute HNO3

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Abstract
Data were taken for the distribution of HTTA and the metals Dy, Ho, Tm, and Cm in the system kerosene/thenoyltrifluoroacetone (HTTA)/tributylphosphate (TBP)/dilute HNO3. The theory first proposed by Tournier (1) and Tournier and Davis (2) for the HTTA distribution was modified and new values of the equilibrium constants resulting from the theory were determined by a least squares fit of the HTTA distribution data. The new values are K 1 = 14 and K 2 = 3.45. An analysis of the HTTA distribution data indicates that one molecule of TBP associates with one molecule of (HTTA·H2O) to form a complex. Analysis of distribution data for the metals, Dy, Ho, Tm. and Cm using the modified theory indicates that the form of the metal complex is M+3(TTA)3(TBP)2 reported by most investigators. A log-log plot of q o/a as a function of [H+] under conditions of constant free TBP and HTTA and constant ionic strength indicates an inverse squared effect of [H+] on the metal distribution ration, q o/a. This in turn supports the indications that two (TTA) molecules are associated with the metal complex. No experimental data to verify the presence of (NO3 −) in the complex have as yet been obtained.

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