Abstract
Quaternary phosphonium salts as effective extractants of zinc(II) and iron(III) ions from acidic pickling solutions Extraction of zinc(II) and iron(III) from hydrochloric acid solutions using quaternary phosphonium salts, Cyphos® IL 101, Cyphos® IL 104, Cyphos® IL109 and Cyphos® IL 111 in mixtures with toluene, was studied. Trihexyl(tetradecyl)phosphonium chloride (Cyphos® IL 101) and trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate (Cyphos® IL 104) showed the best zinc(II) and iron(III) extraction abilities. After three stages of zinc(II) extraction with Cyphos® IL 101 and Cyphos® IL 104 the efficiencies were 100 and 93.6%, respectively. Total iron(III) transport to the organic phase was achieved after two separation stages and amounted to 82.1 and 100% for Cyphos® IL 101 and Cyphos® IL 104, respectively. Zinc(II) and iron(III) could be effectively stripped from the loaded organic phases with 0.5 mol dm-3 sulfuric acid. The more hydrophobic the character of the anion type of phosphonium salts, the lower the efficiency of extraction.
Highlights
Hot-dip zinc galvanizing is one of the widespread technologies used for anticorrosive protection of steel elements
Extraction equilibrium Preliminary experiments have shown that the extraction of zinc(II) and iron(III) ions is very efficient with two chemical compounds of the four quaternary phosphonium salts: trihexyl(tetradecyl)phosphonium chloride (Cyphos® IL 101) and trihexyl(tetradecyl)-phosphonium bis(2,4,4-trimethylpentyl)phosphinate (Cyphos® IL 104) (Table 2)
It is the anion that influences the hydrophobicity of these compounds and as a result their extraction power
Summary
Hot-dip zinc galvanizing is one of the widespread technologies used for anticorrosive protection of steel elements. Zinc layer is deposited by immersion of steel in molten zinc. This main stage requires appropriate pretreatment of the surface to be coated (washing, degreasing, rust removal and fluxing steps)[1]. Pickling permits removal of non-metallic substances (rust, scale) from the surface with specially prepared pickling solutions (150 – 160 g dm-3 HCl, 5 – 20 g dm-3 Fe as FeCl2, inhibitors). The composition of acidic effluents coming from pickling of various surfaces depends on the composition and thickness of the surface. They contain high quantities of both iron and zinc(II)
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