Abstract
Hydrofluoroethers have been applied as diluent for phosphorus acid extractants in the solvent extraction of zinc(II). They are promising alternatives to conventional organic diluents because of non-flammability, chemical stability and non-toxicity. The hydrofluoroethers used in this study are a mixture of ethylperfluorobutylether and ethylperfluoroisobutylether (NovecTM HFE-7200, SUMITOMO 3M Limited.) and a mixture of methylperfluorobutylether and methylperfluoroisobutylether (HFE-7100). Among the extractants examined, two phosphorus acid extractants, di-(2-ethylhexyl)phosphoric acid (D2EHPA) and 2-ehtylhexyl phosphoric acid mono-2-ethylhexyl ester (PC88A), were soluble in both hydrofluoroethers. Because of the hydrofluoroethers' high specific gravity and low solubility in water, phase-separation was rapid and the resulting phases were clear. In the extraction of zinc(II) using phosphorus acids, the system with D2EHPA gave higher extraction than that with PC88A, while there was little difference in the extraction behavior between the two hydrofluoroethers. The combination of these extractants and diluents showed a little higher extractability of zinc(II) than such conventional chlorinated organic solvents as chloroform and carbon tetrachloride. Effects of both concentrations of zinc(II) and the extractants on the zinc extraction were examined, and the stoichiometric relationship of the extraction was proposed with the equilibrium constants determined. Moreover, the back extraction of zinc(II) and the selective separation of heavy metals were satisfactorily attained.
