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.

Photoreductive Stripping of Cobalt Loaded on Hydroxyoxime Extractant in a Liquid−Liquid Extraction System

“…[7][8][9][10] Selective stripping or extraction has also been achieved by photochemical reduction using liquid-liquid extraction systems with acidic organophosphorus compounds. 9,10 In such systems, the extracted species obtained in the organic phase is easier to photoreduce than the metal ion, which exists in the aqueous phase. One can therefore expect to achieve effective stripping if the oxidized cobalt(III) complex can be photoreduced within the organic phase.…”

“…The photochemical redox reaction, based on the principle that the distribution ratios for those metals having the smaller valences are lower than those of the metals having the larger valences, has also recently been studied for improving separation. − Selective stripping or extraction has also been achieved by photochemical reduction using liquid−liquid extraction systems with acidic organophosphorus compounds. , In such systems, the extracted species obtained in the organic phase is easier to photoreduce than the metal ion, which exists in the aqueous phase. One can therefore expect to achieve effective stripping if the oxidized cobalt(III) complex can be photoreduced within the organic phase.…”

Ultrasound-assisted Extraction of Fe (III) from Wet-process Phosphoric Acid

“…However, a negative effect on the extraction yields was observed with an increase in the extraction temperature for both of the two extraction techniques. This phenomenon might be explained as follows: (a) the extraction mechanism for Fe (III) by D2EHPA from phosphoric acid could be expressed as [22][23] …”

Review of Advanced Liquid−Liquid Extraction Systems for the Separation of Metal Ions by a Combination of Conversion of the Metal Species with Chemical Reaction

“…A highly selective separation with a Eu purity of about 99% can be achieved from a Sm/Eu/Gd aqueous mixture with equal metal concentrations by the extraction−photoreductive stripping process. Hirai et al also investigated the separation of V/Mo with photoreductive stripping of the V in a TOMAC system. − The mechanism of such extraction or stripping systems, when combined with the photochemical reductions of Fe(III) and V(V), in acidic organophosphorus compounds has been investigated. − The photochemical reduction of the extracted species proceeds after an initial induction period caused by the dissolved oxygen in the extraction system. The photochemical reduction of the extracted V(V) ions occurs both at the interface and in the bulk organic phase, whereas that of the extracted Fe(III) ions occurs mainly at the interface.…”