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

Abstract

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.