Behaviors and Mechanism of Iron Extraction from Chloride Solutions Using Undiluted Cyphos IL 101

In this study, iron­(III) extraction from acidic chloride solutions using undiluted tri­hexyl­tetra­decyl­phosphonium chloride (Cyphos IL 101) was carried out in a liquid–liquid extraction process. The extraction behaviors under various HCl, chloride, and iron­(III) concentrations; selectivity; and extraction isotherm of iron­(III) were investigated. It was found that iron­(III) was extracted fast and efficiently in a wide chloride concentration range. The highly selective separation of iron­(III) from aluminum­(III), calcium­(II), magnesium­(II), and potassium­(I) in acidic chloride solutions was achieved with a separation factor of Fe­(III) over Al­(III) at 11 000 from a 3 M HCl solution. The maximum loading capacity of iron­(III) reached 83.2 g·L^–1 with a molar ratio of 0.91 for Fe­(III)/Cyphos IL 101. Effective stripping of the loaded iron­(III) was achieved with a 0.5 M H₂SO₄ solution. The iron-chloro complexes in both aqueous phase and Cyphos IL 101 phase were characterized using spectroscopic techniques. Ultraviolet–visible and Raman spectra confirmed that iron­(III) formed a series of iron-chloro complexes in acidic chloride solutions, while present solely in the form of tetrachloroferrate complex ([FeCl₄]⁻) in the Cyphos IL 101 phase. An extraction mechanism was proposed in which both FeCl₃ ion association and [FeCl₄]⁻ anion exchange with the chloride anion of Cyphos IL 101 play the key role during iron­(III) extraction