Selective removal of zinc(II) from spent pickling solutions in the presence of iron ions with phosphonium ionic liquid Cyphos IL 101

Trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101) – a phosphonium ionic liquid – was used as a novel reagent mixed with toluene to extract selectively zinc(II) from chloride media in the presence of iron(II). The extraction of individual metal ions with Cyphos IL 101 increases in the following order: iron(II) < zinc(II) < iron(III). Zinc(II) extraction is preferred over iron(II) when both are present in the feed. Maximum loading capacity of 50 vol.% Cyphos IL 101 amounts to 45, 40 and almost 30 g dm− 3 of Fe(III), Zn(II) and Fe(II), respectively. Selective separation of Zn(II) from mixtures of Zn(II) and Fe(II) model spent pickling solutions is investigated in multistage extraction-stripping. Zn(II) extraction from the feed containing only 5 g dm− 3 exceeds 85% after the first extraction stage, reaching almost 100% after three stages. Meanwhile, iron(II) extraction also increases (after three stages it amounts to 40%). Extraction in the presence of 120 g dm− 3 Zn(II) and 35 g dm− 3 Fe(II) needs four extraction stages to deplete Zn(II) in the feed. At the same time Fe(II) extraction is low and equals less than 20% after four stages. Stripping of the predominant metal ions takes place prior to the deficient ones. Zinc(II) can be selectively transferred from the feed containing high Zn(II) concentration and four times lower concentration of Fe(II) to the stripping phase. The most important from the practical point of view is the ability of Cyphos IL 101/toluene mixture to separate selectively zinc(II) from iron(II) when both are in concentrated zinc(II) feeds.