Trihexyl(tetradecyl)phosphonium bis-2,4,4-(trimethylpentyl)phosphinate micellar behavior in the extraction of Ag(I) from acidic nitrate media

Abstract

The distribution of Ag(I) between acidic aqueous phase (HNO3) and organic phases, composed of trihexyl(tetradecyl)phosphonium bis-(2,4,4-trimethylpentyl)phosphinate (Cyphos® IL 104) diluted in kerosene or kerosene/1-decanol, has been studied. In order to elucidate the interactions in solution and the chemical equilibria responsible for Ag(I) extraction by Cyphos® IL 104, ionic conductivity, dynamic viscosity, and interfacial tension measurements, determination of water and nitric acid extraction were performed, and the organic phases were characterized by infrared spectroscopy (ATR-FTIR). Ag(I) is extracted by Cyphos® IL 104 with high affinity, even under slightly acidic conditions (close to 100% at pH 5). The linear relationship between the logarithm of the distribution ratio of Ag(I) (D) and the logarithm of Cyphos® IL 104 concentration exhibits a slope greater than the stoichiometry expected (1:1), demonstrating an atypical extraction equilibrium. The change in the physicochemical properties as a function of Cyphos® IL 104 concentration permits to deduce the formation of reverse micelles or aggregates in organic phases at the critical micellar concentration CMC = 0.001 mol L-1. The ATR-FTIR characterization showed that Ag(I) was extracted by the phosphinate group of Cyphos® IL 104 with the transfer of water and nitric acid. A thorough analysis of these data indicates a similar mechanism to solvation, and the reverse micelles (or agglomerates) are involved in Ag(I) extraction.