Mechanism of Photoreductive Stripping of Iron(III) in a Liquid−Liquid Extraction System and Its Application for a Hydrometallurgical Process

Abstract

The mechanism of the photoreductive stripping of iron(III) in the liquid−liquid extraction process was investigated by employing (2-ethylhexyl)phosphonic acid mono(2-ethylhexyl) ester (EHPNA) and bis(2-ethylhexyl)phosphoric acid (D2EHPA) as extractants, n-dodecane and kerosene as diluents, and a xenon lamp as the light source. The photoreductive stripping of iron(III) progressed by photoirradiation following an initial induction period caused by dissolved oxygen in the extraction system. The iron(III)−extractant complex was photoexcited in the organic phase and photoreduced to the iron(II) complex by electron donation from the water at the aqueous/organic interface. A kinetic study of the photoreductive stripping of iron(III) revealed that the photochemical reduction of iron(III) was the rate-determining step. The removal of iron from a simulated zinc refinery residue solution by using liquid−liquid extraction combined with photochemical reduction of iron was also investigated, showing that the rare metals in the refinery residue, gallium and indium, were recovered effectively and leaving almost all iron(III) in the aqueous phase.