The mutual effect of iron(III) and silver(I) species in concentrated chloride medium

Earlier studies carried out to evaluate the selectivity of solvating extractants towards silver(I) in concentrated chloride media revealed that an intriguing situation occurs if a given excess of iron(III) concentration is present in the aqueous solution: the extraction of silver(I) becomes almost quantitative and independent of the initial chloride content. On the assumption that this effect may be due to a phenomenon occurring in the aqueous phase, a systematic study involving solutions containing different Ag(I), Fe(III), and HCl concentrations was carried out by solvent extraction and capillary electrophoresis. Capillary electrophoresis suggests that the AgCl32- amount in solution decreases in the presence of Fe(III), whereas FeCl3 seems to be partially converted onto FeCl4-. From the experiments performed, it can be concluded that the presence of Fe(III) seems to facilitate the formation of less anionic Ag(I) species, which are in turn more easily extracted by solvating extractants. Furthermore, the presence of FeCl4- has been detected in the organic phase of triisobutylphosphine sulfide (TIBPS) by UV-Vis spectrophotometry, after equilibration with HCl solutions containing both Ag(I) and Fe(III), which was not identified during similar experiments carried out in the absence of Ag(I). Speciation of silver(I) and iron(III) in concentrated chloride medium has also been worked out by a numerical methodology.