Extractive removal of zinc(II) from chloride liquors with phosphonium ionic liquids/toluene mixtures as novel extractants

Trihexyl(tetradecyl)phosphonium chloride (Cyphos®IL 101) and bis(trifluoromethylsulphonyl)imide (Cyphos®IL 109) – phosphonium ionic liquids – were used as novel reagents mixed with toluene to extract zinc(II) from chloride media. Extraction of zinc(II) was very fast and efficient (EZn over 95%) for molar ratio of Cyphos®IL 101/Zn(II) more than 2. It was found that the presence of HCl in the feed enhanced Zn(II) extraction. The reactions of Zn(II) extraction mechanism were proposed. The values of ΔH° were estimated to be 32.93 (standard deviation (s.d.) = 2.81) and 52.85 (s.d. = 1.90) kJ mol−1 and ΔS° amounted to 120.65 (s.d. = 8.84) and 182.13 (s.d. = 6.02) J mol−1 K−1 for reaction without HCl and with 0.58 M acid, respectively. The extraction of zinc(II) with Cyphos®IL 101/toluene mixture is an endothermic reaction. Successful stripping of zinc(II) from the loaded organic phase was achieved with 1 M sulphuric acid. Cyphos®IL 101 can be reused at least in 3 cycles of extraction-stripping process. Due to low extraction of Zn(II) Cyphos®IL 109 cannot be considered as effective extractant in the studied system.