Synergism in the Liquid-Liquid Extraction and the Extractio Chromatography of Manganese(II), Cobalt(II), and Zinc(II) in the Thenoyltrifluoroacetone–Trioctylphosphine Oxide–Cyclohexane Extraction System

Abstract

Abstract The synergism appearing in the liquid-liquid extraction and the extraction chromatography of trace amounts of manganese(II), cobalt(II), and zinc(II) has been investigated with TTA (thenoyltrifluoroacetone) in various solvents with or without TOPO (tri-n-octylphosphine oxide). For example, the pH1⁄2 of the extraction of Co(TTA)2 differed with the solvent used; it was, for example, 4.1 for nitrobenzene, 4.6 for cyclohexane, and 5.2 for benzene, when examined with 0.1 M TTA. When 0.01 M TOPO was present under the same conditions, the above values became 3.3, 2.4, and 3.1 respectively. The synergism was thus found to become more effective as a less polar solvent was used. The extraction constants of the three metals with only 0.1 M TTA–cyclohexane increases in the order of Mn(II)–Zn(II)–Co(II); however, when 0.001 or 0.01 M TOPO was present, all the extraction curves of the three metals became identical, even in the acidic region of pH 1–4. The overall stability constants of the adducts, M(TTA)2–(TOPO)n, increased in the order of Zn(II)–Co(II)–Mn(II), unlike the case of M(TTA)2. The adducts were found to have two TOPO for Mn(II) and Co(II), but only one for Zn(II). The extraction equilibria were found to be attained within two minutes. Unlike as in the batch extraction, the columnextraction chromatography gave a dissimilar order of the extractability of three metals (Zn(II)–Mn(II)–Co(II)) when 0.1 M TTA–cyclohexane was the stationary phase on Kel–F in the presence of TOPO. The mutual separation could not be achieved among these metals in the presence of TOPO, and the synergism was found to be rather unfavorable for the separation of metals. The relation between the batch extraction and the extraction chromatography was also discussed briefly on the basis of the distribution data obtained.