title: Synergistic extraction equilibrium of gallium(III) with di(2-ethylhexyl)phosphoric acid and 8-quinolinol derivatives into supercritical carbon dioxide.
abstract: The synergistic effect of five 8-quinolinol derivatives (HQs) on the extraction of gallium(III) with di(2-ethylhexyl)-phosphoric acid (D2EHPA or HA) from weak nitric acid into supercritical carbon dioxide (SC-CO(2)) was investigated.  8-Quinolinol (Hq), 5-ethoxymethyl-8-quinolinol (HO(2)q), 5-hexyloxymethyl-8-quinolinol (HO(6)q), 5-(2,2,2-trifluoroethoxymethyl)-8-quinolinol (HFO(2)q), and 5-chloro-8-quinolinol (5-Cl-Hq) were used as synergists.  Synergism was observed for all of the HQs.  The synergistic effect increased in the following order: Hq < HO(2)q < HFO(2)q < 5-Cl-Hq ≍ HO(6)q.  The extent of synergism can be related to both the distribution constant and the acid dissociation constant of the HQ.  The synergistic extraction equilibrium of gallium(III) with D2EHPA and 5-Cl-Hq into SC-CO(2) was investigated; the results suggest that the composition of the extracted complex is as GaA(2)Q·HA.  The synergistic extraction mechanism was the same for both SC-CO(2) and n-heptane.  The synergistic extraction equilibrium constants in both cases were calculated based on the experimental results.
authors.affiliation: College of Science, Ibaraki University, Mito, Japan. oakira@mx.ibaraki.ac.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Ohashi
authors.forename: Natsumi
authors.initials: N
authors.lastname: Kawashima
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Sato
authors.forename: Haeng-Boo
authors.initials: HB
authors.lastname: Kim