Modifier and surfactant dependence of gallium extraction by alkanoyl oxinates from basic solutions

Abstract

The recently developed method of Ga extraction from basic aluminate solution (pH 13) using an alkanoyl oxine, i.e., myristoyl (M.Ox), palmitoyl (P.Ox), and stearoyl oxine (S.Ox), solution in chloroform has been improved by incorporating 2-hexanone as a modifier and cetyl trimethyl ammonium bromide (CTAB) as a surfactant into the extraction system. 2-Hexanone synergistically enhanced the extraction rate and Ga yield as its volume percentage was increased from 5 to 20% in the organic phase. Other oxygen-donor modifiers such as methyl isobutyl ketone (MIBK) and 1-hexanol, were not as effective as 2-hexanone. By using 10% (by volume) of 2-hexanone in chloroform solution, the order of Ga extraction efficiency for alkanoyl oxinates was M.Ox > P.Ox > S.Ox, i.e., extraction increased with decreasing length of the alkyl group of oxine. The ketone-added system showed satisfactory aluminum tolerance at pH 13, and enabled the shifting of the extraction pH to slightly higher values, which is beneficial for the process economies of Ga recovery from Bayer aluminate liquor. Use of CTAB as a cationic surfactant reduced the equilibration time and increased the Ga yield; the most pronounced effect occurred around its critical micelle concentration, indicative of micellar catalysis via interfacial mechanisms.