Removal of zinc(II) and iron ions from chloride solutions with phosphonium ionic liquids

► Phosphonium ILs: Cyphos IL 101 and 104 effectively extract Zn(II) and Fe(III). ► Cyphos IL 101 is applied in polymer inclusion membrane as Zn(II) and Fe(III) carrier. ► Fe(III) is transported through the membrane significantly faster than Zn(II). ► Fe(III) separation from Zn(II) is probable because of difference in transport rate. Recently phosphonium ionic liquids (ILs) are frequently used for separation of metal ions. This paper presents research on successful application of two quaternary phosphonium salts for removal of Zn(II) and iron ions from chloride solutions in classical liquid–liquid extraction and polymer inclusion membranes. Trihexyl(tetradecyl)phosphonium chloride (Cyphos IL 101) and trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate (Cyphos IL 104) are investigated as carriers to extract Zn(II), Fe(II) or Fe(III) from chloride media. Cyphos IL 101 and 104 extract Zn(II) and Fe(III) quickly and almost completely from low concentrated feed (extraction efficiency near 100%). They are effective and prospective extractants. Ion exchange and addition mechanism is proposed as description of extraction mechanism. Further, sulfuric acid is found to be an effective stripping phase. In addition, polymer inclusion membranes containing Cyphos IL 101 are applied for Zn(II) and Fe(III) transport. Although the process is slow, more efficient transport through the membrane (with Cyphos IL 101 as a carrier) is noted for Fe(III) than Zn(II). Fe(III) could be separated from Zn(II) with PIM containing Cyphos IL 101.